CONTENTS

1. INTRODUCTION

2. INDICATIONS FOR OCCLUSAL REHABILITATION

3. GOALS OF FULL MOUTH REHABILITATION

4. ANATOMY AND PHYSIOLOGY OF MASTICATORY MECHANISM

5. THE HINGE AXIS

6. CENTRIC RELATION

7. VERTICAL DIMENSION

8. FUNCTIONAL ASPECTS OF COMPLETE MOUTH REHABILITATION

9. DIAGNOSIS AND TREATMENT PLANNING

10. PREPARATION OF THE MOUTH FOR REHABILITATION ll.PMS

PHILOSOPHY

12. SELECTING INSTRUMENTS FOR OCCLUSAL REHABILITTION

13. MOUNTING MODELS

14. FUNCTION AND IMPORTANCE OF ANTERIOR GUIDANCE

15. PRINCIPLES OF OBTAINING OCCLUSSION IN OCCLUSAL

REHABILITATION

16. RATIONALE AND TECHNIQUE OF BIO MECHANICAL OCCLUSAL

REHABILITATION

1.7. RESTORING LOWER ANTERIOR TEETH

1

18. RESTORING UPPER ANTERIOR TEETH

19. THH PLANE OF OCCLUSION

20. POSTERIOR OCCLUSAL MORPHOLOGY 2!. RESTORING LOWER

POSTERIOR TEETH

22.WAXING TECHNIQUE FOR LOWER POSTERIOR TEETH

23. RESTORING UPPER POSTERIOR TEETH

24. FUNCTIONALLY GENERATED PATH

25. PROCEDURAL STEPS IN RESTORING OCCLUSION

26. REVIEW OF LITERATURE

27. SUMMARY

2

INTRODUCTION

Planning and executing the restorative rehabilitation of a decimated occlusion

is probably one of the most intellectually and technically demanding tasks

facing a restorative dentist.

The term "occlusal rehabilitation has been defined as the restoration of the

functional integrity of the dental arches by the use of inlays, crowns, bridges

and partial dentures". Occlusal rehabilitation therefore involves restoring the

dentate or a partially dentate mouth. The aim is to provide an orderly pattern of

occlusal contact and articulation that will optimize oral function, occlusal

stability and esthetics.

Occlusal adjustment by grinding may be required, as part of the rehabilitation

but does not constitute rehabilitation per se.

Occlusal rehabilitation is discussed in the context of cases where restorations

are supported by natural teeth and doesn't include the restoration of the fully

edentulous arch or maxillofacial defects, nor does it include the use of

osseointegrated implants.

Definition: Full mouth rehabilitation entails the performance of all the

procedures necessary to produce healthy, esthetic, well functioning, and self-

maintaining masticatory mechanism.

3

INDICATIONS FOR OCCLUSAL REHABILITATION

The reasons for undertaking occlusal rehabilitation may include the restoration

of multiple teeth, which are missing, worn, broken-down or decayed.

Increasingly occlusal rehabilitation is also required to replace improperly

designed and executed crown and bridge work. In certain circumstances

treatment of temporomandibular disorders may also be considered an

indication for rehabilitation, but great caution is advisable in such cases.

Regardless of the clinical reason, the decision to carryout any treatment should

be based upon achieving oral health, function, esthetics and comfort, and

treatment should be planned around these rather than the technical possibilities.

If these goals are to be achieved certain biological considerations are necessary

when planning and carringout occlusal rehabilitation. They are

1. The indications for reorganizing the occlusion

2. The choice of an appropriate occlusal scheme

3. The occlusal vertical dimension

4. The need (or otherwise) to replace missing teeth

5. The effects of the material used on occlusal stability control of parafunction

and TMD

The indications for reorganizing occlusion:

When undertaking relatively small amounts of restorative treatment, for

example up to two or three units of crown and bridge work, it is often

acceptable, and it is often advisable to adopt a confirmative approach that is to

construct the restoration to conform with the patient's existing intercuspal

position.

4

The alternative strategy is to reorganize the occlusion by establishing a new

occlusal scheme around a stable condylar position. The condylar position

usually chosen is termed "centric relation' (CR).

The decision to re organize a patient's occlusion may be made on the grounds

either that the existing IP is unacceptable and needs to be changed, or where a

very large amount of treatment is to be undertaken and the operator has the

opportunity to optimize patient's occlusion. The decision should (and can) only

be made after a detailed and careful examination of the occlusion, preferably

with the use of accurate study casts mounted-in a semi adjustable articulator in

the retruded arc of closure. Mounted casts should allow the discrepancy (slide)

between CR and IP to be analysed as vertical, horizontal and lateral

components both at tooth and condylar level. Moreover, adjustments can be

tried and potential restorations waxed allowing the feasibility and difficulty of

reorganization to be judged properly.

It must be borne in mind that jaw movement will be simulated only partially by

any type of articulator. Nevertheless, the semi adjustable articulators are an

invaluable supplement to diagnosis and can save time with occlusa!

adjustments when restorations are fitted.

Reorganization maybe considered when the existing IP is considered

unsatisfactory for any of the following reasons:

Repeated fracture or failure of teeth or restorations:

Clinical experience suggests that persistently failing restorations (for example

crown and bridge debonding) are very commonly attributed to unfavorable

occlusal loading which may be improved by reorganization. Bruxism:

An optimally constructed occlusion will better be able to deal with the forces

generated in parafunction.

5

Lack of interoeclusal space for restoration:

Reorganising the occlusion to eliminate a large horizontal component of slide

between CR and IP can create a valuable interoeclusal space for the restoration

of worn.anterior teeth. Alternatively, the occlusion may be reorganised at an

increased vertical dimension necessitating occlusal coverage for at least one

arch.

Trauma from occlusion:

This may be soft tissue trauma (due to teeth impinging on the cheek or alveolar

ridge) or periodonlal trauma (due to excessive or aberrantly directed occlusal

forces) the latter may have an accelerating effect on periodontal disease

although the evidence is conflicting. Reorganisation of the occlusion to direct

forces axially and eliminate interferences and premature contacts can reduce

tooth mobility. However, the overall gain in periodontal attachment is marginal

and should be considered as no more than adjunct to periodontal management.

Unacceptable function:

Poor tooth to tooth contact with tilting and overeruption of teeth may create

problems with masticatory function, particularly when large number of teeth

have been lost. Unacceptable esthetics:

Alteration in the clinical crown height may be necessary to improve esthetics,

and this may be made possible by constructing the restorations to a reorganised

occlusion, possibly at an increased vertical dimension.

The presence of TMD: The link between the occlusion and TMD is

controversial.

6

Reasons for Full Mouth Rehabilitation:

The most common reason for doing full mouth rehabilitation is to obtain and

maintain the health of periodontal tissues.

Clinical periodontal findings are correlated with radiographs to determine the

extent and character of any disease findings must then be correlated to function

of the mouth in examining the function of the mouth, many factors must be

considered. The most important factor is discrepancy known as the "premature

contact" a contact between an upper and lower tooth that prevents or interferes

with the normal path of closure of mandible. The area that receives the force of

closure after the patient "skids" off the prematurity may relate to a greater

degree of disease. This area receives the force in the form of a rebound as the

normal path of closure is interfered with by the premature contact.

The various excursions of the mandible must be examined to determine how

much harmony exists between the jaw movement and the tooth contacts, and

the teeth that receive most of the load in the different positions should be noted.

A definite correlation between the malfunction and the clinical periodontal

findings is usually possible. This correlation generally precludes all other

potential causes of the pcriodontal condition. Even so, in order to attack the

problem from every conceivable angle, we must consider and investigate each

of the other factors.

In conjunction with malfunction, we must consider oral habits that could have a

bearing on the condition present. These may include such things as bruxism.

lip-chewing, thread-biting, tongue habits, and soon.

Temporomandibular joint disturbance is another reason for full mouth

rehabilitation. This may be difficult to diagnose, and great care must be taken

to determine the etiological factors involved. Frequently, there is a poor

7

relationship between the articulation and the movements of the joint -a

disharmony of function. Sometimes there is a muscular dysfunction that is

caused by some irritant or a nervous affliction. This muscular dysfunction may

be caused by the poor articulation, which produces muscle spasms, and these in

turn may be interpreted as a joint disturbance. In joint cases, the periodontal

condition is usually very good, which is probably why the joint has been

injured instead of the periodontium. When a disharmony exists, we must

ascertain whether the patient is injuring his joint as a result of malfunction, a

bad habit, or an emotional disturbance. Emotional disturbances are very

difficult to deal with and often require the assistance of a competent

psychiatrist.

Still another reason for full mouth rehabilitation is the need for extensive

dentistry. In such cases, some teeth are missing, others are worn down, and

there are old fillings that need replacing. Usually, the patients have little

periodontal involvement and no joint symptoms. These are the easiest cases to

treat, and the beginner should limit his or her full mouth rehabilitation to them.

As long as extensive dentistry is necessary, why not work on the case as a

whole so that ail the parts will be related to each other and to the function of

the individual?

By far, the most difficult patients to treat are the few who have succeeded in

developing a severe periodontal condition as well as a malfunctioning joint.

Even though the joint may be asymptomatic, it may exhibit a behavior pattern

that is troublesome to deal with. It may be mobile, and the dentistry may

require frequent adjustment as the joint begins to function properly with

possible heaiing. In addition, tooth settling and migration will increase the

discrepancies. These are the cases that try men's souls, they require one to

proceed with extreme care and to anticipate the possible contingencies.

8

Sometimes it is impossible to predict the extent of treatment necessary in order

to resolve the condition.

The treatment of the emotionally disturbed patient with a joint probiem is

probably the most exasperating. Although it is possible to treat the condition

physiologically, the emotional disturbance is another problem. Patients

with beautifully functioning masticatory mechanisms may still be able to

produce joint symptoms almost at will. It is unpleasant to have to suggest

psychiatric treatment, but if the dentist is convinced that this is the problem,

then he owes it to the patient and to himself to recommend such a course.

Which Patients Should Not Be Treated by Full Mouth Rehabilitation?

Frequently, friends and relatives of one's rehabilitation patients will request

similar treatment. There are many malfunctioning months that do not need

extensive dentistry and have no joint symptoms. These cases are best left alone.

Some mouths that have the potential to break themselves down, never actually

produce the destruction, for some reason. We are not justified in prescribing a

full mouth rehabilitation unless there is definite evidence of tissue breakdown.

One may argue, as many have, that it should be undertaken as a preventive

measure. But there are many malfunctioning mouths that do not break down,

proving that we cannot predict such things. If there is need for extensive

dentistry, then by all means it should be carefully correlated to the rest of the

mouth by complete rehabilitation. Some times one or two "good" teeth may

have to be operated on in order to satisfactorily accomplish our objective.

Ideally, dental procedures should be directed toward the prevention of such

conditions: in short, no pathology -no treatment.

9

THE GOAL OF FULL MOUTH REHABILITATION

History

The modern practice of renewing and reorganizing (he teeth by prostheses

began with the idea of'raising the bite" to rectify closure resulting from

excessive wear of the occlusal surfaces. Later, such closure was associated with

hearing loss, noted by Costen. This view, though later questioned, served to

stimulate interest increasing the length of the patients own teeth and thus in

increasing the vertical dimension.

In correcting articular disturbances, the best procedure came to be the retention

of the remaining natural teeth in so far as this was possible. To accomplish this,

these teeth were rebuilt to harmonize with the movements of the joints in order

to protect them from further injury.

With our present understanding of traumatic occlusion and its deleterious effect

upon the supporting structures, the procedure known as "bite raising" has

shifted in emphasis and broadened in scope and is now designated by a term

that describes it accurately. Full mouth reconstruction, jt now includes therapy

which will, by improving the relationship of the teeth, improve the condition

and health of the supporting structures.

When the teeth have been realigned through full mouth reconstruction, the

general tone of the supporting tissues invariably improves. What factors

account for this improvement? Obviously, the removal of excessive lateral

forces and the elimination of plunger cusps and similar forces attendant upon

the realignment of full mouth reconstruction lessen continuous injury to the

supporting structure. But these factors, though helpful in improving the

condition of these structures, are less important than the increased stimulation

of and circulation in the tissues that are brought about by the improved

function.

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The masticating apparatus that is normal, healthy, and functioning is able not

only to carry out the work for which it is designed, but also to maintain itself in

health. The various structures involved, through their form and arrangement,

provide for both the synchronization of, and mutual protection against, all

forces. When function is good, a generous blood circulation furnishes the tissue

with the elements needed to keep them in a healthy condition. When function is

disturbed by malocclusion, the relation between the mutually protective parts

of the masticating apparatus is disrupted; moreover, because of lessened use,

blood circulation is diminished.

As indicated by O'Rourke, the force of a persons masticatory muscles remains

fairly constant. It is the use of the force that changes under conditions of

traumatic occlusion. The patient's ability or willingness to use his muscular

force is dependent upon the comfort, or absence of pain, he experiences each

time he brings his jaws together.

Mutilated mouths with chronically inflamed supporting structures, due to

traumatic occlusion, will support very little force without producing some

discomfort. The result is continuous subnormal use of, or at best failure to

make vigorous use of, the teeth and jaws. The vascular tissues of the

periodontium can be stimulated only by the teeth in function. Such stimulation

is lacking when this function is impaired by the inability of the patient to use

the musculature in chewing because of the tenderness of these tissues.

The results, in the words of Merritt, "are" atrophy of the alveolar process,

malocclusion of the teeth, dental caries, impacted and missing teeth,

periodontal lesions, and so on. Unfortunately, subnormal function lower vitality

at the same time that it increases susceptibility to disease.

Patients who have had full mouth rehabilitation commonly say that their

mouths feel "stronger". The masticatory muscles have obviously not been

11

strengthened by therapy. What has happened is that out patients can exert

greater force with comfort and without anticipation of pain than they could

before and that therefore they do exert greater force.

The therapeutic benefit of improved tooth arrangements and improved

functioning have been indicated. The individual patient's reaction bears witness

to these benefits and should inspire us, in terms of human satisfaction as well

as of scientific progress, to strive continuously for improvement in the

techniques of full mouth rehabilitation.

It should be kept in mind that although the operations of all mouth

rehabilitation procedures are performed on tooth units, they have one basic

objective: the equalization of the forces directed against the supporting

structures. Any disharmony at the occlusal or incisal aspects of a tooth will

direct forces against these malaligned surfaces and thus subject the supporting

structure to traumatic injuries. Similarly, any impairment of buccal or lingual

harmony will be reflected in injury to the gingival tissue and subsequently to

the deeper tissues involved in supporting the tooth. The proximal contact

anatomy is also vital in maintaining the health of the underlying soft tissue.

Poor contact relationships encourage food impaction with resultant periodonlal

tissue loss.

12

ANATOMY AND PHYSIOLOGY OF THE MASTICATORY

MECHANISM

An understanding of the anatomy and physiology of the masticatory

mechanism is essential to intelligent diagnosis and adequate treatment. If we

know, how the normal masticating mechanism functions, we will be able to

recognize its malfunction and be, in a position to correct it. A correlation of the

anatomy of the parts and the function of the parts will help one understand the

intricacies of the mechanism.

The Osseous Structures:

The masticating mechanism is primarily made up of three osseous structures:

the temporal bones, the maxillae, and the mandible. The maxillae and the body

of the mandible house the teeth -the instruments of mastication. The temporal

bone and the condyle portion of the mandible form the contact or articulation

between the osseous structures of the mechanism. In addition, the muscles that

activate, the chewing mechanisms obtain their anchorage from and are attached

to these osseous structures. Continuous contact is made between the mandibles

and the temporal bones by means of the temporomandibular joints. The glenoid

fossa of the tempoial bone is concave antero-posteriorly as well as

mediolaterally. It is the shape of the anterior slope of the-fossa that determines

the condyle paths (lateral, protrusive, and lateral-protrusive). The head of the

condyfe is oval in shape, with its long axis at an oblique angle to the median

axis of the skull. The synovial membranes and the meniscus are inter-posed

between the fossa and the condyle(fig-l).

In function, the head of the condyle rotates on the undersurface of the

meniscus. It is in this compartment of the joint that the hinge-like action of the

joint takes place. The hinge-like action is the center of action of the parts: the

disc, the condyle head, and the synovial membranes. The upper surface of the

13

disc makes contact with the articular eminence of the glenoid fossa. It is the

simultaneous sliding of the disc and condyle that produces the translatory

movement of the temporomandibular joint. In other words, the head of the

condyle rotates on the undersurface of the disc the condyle and the disc

together translate in the fossa (anteroposteriorly, mediolaterally, or in-

between).

The meniscus, or disc, consists of fibrocartilage, which is oval in shape and

thinner at the center than at the circumference. "The inferior surface is concave

and Fits on to the condyle of the lower jaw; while its superior surface is

concavoconvex from before backward, and is in contact with the articular

surface of the temporal bone" (Morris. 1933).

The stress-bearing character of the disc is evident in the fact that ihe blood and

nerve supply is in the periphery, the center being devoid of these tissues.

Contact between the head of the condyle and the articular eminence is made by

the cenier of the disc. The stress of mastication in the joint is absorbed in this

relation. The meniscus has its bearing against the articular surface of the

temporal bone(fig-2), which forms the anterior wall (articular eminence) of the

glenoid fossa. It is in this relationship that the forces of mastication are

absorbed by the temporomandibular joint.

Lubrication of the joint is accomplished by the synovial membranes. Each

compartment of the joint has its own synovial sac.

The disc and the synovial membranes are neither compressible nor variable in

the normal course of events, but serve as ball bearings between the skull and

condyle.

Function of Ligaments and Muscles:

14

Ligaments and muscles hold the temporomandibular joint and the chewing

mechanism together. The ligaments limit the amount of movement of the

mechanism and prevent the mechanism and joint from falling apart when the

muscles are relaxed.

They help to determine the position to the mandible when the muscles relax:

thus, to some extent, physiological rest is govcrneu by these ligaments.

The most important ligaments of the temporomandibular joint are the capsular

and the temporomandibular. The temporomandibular ligament forms the lateral

part of the capsule and reinforces it. The upper part of the ligament is broad and

is attached to the zygoma and to the tubercle (articular eminence of the

zygoma). It is inclined downward and backward and is inserted into the

condyle and neck of the mandible laterally(fig-3). The fibers coming from the

tubercle are short and nearly vertical. Together, the capsular and

temporomandibular ligaments enclose the structures of the joint and tend to

limit its1 movements. Sphenomandibular and stylomandibular ligaments are the

two accessory ligaments that protect the joint during wide excursions (fig-4).

These ligaments are loosely attached in the upper compartment of the joint to

permit translator;' movements. They are more firmly ' attached in the lower

compartment where the hinge-like action takes place. The temporomandibular

joints are movable fulcrums activated by the muscles of mastication. These

joints have some of the elements of a ball and socket. They glide forward and

backward as well as sidewise. Actually, they can glide and rotate at the same

time in the manner of a movable ball and socket.

Muscles of mastication:

In a discussion of the muscles of mastication, there is a tendency to speak of

individual muscles and describe I heir separate actions, but muscles function in

groups as kinematic chains. The Temporalis Muscle:

15

The temporal is muscle is a large, strong muscle of mastication. It has its origin

in the temporal fossa on the side of the skull. Its origin covers a considerable

area and. by means of an aponeurosis, it connects with its mate on the other

side of the skull very much in the manner of a saddlebag. Its insertion is in the

coronoid process of the mandible and reaches down to the ramus of the

mandible should be noted that the insertion is anterior to the

temporomandibular joint. Although the fibers of the temporal is muscle are

described as vertical, oblique, and horizontal, contraction of any or all of these

fibers has a definite tendency to elevate and relrude (he mandible. This is

understandable if we recall that the temporomandibular joint is made up of the

glenoid fossa, the anterior surface of which slopes upward and backward, and

that the meniscus is interposed between the head of the condyle and this slope.

Any contraction of a muscle attached in front of this upward slanting guide

must have a tendency to brace the condyle head in a posterior and superior

position(fig-5).

The Masseter Muscle:

The masseter muscle has its origin in the zygomatic arch. It arises in two heads:

a superficial one from the outer border of the arch, and a deeper one from the

inner and more posterior portion of the arch. Its insertion is in the outer angular

region of the mandible. Fibers of the masseter muscle are almost at right angles

to the occlusal surfaces(fig-5).

The masseter is a very powerful muscle of mastication. Its contraction elevates

the jaw and forcibly brings the teeth together. Like the temporalis muscle, its

contractions tend to seat the condyle in a posterior-superior position in the

glenotd fossa. Neither the temporalis nor the masseter has anything to do with

lateral movements of the jaw. Their contractions primarily elevate the jaw and

bring the teeth together. It is because of this action that the occlusal surfaces of

the teeth must harmonize with the hinge-like action of the mandible. The

16

masseter can snap the teeth together in any position from centric to protrusive.

Having the occlusal surfaces of the teeth in harmony with this action permits a

better dissipation of the forces of this muscle to the periodontal tissues of the

teeth as they come together through a bolus of food.

The External and Internal Pterygoid Muscles:

The external and internal pterygoid muscles are responsible for the lateral

movements of the mandible. The external pterygoid has its origin, by means of

two heads, in the great wing of the sphenoid bone and the outer surface of the

pterygoid plate. The uppermost fibers of this muscle are inserted in the articular

disc through the articular capsule. The majority of the remaining fibers are

inserted in the anterior surface of the neck of the mandible.

The fibers of the external pterygoid muscle are in a horizontal and medial

direction, and their contraction pulls the head of the condyle and the meniscus

forward and medially. This action sets the mandible into position for chewing.

If the external pterygoid on one side relaxes while the one on the other side

contracts, the mandible will be moved into a lateral position. It guides the

mandible into lateral position and steadies it while the subject bites (contraction

of the temporal and masseter) in the lateral position, Contraction of the fibers

of the external pterygoid also tends to act as a brake against the posterior pull

of the temporalis muscle. It effects a muscular balance against any violent

jamming of the head of the condyle posteriorly(fig-6).

The internal pterygoid muscle originates from the palatine bone and the maxilla

and from the internal surface of the pterygoid plate. Its fibers are inserted in the

lower part of the inner surface of the ramus of the mandible at the angle. They

run laterally, downward, and backward(fig-7).

17

Neuro-Muscular Coordination:

The various structures and individual movements just described are

coordinated by a complex integration of the nervous function. During

mastication, sudden contact of a tooth with a hard object produces discomfort

and reflexively opens mouth. This is called a nociceptive reaction and is

partially responsible for protecting the chewing mechanism when there are

premature contacts in the articulation.

Reciprocal Inncrvation:

The nociceptive reaction is able to protect the mechanism because of the

phenomenon known as reciprocal innervation. This is the simultaneous

activation of a flexor reflex and the inhibition extensor (stretching) reflex, and

vice versa.

Rhythmic chewing is made possible by the efficient reciprocal innervation of

the masticatory muscles as they alternately depress and elevate the lower jaw.

During mastication, proprioceptors in the muscles, tendons, and joints send

messages through afferent fibers in the trigeminal nerve to the chief sensory

nucleus of this nerve. Secondary fibers cross the brain stem, ascend to the

thalamus, and finally arrive in the sensory cortex via tertiary tracts. In this

manner, awareness of motion in the jaws and of the position of the mandible in

relation to the maxillae during chewing movements is permitted. Some

proprioceptive impulses pass from the chief sensory nucleus to the cerebellum,

thence through a chain of neurons to the motor cortex. The motor cortex is thus

informed of the position of the teeth and jaws. and its action makes possible the

synchronous mastication movements. Motor activity, whelfter reflex or

voluntary, demands little conscious effort: so it becomes necessary to have all

the parts of the masticating mechanism working in harmony with each other to

prevent its self-destruction.

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Movements of Mastication:

The masticatory movements of the mandible are automatic and occur under

considerable force. Mastication begins with the incision of a morsel of food: To

accomplish this, the mandible is dropped open by the contraction of the

external pterygoids and the infrahyoid and digastric group of muscles. If the

external pterygoids contract equally (which is improbable), the patient will

execute a straight protrusive movement. More likely they will contract

unequally, and a lateral protrusive position will be assumed. Now the

incisor teeth have to be propelled through the food to cut it, and this is

accomplished by the contraction of the elevators of the jaw: the lemporalis,

masseter, and internal pterygoids.

After some food has been grasped, mastication proceeds. The bolus is

propelled into the mouth by the lips, tongue, and checks and probably is rolled

onto the bicuspids, which cut it up further with the crushing and shearing action

of their blades. The temporalis and masseter muscles partially relax allowing

the food to be replaced on the chewing surfaces. The external and internal

pterygoids are in a state of alternate relaxation and partial contraction, and the

temporal is and masseter again contract to crush the food some more. By this

time, and after several strokes, the bolus has reached the molar teeth, where

now it will get a final milling before is swallowed. The masseter and temporalis

muscles relax; the external and internal pterygoids on the same side contract

while those on the opposite side relax, thus cocking the mandible in a lateral

protrusive position. The food is now repositioned on the occlusal surfaces of

the molars, and the real power of mastication is applied by the masseter,

temporalis, and internal pterygoid muscles. As the masseter and temporalis

muscles contract and crush the food, the alternate contractions of the internal

pterygoids cause a wiping of the lower occlusal surfaces of the molars across

19

the upper occlusal surfaces in a finely triturating action that comminutes the

food preparatory lo swallowing.

More specifically, if the bolus of food is on the lower right first molar and

ready for its final comminution, the temporalis and masseter muscles on both

sides relax. The external and internal pterygoids on the right side relax; the

external and internal pterygoids .on the iefi side contract and cock the mandible

to execute a working occlusion on the right side. Now the temporalis and

masseter muscles on both sides contract forcibly to crush through the food. The

external pterygoid on the left side relaxes, permitting she mandible on the left

side to return home. As the condyles both approach centric position, the

internal pterygoid of the right side contracts, executing the Bennett movement.

The masseter and temporalis on the right side soon relax, permitting the follow-

through of the masticating stroke as the external pterygoid on the right side

contracts.

It must be remembered that during all of the jaw movements the condyles and

menisci are moving together. Again we must emphasize the harmonious

relation of the teeth to these movements that should exist if the investing

structures are to be protected from destruction.

Harmony of Form and Function:

Because of the complexity, automation, and force fullness with which the

chewing cycle is executed, it should be apparent that a high degree of harmony

must exist between the form and function of the 'parts. Although nature has a

buiit-in safety device in the proprioceptive reflex mechanism, repeated insults

in the form of a premature contact may impose the learning of a new reflex

pattern. It may not be as effective as it should be, and soon the additive trauma

will begin to take its toll. Then too, with advancing age the sharpness of the

protective reflex is lost, and more and more damage is done to the mechanism.

20

Protection by Proprioception:

It is interesting to note that the protective proprioceptive reflexes operate best

during normal function. The self-protective mechanisms are weak or missing

during non functioning movements. It has also been shown that reflex activity

is reduced during sleep, with the nonsecretion of the parotid gland. The

protective proprioceptive reflex apparently fails to function during bruxism.

This is one reason for correcting the malocclusion of patients who practice

bruxism, for while it may not cure the habit, it will minimize the damage that is

done.

Up to now we have attempted to briefly outline the chewing movements and tc

describe the anatomy of the masticatory mechanism. Very little has been said

about the teeth, the chewing implements: but we have implied that a harmony

of form and function is necessary.

The objective of maintaining the health of the structures of the mechanism is of

prime importance. To accomplish this, we strive to prevent any part of the

mechanism from overworking or being abused. A certain amount of work has

to be done in the form of chewing. For the moment, let us disregard any bad

habits and consider only the normal use of the apparatus to masticate food.

A certain amount of muscular force is necessary and available. How that

muscular force is dissipated by the various components (the joints, teeth, and

investing structures) is of extreme importance. For instance, if, in the chewing

cycle previously described, a single tooth came into contact before the others,

what would be the result? As the patient penetrated the food bolus, the

premature tooth would receive all the muscular force exerted after penetration

of the food. This force in turn would be transmitted to the periodontal tissues

and in time would cause their destruction.

21

By harmony of form and function, then, we mean an equal distribution of the

forces of mastication that will permit the periodontal tissues of all the teeth and

the stress-bearing portion of the joints to equal) absorb this muscular force.

Equal distribution of the functional forces over as much tissue and as great an

area as possible will guarantee the health of the entire mechanism: this is the

objective of our treatment.

22

THE HINGE AXIS

The successful application of the hinge axis in dentistry was the greatest single

contribution of the Gnathological Society. It was the cornerstone of all future

accomplishments and still is the basis for articulation.

The hinge-like action of the temporomandibular joint has been described by

anatomists for over a hundred years. Its application to dentistry, however, had

to wait for the Gnathological Society in the 1920s. Prior to that, Snow, Gysi,

and others had been aware of the presence and importance of an opening and

closing axis. Yet their methods were so crude that they concluded that the axis

was somewhere below the condyles. This inaccuracy led them to believe that

changing vertical dimensions was still a chair operation.

The desirability of being able to reproduce the opening and closing component

of jaw movements on an articulator must have been evident. That they were not

able to accomplish this was the fault of the methods used and the fact that there

was no articulator that could duplicate this movement. The Gnathological

Society developed a means of attaching a face-bow rigidly to the mandibular

teeth. This permitted accurate location of the opening and closing axis. Many

refinements in equipment were, of course, -necessary to make this a practical

procedure. For example, easy adjustment of the caiiper points was a "must."

After it had been clinically demonstrated that there was a usable hinge axis, it

became necessary to design an instrument that would duplicate this component.

The articulator had to have an intercondylar axis that could be aligned with 'he

axis located on the patient.

23

Definition of the Hinge Axis:

What is the Hinge Axis?

The head of the condyle rotates on the undersurface of the meniscus. While it

rotates on the-meniscus, the meniscus and condyle can move on the surface of

the articular eminence. The movement can be forward, to the side, or anything

in between. While the meniscus and condyle are thus translating, the condyle

can execute a pure hinge movement anywhere along this translation.

Consequently, mandibular movements appear to be very complicated and

confusing. It is practical to locate the center of vertical motion; it is also

practical to locate the center of lateral motion. The center of vertical motion

and the center of lateral motion are one and the same -the center of rotation -

and there is one in each condyle.

The hinge axis is an imaginary line connecting the center of rotation of one

condyle to the center of rotation of the other condyle(fig-8). The vertical

opening and closing movements, as well as the pure lateral movements

originate from the centers of rotation. Any combination of vertical and lateral

movement has its center in the same point. The center of rotation of each

condyle is constant to the condyle, and therefore to the mandible. The hinge

axis (the imaginary line joining these centers) then is constant to the mandible

(and teeth). As the mandible moves in its various excursions, the hinge axis

moves right along with it. The mandible is capable of executing a hinge-like

closure in any position(fig-9). This is one reason why the hinge axis is so

important. It permits us to duplicate all the arcs of closure of the mandible on

an instrument and thus tailor our cusps to harmonize with these arcs.

One point of confusion about the hinge axis stems from the method of locating

it. It is located in the rearmost position of the mandible - the terminal hinge

position. It is located in this position because only here can it be repeatedly

24

separated from the other components of jaw motion. The patient, of course,

does not function in this terminal hinge position. We purposely make him

execute a terminal hinge closure so that we can locate the center. Once it is

located, we endeavor to trace the path of this center to enable us to duplicate

every possible combination of the two movements (rotation and translation)

that the patient will use in function.

By determining the hinge axis and transferring it to an articulator, it is possible

to make casts of the mouth (teeth) in the exact dynamic relationship to each

other that exists in the patients head. Only by use of the hinge axis is it possible

to have teeth approach each other on an articulator exactly as they do in the

mouth. The hinge axis permits us to have the vertical dimension under our

control on the articulator and to duplicate all the eccentric relations and all the

possible contacts of the teeth in these relations. We can study and diagnose

tooth relations thoroughly; confident that they are exactly as they exist in the

patient's mouth, and we can return our work (whether dentures or natural tooth

reconstruction) to the instrument for correction with knowledge any changes in

vertical relations will be harmonious when placed in the patients mouth. It is

only by means of the hinge axis (and centric relation) that the teeth can be

related accurately to the terminal hinge position.

The Hinge Axis and Centric Relation:

To secure a centric interocclusal record, we attempt to "freeze" the terminal

hinge closure at a convenient opening. Without the hinge axis, we would be

unable to secure an accurate centric interocclusat record because to obtain such

a record, the recording medium must not be penetrated by the teeth or the

occlusion rims. (The implication is that the mandible would deviate because of

the guidance of the penetrating teeth or rims). In order to avoid penetration (at

least in dentulous cases), we must obtain centric interocclusal record in an open

relationship, and if we were not on the same arcs of closure, our efforts would

25

be useless. It is impossible to check a centric inlerocclusal record without an

axis mounting.

Technique for Locating the Hinge Axis (fig-10):

The location and transference of the hinge axis are not very difficult

procedures, but they must be carried out with great care because they form the

foundation for many other procedures. A convenient type of facebow is used. It

must be rigidly attached to the mandible so that it actually forms an extension

of the mandible.

A reference plate or clutch is cemented to the lower teeth with Truplastic.

Graph-lined flags are placed on the side of the face over the condyle areas to

eliminate any skin movement distraction. These flags may be attached to the

maxillae by means of a crossbar and a maxillary clutch, or they may be held in

place by a head frame or other contrivance. A crossbar is attached to the lower

reference plate or dutch.

Adjustable side arms are placed on the lower crossbar with the styli in the

vicinity of the condyles. The patient must now be instructed in the hinge-type

of movement. As previously indicated, this is not a normal movement for the

patient it is for our convenience only. The patient must be coached to let his

mouth drop open. This necessitates the relaxation of the external pterygoid

muscles, and some patients may have difficulty in comprehending this

movement. It helps sometimes to have the patient place his hand on our chin as

we demonstrate the type of relaxed opening and closing desired.

Possible Need for Bite Plane Therapy:

If a patient has difficulty in executing a pure hinge movement, it may be

necessary to train him in This abnormal opening and closing movement.

Training can be accomplished by using the jig.

26

In some cases where joint pathology may be present it may be necessary to

have the patient wear a bite appliance of some kind to disclude the teeth and

allow the joint to return to a more normal condition. Three or four days will

usually suffice, but sometimes several months of bite plane therapy may be

required. The patient must be carefully monitored during any extended period

of wearing a bite appliance for tooth movement.

The patient naturally opens downward and forwards a combination of rotation

and translation. We must separate the rotation from the translation so that we

can locate the center of vertical opening. In addition, this opening and closing

must be accomplished in the terminal hinge position, for here we can get

repeated concentric arcs that will permit us to locate their center. Any other

arcs will serve only to confuse the issue, at this point. What we actually have is

a compass with bent rigid arms. The pivoting part of the compass is on the

center of rotation in the patient's condyle. The stylus point is the tracing part of

the compass. If we succeed in getting the tracing point exactly over the

pivoting point, there will be no arcing of the tracing point. Geometrically, if we

had two concentric arcs, and if we erected bisecting perpendiculars to the

chords of these arcs, they would intersect at the center of the arcs(fig-11).

However, there is no practical method for making such a plot. The trial and

error method first used by Dr. McCollum is still the only practical way to

locate the axis.

When we succeed in getting the patient to execute a rhythmic opening and

closing in the terminal position and the stylus point is arcing, we visualize

where a center would have to be for scribing such an arc. Thus, we will have an

idea of which way to move the stylus in order to reach the center. After making

an adjustment in this direction, we try it again. As we approach the center, the

arcs will become smaller and a little more opening will be required to magnify

the arc. After several adjustments, we will be close to the center. A magnifying

27

glass should now be used to help us see whether there is still any arcing of the

stylus tip. The graph lines will aid the eye in determining this. By viewing

down one line and then down the crossing line, we can see whether there is any

slight arcing. If there is, we continue adjusting until it disappears completely.

We must learn to distinguish between the pure hinge movement and the

movement with some translation. The patient will inadvertently make a

translatory movement every third or fourth try. Some patients will

be most cooperative; others will be exasperating. Nevertheless, we must arrive

at an axis if the rest of the procedures are to be correct.

The axis center must be located on each side. What we arc locating is the hinge

action on the side of the face. It is a point on the hinge axis and not the actual

center of rotation. The actual center is approximately 10 or 11mm medial to

this location. Consequently, the location of this point must be made as close to

the skin as possible. This means that the flag must be very close to the skin

(fig-12).

Marking the Axis Location on the Patient:

When we are satisfied that we have located these points on the axis, we remove

the flags from the patient. A marking medium, such as an indelible pencil, is

rubbed on the end of the stylus. We make sure the patient is in the terminal

hinge position and then have him move his head out of the headrest, making

sure that he does not also move out of the terminal hinge position. The stylus is

gently pushed against his face to transfer the paint to the skin. These marks are

made permanent by using a special needle and a little pink marking dye -

sulfide of mercury (fig-13).

In all of our subsequent transfers we must try to simulate these conditions -the

skin in the same relaxed position and the stylus pins locked the same distance

from the face as they were before the flags were removed. This is usually 1/16

28

of an inch from the skin. By doing so, we reduce to an absolute minimum any

possible error in transference. In addition, the stylus pins must be locked and

not moved until the mounting is completed. The articulator has to have an

intercondylar axis that can be extended to these points so that the transfer is

accurately lined up with the axis of the machine.

Selection of a Face-Bow:

From a purely theoretical point of view, an ordinary face-bow such as a Snow

or Hanau can be used to locate the hinge axis. To attempt to use either one of

them in actual practice, however, is impossibility. It is a bit more practical to

use one of these bows as a transfer instrument, provided the styli are perfectly

lined up one to the other. As a matter of fact, if the styli are perfectly lined up

and we are able lock the bow by means of the universal joint in front so that the

points of the styli are on the axis locations then it will not be necessary to have

an articulator with an expandable intercondylar axis. Under these

circumstances, it is possible to bring in the styli pins an equal degree towards

the intercondylar axis of the articulator and still stay on the axis. However, it is

far easier and more accurate to use a fully adjustable face-bow (i.e.. one with

arms that can be independently adjusted by means of micrometer screws) for

both the axis locations and transfers.

By means of a face-bow transfer and the mounting frame, the upper cast can be

properly mounted to the axis of the patient.

The Hinge Axis and the Plane of Reference:

The hinge axis is constant to the mandible, as has been indicated. The terminal

hinge position, which is actually the centric relation, is constant to both the

mandible and the maxillae. All our mountings are made in this relation.

Therefore, the only practical way to maintain constant relationships throughout

treatment is to use the axis points and a fixed third point at the base of the right

29

orbit as our plane of reference. Thus, the axis orbital plane gives us a constant

position for the upper jaw, and a correct centric interocclusal record will

establish the position of the lower jaw to the constant upper jaw. In this way,

repeated mountings will have a constant, relation to our records and to the

patient's centers of rotation.

Discussion and Conclusion:

Many have attempted to find fault with the hinge axis and to disprove it. Their

criticisms cover such things as skin mobility, change of the axis, the

introduction of errors by moving the stylus tip a slight degree, and the presence

of a separate axis for each condyle.

Actually, skin mobility is reduced to a minimum by the precaution of having

the patient move his head out of the headrest when all references are made to

the marks. Any changes that might occur over the years from loss of weight

and the like would be minor. As far as change of the axis is concerned, the only

changes observed have been in the joints with some pathology.

If a patient has a painful joint, or if a patient does not execute a hinge-like

closure after a few guided opening and closing movements, it would be

desirable to do one of two things: either train the patient with the jig as you do

when getting a centric relation record, or put the patient on a bite plane for

several days. This will usually relieve the pain and give a smoother hinge-like

movement.

If there are symptoms in a temporomandibular joint, there may be some slight

change in the axis location. Always plan to relocate the axis on such patients a

year or two after the pathology has cleared up.

30

Why use the hinge axis in these cases?

The answer is simple: it is still the only means of establishing a starting point to

which we can repeatedly return and to which we can definitely relate our work

as it progresses. In every normal joint case that we have rechecked over the

years for demonstration purposes and to satisfy our own curiosity, we have

always been able to relocate the axis within very acceptable limits, that is, by

the thickness of the tattoo mark.

The most ridiculous criticism is the charge that error is introduced because the

stylus pin has to be moved through the thickness of the card covering the face.

A Single Transverse Axis:

The allegation that there is a separate axis for each condyle is mumbo-jumbo.

The anatomy and physiology of the joints would not permit a two-axis

arrangement.

About 1950, Dr. William Branstad, Dr. Raymond Garvey, and Dr. Robert Okey

conducted an experiment to determine whether there was one transverse axis

through both condyles or an axis for each condyle. They found that there was

one transverse axis. Dr. Arne Lauritzen, working with a study group, repeated

the same experiment about 1957 and arrived at the same conclusion. Dr. Frank

Celenza and V.O.Lucia repeated the experiment during the summer of 1959,

with the same result. In the fall of 1959, the Hinge Axis Committee of the

Greater New York Academy of Prosthodontics repeated this experiment and

concluded that there was only one transverse axis through both condyles.

This, in brief, was the experiment:

Clutches were cemented to the patient's teeth. A crossbar, 36 inches long, was

attached to the upper clutch, and another of the same length was attached to the

31

lower clutch. Four graph-lined flags were attached to the, upper bar for the

purpose of accurately locating the center of rotation(fig-14).

One flag was placed on each side of the face, close to the skin. The other two

were attached near the ends of the upper bar, about 12 inches from the Hags

against the face. Attached to the lower bar were four adjustable side arms, to be

used in locating the center of rotation. Each side arm was placed against a flag.

The center of rotation was located in each of the four areas, that is, each side

arm was adjusted against its corresponding flag until there no longer was any

arcing, but only rotation of the stylus point. When all four centers of rotation

had been accurately located and the patient was held in centric relation

(terminal hinge position), the cards on the flags were carefully marked with the

tips of the styli. The upper bar with flags attached was then removed from the

clutch. With a fine, heated instrument, a tiny hole, was burned through each

card where it had been marked. When the four flags were held up to the light, it

was possible to see the light through all four flag holes, proving that the four

points had to be on a straight line(fig-15). Thus, it was concluded that there was

only one transverse axis.

To demonstrate this more emphatically, we set up the bar and flags and with a

small penlight passed rays of light through the four holes. The camera at the

other end of the four flags recorded the light rays coming through the four

pinholes. In addition. a piece of dental floss was threaded through the holes.

When pulled taut, it was perfectly straight. This was conclusive proof of the

existence of only one transverse hinge axis.

The existence of a usable hinge axis component to the temporomandibular joint

movement is one of the greatest luxuries that we could have when treating the

oral mechanism.

32

Proof Positive of a Usable Hinge Axis:

On a patient whose axis was located, we proceeded to take centric relation

records at increasing vertical dimensions and compared them with a split cast

mounting. An accurate set of casts was made of the patient's teeth. The upper

cast was prepared for a split cast to accurately examine the likeness of the

various records. The

CENTRIC RELATION

Centric relation means many things to many people: to some, it means the

contact of teeth after a jaw closure; to others, it means a closure in a particular

position, the particular position having many interpretations, varying from an

habitual closure to a forced retrusion, or somewhere in between. Still others

identify it as the most retruded position from which right and left lateral

excursions can be made. Some dentists refer to centric relation when they are

talking about the mandible, disregarding the teeth depending upon their belief

and understanding, they decide that the mandible is in centric position, and that

if the teeth occlude in this mandibular relation, then the teeth are in centric

relation. Other dentists describe "mandibular centricity" as a mandible-to-

maxillae relationship at a certain vertical dimension. It is unfortunate that

centric relation means so many things to so many people, because no other

phase of dentistry is as important as a clear understanding of centric relation.

Obviously, it should have one and only one connotation to the dentist.

To understand centric relation and to appreciate its great importance, we must

understand how the jaw functions. We must set about to make restorations that

will function normally in that jaw: they must neither interfere with nor force a

particular action on the chewing mechanism. In other words, the restorations

must fit into the pattern of jaw movements: they should follow, without any

detrimental effects, the movements of the masticating mechanism. Our present

33

concern is with the type of motion, how it takes place, and its bearing on the

all-important subject of centric relation. This, of course, directs our attention to

the temporomandibutar joint. For the moment, we may forget about the ether

important structures -the muscles, tendons, ligaments, nerves, blood supply,

and teeth and confine our consideration to the action of the temporomandibular

joint.

Location of the Centers of Rotation:

It is possible to demonstrate beyond any doubt that there exists a recordable

center of vertical rotation in the condyles. An imaginary line joining these

centers has been termed the hinge axis.

In practice, when we locate the point on the side of the face for the hinge axis,

we are actually locating the hinge action in the facial plane (on the side of the

face).

This is not the true center of vertical motion, however, for that is located in the

condyle. What we are locating is a point on a line-that has been extended from

the centers of vertical motion. In other words, the point we locale on one side

of the face is on the same line passing through the actual centers of vertical

rotation in each condyle and through the point on the other side of the face. For

this reason, when making a transfer, we must not move the points of the stylus

in or out once we have located the point of hinge action. In practice, we must

have a means of transferring these hinge- action points to a suitable articulator,

the intercondylar axis of which can be lined up with these points. This is

accomplished with the mounting frame.

We can locate the centers of hinge action only when the condyle is in a position

where it can repeatedly perform the hinge action. Because patients normally do

not execute a hinge action in the most retruded position of the mandible, they

must be educated to this movement. When we consider this, as well as the

34

many habits patients can acquire over the years and the conditioned reflex

action forced by habits and tooth relations, it is easy to understand why some

patients reluctantly produce the hinge action during treatment.

This hinge action (and the imaginary line called the "hinge axis") is constant to

the mandible. In other words, the vertical motion of the mandible (and

condyles) is produced by the action of the heads of the condyles on the

undersurface of the meniscus. Thus, as the condyle and the meniscus translate-

move down the incline of the glenoid fossa or across the trough of the fossa in

the Bennett movement the mandible can produce this hinge-like action in any

position of the condyle. As a matter of fact, it will start to produce a hinge-iike

action as it glides down or across the condyle path. We must remember that the

hinge action is constant to the meniscus in any position in which it may find

itself, but it is constant to the maxillae or fossae only when the condyle is

executing the hinge action in the terminal position..

In addition to the centers of vertical (opening and closing) motion of the

mandible, there exist centers of lateral rotation: The patient can make pure

lateral movements that have centers of rotation located in the condyles. At one

time, there was considerable confusion about these centers because they are

seldom stationary. In other words, the centers themselves move as the mandible

(condyle) is making the movement. The-path of these centers of lateral rotation

on the rotating or working side is the Bennett path. The confusion arose

because it was claimed that the center of lateral rotation was some where in

back of each condyle or in the vicinity of the foramen magnum. The moving

centers of lateral motion were called "loci." Actually, what was termed the

center of lateral movement behind the condyies or "somewhere else" was the

center of the locus. The center of the path that the center of lateral movement

was making on the working side was, in fact, the center of the Bennett path. It

is practical to locate the exact centers of lateral rotation by means of two gothic

35

arch tracings taken in the same plane in front of each condyle and on either side

of the midline of the face and reproduce their path across the fossae (fig-16).

When this has been done in conjunction with the location of the centers of

vertical rotation (hinge action), then we have truly found centric relation. The

terminal hinge action is the vertical component of centric relation; the centers

of lateral rotation are the lateral components of centric relation. Why this is

centric relation, we shall now attempt to explain. We shall also show why. it is

so important.

It might be stated categorically that unless we locate the centers of rotation, we

are disregarding centric relation. This statement will immediately draw protests

because, regardless of one's understanding of centric relation, all will agree that

centric relation is essential to the practice of dentistry and cannot be ignored.

Let us analyze what really happens:

In the course of constructing occlusal surfaces for dentures, bridges, or natural

teeth, we take a centric interocclusal record, using the material of our choice.

The casts on which the restorations are going to be fabricated are mounted on

some sort of instrument, and the case is constructed.

In order for a centric interocclusal record to be usefui, it must register the

maxillomandibular relationship without any tooth contact or tooth penetration

of the recording medium. If tooth surfaces contact through the recording

medium, we can be sure that the proprioceptive reflexes have crossed us up and

caused us to record an improper relationship.

It is apparent that one of two things must be done even to begin to get an

accurate interocclusal record either it must be secured at the exact level of

vertical dimension without tooth contact (a nice trick if it can be

accomplished), or else the casts must be mounted on the articulator to the same

opening axis that the mandible has to the maxillae of the patient. If the latter is

36

done, then the centric interocclusal record can be secured in an open position to

clear the tooth contacts; and when the registering medium is removed, the teeth

on the casts can be approximated as they are in the mouth.

It is also most desirable that we check our centric mounting because many

hours of laboratory work will depend on this relationship. It is utterly

impossible to check a centric interocclusa! record accurately unless hinge axis

procedures and transfers have been used.

In order to check a centric intcrocclusal record, it is necessary to take a second

record, using all the care taken with the first one. It would be pure chance if the

second record were of the exact thickness as the first. The wax might be softer,

or the patient might close further. Whatever the reason, chances are against our

getting records of exact thickness. Yet, unless we were on the same arc of

closure on the articulator as in the mouth, the thick ness of the two records

would have to be absolutely identical.

The seating of a wax interocclusal record on casts can be quite deceptive. The

second record might appear to fit between the casts without causing any

malposition of the articulator parts. However, if we really want to determine

whether our two centric interocclusal records are identical, we must resort to

the following procedure frequently demonstrated in the clinics of Dr. Arne

Lauritzen

The Split Cast Technique:

Before mounting the upper cast on an articulator, second section (the split cast)

is carefully prepared. First, it is very important that the upper cast be poured

with extreme accuracy, care being taken to avoid any bubble formation. The

mounting side the upper cast is trued up on a model trimnifr. "V'notches are cut

on the edges of the mounting side of the upper cast -two in front, two on the

sides, and one in the posterior region. These notches are carefully made so that

37

they are truly wedge shaped. A piece of electrician's tape is wrapped around the

periphery of the cast, producing a form into which the second section of the

split cast is poured. Prior to this pour, the cast has been carefully lubricated

with Kerr Separating Medium. Three knobs of stone are placed on top of the

pour to serve as handles in the separation of the disc from the original cast. In

pouring the disc, it is extremely important to prevent any bubbles from

forming. When the disc pour has hardened, the cast is separated from the disc

by removing the electrician's tape and using the stone knobs on the disc as a

handle. Immediately after separation, the two parts are reassembled to prevent

any dust or loose fragments of stone from adhering lo the contacting surfaces.

The knobs are now cut down with a model trimmer, leaving just enough of

them to engage the new mix of stone that will be used to fasten the disc and

cast to the upper bow of the articulator.

An impression (whether it is for a study cast, a master working cast, or a

remount cast) is poured in stone. The excess stone is vibrated into the plastic

mold groove former and quickly inverted and placed on top of the poured

impression. Press it into place as you center and level the former. Do not invert

the impression. When the stone has set, remove the former and replace it with

the ring mold and secure it with periphery wax. Lubricate the grooved stone

with a separating solution and vibrate a mix of stone of a different color into

the ring mold. Level the surface with a spatula and place several knobs of

excess stone for retention when mounting to the articulator. Remove the ring

'after the stone sets and separate the impression. Trim the sides on ? model

trimmer and you are ready to mount it on the articulator by means of the face-

bow transfer.

By means of a face-bow transfer, the upper cast and disc are accurately

attached to the upper bow of the articulator. By means of our centric

interoccltisal record, the lower cast is next attached to the lower bow of the

38

articulator. This completes the mounting of the split cast and the lower cast in

what we believe to be a centric relation.

If we now open the articulator, separate the disc from the upper cast, press the

upper cast into the centric interocclusal record to be sure it is accurately seated

in place, and then attempt to close the upper bow and disc into the "V" notches

on the upper cast, we will soon find out whether: our mounting was accurate. If

it is satisfactory, we proceed to check this mounting and interocclusal record

with the second record taken. The first wax record is replaced by the second

one; the upper cast is seated into the indentations; and again an attempt is made

to close the disc into the "V" notches of the upper cast. It is amazing how often

an apparently acceptable interocclusal record is inaccurate. This technique

should be ample proof that a centric interocclusal record cannot be accurately

checked unless the hinge axis and hinge transfer procedures are used.

If these procedures are as far as we go, the restorations constructed on such

casts will come together accurately in centric closure. If we add one more step

and reproduce a protrusive path with a protrusive record, it is possible to have

proper contacts in both the centric and protrusive relationships. Unfortunately,

though, patients do not chew only in these positions. .

How does a dentist manage without using the axis and a protrusive record?

Like the dentist who simply takes a static closure, by proceeding to do a great

deal of work in the mouth, grinding here and there until some surfaces come

together. Considerable work is involved for an inferior result.

The dentist who takes a hinge-closure record, relating it properly to an

instrument by means of a face-bow, and then takes a protrusive record is only

slightly better off because there are all the laterals to contend with. Even if one

believes that the patient does not use his lateral excursions, the fact is that he

will use them if he is permitted to. The apparent shortcuts -not locating an axis,

39

not reproducing all of the patient's movements are responsible for the creation

of flat, useless occlusions. To avoid these headaches, we must locate the

centers of rotation. In addition to locating the hinge axis and obtaining a proper

centric interocclusal record, we must locate the centers of lateral rotation. This

is accomplished by means of the twin gothic arch tracings. Moreover, we must

trace the paths of these centers of lateral rotation. This is done with an extra-

oral tracing device, the pantograph: the pantograph is the only practical means

of accomplishing this today. With the pantograph, we can trace the protrusive

paths of the centers of rotation, as well as the right and left lateral paths. From

the pantograph tracings made by the path of travel of the centers of rotation, we

can reverse the procedure and duplicate the centers and their paths on an

articulator capable of full adjustment. Now when the restorations are

constructed and placed in the mouth, they will be in harmony with the patient's

movements. It will not be necessary to grind them, with the resultant

destruction of proper function.

To recapitulate: A thorough understanding of centric relation is essential 10 the

proper practice of dentistry. However, unless we locate the centers of rotation,

we are disregarding centric relation, which entails the following:

1. Location of the hinge axis

2. Location of the centers of lateral rotation

3. Transference of the casts to the axis

a) Face-bow transfer of the upper cast to the axis

b) Relation of the lower cast to the upper by a correct centric interocclusal

record.

40

Obtaining Centric Relation - Various Materials for Various Situations

Methods of manipulation for centric relation:

1. One handed technique by Anderson and Tanner (fig-16a).

2. Anterior stop technique a) Lucia jig technique

b) Leaf gauge technique advocated by Long (fig-l6b)

3. Central bearing point method (fig- 16c)

4. Bilateral manipulative technique (Dawson technique fig-l6d) Methods for

taking centric bite records

l. wax bite procedures

2. Anterior stop techniques

3. Use of preadapted bases

4. Central bearing point technique.

The technique for obtaining a centric relation is secondary to an understanding

of the phenomena. Various materials will produce acceptable results, but the

important thing is to know what we have to get and to be aware that we have

what we want.

From our preceding discussion we know that we must locate the centers of

rotation. By means of the two gothic arch tracings we are able to locate the

centers of lateral rotation, and by means of the hinge axis location we are able

to locate the centers of vertical rotation. Our practical problem now is to couple

these two centers of rotation into the center of rotation. To do this, we must

relate the lower jaw to the fixed member, the upper jaw. Having related the

upper jaw (cast) to the center of vertical rotation by means of the face-bow and

41

having set the articulator for the centers of lateral rotation, it now remains for

us to orient the lower jaw (cast) to these centers.

We accomplish this by "freezing" the lower jaw (cast) in the terminal hinge

closure at a convenient vertical dimension. This is the problem of obtaining

centric relation. There are many factors that complicate this procedure; and

patience and experience are required to complete the task satisfactorily. Among

the complicating factors are the patient's reluctance to make a pure hinge

closure; the patient's neuro-muscular pattern, which may have developed

around a deflective occlusal contact; the natural tendency of many patients to

go into a physiological rest position at the completion of any jaw movement;

and the natural tendency of a patient to exercise his prehensile reflex whenever

anything is placed between the teeth.

Certain procedures and materials are required lo overcome these factors. The

very first procedure is to practice with the patient until he is able to execute a

pure hinge closure. Second, we must block out some of the neuro-muscular

reflexes by preventing the teeth from coming together. We can accomplish this

by using our thumbnail as a controllable anterior stop. Third, we must keep the

patient under function, swinging up and down so that he cannot go into

physiological rest. As long as the jaw is functioning, its bracing position is

maintained. The natural prehensile reflex can be minimized if we have the

patient close his eyes during these procedures. If he sees the wax wafer (the

recording medium) approach his mouth, he will automatically begin to reach

out to grasp it with his teeth; and this is not a centric closure. We must take

care not to violate these precautionary procedures as we make our recording.

This presents quite a problem because what is really needed is a magic material

-a material that by its lack of resistance will not cause any unequal

displacement of the joint or teeth; a material that will remain sufficiently soft

42

long enough to ensure a dynamic registration, but will "freeze" just as soon as

all the procedures are completed.

Two-Stage Registration:

One method that has proved acceptable is a two- stage registration. A wafer is

made of one sheet of DeLar wax and one sheet of Tenax wax. These are luted

together. The reason for using two kinds of wax is to permit an easy

indentation on one side and to provide a stiffer side that will act as a carrier.

The wafer is placed vertically- in a water bath at 138°F. The anterior part is

kept out of the water so that it will remain stiffer and offer some resistance

anteriorly, thus ensuring the bracing position of the condyles.

While the wax is softening, the patient is rehearsed in the terminal hinge

closure. The patient is instructed to open and close his jaw without clenching

his teeth together. By avoiding the tooth contacts, the patient does not receive

the pcriodontal proprioception that could cause an abnormal reflex closure.

This is what we are trying to avoid: we desire a pure hinge closure free of any

"acquired" malpositions. This procedure will help the patient to execute a pure

hinge closure. It permits the temporomandibular ligament to be extended to its

normal position. It trains the patient to separate the rotation from the natural

combination of rotation and translation that makes up all functional

movements.

The patient is rehearsed in the terminal hinge closure while the cheek retractors

are in place. These conditions will simulate the actual taking of an interocclusal

record. The patient is instructed to close his eyes, and when the wax wafer is

sufficiently soft on the Tenax side, it is inserted into the mouth, with the Tenax

side against the upper teeth. The patient is told to swing his jaw several times

without closing on the wax, and then when we can "feel" the terminal hinge

closure, lie is instructed to close lightly against the wafer. At this stage we are

43

chiefly interested in getting an accurate imprint of the upper teeth in the Tenax

wax(fig-!7).

The wafer is removed from the mouth and placed in water of room

temperature. After partial chilling, it is trimmed to the outside edges of the

tooth indentations to remove the bulk. We also remove the anterior portion,

cutting it off across the center of the cuspids. There is a twofold reason for

removing this part of the wafer: first, with the anterior teeth exposed, we can

use our thumbnail as the anterior resistance; and second, without the anterior

portion, there is that much less area to seat against the casts when we make the

mounting. Consequently, should there be a slight discrepancy in the anterior

part of the casts, it will not cause their malrelationship. In short, our only

concern will be with the posterior areas.

The wax wafer is now replaced on the upper teeth and held in place with the

thumb and forefinger of the left hand. It must be evenly seated against the

upper teeth. The patient is instructed to close into it again to correct any

warpage. The wafer is then removed, and with a Bard Parker knife4 we trim

away with the excess wax around the indentations on the Tenax side, leaving

only the cusp tip indentations so that the cast may be accurately seated when

we make our mounting. Again, we seat it on the upper teeth and have the

patient close once more to eliminate any warpage that may have resulted from

the trimming process. When we are satisfied that we have an accurate seating

of the wafer against the upper teeth, we proceed to complete the interocclusal

record.

We remove the wafer and dry it with a blast of compressed air. Taking a sheet

of AI u wax, we form a "pencil," melt it, and apply the softened wax to the

underside (DeLar side) of the wafer, dripping it on as if using a candle. Aluwax

melts at a lower temperature than DeLar or Tenax, and thus provides us with a

soft surface that can be easily carried to the mouth without warping the

44

wafer(fig-18). We place the wafer on the upper teeth, holding it in place with

our left thumb and forefinger. With our right thumb on the patient's chin, we

guide the patient into the terminal hinge closure.

During this procedure, the patient's eyes arc closed. We have him execute the

terminal hinge closure, but do not allow him to contact the softened Aluwax

until we are sure of the "swing." Gradually, we let him close more and more

after each swing until the Aluwax is contacted. It may be necessary to add wax

several times before we can obtain an acceptable interocclusal record(fig-!9).

The Tests of an Accurate Interocclusal Record:

There are several ways of determining whether an interocclusal record is

accurate.

1. We should hold the wax wafer up to the light to see whether there is any

penetration. If there is. it will not be correct. Likewise, if there are one or two

thin spots, the chances are that it is incorrect. Areas of penetration or thin areas

are likely to cause a slight deviation of the mandible -so slight that we may be

unaware of it. Variations of thick and thin spots will offer variations in

resistance and may cause as much inaccuracy as a penetration.

2. If the thickness is satisfactory, we place the wafer on the upper teeth and

carefully examine it to determine whether the seat is accurate. There must not

be any "give" in any area.

3. We have the patient close into the wafer, first guiding him as we did during

the taking of the interocclusal record and then allowing him to close by his own

muscular force. If there is a hesitation in finding the indentations, the

interocclusal record is probably inaccurate,

4. If the foregoing requirements are satisfied, there is one final test lo make:

we have the patient close into the wafer and hold it firmly; then we examine the

45

posterior portion for any play between the teeth. Both sides should be

examined carefully.

If the interocclusal record meets all these tests, we are justified in accepting it

as correct. This may seem to be a long and tedious procedure but bear in mind

that everything we have done previously and everything we do subsequently

will depend absolutely upon this one procedure. An error in some other part of

the operation may be tolerated but an error here is disastrous.

Up until 1961, the preceding technique was reasonably successful. We still use

this technique for a preliminary record, before locating the hinge axis.

In 1961 and 1962 the "jig" was developed. There was nothing new in the

principle of the jig. The late Ernest Granger used his thumbnail as an anterior

resistance. His analogy of taking a centric record to the driving of a golf ball

said a great deal. He described it. as an art -driving a golf ball well is not

accomplished by many. The late Steve Brown used a wax wafer with chilled

wax anteriorly to seat the condyles. Dr. Grubb and his technician, "Jonsey".

used a gold casting on the lower teeth to maintain vertical and centric relation

while they carved the restorations in the mouth. I am certain that Dr. Pete

Dawson captures the correct centric relation with his jaw manipulation

technique. Dr. Stuart uses a tongue blade for his anterior resistance.

The Jig Technique:

Constructing the Jig:

It is preferable to make the jig on an upper study cast. Some clinicians make it

in the mouth, but this can be dangerous because of the heat generated when the

self-curing plastic cures.

46

Block out any undercuts in the anterior teeth of the cast with wax. Adapt tin

foil over the anterior teeth of the prepared cast. Lubricate the tin foil with

petroleum jelly.

Make a mix of Dura Lay in a dappen dish. When the mix has a doughy

consistency, place it on the tin foil and adapt it labially and lingually over the

centrals. Labially it should extend just over the margin of the gums. Lingually

it can extend onto the palate about 1/2 inch. The sides are tapered to the lingual

'and extend to the distal of the two centrals. Occlusally, ihe surface is a flat

plateau, thick enough to have sufficient material to adjust and separate the

teeth. As the Dura Lay polymerizes, keep removing and readapting it so that

you have a well-fitting jig that can be removed from the model without

breaking the model.

The occlusal surface is not inclined -we don't want a wedge effect Some

dentists have used the jig as an inclined plane. This is absolutely wrong! The

wedge is one of the most powerful mechanical devices in existence. A wedge

can split a mighty oak. The jig used as a wedge can displace the

temporomandibular joint distally with great ease. The platform on the

mandibular surface of the jig is just that a platform against which the lower

anterior teeth will close. It acts as the third leg of a tripod -the other two legs

are the condyles. The platform (mandibular surface of the jig) must not

influence the direction of closure. It must not force the lower jaw to the right or

to the left- It must not force the mandible forward or backward. It just stops the

closure. A very, very slight posterior inclination will assist the patient in

holding this position while the recording material sets. Even in very deep

overbite cases, the contact area is a flat platform, not an incline.

When the jig has cured, we trim it as shown in(fig-20). The labial frenum is

cleared and the labial margin of the jig just goes beyond the tree margin of the

gums. It should fit onto the anterior teeth without being displaced.

47

Three wax wafers are prepared on the upper study cast. Use one sheet of DeLar

wax. Soften the wax in water and place it on the cast so that you can cut it to

proper dimensions. Have the wax extend about % inch outside the buccal

surfaces of the teeth. In the anterior region, cut out a "U" large enough to

accommodate the Dura lay jig

We are now ready to go to the patient. A DeLar wax wafer is softened in water

at 1380 F. The wax wafer is placed in the mouth and the patient is guided into a

closure (hopefully somewhere near centric relation). Before the wax solidifies,

bend the corners of the wax over the labial of the cuspids{fig-21). These “ears"

will serve to reposition the wafer after we cover the indentations with the zinc

oxide and eugenol paste that we will use later. The indentations will be covered

with the paste and will not help us to reseat the wafer in the same position in

which it was imprinted. The "ears" will help us to reseat it in the same place as

when it was formed. The three wafers are so prepared.

Now we are ready to train the patient with the jig. This is one of the important

functions of the jig-to break the patient's habitual closure. It prevents the teeth

from reinforcing together, and thus it prevents the teeth from reinforcing the

reflex act of closure. It short-circuits the proprioception that directs the engram

of closure. Therefore, it is essential that the teeth are not allowed to come

together during the training process. If they did contact, the reflex act would be

reinforced and we would defeat our efforts. A piece of carbon paper is placed

between the mandibular surface of the jig and the lower anterior teeth. The

patient is instructed to move to the right, move to the left, move forward, and

move backward. This has the tendency to free the jaw movement. The jig is

removed and the patient is prevented from bringing his teeth together by

placing a saliva ejector in his mouth. The jig is reduced in thickness with an

abrasive rubber wheel. There usually is a gothic arch traced on the jig. Remove

the tails of the gothic arch and slowly reduce the apex -the area of lower

48

tooth contact. This is area is ground flat -not inclined. The procedure is

repeated again and again until the vertical is reduced, but there is still ample

intcrocclusal space. This should be continued for about 20 minutes. When you

are finished, place one of the wax wafers between the teeth, and with the

patient closing firmly against the jig, the wax wafer must still be free to be

moved up and down between the teeth. There must not be any contact between

the teeth and the wax. When we take the zinc oxide and eugenol wash, the

wafer should literally be floating between the teeth. In this way, there is no

conduction of stimuli from the upper teeth to the lower teeth.

We are now ready to take our final registration. The teeth are lubricated with

petroleum jelly. The jig is secured on the anterior teeth with denture adhesive.

A mix of Temp Bond or a bite registration paste is made and applied sparingly

on the indentations of the wax wafer on both sides. The wax is sandwiched

between the paste. Do not use too much paste. Place the paste-covered wax

wafer in the mouth using the "cars" to seat the wafer on the upper teeth. The

patient is guided into a hinge closure and instructed to hold this position firmly.

The patient is closing firmly against the jig. Hold your thumb on the patient's

chin with the index and middle fingers cradling the undersurface of the

chin(fig-22). This will enable you to know if the patient relaxes before the

paste sets. Keep reminding the patient to close firmly. This will place the

condyles upward and on the posterior slope of the articular eminence -a

position that most believe to be the correct position for the heads of the

condyles.

The record is carefully removed after the paste has set. In order to avoid

warpage, a simple procedure is followed. The thumbs of both hand* are placed

on the patient's 'chin, and the index fingers are placed on the outer edge of the

wax record. The patient is instructed to gently separate his teeth. The wax

49

wafer is braced against the lower teeth -the lower jaw acts as a form. Then the

patient is guided into closure again. Now the thumb and index fingers of the

left hand are placed to support the wafer against the upper teeth, and the patient

is again instructed to gently separate his teeth. The upper jaw now acts as the

form to prevent the wafer from being distorted. The wax wafer is removed

from the mouth and chilled. With a pair of surgical scissors (those with a

serrated jaw to grab the set paste), the excess paste is removed. All we want are

the cusp tip indentations so that we can accurately seat the casts into the wafers

and see if they are perfectly seated. The trimmed wafer is returned to the mouth

(with the jig in place) and the patient is guided into centric relation closure.

This will correct any possible slight warpage that could have taken place in the

removal and trimming. The two other wafers are treated the same way. After

the third record has been taken and trimmed and reseated, we remove the jig

and again guide the patient into centric closure (this time with out the jig).

Remove the third wafer "and don't allow the patient to close. Insert each of the

other two records, one at a time, and have the patient close into them (guided)

without the jig in place. The records are now completed and we arc ready to go

to the laboratory and make our mounting and check our centric relation

records.

There are some considerations for special situations. When taking a centric

relation record for working (master) casts, it is necessary to use several

thicknesses of wax for the record. The reason for this is that because of the

increased interocclusal space after tooth preparations, the paste will not register

the tips of the preparations unless the space is reduced by means of the thicker

wafer. In other words, the paste will not stand up long enough to capture an

imprint.

In a remount record, a single wax wafer is sufficient, because now the

restorations are in place and the interocclusal space is reduced. When anterior

50

teeth are missing, you might have to make a Duralay bridge. Your own

ingenuity is your only limitation. When posterior teeth are missing, you may

have to make a Forma Tray wafer with cones to contact the soft tissue in very

small areas. A little thought will allow you to handle almost any situation.

In the laboratory, the upper cast with the split cast wafer is attached to the

upper bow of the articulator, related by a face-bow transfer. A centric relation

record is used to relate the lower cast to the lower bow of the articulator. When

the mounting in completed, we are read;' to verify our results.

Open the articulator separating the two halves of the split cast arrangement.

Make sure the centric relation record is satisfactorily seated between the upper

and lower casts, and close the articulator. The split cast should come together

perfectly. This assures a correct mounting. Next we must verify the centric

relation records. Remove the record used for mounting the lower cast and

replace it with one of the other records. Again, make sure of correct seating of

the casts in the record and close the articulator. The split cast should go

together as it did with the first record. Repeat with the third record. If ail three

records check out the same, there can be no doubt about the accuracy of the

centric relation you obtained.

The Jones Bite Frame:

Another method of taking an interocclusal record is with the Jones Bite Frame.

After the patient has been "trained" with the bite jig. the recording is made with

a zinc oxide and eugenol paste, taken in a gauze "sandwich." This is a rather

tricky, but accurate, procedure. A Jones Adjustable Bite Frame is used to carry

gauze strips. These are glued to a thin wire insulation known as "spaghetti" in

the radio trade. The insulation tubes with the gauze strips attached are cut into

1 1/2 -inch lengths. These are slipped on the wire frame, which is adjusted

51

according to the size of the patient's jaw. This is best done on a cast of the

upper jaw.

A zinc oxide and eugeno! paste, such as Opotow's Mandibular Paste? or Kerr's

Registration Paste is used. The mixed paste is placed on the surface of the

gauze, and the gauze, which is about 3 inches long, is wrapped around the

outside wire of the frame and then around the inside wire until there is no loose

end. In other words, the gauze, with paste on its surface, is wrapped around the

buccal and lingual wires of the frame. This neatly wraps the paste between the

gauze and between the buccal and lingual wires. A slight amount of paste may

be applied on the upper and lower surface of this roll, on both sides of the

frame. It will take a little practice to learn to manipulate the paste without

becoming entangled in it.

The patient is retracted, after being trained with the jig, and the loaded bite

frame is inserted between the teeth. The patient closes firmly against the jig

until the paste sets (fig-23). The lower jaw is supported by your thumb and first

two fingers to ensure against patient relaxation. The set gauze "sandwich" is

removed and carefully trimmed (fig-24), This record is used tc accurately relate

the lower cast to the upper cast. It is best used to remount procedures where the

actual restorations are involved.

VERTICAL DIMENSION

A simple rule to help us determine the vertical dimension of occlusion on

patients with natural teeth is: do not change the vertical dimension of occlusion

that the patient has when the teeth are intcrcuspated in maximum contact.

Another rule that can be used with natural teeth to keep out of trouble is: do not

open the bite.

Bite raising refers to increasing the vertical dimension of occlusion. It is usual!;

done for one of the following reasons:

52

1. To relieve a temporomandibular joint syndrome

2. To restore "lost" vertical dimension in a severely worn occlusion

3. To get rid of facial wrinkles

None of these reasons is valid:

Opening the vertical in each of these situations is an invitation to problems. U

is almost always contraindicated. Some facts should be understood about each

of these problems before any treatment is considered.

Bite raising for temporomandibular joint syndrome:

The vertical dimension has nothing to do with temporomandibular joint

syndromes. The pain-dysfunction syndrome can be solved at any vertical

dimension up to the point of condylar translation and down to the point of

coronoid impingement. As long as the condyles are free to go to their terminal

hinge position, the syndrome can be relieved.

Correcting the occlusion at an increased vertical may eliminate Lhe joint pain

but it almost always results in depression of the teeth, instability of the

occlusion, and excessive stresses on the periodontium. Besides, the

temporomandibular joint syndrome often recurs as the teeth shift under the

added stress.

Restoring "lost" vertical dimension:

More study is needed, put much clinical evidence indicates that even severely

worn occlusions do not lose vertical dimension. Restoring "lost" vertical

dimension in a worn occlusion really amounts to opening the bite because wear

does not normally produce a loss of vertical dimension. Patients can wear their

teeth down to the gum line and still not lose vertical dimension, because the

eruptive process matches the wear to maintain the original vertical dimension.

53

This process of eruption and alveolar development may continue throughout

life as teeth are worn because of the continual addition of layers of cementum

on the root and concurrent passive vertical development of the alveolar process.

So even with wear the jaw-to-jaw relationship remains the same when the teeth

are together.

Opening the bite to eliminate facial wrinkles:

On patients with natural opposing teeth, this procedure may have very

detrimental effects. When the masticatory and facial muscles are at rest, the

teeth should not be in contact. Increasing the vertical dimension to the extent of

stretching the wrinkles out puts such an unnatural demand on the stretched

muscles that It may actually accelerate further wrinkling. The increased length

of the teeth positions them in continuous interference to both normal

contracting and resting lengths of the muscles. Such continuous stretch

stimulation may cause reflex contraction of the muscles with damaging results

to the teeth and supporting structures. The stresses exerted on the teeth are

amplified by unfavorable crown root ratios that result from increasing the

length of the clinical crowns. Furthermore, the effect on the continuously

stretched muscle is to "age" it faster and produce worse wrinkles.

Patients who have previously had bite raising procedures to eliminate wrinkles

are often very insistent about further increases. As the teeth depress or the

wrinkles return, they express the need for more and more increase in vertical

dimension. Some patients tell us they were more comfortable when the bite

was first raised and they would like to regain that comfort. It is difficult not to

give in to such z request because it sounds so reasonable. If we understand that

their early comfort was the result of an improved occlusal relationship rather

than the increased vertical dimension, we can almost always regain the comfort

by equilibration without further increase of vertical dimension.

54

The patient must be made to understand that the muscles should be allowed to

position the jaw without interference from the teeth. "Support" from the teeth at

an opened vertical dimension constitutes an interference to the contracted

muscle in a normal power stroke.

Why not increase vertical dimension?

Occlusions get into trouble primarily from stress. The safest approach when

restoring an occlusion is to keep the teeth from interfering with normal muscle

activity.

When a muscle is neither hypotonic nor hypertonic, it is said to be "at rest".

Even resting muscle is in a mild state of contraction. This mild contraction of

antagonistic muscles is necessary to maintain the posture and position of the

bony parts. We cannot contract one muscle beyond its resting length without

affecting its antagonistic muscle to some degree. The antagonist must release

and give the contracting muscle its way or it may respond by isometrically

contracting more forcefully itself to counterbalance the effect of its antagonist.

Either way, the harmony of resting muscle is disturbed. Any restoration,

appliance or denture that interferes with the optimum lengths of the resting

muscles serves as a stimulus that produces hypertonicity. Such hypertonicity

may result clinically in destructive clenching or bruxism patterns.

Many years 'ago, Niswonger defined the rest or postural position as "that

position of the mandible in which it is involuntarily suspended by the

reciprocal coordination of the muscles of mastication and the depressor

muscles with the upper and lower (teeth) separated". He referred to this as a

neutral position of the mandible.

The rest position has often been a popular starting point for determining the

occlusal vertical dimension, but it is an unreliable approach because the

dimension between the rest position and occlusal contact is not a consistent

55

measurement for different patients. The rest position itself is not consistent.

Atwood found variations as great as 4mm, at the same sitting and even greater

variations at different sittings. Finding the vertical dimension of the rest

position and then arbitrarily closing a specific amount is a very unsatisfactory

approach.

If the occlusal vertical dimension can be established in harmony with the

optimum length of contracting muscles, the muscles will be free to rest at

whatever length is comfortable. The practical approach therefore is to

concentrate on accurately recording the occlusal vertical dimension and

allowing the freeway space to be the natural result of the difference between

the optimum length of contracted muscles and the length of the muscles at rest.

Stoneking has proposed that the definition for occlusal vertical dimension be:

"The vertical relationship of the dental arches when there is maximum

inlercuspation of the natural teeth, and the mandibular muscles arc contracting

through their maximum power cycle".

Some muscles may contract as much as 50% to 75% of their natural length.

Mahan has pointed out that the maximum force with which muscle resists

elongation is applied when it is completely committed to contraction.

It is also apparent that an increase in the vertical dimension would interfere

with the optimum length of contracting muscle in its power stroke.

Several studies have shown that there is a significant relationship between the

power point" of muscular contraction and repcatable phonetic and comfort

measurements. Tueller, using electronic means on dentures, found an average

variation of less than 0.5mm from the vertical established at the muscular

power point when compared with either preextraction records or phonetic

methods.

56

Silverman has reported consistent results in measuring the vertical dimension

of occlusion by phonetic methods. When a patient has lost natural occlusal

stops for recording the vertical, we have found that Silverman's closest

speaking technique has provided consistently reliable results. The vertical

dimension established in this manner is rcpeatable with extreme accuracy, even

over a period of months.

Phonetic method of measuring occlusal vertical dimension:

The phonetic technique is used when there are no opposing teeth in contact. To

understand the principle, one must perform the following steps, as outlined by

Silverman. on 8 patient with opposing teeth.

1. The patient is seated in an upright position with the occlusal plane parallel to

the floor. He is asked to close Firmly (centric occlusion), and a line is drawn

on a lower anterior tooth at the exact level of the upper incisal edge. This line

is called the centric occlusion line.

2. Now the patient says "yes" and continues the "s" sound like yessssss. While

he is pronouncing the "s" sound, a line is again drawn on the same lower

anterior tooth at the level of the upper incisal edge. This line is called the

closest speaking line. The space between the lower centric occlusion line and

the upper closest speaking line is called the closest speaking space.

3. To analyze how repeatable this record is, the patient should be asked to

count from sixty to sixty-six. One should note how the upper incisal edges

comes right back to the closest speaking line with the pronunciation of each "s"

sound. If it does not, the line should be altered slightly to match the "s" position

when the patient reads or talks fairly rapidly.

57

4. If such a measurement is to serve as a preextraction record, the difference

between the closest speaking line and the centric occlusion line is recorded.

The closest speaking space must be maintained in the finished denture.

5. If the determinations are being made on a patient who has already lost his

natural occlusal vertical dimension, the missing teeth can be

substituted for on temporary restorations or fabricated bases. After proper

lip support, esthetics, and incisal edge position have been determined, the

phonetic method can be used to establish the vertical dimension. Since the

vertical dimension of occlusion is unknown, we determine the closest speaking

position first and then close the vertical 1mm from that point. A wax esthetic

control rim(fig-73) can be used in place of upper teeth, it can be attached to

the upper denture base and adjusted for lip support, smile line esthetics, and the

like. If it interferes during the phonetic exercises, it can be easily corrected.

By placing several marks on the lower anterior teeth, we can note which mark

aligns with the incisal edge of the esthetic control rim or the artificial upper

anterior teeth when the S sounds are made(fig-74).

When normal phonetics function can take place comfortably, the closest

speaking level should be noted and the centric bite record should be made by

closing I mm further to the vertical dimension of occlusion.

Restoring extremely worn occlusions:

Excessive wear on upper anterior lingual inclines is most often the result of

posterior interferences that deflect the mandible forward. The forward

deviation of the mandible drives the lower incisal edges into the upper lingual

surfaces, and bruxism patterns may wear the surfaces nearly to the pulp. If we

observe the relationship of the teeth in centric occlusion, it will appear

impossible to restore the lost tooth enamel without opening the bite. If the

58

mandible is manipulated into centric relation, however, we will often find it is

somewhat posterior to the acquired worn position.

The interferences should be eliminated by selective grinding so that the

mandible can close without forward deflection to the same vertical dimension

as the acquired centric occlusion. When this is accomplished, we will usually

find that we have sufficient clearance between the lower incisal edges and

upper lingual inclines without changing the vertical dimension(fig-75).

It is not always practical, however, to restore a worn occlusion without some

increase in vertical dimension. As the anterior teeth wear, the lower incisors

have a tendency to drift forward. Severe wear may produce an end-to-end

relationship of the anterior teeth that is very difficult to solve. The problem is

intensified when the wear approaches the pulps of both upper and lower

anterior teeth. Sometimes the only choices open are either to devitalize several

teeth to make room for the restorations or to choose the alternative of

increasing the vertical dimension. The dentist must decide which decision is the

lesser of evils. The usual choice would obviously be to open the bite.

If the vertical dimension must be increased, it should be opened no more than

is absolutely necessary to provide room for the restorative materials. This

would rarely exceed 1 to 1 '/j mm. Even then, the dentist should be aware of the

potential problems that might result, mainly instability following the restorative

increase in vertical dimension.

When the vertical dimension must be increased, patients should be advised of

the possibility of some shifting of the restored teeth until the occlusion

stabilizes. Even an increase of lmm requires careful checking and periodic

occlusal adjustment for up to a year before normal stability of the occlusion

results.

59

When the vertical dimension is increased in combination with splinting, we do

not notice the same degree of shifting of the teeth.

Badly worn anterior teeth that have drifted into near end-to-end relationships

present a real restorative challenge. It is difficult to lengthen the upper anterior

teeth without severely steepening the anterior guidance, and patients who have

developed almost horizontal function do not readily change over to vertical

functional patterns. A compromise is usually called for that permits the anterior

guidance to start out as flat as possible and then progress into the steeper

guidance as gradually as possible by way of concave pathways.

By moving the incisal edge lingually we arc able to lengthen the lower anterior

teeth and provide some overjet for the upper teeth. Which we can produce

sufficient overjet, we can then curve down from the cingulum contact and

provide more length for the upper anterior teeth. Both esthetics and function

are improved by such a procedure.

Anterior wear is not always equal on both arches. There is no possibility of

cingulum contact in these cases so there is no good alternative but to have

contact on fairly wide upper incisal edges. Upper anterior teeth that do not have

fairly strong bone support may need to be splinted if the guidance is steepened.

Unless it results in labially directed stress on the upper anterior teeth, there do

not appear to be any problems associated with closing the vertical dimension

on natural teeth. It does not produce stress because a closed vertical dimension

does not interfere with muscle lengths.

Closing the vertical dimension to an extreme degree could cause coronoid

impingement against the zygoma, but it is highly unlikely that there would ever

be a need for that much closure. Tenderness to palpation in the zygoma area

would alert us to this.

60

Relationship of the anterior teeth to vertical dimension;

One of the most important considerations in any change of vertical dimension

is the direction of the arc of closure. As the mandible is elevated, the lower

incisors travel forward on the closing arc. Any time the vertical dimension of

occlusion is reduced, the lower incisal edges are automatically moved forward

at the more closed vertical dimension.

If the lingual surfaces of the upper anterior teeth are in the way of this forward

movement of the lower teeth, it results in horizontal stress directed labially

against the upper anterior teeth and lingually against the lower anterior teeth.

The axis of closure on most simple articulators is much closer to the occlusal

plane level than the true condyiar axis (which is higher). The arc of closure on

the erroneous "simple" articulators is nearly vertical, rather than forward, if the

bite is closed during restorative procedures, the interference to the front teeth is

not noticed on the improperly mounted models.

If such restorations are placed in the mouth. the resultant stress against the

anterior teeth is not easily picked up without digital examination. The incline

contacts are so steep and the vector of force is so horizontal that the upper

anterior teeth are forced out of the way and the lower anterior teeth are forced

inward. The result is continuous complaints by the patient that the front teeth

"hit too hard".

The vertical dimension can sometimes be closed to improve anterior

relationships in anterior overjet problems. Closing the vertical dimension may

arc the lower incisors forward into contact that they did not have al their

original occlusal vertical dimension.

61

FUNCTIONAL ASPECTS OF COMPLETE MOUTH

REHABILITATION

A BIOLOGIC AND FUNCTIONAL approach to restorative dentistry is

essential for the satisfactory performance and fulfillment of those requisites

basic to Prosthodontics. Accordingly, the masticatory organ must be considered

as a functional consolidated unit, with proper attention being directed to all the

elements that comprise this unit. All functional factors are interrelated, and

proper regard for each aspect is essential, if the restoration and maintenance of

the health of the entire functioning mechanism is lo be a realization.

Consequently, a comprehensive study and practical approach must be directed

toward the interrelation of the teeth and their supporting periodontal structures,

the myofunctional aspects of mastication, the intricacies of vertical dimension,

freeway space, centric relation, and centric occlusion.

The objective of complete mouth rehabilitation is the reconstruction,

restoration, and maintenance of the health of the entire oral mechanism. The

accomplishment of this goal requires an understanding and utilization of all

available dynamic potentials.

Complete mouth rehabilitation is a dynamic functional problem, and embodies

the correlation and integration of all component parts into one functioning unit.

The aim and endeavor, therefore, must be reconstruction and rehabilitation of

the whole satisfying all the related factors.

The science of complete mouth rehabilitation rests upon three proved and

accepted fund a mentals: namely, the existence of a physiologic rest position of

the mandiole. which is a constant; the recognition of a variable vertical

dimension; and. finally, the acceptance of a dynamic, functional centric

occlusion, These principles ha\e been basic in the development of the

62

myofunctional concept of mastication and have furthered the development of

the physiologic approach to occlusion.

Physiologic rest position:

Investigations have proved that the physiologic rest position of the mandible is

fixed and constant, and that it does not vary with age or with the presence or

absence of teeth. Thus, it is a reliable starting point for the design of a

physiologically correct occlusion. The physiologic rest position is a relaxed,

normal, physiologically balanced maxillomandibular positioning, wherein

antagonizing tensions that exist during function are in a state of equilibrium.

All functional movements of the mandible begin and end, at this rest position.

From a practical point of view, techniques have been devised whereby this

position can be recorded, registered, and maintained.

In order to study and determine mandibulocondylar changes that occur when

the mandible assumes the various functional positions common to it,

roentgenographic techniques for obtaining laminagraphs and cephalograph can

be adapted. The laminagraphic technique affords a means of comparative study

of mandibular positions and their respective, corresponding condyle

relationships. Exposures are made at the original tooth contact position, the

physiologic rest position, the wide-open position, and the proposed restorative

functional position. By a double exposure technique, laminagraphic

superimpositions are secured of the physical contact position and the

physiologic rest position of the mandible. Laminagraphy has proved a valuable

adjunct in temporomandibular joint radiography, for it offers a means of

securing undistorted, clear pictures of these joints. These studies enable one to

detect abnormalities of the articulating surfaces, deviations in the functional

pattern, and any gross pathology. It enables the dentist to gain a perspective of

the path of the condyle during closure, noting its displacement if any, as the

mandible travels from its physiologic rest position to its physical contact

63

position. It further enables the operator to observe the possibilities of

eliminating and correctirg this displacement by means of comparative study of

the mandibular positions. The size, shape, form of the condylar head and neck,

the fossa, and the aiiicular tubercle, tubercle, together with variances in the

condylar free-way space, may be observed in the superimposition of the

physical contact position and the physiologic rest position. Deviations and

changes from the natural will be observed in accordance with the particular

type of occlusal anomaly. Thus, this affords an opportunity of observing the

existing condyle positions, and offers a radiographic blueprint of the positions

that the condyles will assume at the completion of the restorative work.

Another important diagnostic aid in the recording and study of the mandibular

position is the cephalometer. The technique consists of positioning the head in

a fixed reference frame and of standardizing all the component, factors: the

central ray. The position of the head, and the x-ray film. Roentgenograms and

tracings of the successive positions of the mandible may then be obtained for

accurate comparative study. Exposures arc obtained at the physical contact

position, the physiologic rest position, and the proposed vertical opening. The

resulting cephalograms then may be superimposed, one upon the other, and a

composite tracing of the three mandibular positions can be obtained. This

offers a simple and concise means for comparative study, and affords a

blueprint of the exact amount of existing freeway space. The possibilities of

utilizing this potential freeway space in the rehabilitative process can be noted,

and it is possible to observe the functional freeway space that will exist after

rehabilitation. These methods of study are invaluable and act as a guiding

factor in the diagnosis and treatment planning by revealing the possibilities as

well as the physiologic limitations of treatment.

64

Functional analysis of occlusion:

A functional analysis of occlusion is pertinent to the formulation of a proper

plan of treatment for complete mouth rehabilitation. It must include: (1) The

determination of the proper vertical height by utilizing the physiologic rest

position of the mandible as a guide, and 'noting the existing functional freeway

space. (2) An examination and study of the path of closure from rest position to

the physical contact position of the teeth, noting whether condyle displacement

occurs. (3). The effects of the occlusal pattern upon the periodontal structures.

(4) A study of the temporomandibular joint positions relative to the occlusal

pattern by means of rocntgenographic evaluation.

65

TREATMENT PLANNING

Before we begin treatment, it is important to have a complete plan of operation.

The patient usually wants to know just what we are going to do. so that he may

plan his life accordingly. He should be told the probable length of time

involved in the treatment, the length and frequency of the appointments, and

the possible indisposition. A person in business may not want to return to his

office feeling numbness or discomfort after a two-hour session. He may

therefore prefer to have his appointment in the afternoon in order that he may

return directly home. Other patients would rather have the work done early in

the morning to get it out of the way. For the best dentist-patient relationship, all

these things should be considered.

Some patients have great distances to travel. We should plan their treatments

and appointments with a view to keeping the number of trips to a minimum.

Where patients come from out of town, our laboratory schedule should be

arranged so that the necessary work can be finished in a reasonable time.

In most cases it is advisable to give the patient a general outline -not the

particulars -of the planned procedure. The details will serve no purpose except

possibly to confuse, scare, or impress him. He will be more impressed,

however, by the results. Occasionally a patient is interested and intelligent

enough to want to know more about the projected work. In such instances, a

more detailed exposition of what is involved may help the general because of

patient education, since these patients may discuss the type of treatment with

their family and friends. In any event, it is extremely important that we outline

exactly what we plan to do.

Periodontal Treatment:

From our examination and diagnosis, we will have decided whether our first

course of action is to be periodontal treatment. Depending upon the case, this

66

may be extensive or conservative. Depending upon our personal judgment,

periodontal therapy may be postponed until the more important phases of

correct function are established.

A sensible procedure is to combine the periodontal treatment (if not too

extensive) with the appointment for the preparations. At this session, we

usually anesthetize one quadrant of the mouth. By the time the preparations are

finished, we have ample access to all the gingival tissues, and the interproximal

areas arc as accessible as they arc ever going to be. Deep scaling and curetting

is easily accomplished, and if any pockets are to be removed, they can be

quickly attended to. Mow often have we taken an impression that went beyond

(he margin and found an area covered with calculus? Now is the best time to

remove it. Furthermore, periodontal treatment (or curetting) will enable us to

get better gingival retraction at this time than we could other- wise obtain

without additional tissue trauma. Moreover, since we have to place temporary

coverage on the teeth anyway and cement it to place, this can be just as well

accomplished with a surgical dressing such as Ward's WondrPak. All we do is

to extend the dressing over the gingival tissues. This is recommended if the

periodontal condition is not extensive. If the periodontal treatment is

complicated, and is referred to a periodontist, then there are several ways to

proceed.

From the periodontist's point of view, it would be best to have the teeth initially

prepared and stabilized with temporary splints. These could be removed to

allow better access for the periodontal procedures. From the prosthodontist's

point of view, this means that the teeth have to be prepared twice. It is true that

with this sequence there is less likelihood of having margins of gold exposed

after tissue healing; on the other hand, it means double jeopardy to the pulps.

Every time a tooth is prepared, no matter how minor, the pulp is irritated.

Usually it recovers, and fortunately the time required for periodontal healing is

67

sufficiently long to allow the pulps to recuperate. In addition, the patient docs

not appreciate being assaulted twice.

Another way to proceed is to have all the periodontal treatment completed

before starling the tooth preparations. The periodontist has less access to the

areas, but usually he or she can manage. Any root resection can be performed

a! the time of periodontal treatment. The endodontic treatment can be

completed before or after root resection (for the remaining roots). Today, most

periodontisls are trained for minor tooth movement. If there is need for this

therapy, it can be incorporated at the same time that periodontal treatment is

being performed. Most prosthodontists can lake care of minor tooth movement.

However, if more complicated tooth movement is required to enhance a result,

then an orthodontist should be called upon to treat this phase of it.

The third way to proceed is to complete the prosthodontics and then have the

periodontist touch up the case. This is the least desirable, because there will

almost always be an esthetic problem.

As you must now be aware, we are recommending a very long tedious, painful

course.

From our examination and diagnosis, we should be in a position to recommend

one of several courses lo take. Some patients will not want (o go through

orthodontic therapy. These cases may have to be treated only by prosthetics.

even if there is some compromise in the end result Some patients may not want

to undergo extensive periodontal treatment: a compromise, with possible

deleterious results, may have to be made. There may be questionable teeth

involved. These questionable teeth may mean the difference between fixed

restorations and removable partial dentures. If the patient is set against a

removable appliance at this time, it may be necessary to use the questionable

abutment teeth, making sure that the patient is aware of the possible short life

68

of the restorations. Some patient are willing to take the chance in order to gain

a few more years of not having to wear a removable restoration. In these cases,

we may or may not build in contingencies for future changes in the restoration:

for example, precision attachments that could later be used for a removable

restoration.

It should be obvious that each case is an individual consideration. After an

honest presentation of all the factors, then the patient must make the final

decision. Don't try to insist on an ideal procedure for every patient, if the

particular patient will rot accept or cannot accept the ideal program. As long as

the patient understands all the possible problems due to the compromises, there

is nothing more that you can do. You may be amazed at the results cf cases that

are not given the ultimate treatment: many bifurcated and trifurcated teeth give

much more service than anyone expects: and many pockets of 2,3, and 4 mm.,

with proper home care and frequent office visits. do not get any worse for

many years.

When it all is said and done, there is one very important faci to remember: the

most perfect treatment possible will fail if the patient does not take good care

of it. This means excellent home care. A perfectly treated mouth that doesn't

get good home care will fail- it only takes a little longer. Treatment failures,

almost without exception, are with patient who are not sufficiently motivated to

execute good home care. The most intelligent people are often the most

disappointing: they seem to think that if they have paid a substantial fee for

something, it should take care of itself.

So. after a comprehensive diagnosis, and after evaluating the patient's altitude,

should be able to predict the course of events for each case.

In any event, the first part of treatment planning should encompass the soft

tissues. Any residual infections, abscessed teeth that cannot be salvage and

69

acute Periodontal pocket should be eliminated. Endodontics and possible root

resections should be executed.

Mandibular Registrations:

If registrations were not taken as part of the complete diagnosis, then they

should be taken now. This step must precede our decision as to the type of

restorations and preparations that will be necessary.

Clutches are to be constructed on the casts previously mounted for the purpose

of diagnosis, or reference plates are fitted to these casts. By means of the

pantograph, the patient's individual mandibular movements will be recorded,

and the pantograph registrations will then be transferred to a suitable

articulator. After adjustment of the articulator to the pantograph registrations,

the study casts will be remounted to the correct axis by means of a face-bow

transfer and a centric relation record.

It is advisable to have a duplicate set of study casts accurately mounted on the

articulator. Usually it is possible to pour a second set when alginate material is

used for the impressions. One face-bow transfer and one centric relation record

arc sufficient to mount both sets of casts. One set is preserved as a permanent

record of the pretreatment condition. The second set is utilized for making

temporary restorations, if they are to be used. In addition, the second set is used

in making the diagnostic preparations and diagnostic wax-up to determine the

type of preparations required and the amount of tooth structure to be removed

in each area.

Restorations:

At this point we plan our restorations.

With our knowledge of the principles of articulation and the development of an

articulation in wax. we proceed to survey the problem before us. Our study

70

casts now will duplicate the patient's relationship in every detail. The long a\is

of each tooth can be examined as it is related to the others in the various

excursions. The anterior overlap and overjet can be studied, and any changes

can be planned. Some orthodontic procedures may be indicated. The

buccolingual relationship of the posterior teeth is evident and will be helpful

in determining the type of restoration to be employed. The curve of Spee and

(he plane of occlusion are now observable in their true relationship to the oral

mechanism. Any changes in these conditions are planned before tooth

preparation begins.

The necessary cusps can be visualized or actually carved on the study casts.

This will dictate the amount and location of any tooth reduction necessary to

establish proper articulation. Edentulous areas arc outlined, and their

restoration planned. Abutment teeth are examined in the light of the

replacements they are to support. If precision attachments are contemplated, the

preparation of the abutment teeth is planned to enhance the results of the case.

The cuspid relationship is carefully examined, and the type of restoration is

projected. This is an important decision that cannot be made until we have

accurate mandibular recordings because the path of (ravel of the lower cuspid

is determined by the Bennett movement of the case.

By considering all the foregoing factors and conditions, it will be possible for

us to plan our treatment and decide which type of restoration will best

accomplish the desired objective. Our first preference would be for restorations

of the onlay type, but these are neither always practical nor possible. We may

have to resort to veneer crowns in some or all areas, in which case a decision

will have to be made as to the type of veneer material to be used. The

preparations will depend upon the material selected. The order in which the

teeth are to be prepared may require some planning. If the patient is wearing a

removable appliance, we should plot our work to enable him to wear it as long

71

as possible, or we should arrange for its replacement to prevent any

embarrassment to the patient. This is especially true if an anterior tooth is

involved. Usually we prefer to prepare the anterior teeth after alt the posterior

restorations are in place, but sometimes this is not possible, and they may have

to be prepared and temporarily covered before anything else Is done. Good

judgment should dictate the course of action in each case.

In planning our treatment, we must consider the edentulous areas. If a

removable appliance is to be made, the impression can be made for a custom

tray even before the preparations are started. In this way, the tray can be

constructed and ready by the time the mouth is fully prepared. Dovetailing

these procedures will expedite the completion of the entire restoration. The

final impression of the edentulous area should be taken after the attachments

are in the abutment castings. This insures a better relationship of the base lo the

abutment castings.

If any teeth are to be removed, this should precede all other treatment to allow

maximum time for healing. It might be advisable to plan the work so that the

preparations are not started until a reasonable time has elapsed for healing. In

this way, we will not have to wait so long after the teeth are prepared before

proceeding with the construction of the case.

In special situations, any extractions could be done at the same time as tooth

preparation, thus avoiding a second injection al a later dale. For instance, if a

first molar is to be removed in a quadrant that is to be prepared, the adjoining

teeth are prepared and the first molar extracted. After bleeding is somewhat

arrested, the temporary can be made, replacing the extracted molar, In this case

the final quadrant impression is not taken until sometime later when the healing

has taken place. The ridge area will later be recorded in the remount procedure,

which usually is several months later. By this time, the ridge area is sufficiently

healed to allow a good pontic relationship.

72

If an anterior tooth is to be removed, the same procedure is advisable: prepare

the adjoining teeth and then extract the tooth to be removed and make an

immediate temporary. The patient will appreciate this sequence of treatment.

Prognosis:

When we have completed our plan of treatment, we should arrive at a

prognosis for the case. This should be explained to the patient. Often teeth are

involved that are quite questionable. There is no sure-fire method of

determining just how certain teeth will respond to treatment. Sometimes,

happily, the results are amazing. Although we should try to save as many teeth

as possible, occasionally in our enthusiasm we may overstep the bounds of

reason. This is all right as long as we are prepared to change our treatment plan

as the case may warrant. It is good practice to plan our restorations so that, if a

questionable tooth does not respond to treatment, we have an alternative

solution.

Sometimes a case has to be completed with a precision attachment in a healthy

tooth next to a questionable one. For instance, if the upper first bicuspid has a

good periodontium, the second bicuspid and second molar are doubtful, and the

first molar is missing, we would construct a fixed bridge from the second molar

to the second bicuspid and place an attachment in the first bicuspid.

The male attachment, which is pan of the fixed bridge, helps to stabilize the

bridge by virtue at its insertion in the first bicuspid. If the bridge abutments are

to be removed at a later date, the attachment is already in place. Usually there

is a similar condition on the other side, and another attachment has been placed

and paralleled to the first one.

This, then, is what we mean by "treatment planning" and why it is so important

to make a careful study of all the factors involved before treatment is begun.

73

PREPARATION OF THE MOUTH FOR REHABILITATION

Having completed the necessary diagnostic procedures, having decided that

complete oral rehabilitation is indicated, and having made our treatment plan,

we must now prepare the mouth for the restoration.

Depending upon our findings, we will remove or have removed any infective

processes such as retained roots, impactions, unimportant devitalized teeth, and

the like. Today, with proper endodontic treatment, the retention of questionable

strategic teeth is possible. However, since these teeth are potential liabilities

from the standpoint of the complete treatment, often it is wise to include in our

restoration plan the possibility of their loss at a subsequent time. In other

words, we should be prepared for such contingencies as fractures, undetected

decay, and recurrent infection. Whenever feasible, we should provide insurance

against fracture by the use of a metal post and/or collar of metal. As with most

general rules, exceptions are sometimes in order; for example, the retention of

an impacted third molar. If its removal would jeopardize a second molar

needed for a bridge abutment or the removal of a devitalized strategic root in a

patient suspected of having a focus of infection. Occasionally, a perfectly good

tooth may have to be sacrificed because of its relation to the other teeth. It is

not wise to compromise the result of the entire effort just to save a single

tooth".

Treatment of the Soft Tissue:

Most of the cases that we are called upon to treat have some periodontal

involvement, it may vary from slight to very severe. The time of treatment will

depend upon the type and severity of the condition. If it is mild, routine therapy

(scaling and curettage) is sufficient. If the condition is severe, however, certain

considerations must be taken into account. Extensive periodontal surgery may

74

be necessary, and this frequently leaves a noncsthetic result. Although the

removal of infected tissue is very definitely part of our treatment, and, in fact,

one of the criteria of a successfully treated case, still the esthetic considerations

are also important.

What we recommend here is a conservative approach; in other words, only the

very necessary minimum periodontal surgery until the case has been

functioning for a while. It is amazing how much tissue improvement can take

place as a result of good dentistry with correct contours and proper function. In

many cases the necessary surgery is minimized remarkably.

There is a possible disadvantage to this approach because we cannot determine

beforehand exactly how much change will take place; it sometimes becomes

necessary to re-prepare several teeth in order to obtain a more esthetic effect.

This may be the price of conservatism. However, after one observes the

improvement of several cases following the establishment of proper function, it

is natural lo conclude that this is the better approach. It becomes a matter of

personal judgment.

Posterior Region:

The location of the severely involved tissue is important. The posterior

segments are more difficult to keep clean and stimulated by home care. From

an esthetic standpoint, they are not so essential as the anterior. Consequently, it

seems more logical to strive to remove all periodontal pockets posteriorly, even

if this entails extensive surgery. The abnormally long crowns required by these

procedures are less conspicuous in the posterior region. The restorations, if

they are full crowns, should be made to cover all exposed tooth structure to

prevent the possibility of secondary decay. Just as the soft posterior tissues are

difficult to care for properly by home care, so is it difficult to keep the tooth

surfaces clean to prevent decay.

75

Anterior Region:

In the anterior region, where esthetics is so important, it may be necessary to

accept a compromise. Shallow pockets, which can easily be kept under control

by home care and frequent visits to the dentist, may be the lesser of two evils.

Our experience indicates that when a mouth is restored to proper function, such

pockets as remain either improve or stay the same. They seldom become worse.

All that is required is proper function, frequent curettage, and good home care.

From an esthetic point of view, this is better than denuded root surfaces or

excessively long crowns, which would require a gingival mask to restore the

esthetics.

Preparation of the Teeth:

The type of preparation to be used in the treatment of the function of an entire

dentition is dependent on several conditions. It is our problem to attach or place

restorations that will function properly. How these restorations arc to be placed

in or on the teeth will depend primarily upon the relationship of the teeth to

each other and to their opposing members. In order to be able to plan this

procedure correctly, we need carefully made study casts, properly mounted on

an adjustable articulator that duplicates the patient's jaw movements. This

presupposes that accurate registrations have already been taken and a proper

mounting of the casts made with a face-bow transfer and a good centric relation

record. If such is the case, we are now in a position to observe the relationship

of the teeth to each other.

It should begin to be apparent that the decision on how the teeth are to be

prepared will rest on a determination of the cuspal relationship necessary to

make the mouth function properly. In other words, we will have to visualize the

finished articulation before we can grind away tooth surfaces. It is usually a

wise procedure to prepare the teeth of the mounted casts and to wax up the case

76

sufficiently well to arrive at an accurate picture of where the cusps are going to

fall.

Once we have a substantial idea of the articulation to be established, we are in a

position to decide how the teeth are to be prepared. Certain areas will have to

be removed to allow space for an opposing cusp. Certain-areas will have to be

built up to make the proper contact. Certain teeth will have to be warped in

order that they may interdigitate properly with the opposing members. The

forces of articulation will have to be visualized, and their dissipation planned.

Method of Treatment:

There are a number of factors that will determine whether a case can be treated

by onlays or whether it must be treated by full coverage.

Adverse relationship of the Long Axis of the teeth: Frequently, when the

properly mounted study casts arc examined, it will become evident that the

long axes of the upper and lower teeth are not ideally related. The long axis of

an upper tooth may be directly over the long axis of the opposing lower tooth.

Such an arrangement precludes the use of onlays in the reconstruction

procedures, for it would not be possible to interdigitate the upper and lower

cusps properly without producing a monstrous result. This situation, of

necessity, requires the use of full coverage.

In some cases where the long axes of the upper and lower posterior teeth arc

not ideal, it may be possible to achieve a suitable articulation by warping onlay

preparations. For example, by overbuilding the mesial of a lower onlay and the

distal of the opposing upper onlay, we may be able to effect a functioning

articulation without too great a display of gold on the mesial proximal surfaces

of the upper teeth. On the other hand, it may be necessary to overbuild the

mesial of the upper posterior teeth while overbuilding the distal of the opposing

lower teeth. This is less desirable from an esthetic stand- point because of the

77

excessive display of metal. It is possible, of course, to overcome this condition

by using full veneer coverage. Still, after observing the change that has taker,

place in some veneers after a number of years, I am inclined to wonder whether

it would not have been better in these cases to have had a display of metal

rather than discolored veneer material. The use of porcelain veneers has

overcome this to some extent.

Insufficient Overjet of the Posterior teeth: In our discussion of articulation, it

was demonstrated that properly articulated occlusal surfaces require an overjet

of the upper posterior teeth. If there is an insufficient buccal overjet, then

onlays are again precluded. A condition such as this would necessitate the

construction of onlays that have a ledge from the gold to the tooth surface, and

this would not be satisfactory. Therefore, to establish proper buccal overjet and

have restorations that blend with the tooth structure, full coverage is here

indicated.

Cross-Bite Relationship: Very seldom can natural teeth in a crossbite

relationship be restored to proper function by means of onlays. Occasionally

this is possible if the teeth happen to be properly tipped and ideally

interdigitated. Usually, however, a cross-bite relationship must be treated by

full coverage. This is not to imply that the teeth can be restored to a normal

relationship by full coverage, for that would require too much tilting of the long

axis. Rather, we mean that full coverage is the only method by which a proper

cross-bite relationship can be established when it is indicated.

Caries-Susceptible Mouth: Mouths that have required many fillings over the

years are usually candidates for full coverage. Where we find M.O.D.

restorations as well as Class V restorations, both buccal and lingual, it hardly

seems wise to labor merely to have a few islands of enamel. Full coverage, of

course, does not rule out the possibility of future decay. As a matter of fact, a

caries- susceptible mouth must be watched very closely after full coverage

78

because the margins of the restorations are, for (he most part, hidden under the

free margin of the gingiva.

Thus far, it might appear that the obvious way to treat all cases is by full

coverage. Although it is true that it is much easier and quicker to prepare a full

crown or a series of full crowns than to prepare satisfactory onlays, it is also

true that considerably more tooth structure has to be sacrificed in a full crown

preparation. Also, it is extremely difficult to properly contour full crowns. To

date, there is no satisfactory substitute for natural tooth structures. From many

standpoints, plastic veneers are far from desirable, and porcelain has its

drawbacks.

Wherever possible, the restoration of choice is the onlay, and for these reasons:

-There is less destruction of tooth structure.. - There are no veneers to construct

or maintain. -There are fewer margins in areas susceptible to decay. -There are

more guides left for proper contouring.

Use of Full Coverage:

In cases where it is not practical to use onlays, a definite compromise is

indicated, and we must resort to full coverage. If the result is to be satisfactory,

we must be guided by certain considerations.

The reduction of the occlusal surface must be executed so as to allow sufficient

depth for the opposing cusp. In other words, it visually is not enough to cut

straight across the occlusal surface; it has to be reduced more mesially and

distally. depending upon the relationship of the tooth to its antagonist. Here is

another advantage of the onlay preparation: in most cases it provides ample

space in its proximal box form.

The reduction of the buccal surface must be made with the requirements of a

veneer in mind, when one is indicated. Sufficient tooth structure must be

79

removed to allow for an adequate thickness of veneer material. Furthermore,

the reduction must be carried below the gingiva when esthetics is a prime

factor.

The most satisfactory type of full coverage preparation is the chamfer. This

conclusion is based on a long and careful observation of both chamfer and full

shoulder preparations. In reconstruction cases, restorations are temporarily

cemented for rather lengthy periods, and it has been found that washouts occur

less frequently under chamfer-type preparations than under full shoulders.

It Is almost impossible to cast accurately to a complete shoulder preparation. It

is also considerably' more difficult to adequately seat a restoration that has a

full shoulder. Moreover, when the full shoulder is used as a fixed bridge

abutment, the problem of perfectly seating the restoration is increased.

Use of Onlays:

Onlays, too, must be intelligently prepared, and the following principles and

procedures observed:

-The cavity outline should permit the restoration (o blend naturally into the

remaining contours of the tooth structure.

-The cavity margins should be carried to immune areas; in other words,

extension for prevention.

-The margins must be carried beyond the occluding surfaces so that function

will not tend '.o open them.

-All functioning surfaces should be covered or "shoed" to minimize the

possibility of a sheared cusp.

- Flat gingival seats, square walls, and reasonable depth for a sufficient

thickness of filling material are required to insure retention and adequate

80

strength against swaging and opening of the margins. Slice preparations are not

suitable.

- Cavity margins should end in sound tooth structure.

- As long as sufficient retention is obtained, it is not necessary to carry the

proximal margins below the free margin of the gum.

- Cavity outlines must include sufficient areas to permit

articulation to be established without an undue display of filling material.

This is especially important for the cuspids and the anteriors.

- Proper bevels should be employed to enhance the life of the restorations.

Short, thick bevels are preferable to thin ones.

- Accessory anchorage in the form of pits or grooves may occasionally be

required for adequate retention.

- A!! ground surfaces should be polished with fine stones, diamonds, or cutile

fish discs.

Pin-Ledge Restorations:

Extremely valuable in full mouth rehabilitation is the pin-ledge type of

preparation. Until recently, it was a rather difficult restoration to construct and

therefore was not often used. Now, however, because of the technique

developed by

Dr. B: David Shooshan (I960) of Pasadena. California, the pin-ledge has again

assumed its rightful place in dentistry. New burs and drills, coupled with pylon

bristles for making the indirect impressions and the wax patterns, have

simplified the construction of this type of restoration.

81

In many instances where the lingual area of an anterior tooth has to be but it up

for contact, it is easy to make a pin-ledge preparation. Often the enamel does

not have to be removed at all. The pinholes are located clear of the pulp and

started with a A -round bur. A 24- or 27-lhousandth twist drill is then used to

make the pinholes. If desired, a slight ledge may be added for gold bulk. The

pinholes must be parallel. This is an easy procedure, provided one docs not

move his finger-rest after starting to drill the holes. The hand and arm must be

kept rigid to maintain the parallelism of the hand niece and bur. If one is not

experienced in this procedure, it is wise to practice on extracted teeth on a

manikin.

Depending upon the particular conditions present, many variations arc possible.

Frequently a Class 111 cavity is encountered on one side of the preparation,

and here we may make an old-fashioned groove and a proximal slice.

If the pin-ledges are to be used as a periodontal splint, then the proximal

contact areas may be slightly prepared with a flame stone or disc to permit

soldering to the adjacent pin-ledge. Pin-ledge preparations are adequate to

carry anterior pontics without destruction of all the abutment tooth

structure(fig-25). A much stronger, more retentive pin-ledge preparation is

taught by Dr. William H. Pruden, 11.

The lingual area is reduced with a football-shaped diamond (Wl). The ledge is

cut lingual to the incisal edge, leaving enough thickness of tooth structure so

that the gold will not cast a shadow. Use a cylindrical diamond for this ledge.

Use the same diamond to make the seats for the pinholes -one mesial, one

distal, and one in the cingulum. Start the holes with a !/2-round bur. Then with

a slow-speed hand- piece and a 699 steel bur, make the pinholes, going from

one to the other, maintaining parallelism with the hand piece. The holes are

made parallel to the- labial surface of the tooth to avoid the pulp. The holes are

trued up with a 700 steel bur. (On lower anteriors stop at 699). With a flame-

82

shaped, smooth cutting diamond; place a finishing bevel around the edge of the

lingual area, and on the incisal edge of the mesio-distal ledge. The impression

is taken in hydrocolloid. using a 25-gauge needle lo deposit the syringe

hydrocolloid in the pinholes. Deposit the syringe material slowly so not lo trap

any air. The heavy-bodied, tempered hydrocolloid in a water-cooled tray is

quickly placed over the syringe material and the impression is cooled for 5

minutes. A stone cast is poured in good die stone. After lubricating the die, the

wax pattern is formed, invested, and cast in a hard gold. The main difference

between this pin-ledge and the previously described technique is the size of the

pinhole. A larger, tapered pin is much stronger and more retentive than the

thinner .027 pins. The length of the pins is approximately 2 to 4 mm., or as

long as is feasible without reaching the pulp.

High Speed:

Methods of preparing the teeth are changing so rapidly today that it is

impossible to cover all of their ramifications. Some generalizations, however,

can be made.

High speed in dentistry is here to stay. Preparations are easier to make, and the

procedure is less fatiguing to the patient. Whereas in the past, tooth preparation

in full mouth rehabilitation was a real task, now, thanks to improved

anesthetics, diamonds, carbides, and high-speed equipment, this phase of the

treatment is the easiest. Many precautions, of course, have to be observed with

the rapidly cutting instrument. Since good vision is obviously necessary, the

lighting facilities should be better than average. Only good carbide burs and

diamond points should be used, and careful control is mandatory. To avoid

possible trauma, the oral tissue must be retracted (preferably by an assistant).

So that there are no "fried pulps." adequate cooling Is essential. The use of air'

and water with an automatic attachment is recommended. Adequate aspiration

83

is also necessary with fluid coolants, and are should be taken to prevent the

propulsion of tooth and restoration material into the patient's throat.

Helpful Hints:

Because they have proved to be of value, the following work habits and

procedures are recommenced:

-Whenever possible, work in a sitting position. Apart from the fact that this is

less tiring to the operator, a more relaxed feeling is transmitted to the patient. -

Prepare the teeth in quadrants. With one injection of anesthetic, it is usually

possible to prepare four teeth as readily as one or two.

-Make the same cuts on all the teeth before discarding the cutting point, thereby

getting the maximum work out of an instrument before changing to another. -

Frequently examine the progress made. Using air to clear the field. -At the

preparation stage, remove only enough decay necessary to prepare the tooth.

Complete removal at this time may sometimes create problems in impression

inking. The only exception is where there would be danger of pulpal

involvement unless complete removals were resorted to. In this case, the decay

should be removed and replaced with cement. This cement, in turn, should

be removed prior to final cementation so that there will be just one mix of

cement between the restoration and the tooth.

- Carefully examine all margins and the tooth structure adjacent to the margins,

especially in the gingival areas. There may be calculus present that must be

removed. Restorations, after all, are to be made against sound tooth structure,

not against a layer of calculus.

-Carefully examine all preparations for under cuts, for definite, smooth finish

lines, and to determine whether the tooth structure has been adequately

removed in the proper places.

84

When the preparations are finally completed to our satisfaction, we can proceed

to make the impressions

Temporary Coverage of Prepared Teeth:

After we have prepared the teeth and made the impressions, it is necessary to

give some temporary protection to the preparations Usually we make our

"temporaries' before making the impressions. Those made of gutta-percha will

help retraction. Those made of acrylic can be trimmed and polished by the

technician while we make the impressions.

On lay Type:

If the preparations are of the onlay type, hard gutta-percha is used to form a

continuous bridge from one preparation to the next (usually there are four in a

row). The gutta-percha bridge is trimmed and adjusted to the opposing teeth

and then cemented in place with a temporary cement, such as MOYCO,

Pulprotex, or Temp Bond to prevent sensitivity. A temporary gutta-percha

filling should never be placed without some type of temporary cement to keep

saliva from seeping between it and the preparation. This type of temporary

coverage is adequate for a week or ten days, during which time a temporary

splint is made of good scrap gold.

Occasionally, an aluminium shell is used for temporary protection of a

preparation. The shell should be carefully fitted and lined with soft gutta-

percha and then cemented to place with temporary cement.

Full-Coverage Type:

In most cases, where full coverage is indicated, the best temporary coverage

can be quickly made with self-curing plastic. Prior to preparation of the teeth,

but after diagnosis and treatment planning, the study casts are marked

according to the quadrants to be prepared. Any edentulous areas between the

85

teeth are filled in with wax and carved into suitable pontics. A thin layer of wax

is applied with a spatula to the buccal and lingual areas of the remaining teeth

and over the gingival tissues adjacent to the teeth(fig-26). This thin layer of

wax permits us to make a slightly oversized eggshell. The over sizing will

allow for the shrinking of the self-curing plastic; it will provide sufficient

thickness in the eggshell; and it will enable the shell to clear the preparations

when it is seated in the relining procedure that follows. The gingival relief will

prevent impingement of the soft tissues by the eggshell.

After (he study cast has been prepared as described (both sides can be done at

(he same time and the anteriors, too, if involved), an alginate or hydrocolloid

impression is taken of the cast. The impression is separated from the cast, and a

thin layer of self-curing plastic is then applied(fig-27) with a camel's-hair

brush. Small amounts of the powder and liquid should be picked up with the

brush in his application. The liquid causes the powder to spread evenly in the

impression. The impression is lilted to permit the material to flow where we

want it. Since the desired result is to have an eggshell of equal thickness in

every area, we should avoid overbuilding the material in any section. When the

surface of the impression of the teeth is evenly lined, some material should be

allowed to build up the gingival tissue areas, about 2 or 3 mm. beyond the

preparation.

After the plastic has cured, the eggshell can be removed in quadrants and stored

until the preparations are made. The shells should be kept in a proper storage

container so that they will remain moist.

When a quadrant is prepared, and before the impression is made, the eggshell is

tried on the preparations to make sure that it seats perfectly. It is then relined on

the prepared teeth. The teeth and gingival tissues are lubricated with mineral oil

or petroleum jelly (Nu-Life Nu-Lube4). and the eggshell is tilled with a mix of

self-curing plastic. The shell is placed on the preparations, and the patient is

86

instructed to close the teeth slowly. Any gross excess is removed with a plastic

instrument, and the patient is again instructed to close. After a minute or so, the

relined shell is gently lifted to insure its removal, but it is not removed

completely. It is then reseated; the patient is told to close once more; and the

shell is cooled with water to prevent overheating.

When the self-curing plastic has hardened, the eggshell is removed and

trimmed, and the impression procedures are carried out. After the impressions

are obtained, the relined and trimmed shell is ready to be cemented to place

with temporary cement(fig-28). It seldom requires any occlusal adjustment;

when it does, this can be accomplished very easily with a rubber wheel.

Another method of making a more durable temporary plastic splint has been

developed by Dr. Morton Amsterdam (1959) of Philadelphia, who uses soft

gold shells for marginal adaptation.

There are several other ways to make good plastic temporaries. Instead of an

alginate impression in which an eggshell is made, a wax impression can be

taken either from the mouth or the study model. If an edentulous area is

present, the area can be scooped out of the wax impression with a heated

vulcanite scraper or similar wax instrument. This area will need some

reshaping after the temporary is made, but if time is of the essence, it may be

worthwhile. The prepared wax impression is filled with self-curing acrylic

resin and seated over the lubricated teeth. Removal before polymerization will

insure against locking it to place. If your timing is just right, you can peel the

acrylic out of the wax impression and. while it is in a plastic state, trim it with a

pair of scissors. Replace the stiil-pliable temporary on the teeth and have the

patient bite down. This will reduce the amount of occlusal adjustment needed.

Probably the easiest and best temporary can be made by means of the Omnivac

technique. The study cast is prepared as necessary. Missing teeth are waxed in

87

place; any desirable occlusal corrections may be made. Then an alginate

impression is taken of the entire cast. A cast is poured up in stone and the new

cast is removed from the impression. A hole is made through the center of the

cast with a large vulcanite bur. The cast is placed on the Omnivac stand, a sheet

of .020 Temp Splint material made by Omnivac is placed in the frame, and the

heating element is turned on. When the sheet is sufficiently heated it will sag in

the middle about an inch. At this point, the frame is dropped onto the model at

the same time that the vacuum is turned on. The heated sheet will be adapted to

the cast. When it is cool enough, remove it from Ihe frame and trim it to just

beyond the gingival margins. On the upper, the vault area is cut out to remove

the projection into the suction hole. On the lower, the lingual is trimmed to just

beyond the gingival margins(fig-29).

When one quadrant is prepared, lubricate the inside of the shell and the

prepared teeth. Fill the shell on the prepared side with self-curing plastic (a

very good one is Coidpac). Seat the full splint with the plastic on the side of the

prepared teeth and have the patient close firmly against it. The full splint will

help to equalize the bite relationship so that there will be a minimum of

occlusal adjustment necessary Again, if you watch it carefully, you can

remove, the spiint before it sets. Peel it out of the Omnivac shell and roughly

trim the excess with a pair of scissors. While it is still pliable, replace it on the

preparations and have the patient close firmly.. Repeatedly lift it and reseat it to

avoid locking in place. When it is set. remove it and trim and polish it. It may

desirable to refit the splint in the gingival areas. Apply a little petroleum jelly

to the sulcus. Blow the excess out with a gentle blast of air. Then, with a

camel's-hair brush, apply some powder and liquid in sulcus. Moisten the

trimmed splint with some of the monomer and seat it so that the gingival

application will unite with the set shell. A gingivatly well-adapted shell can

thus be produced. Complete the polishing and temporarily cement it to place.

88

PANKEY-MANN SCHUYLER PHILOSOPHY OF COMPLETE

REHABILITATION

One of the most practical philosophies for occlusal rehabilitation is the

rationale or treatment that was originally organized into a workable concept by

Dr. L.D. Pankey. Utilizing the "Principles of occlusion" espoused by Dr. Clyde

Schuyler. Dr. Pankey integrated different aspects of several treatment

approaches into an orderly plan for achieving an optimum occlusal result \\\&i

minimum stress on the patient or the dentist,

Dr Arvin Mann Contributed to the concept b> working with Dr. Pankey in the

development of the first specialUed instrument for developing the occlusal

plane. The instrument became known as the Pankey-Mann instrument, and

even though it has long ago been replaced by a simpler system the over all

concept of treatment is still referred to as the Pankey-Mann-Schuyler

Philosophy (abbreviated to P.M.S)

Contrary to some popular misconceptions, the P.M.S. approach is not so much

a technique as it is a philosophy of treatment that organizes the reconstruction

of an occlusion into a sequence of goals that must be fulfilled. It is true that

certain techniques have become closely associated with the P.M.S, philosophy,

but it is also true that there has been a continuous trend toward improving and

simplifying almost every aspect of treatment without noticeably changing the

basic philosophy of treatment. Furthermore, the overall concept of treatment is

not limited to any specific instrument or method. There is consideration

flexibility of treatment within the PMS. philosophy as long as its goals of

optimum occlusions are not sacrificed.

Since its inception, the philosophy has had as its goal the fulfillment of the

following principles of occlusion as advocated by Schuyler:

89

1. A static coordinated occlusal contact of the maximum number of teeth when

the mandible is in centric relation.

2. An anterior guidance that is in harmony with function in lateral eccentric

position on the working side.

3. Disclusion by the anterior guidance of all posterior teeth in nrotrusion.

4. Disclusion of all nonworking inclines in lateral excursions

5. Group function of the working side inclines in lateral excursions.

Many P.MS, advocates now vary the fifth goal of working side group function

to permit more flexibility in distributing lateral stress.

In order to accomplish these goals, the following sequence is advocated by the

P.M.S. philosophy:

PART I. Examination, diagnosis, treatment planning, prognosis PART 2.

Harmonization of the anterior guidance for best possible esthetics, function,

and comfort

PART 3. Selection of an acceptable occlusal plane and restoration of the lower

posterior occlusion in harmony with the anterior guidance in a manner that will

not interfere with condylar guidance.

PART 4. Restoration of the upper posterior occlusion in harmony with the

anterior guidance and condylar guidance. The functionally generated path

technique is so closely allied with this part of the reconstruction that it may

almost be considered part of the concept.

Bach one of these steps has undergone continuous metamorphosis as

techniques to accomplish the goal have been improved and modified with a

wide choice of sophisticated options. One of the most impressive advantages of

90

P.M.S. is the latitude of sophistication it permits. Treatment modes within the

concept can be varied from the simplest techniques for the beginning

restorative dentist to the most precise details of the master reconstructionist.

The determination of an acceptable occlusal plane was first simplified by

Fillstrc and then further improved by Broaiirick. The Broadrick occlusal Plane

Analyzer is so simple to use that it has become the standard method of

analyzing ccclusai plane for posterior occlusal reconstruction.

The PMS philosophy is not limited to any specific instrument. Swanson and

Wipf adapted the Broadrick "flag" for their temporomandibular joint

stereographic articulator. and Fillastre developed a device for the same

instrument that determines ridge and groove directions on the lower occlusal

wax patterns. The advantages of the technique are many. Some of the major

ones are as follows;

1. It is possible to diagnose and plan treatment for the entire rehabilitation

before preparing a single tooth.

2. It is a weII-organized, logical procedure that progresses smoothly with less

wear and (car on the patient, operator, and technician.

3. There is never a need for preparing or rebuilding more than eight leeth at a

time.

4. It divides the rehabilitation into separate series of appointments. It is

neither necessary nor desirable to do the entire case at one time.

5. There is no danger of "getting at sea" and losing the patient's present

vertical dimension. The operator knows exactly where he is at all times.

91

6. The functionally generated path and centric relation are taken on the

occlusal surface of the teeth io be rebuilt at the exact vertical dimension to

which the case will be constructed.

7. All posterior occlusal contours are programmed by and are in harmony

with both condylar border movements and a perfected anterior guidance.

8. There is no need for time-consuming techniques and complicated

equipment.

9. Laboratory procedures are simple and controlled to an extremely fine-

degree by the dentist.

The Pankey-/Mann-Schuyier philosophy of occlusal rehabilitation can fulfill

the most exacting and sophisticated demands // the operator understands the

goals of optimum occlusion. And it can achieve these goals with great

simplicity and orderliness of technique, ll can be combined with other

techniques and it can be adapted to any occlusal problem. An understanding of

the P.M.S. philosophy is a tremendously valuable aspect of the complete dental

education.

92

SELECTING INSTRUMENTS FOR OCCLUSAL REHABILITATION

There are four basic type of instruments that can be used with equal success to

achieve fine results in restorative procedures. The purpose of all good

instrumentation is simply to capture accurately the border pathways of the

teeth, This may be done by reproducing the border movements of the condyles

and then combining the reproduced condylar pathways with corrected anterior

guidance paths. Or it may be done by recording the results of anterior and

posterior determinant pathways at the site of the teeth themselves.

In using any instrument, it must be remembered that anterior guidance is a

product of functional border movements that fall within the outer limits of the

envelope of motion. Recording only condylar pathways does not furnish

enough information for the instrument to precisely reproduce tooth movements

that are in harmony with the envelope of function. The anterior guidance is a

separate entity that must be recorded and programmed into any articulator in

addition to condylar pathways if the instrument is to be used as a device for

reproducing jaw movements.

Anterior guidance is not determined by condylar guidance, so there is no

instrument that is capable of determining how the front end of the mandible

should move. If anterior guidance is correctly determined in the mouth and its

pathways are recorded at the "front end" of the articulator, any one of several

instruments can be used with excellent results.

The simper the articulating device, the more compensation must be made for its

shortcomings. But if compensations can be made easily and accurately, there is

practical value in keeping the instrumentation as simple as possible.

93

Semi adjustable instruments (fig-30):

The biggest shortcoming of semi-adjustable articulators is that condylar

pathways are limited to straight line. Because of this limitation, these

instruments are referred to as check bite articulators. This means that the

horizontal condyle paths are set to align with a bite record made at centric

relation and another bite record made in the protrusive position. The resultant

path is a straight line between the two points. Lateral pathways are set from the

centric bite record plus bite records made in the left lateral and right later jaw

positions. The resultant straight-line gradual side shift of the balancing condyle

determines the amount of immediate side shift for the working side condyle.

If pathways in the skull curve between the two check bite positions, the curve

will not be duplicated on the articulator. Only the two points of the check bite

position will be correct. The path between the two points will be in error.

To minimize the errors of the check bite technique, protrusive and lateral bite

records should be made fairly close to centric relation. The most important part

of the condylar pathway is right after the condyle leaves centric relation, so

taking the eccentric bile record within about 5 mm from centric relation gives

greater accuracy where it is needed most(fig-3 I).

Semi adjustable instrument cannot record the full range of lateral and

protrusive condylar movements, but the mechanical equivalent of tooth

movements can be recorded with as much accuracy as is possible on any

available instrument if the instrument's shortcomings are compensated for with

the following.

1. Customized anterior guidance procedure

2. Simplified fossae contours technique to relate lower fossae form to the

anterior guidance.

94

3. Functionally generated path procedures to capture the precise border

movements of the posterior teeth at the correct vertical dimension.

When recorded in this manner the pathways of the posterior teeth reflect the

precise influence of all condylar border movements as well as the anterior

guidance. No interpolation of condylar movement is required because the

border movements are recorded directly at the site where the path of

movements is important at the posterior teeth themselves. The articulator is

thus not used as a duplicator of jaw movements but rather as a device that

relates the functional pathways to the prepared teeth. Since each of the above

refinements can be used with advantage in any instrument approach, they do

not constitute unnecessary added work.

Semi adjustable instruments do not precisely record the Bennet shift, but the

necessary compensations can be easily made. However, even if the instrument

is used with check bite records to set condylar pathways without functionally

generated path procedures, the occlusa! adjustment should still be minimal. It

is possible to record centric relation perfectly, and since it is an easy matter to

disclude all posterior contacts in protrusive and non-working side excursions,

adjustments to these excursions should be minimal.

There are a number of other semi adjustable articulators that can be used with

the same effectiveness as the University Model Hanau. The Whip Mix

Articulator is a popular instrument that has three variations that can be used for

intercondylar distance.

The Hanau Model H. or the Dentatus and Girrbach articulators are among the

most popular nonarcon instruments.

95

Fully adjustable articulators:

The term "fully adjustable" refers to the reproducibility of the patient's

condylar paths. In evaluating any articulator, it should first be noted that no

matter how complex the instrument may be, it can still do no more than the

following:

1. Reproduce the terminal horizontal axis of condylar rotation.

2. Reproduce the vertical axis of condylar rotation.

3. Reproduce the saggittal axis of condylar rotation

4. Permit simultaneous multiple axes of rotation during condylar translations.

5. Reproduce straight protrusive pathways of each condyle.

6. Reproduce the pathways of each condyle during straight lateral excursion

of the mandible.

7. Reproduce the multiple pathways of each condyle during all possible

excursions of the mandible between straight lateral and straight protrusion.

All though there are many claims made regarding complete adjustability, very

few instruments are actually capable of reproducing ail seven of the above

condylar movements without some degree of interpolation.

The first six listed movements cab be accurately reproduced by most quality

gnathologic instruments, but the seventh requirement, the multiple protrusive-

lateral pathways, must be interpolated from straight lateral and straight

protrusive paths.

There are two basic methods for recording the condylar paths: pantographic

tracings and stereographies. Actually, neither method records the true anatomic

96

contours of the temporomandibular joint, nor does the articulator reproduce the

anatomy of the joint. H is merely a mechanical equivalent that makes the back

end of the articulator capable of going through the same movements that the

back end of the mandible follows in function.

Pantographic instruments:

The use of pantographics has become far more practical since the introduction

of the Denar Pantograph. Because of a simplified procedure of using vinyl

clutch formers, a central bearing point set of clutches can be fabricated in a

matter of a few minutes. The clutches are then adapted to the Denar

Pantograph, which traces mandibular movements on tracing plates.

The pantographic technique does have the advantage that goes with the use of a

central bearing point. With a properly located central bearing point, all occlusal

interferences are disengaged when the condylar pathways are recorded. There

is no tooth contact during the tracing procedures. Manipulation of the mandible

is simpler because of the complete absence of any occlusal interferences at the

opened vertical.

If pantographic tracings are to be used to program the articulator. it is necessary

for the pantograph to be correct. Unfortunately, the pantograph can be no better

than the operator's ability to manipulate the mandible with the pantograph

attached. Allowing the patient to record border movements without expert

assistance from the operator will result in incorrect tracings. They will

generally fall short of the outer border limits. The mandible must be

manipulated to correctly capture the outer limits of movement.

Manipulation should start with the recording of the terminal hinge position and

ail lateral tracings should emanate from it, Failure to do so will result in

restorations with interferences in the extreme border positions just lateral to

centric relation.

97

When manipulating the mandible or a correct pantographic tracing, it is

extremely important that the condyles be in their most superior position for the

centric relation part of the tracing. The central bearing point permits easy

positioning of the condyles into this superior position, but it also permits a very

common error to occur if correct manipulation is not used.

It is very difficult to record correct centric and border movements with patient

sitting up straight. The supine position makes manipulation much simpler.

If a one-handed technique is used lo position the mandible in centric relation

with the central bearing point in place, the dentist must be certain to exert a

downward force on the chin, as the mandible is retruded. This has the effect of

seating the condyle upwards.

The popular Stuart Articulator is another instrument that will also adjust to

paniographic tracings. The selection of which instrument to use is purely a

matter of personal preference.

Disadvantage of pantographic devices is that the tracings must be made at a

considerably opened vertical dimension to make room for the clutches. It is

essential that the terminal hinge axis must be recorded precisely or the incorrect

axis of closure will introduce errors.

It is also probable that in some mouths, at least, the border movements are

different at the opened position from what they are at the correct vertical.

Stercographic instruments (fig-32):

One of the simplest "fully adjustable" instruments to use is the TMJ

Articulator. All border movements can be accurately recorded in three

dimensions by means of simple intraoral clutches that are stabilized by a

central bearing point.

98

The recordings are made by indenting three or flour points into doughy self-

curing acrylic on the surface of the opposite clutch and then moving the

mandible through all border movements. Protrusive lateral movements can be

included. When the stereographic recording is completed, the acrylic guide

paths are allowed to set hard. The condyle paths on the instrument are then

made in self-curing acrylic as dictated by the points of one clutch sliding in the

indented recordings of the other. Since the three dimensional recordings were

made in the mouth by the paths of the condyles. the procedure can be reversed

and the paths in the clutch can dictate the mechanical equivalent of condyle

movement on the articulator(fig-33).

Stereographic techniques have a decided advantage in the use of the three

dimensional recordings. All border pathways can be programmed into the

condylar guidance, including protrusive-lateral movements. The instrument can

be used in combination with customized anterior guidance procedures. It lends

itself well to sophisticated Panl.l;y-Mann-Sen uyler procedures.

The TMJ instrument is an excellent articulator for fabricating dentures. The

intraoral clutches are stabilized by the centra! bearing point and all recordings

are made intraorally within the central area of the bases. This is a decided

advantage over pantographic devices that frequently have a tendency to tilt the

denture base with the weight of the external appendages.

Nonarticulator instruments:

All border movements of the teeth can be accurately recorded and duplicated

without even using an articulator. It is not necessary to reproduce condUe

pathways as long as the effect of the condyle movements can be recorded at the

site of the teeth. An instrument that accomplishes this is called the Gnathic

Relator. It is accurate and adaptable to all the techniques. It is used to best

99

advantage in combination with some type of semi adjustable articulator. but the

articulator itself is not used for reproducing border movements.

It is essential that the anterior guidance by perfected prior to use of the Gnathic

Relator for fabrication of posterior occlusai restorations. A stereographic

device is then set up on centrically related models after the posterior teeth have

been prepared. The relator is then transferred to the mouth for the recording.

No central bearing point is needed because the anterior teeth contact during the

recording.

Because the siereographic recording is made at the correct vertical dimension

with both anterior guidance and condylar guidance influencing the border

movements, no interpolation is required. The recording device itself is

rcpositioned on the master die models, where it becomes the guide for all

movements of the models in relation to each other (fig-34).

The models with the Gnathic Relator attached can be handheld in perfect

centric relation and can be moved through any border pathways by hand. Wax

up and completion of the restorations can be perfected on the handheld models.

"Simple" articulators:

The most important single purpose of an articulator is to relate the upper and

lower models to the correct horizontal axis. Simple hinge articulators do not

permit a correct relationship to the axis of closure. Sizable errors are introduced

into all aspects of occlusai form when correct horizontal and vertical axes are

not used. The problem with simple hinge type articulators is that the only

movements they can make are movements the patient cannot make.

A facebovv mounting is essential for the proper utilization of any articulator.

Articulators that do not accept a facebow mounting have virtually no value for

restorative procedure or occlusal analysis.

100

Without correct mounting procedures, even a perfectly made centric bite record

has limited value. Many dentists who are genuinely striving for preciseness

waste a great amount of time meticulously carrying out procedures that are not

needed.

The use of an infraorbital pointer, as an example, is an extra step that many

dentists use unnecessarily. It has limited practical value because a simple

laboratory procedure can fulfill all the functions of the pointer with far more

accuracy and repeatability. The tattooing of condyle axes is a similar waste of

time.

A facebow recording is one of the essential steps for proper mounting of casts.

After location of the condylar axis in the skull, it provides a method of

transferring that axis to the articulator by relating it lo the upper cast. If a

centric bite record is made at an opened vertical dimension, the accuracy of the

bite record will only be maintained if the closing axis is the same on the

articulator as it was on the patient.

Any change of axis changes the direction of the closing path. Built-in error

results when models are mounted on instruments that do not reproduce the axis

correctly. Instruments that arc capable of reproducing the axis will only do so if

the models are mounted with a facebow. It is good practice to record centric

relation as close to the correct vertical dimension as possible.

The most accurate method for recording the correct horizontal axis include the

use of some type of kinematic device for locating the terminal hinge axis. A

hinge axis can be recorded at any point along the protrusive pathway. Unless

good manipulative technique is used to position the condyles in their terminally

braced position, the recorded hinge axis will be incorrect. Furthermore, even

the most precisely recorded hinge axis cannot compensate fur a missed centric

bite record.

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A kinematic facebow recording is almost a necessity if the centric bite record is

made at an extreme opened vertical. Bite records made with clutches in place

often fall into this category. However, if the centric bile record can be made at

or near the correct vertical dimension, clinically acceptable accuracy can be

achieved by palpating to locate the axis.

Method of palpation for locating the condylar axis:

From a position behind the patients the operator should place the index finger

over the joint area and ask the patient to open wide. As the condyle translates

forward, the fingertip will drop into the depression iefl by the protruded

condyle. The patient should then close. As the condyle is pulled back into

centric relation, its position can be located by the fingertip. By asking the

patient to repeat an opening-closing arc, it will be possible in most patients to

feel the condylar rotation and to locate the axis within acceptable limits of

accuracy. Once the general center of the condyle is located, accuracy is assured

to within 2 or 3mm. This is acceptable on any mounting that is to be articulated

reasonably close to the correct vertical dimension. The located axis should be

marked on the skin.

It is not always possible to articulate the original diagnostic models of

unequilibrated occlusions near the correct vertical dimension. The centric bite

record must be made before the first tooth contacts

Using the facebow:

The facebow is simply a device that relates the upper cast to the same axis on

the articulator that is present in the skull. A facebow recording is simple to

perform and requires only a minute or two of chair time,

1. Softened wax is wrapped around the bite fork and positioned against the

upper teeth, indentations into the wax should be sufficient to stabilize the

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upper model. The wax should not be penetrated to the metal. For upper

edentulous ridges, a stable base plate should be constructed and the bite fork

should be attached to a bite rim on the base.

The lower teeth can usually be closed into the underside of the wax to stabilize

the bite fork. If stability cannot be achieved this way. the bite fork should be

held firmly against the upper teeth by the chair side assistant.

It is not necessary to close into centric relation on the bile fork. Its purpose is

for orientation of the upper cast only.

2.While the wax on the bite fork is being chilled by the assistant, the facebow

is positioned and the intercondylar width is recorded. The facebow is set

according to the patient's facial width.

3. The bite fork is reinserted and the facebow is positioned by the dentist so

that the axis locators are positioned in line with the marks on the skin.

4. While the dentist holds the axis locators in position, the assistant,

without contacting the facebow at any other point, tightens the set screw

mechanism that locks the bite fork into the correct relationship with the

facebow(fig-35).

5. The axis locators are loosened and their relationship to the marks on the

skin checked. Both locators should be at the same setting and should lightly

contact the skin directly over the marks. If the position is incorrect, the

locking device should be loosened on the bite fork and the procedure repeated.

If the relationship is correct, the recording is removed from the mouth.

Mounting with the facebow:

The width of the palient's head is recorded on the facebow, but the inter-

condylar distances will be less, because the condyles are inside the skin and fat

103

layers. Measuring to the outside of the condyle post on the articulator will

compensate for soft tissue thickness and will result in a more accurate

intercondylar distance. This dimension is set on the articulator so that both

condyle posts are at the same setting.

After the intercondylar distance has been set, the axis locator bars are released

and reset to the axle on the articulator. When the facebow is positioned on the

articulator's axle, the upper model is placed in the indentations in the bite

fork(fig-36). The support screw in the front of the facebow is lowered to

support the cast. While an infraorbita! pointer is often used to determine the

vertical position of the cast, it is an unnecessary procedure. If the labial surface

of the upper incisors is aligned with the perpendicular, the cast position will be

in a good relationship.

A common mistake in positioning the upper model is to align the incisal edges

with the groove on the incisal guide pin. This usually results in positioning the

model too high on the articulator. Negative horizontal condylar paths are often

a side result of such cast positioning. The mark on the guide pin should be

ignored.

When the cast height has been determined, it should be supported during the

mounting procedure.

When the upper mode! is joined to the mounting ring on the articulator, the

facebow can be removed. The lower model is then articulated to the upper with

a centric relation bile record. If the incisal guide pin is lengthened an amount

equal to the thickness of ihc bite record, the upper bow of the articulator will be

horizontal when the bite record is removed and the models are in contact.

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Setting the horizontal condylar guidance:

After the models are mounted in centric relation, a second bite record made

with the mandible protruded approximately 5mm. can be used to set the

horizontal condyle paths. As check bite techniques do have limitations, but in

most cases the procedure can be used with reasonable practicality if the

protrusive bite record is not made too far forward of centric relation.

When using a protrusive check bite, it should be trimmed back to the tips of

each upper and lower cusp so that the stone model is clearly visible where it

contacts the wax bite. The centric locks are released at the condyle path and the

upper model is moved back into the indentations in the protrusive bite. The

condyle path is now altered Lo varying degrees of steepness until the model fits

precisely into the bite record with no separation between the stone and the bite.

If there is a separation at the distal part of the bite, the guidance is too steep. An

anterior separation between model and bite record results form the condylar

guidance being set too flat.

Setting the lateral condylar guidance:

Check bites made in each lateral excursion can be used to set the lateral

condylar paths. The centric lock is released and the lateral adjustment lock

screw is loosened on each side. The lateral pins are opened to the widest

positions. The left lateral check bite i? place and the models are positioned into

the bite record indentations. The balancing side condyle path on the right side

of the articulator is rotated in until it contacts the lateral centric stop on the

axle. This repeated for the opposite side. The protrusive check bite should be

rechecked after setting the lateral guidances.

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Using transfer bite records to eliminate the infraorbital pointer procedure:

The infraorbital pointer provides a uniform method of establishing the vertical

position of the upper cast on the articulator. Once the condylar pathways are set

(either by check bite, pantograph, or stereograph), there will be .',o need to

reset them if the original upper model and all subsequent models are all at the

same position. As a restorative case progresses, teeth are equilibrated,

prepared, and restored. New models are required at each step of the restorative

procedure. The usual procedure is to mount each new set of models with a new

facebow recording that also employs an infraorbital pointer repeatedly set to

the same spot on the patient's face. Condyle axis location is often tattooed on

the skin to assure accuracy of that part of the facebow recording. While the

procedure is effective, it requires an unnecessary waste of time. The same

results can be aeh ieved v. ith a simple laboratory step.

As already discussed, the vertical position of the upper cast can be set by

raising or lowering the front of the facebow until the labial surfaces of the

central incisors are vertical. Some anterior teeth are tilted inward and some are

near horizontal. If the centra! teeth are not in a normal relationship, the occlusal

plane can be used as a guide for positioning the upper cast. The front of the

occlusal plane should be set slightly lower than the back. This may seem

arbitrary, but regardless of the position of the casts vertically they will not lose

their correct relationship with the terminal axis as long as the model is

positioned on the bite fork and the axis locators are in position on the

articulator. Condylar guidances are not set until the casts are mounted and then

these guidances are relative to whatever vertical cast position is used.

When changes are made in the mouth and new models are poured, they can be

mounted in precisely the same relationship as the previous casts by using a

transfer bite. Let us use an example to explain the procedure. The original

diagnostic models have been made. Equilibration procedures arc then

106

completed that change the occlusal surfaces and new impressions are made.

The new models can be mounted in the same relationship to the condyles

without taking a new facebow. A simple wax bite is made on the original

models in centric relation on the articulator. When the wax is in place, the bite

is opened so the incisal guide in pin is dropped to contact the guide table. The

upper cast is then removed and the new cast is positioned into the bile record.

The original lower model is still in place and the guide pin is still lengthened at

the same position.

The new upper model will have voids against the transfer bite record, but there

will still be ample numbers of untouched stops so that the new model will be

completely stable in the bite record in spite of the voids. It should be joined in

that position to the upper mounting ring. After the new upper model is

mounted, the guide a restorative case progresses, teeth are equilibrated,

prepared, and restored. New models are required at each step of the restorative

procedure. The usual procedure is to mount each new set of models with a new

facebow recording that also employs an infraorbital pointer repeatedly set to

the same spot on the patient's face. Condyle axis location is often tattooed on

the skin to assure accuracy of that part of the facebow recording. While the

procedure is effective, it requires an unnecessary waste of time. The same

results can be achieved with a simple laboratory step.

As already discussed, the vertical position of the upper cast can be set by

raising or lowering the front of the facebow until the labial surfaces of the

central incisors are vertical. Some anterior teeth are tilted inward and some are

near horizontal. If the central teeth are not in a normal relationship, the occlusal

plane can be used as a guide for positioning the upper cast. The front of the

occlusal plane should be set slightly lower than the back. This may seem

arbitrary, but regardless of the position of the casts vertically, they will not lose

their correct relationship with the terminal axis as long as the model is

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positioned on the bite fork and the axis locators are in position on the

articulator. Condylar guidances are not set until the casts are mounted and then

these guidances are relative to whatever vertical cast position is used.

When changes are made in the mouth and new models are poured, they can be

mounted in precisely the same relationship as the previous casts by using a

transfer bite. Let us use an example to explain the procedure. The original

diagnostic models have been made. Equilibration procedures are then

completed that change the occlusal surfaces and new impressions are made.

The new models can be mounted in the same relationship to the condyles

without taking a new facebow. A simple wax bite is made on the original

models in centric relation on the articulator. When the wax is in place, the bite

is opened so the incisal guide in pin is dropped to contact the guide table. The

upper cast is then removed and the new cast is positioned into the bite record.

The original lower model is still in place and the guide pin is still lengthened at

the same position.

The new upper model will have voids against the transfer bite record, but there

will still be ample numbers of untouched stops so that the new model wilt be

completely stable in the bite record in spite of the voids. It should be joined in

that position to the upper mounting ring. After the new upper model is

mounted, the guide pin is reset back lo its regular position. The new lower

model is then mounted by means of a new centric relation bite record made on

the patient.

This procedure can be repeated at each new step of the restorative treatment.

As an example, when the lower posterior teeth are prepared, that model is

articulated against the correctly mounted upper cast. After the lower

restorations are completed, a transfer bite record is made on the articulator with

the restorations in place. The guide pin is dropped to contact the guide table

when the bite record is in position. After placement of the restorations, a lower

108

impression is made and new model is positioned into the transfer bite record

and joined to the lower mounting ring. The guide pin is then reset and the new

upper cast (which may be a die model of prepared upper teeth) is articulated

against the lower model with a new centric relation bite record.

This procedure is simple, yet very accurate, ll eliminates the chair time required

for taking repeated facebow records and simplifies the laboratory remounting

procedures. It works as well on gnathologic instrumentation as it does on semi

adjustable articulators.

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ANTERIOR GUIDANCE

Perhaps the most sophisticated test of a restorative dentist's skill is how happy

his palients are when the anterior teeth have been restored. The correct

relationship of the upper and lower anterior teeth is so critical that differences

of a millimeter or less in incisal edge posilion can feel grotesque to a patient.

Radical changes in lip support, incisal edge position, and lingua! contours may

change more than a patient's natural appearance. Along with the discomfort and

the look of artificiality, improperly restored anterior teeth may contribute to the

destruction of the entire dentition.

One thing that every dentist should know before he attempts to restore anterior

teeth is that besides being nice to look at and to bite sandwiches with, the

anterior teeth have the very important job of protecting the back teeth. So

important is this job of the anterior guiding inclines that posterior teeth that are

not protected from lateral or protrusive stresses by the anterior teeth will, in

time, almost certainly be stressed beyond the resistance of their supporting

structures.

In spite of how good the upper front teeth may look their chance of staying

healthy and keeping the back teeth healthy depends on their lingual contours,

specifically the contact of the lower anterior teeth against the upper anterior

teeth in centric, "long centri'c", straight protrusive, and lateral excursions. This

dynamic relationship of the lower anterior teeth against the upper anterior teeth

through all ranges of function is called the anterior guidance. As such, it

literally sets the limits of movement of the front end of the mandible.

We will imagine that all the back teeth have been shortened through

preparation so that they cannot touch in any position of the mandible. Now

without any possibility of posterior tooth interference, we visualize the

mandibie closing in a terminal axis closure until the front teeth contact

110

simultaneously against stable centric stops at the correct vertical dimension, the

First requirement of good anterior relationship has been fulfilled. The mandible

should be closed into a stable tripod and the terminally braced condyies serving

as the other two legs(fig-37).

Since this mandible tripod is a lever that hinges at the condyies. it will be

apparent that the power for cosing this lever is in muscles that exert the closing

force between the condyies and the front teeth. The anterior teeth are ail

forward of the closing muscle power, so to exert stress on the anterior teeth.

The mechanical result of the closing muscles would be like trying to crack a

walnut by placing it at the tips of the handles of a nutcracker and squeezing the

handles up by the hinge. This is the unique position of resistance to stress that

the anterior teeth enjoy by virtue of their relationship to the condylar fulcrum

and the source of muscle power(fig-38).

The condyles. braced firmly against bone and dense ligaments, form a very

strong hinge that is completely capable of resisting the power of the closing

muscles. The anterior teeth, when their position allows it. should be made to

form a very stable stop for the front of the mandible and thereby limit its

closing motion. If the closing motion of the mandible is stopped by the incisal

edges of all six lower anterior teeth against stable holding contacts of the six

upper anteriors, we have not only taken advantage of the position of the front

teeth, we have also strengthened that position by distributing the stresses.

It is a popular fallacy, however, that whatever path the condyles follow must be

duplicated in the lingual surfaces of the upper anterior teeth so that the lower

anterior teeth can follow the same path. This is wrong. Condylar paths do not

dictate anterior guidance, and there is no need or even advantage to try to make

the anterior guidance duplicate condylar guidance. Advocates of such a concept

have failed to recognize that the condyles can rotate as they move along their

111

protrusive pathways. This allows the front end of the mandible to follow a

completely different path without interfering with condylar path.

The path that the condyles travel dictates the cuter limits to which the mandible

can move. These outer limitations are referred to as the envelope of motion.

The path that the front end of the mandible follows is dictated by functional

movements of muscle as it relates the lower anterior teeth to the upper anterior

teeth in the chewing cycle. The outer limits of these functional movements are

referred to as the envelope of function, Such functional movements occur

within the limits of condylar border movements and consequently should be

treated as separate entity.

To better understand how the anterior guidance differs from the condylar

guidance, we return to our visualization of the upside-down tripod. Since the

condyles on the back two legs of the tripod are rounded (so that the mandible

can rotate around them), it is easy to see how the lower incisors that form the

front leg of the tripod can slide forward on a variety of paths without conflict to

either the front path or the condyle path. The same condylar path that permits

the lower anterior teeth to follow a horizontal path forward will just as easily

permit them to follow a 10-degree. a 30-dcgree, or even a steeper path. It does

not matter whether the anterior path is flat or curved, concave, convex or

parabolic, the rotating condyles sliding down the unchanged condylar path

permit the lower anterior teeth to follow any number of path variations without

interference.

If the nature of the condyle path does not dictate the anterior guidance, it

should be clear that the recording of condylar pathways does not in itself

furnish enough information to optimally restore anterior teeth. The dentist who

prepares all the teeth in either arch (or worse yet. in both arches) sometimes

believes he has all the information needed if he mounts his models on a

completely adjustable instrument. When he has properly recorded and

112

transferred all the condylar pathways to a fine instrument, he may think that he

"has the patient's head on his laboratory bench". Such is not the case. The best

that any technician can do with such information is to guess at the contours of

the anterior teeth. We do not wish to belittle the importance of condylar

guidance. It is extremely important, and capturing the effect of condylar

pathways by some method is one bit of information that is essential to the

completion of theocclusal contours, but is only of the needed information.

Condylar pathways do not dictate the correct smile line. The precise incisal

edge position varies greatly as the length of the lip and the degree of flaccidity

or tightness of the lip varies. People with tight lips usually have anterior teeth

that are positioned more vertically than those of people with flaccid lips, and

even if the condylar guidance were the same in both types of patients, the

anterior guidance would be different. It would almost always be steeper in the

tight-lipped individual.

It is both practical and logical to work out the details of anterior contours in ihe

mouth. When done in an orderly sequence, we can determine precisely how

much "long centric" is needed, we can test variations in incisal edge position

for phonetic correctness, and we can be guided by the mobility patterns of teeth

as they are subjected to varying degrees of lateral stress. The greater the

hypermobility, the greater the need for minimizing lateral stresses. The less the

mobility, the less need for changing even steep anterior inclines. By making

any changes directly in the mouth, the patient is given the opportunity of

approving the appearance and trying out the function comfort and phonetics

before accepting the changed contours. Once the correctness of the incisal edge

positions, labial contours, and lingual curvatures has been verified and accepted

by the patient, the permanent restorations can be fabricated with confidence.

All the information must be preserved in a usable manner, however, so that the

113

finished anterior restorations duplicate the contours that have been tested in the

mouth and confirmed as correct.

Lateral anterior guidance:

Reason for not using the term "incisal guidance" is that the connoted limitation

to the four incisors is often confusing. Incisal guidance is frequently described

in terms of protrusive movements only. Actually, [be lateral pathways that are

established on the anterior teeth have a far greater influence on posterior

occlusal form, and the cuspids play a major role in determining the lateral

stress-bearing capabilities of all the anterior teeth.

The occlusal contours of all the posterior teeth are dictated by both condylar

guidance and anterior guidance. No posterior tooth should interfere with either

anterior guidance or condylar guidance. Posterior teeth may either be discludcd

from any lateral contact by the anterior teeth or they must be in perfect.

harmonious group function with them and the condyles. Either way, the

anterior guidance, as a determinant of posterior occlusal form, must be

perfected before occlusa! contours can be finalized.

Whenever it is practical to eliminate posterior contact while working out the

anterior guidance, it is helpful. This can be accomplished in mouths that require

posterior occlusal restorations by completing the preparation of the posterior

teeth prior to working out the anterior guidance. If the posterior teeth do to

require restorations, the anterior guidance musi be worked out simultaneously

with equilibration of the posterior teeth.

Since the anterior guidance is a protector of the posterior teeth, our goal is to

make the anterior teeth as strong as possible so that they may carry out their

protective function. Adjusting the anterior inclines when there is no support

from posterior teeth enables us to fully evaluate the stress resistance

capabilities of the anterior teeth and to correct them accordingly.

114

The ultimate goal of a correct anterior guidance is that is should be

comfortable, functional, and stable even without posterior contact.

After the anterior guidance is perfected to the optimum degree possible, it can

be determined how much help is needed from the posterior teeth. If the

anterior teeth are strong enough to function on their own, posterior contact in

centric relation may be sufficient. If the anterior teeth are weak in resisting

lateral stresses, ihe posterior teeth may be brought into group function to help

share the load of lateral forces. If the anterior guidance has been optimally

corrected and is still too weak to serve its protective requirements, splinting

may be necessary to bring the anterior teeth up to the necessary strength.

Close observation of the anterior teeth in the mouth is the best way to

determine whether lateral movements are stressing them. Both visual and

digital examination should be used to determine whether any teeth are being

moved during lateral excursions. Noting the contact areas between the cuspid

and the lateral incisor during lateral excursions is often a good indicator of

stress. Movement of the cuspid will frequently open the contact as the jaw is

moved laterally.

Upper anterior teeth that are noticeably moved by any functional excursion

should be corrected. Correction usually consists of reshaping the upper lingual

contours. Centric stops should always be established prior to refinement of

excursive inclines, so the lower incisal edges are rarely involved in the

correction of any lateral excursion interferences. Changes in the lower anterior

teeth should be limited to minimal adjustments that do not involve the centric

stops on the incisal edges.

Correction of upper lingual contours is patterned to accomplish two effects: re-

direction of force's and improved distribution of forces. Forces are redirected

by changing the shape of the contacting surfaces. The main vector of force is at

115

a right angle to the surface contacted. Changing the surface changes the vector.

The main vector of force against a steep incline is directed nearly horizontally.

Changing the steep incline to a flat incline would redirect the forces more

nearly up the long axis(fig-39&40).

Improved distribution of forces is accomplished by bringing more teeth into

simultaneous contact during excursions. This is often accomplished as a side

benefit when force direction is improved, because more anterior teeth are

brought into lateral function as steep convex inclines are changed to concave.

In mouths with poor periodontal support, poor crown root ratios, poorly shaped

roots, or poor quality alveolar bone, drastic changes in contour may be

necessary. To reduce stresses to the minimum, it is almost always necessary to

both redirect and redistribute all lateral forces on the teeth.

Correction of upper lingual contours is accomplished by reducing the steepness

of any inclines that, when contacted, cause the tooth to move. Steep inclines

just lateral to the centric stops are the most common source of stress. The need

for corrective flattening from centric stops out is greatest close to the stops and

then diminishes as the jaw moves laterally. This most often produces concave

lingual inclines that are flattest near the centric stops but may then curve into

quite steep inclines to permit effective incising.

It is almost never necessary to reduce the length of an esthetically correct

100th. It is not necessary to flatten the lateral or protrusive angles all the way

through ihc teeth to reduce stress. To do so in protrusion is esthetically

disastrous, and the resultant reverse smile line "ages" the patient many years. If

lateral stresses cannot be minimized enough with concave contouring of upper

lingual inclines, it would be better to stabilize the anterior teeth by splinting

than to ruin the appearance of a person's smile.

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The determination of whether splinting is needed or not is dependent on

whether or not an esthetically acceptable anterior guidance can be worked out

that does not stress the anterior teeth to noticeable movement when firm

excursions arc made.

It may be quite surprising how practically the correct concave inclines can be

worked out in the mouth. As the mandible moves laterally, the orbiting condyle

moves downward and the natural tendency of the jaw is to open as it moves to

the side. The resultant over and down movement of the lower anterior teeth

produces the concavity in the upper lingual contours, which permits lateral

function with minimal stress.

An anterior occlusal problem that will iiavc to be solved quite often involves

hypcrmobile cuspids in a cuspid - protected occlusion. The lingual incline of

the cuspids is too steep to permit any other tooth inclines from sharing the

lateral stresses. Very often the cuspid inclines are convex, which forces the

cuspid laterally when the jaw moves to the side. If very little bone has been lost

around the cuspids, it may be possible to eliminate the hypermobility with

minimal changes to the cuspids. Changing the convexity to a straight steep

incline with just a little concavity at and just lateral to the centric stops may

solve the problem and be very compatible lo a vertical envelope of function.

This may sometimes be accomplished without even bringing other teeth into

group function. Slight changes very often make major improvements in

function and stability. Making such corrections in the mouth, where patterns of

tooth mobility can be observed, enables us to keep changes to the minimum.

The cuspid with steep or convex lingua! inclines that has lost a considerable

amount of bony support will need to have the inclines opened out to allow an

almost flat area from centric relation laterally to accommodate the lateral side

shift of the mandible (Bennett) and to permit other anterior teeth to come into

group function with it. As more teeth are brought in to share the lateral stresses,

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the that inclines can then curve into sleeper ones to produce the concavity. At

the same time, the mobility of the cuspid will diminish until even moving the

mandible laterally with firm help from the operator will not cause noticeable

movement of the teeth.

Bringing more anterior teeth into group function not only distributes the

stresses over more teeth, it distributes them to teeth that are progressively

farther from the condylar fulcrum and in a better position to withstand the

stresses. It is often possible to extend group function around to include both

central teeth, and sometimes even the balancing side lateral incisor can

contribute support.

While concave lingual contours usually work out quite naturally for normal to

deep overbite patients, they may be contraindicated for patients with minimal

overbite. The near end-to-end anterior relationship will end up with an anterior

guidance that is almost flat. Lateral guide pathways may have no curvatures at

all. As long as the inclines permit firm excursions without noticeable

movement of teeth, the centric stops are stable, and the esthetics and function

are acceptable, all requirements for the anterior guidance have been fulfilled.

When anterior guidance inclines must fellow fairly straight paths, better

esthetics usually results from having protrusive inclines that are steeper than

lateral inclines. This gives the upper smile line a more natural curvature. Flat

protrusive paths in combination with steeper lateral paths accentuate the

cuspids and produce a harsh, unesthetic, reversed smile line.

Steps in harmonizing the anterior guidance:

Preliminary Steps:

1. When indicated, lower anterior teeth should be reshaped or restored first.

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1 All posterior occlusal contact should be eliminated {if posterior occlusal

reconstruction is indicated). When the occlusal surfaces oi'lhe posterior teeth

are lo be restored, it is advantageous to prepare them before harmonizing ihe

anterior guidance. Taking ihc posterior teeth out of contact eliminates their

proprioceptive influence and makes it simpler to record centric relation slops

on the anterior teeth. Functional border movements are more easily and more

accurately harmonized since there arc no restricting influences from posterior

proprioception.

The four steps to harmony:

Step 1: Establish coordinated centric relation stops on all anterior tceth(fig-4I):

The dentist must manipulate the mandible and guide it into a terminal axis

closure, marking with thin silk marking ribbon and adjusting until each layer

incisor makes a definite mark. In most mouths, minimal adjustment is required

to establish good centric stops.

Some of the common problems faced at this step are following. Deviation from

first centric contact into a more closed position: All interferences should be

eliminated so that the mandible may close all the nay to maximum closure

without any deviation. This is the most common problem and the easiest to

solve. No contact on some teeth after deviation is eliminated: This is the patient

who has solid centric steps, but not on all teeth. What do we do with the teeth

than are not in contact? We have three choices.

1. We can close "he vertical by grinding down [he centric stops until all teeth

contact. This ma> sound harsh, but a slight closure of vertical does no harm. In

teeth with severe bone loss, it may have an advantage hy improving the crown-

root ratio. Even with firm teeth, slight closure to gain contact is usually better

than having to restore teeth to contact.

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2. We can build up teeth to contact it is often necessary to make temporary

restorations to build out the lingual contours into contact.

3. We can do nothing. Sometimes nothing is what we should do. Anterior

teeth that arc not in contact but that are stable because of a substitute contact

such as lip or tongue position are sometimes better left as they are. We must

just be certain that they are stable without tooth contact before selecting to

leave them that they are stable without tooth contact for electing to leave them

that way. If noncontacting teeth need lo be restored and if we can establish

enough centric stops from other teeth to program, the customized guide table,

we do not have to worry about missing contacts. The restorations can be

corrected on the articulator.

Missing anterior teeth: This problem is solved by making a temporary

anterior bridge from articulated models and then finalizing all contours on the

temporary bridge in the mouth. Correct esthetics can be established right along

with correct lingual contours.

Arch relationship problems that do not allow centric contact on all teeth: As a

general rule, we must determine which teeth should contact in centric relation

before proceeding to the next step. If lower anterior teeth need to be moved or

reshaped, their position and contours must be corrected before proceeding with

finalizing the anterior guidance.

Habits that keep anterior teeth from contacting: Before any noncontacting tooth

is brought into contact, we must make sure it is not being held out of contact by

an unbreakable habit. Many habits of lip biting actually result from

unconscious attempts to cushion the teeth from interfering contacts. Such

habits usually disappear when the occlusion is corrected. Equilibration

procedures should be carried out to produce as much stability as possible prior

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to preparation. Any anterior teeth that could touch but do not should be

evaluated carefully before they are brought into contact.

Contouring the centric stops: It is necessary for the entire incisal edge of the

lower incisors to contact in centric relation. This usually produces too much of

a ledge in the upper teeth. If upper contours are rounded, contact with just the

labial portion of the incisal edge is sufficient. The shape of the upper contacts

should direct the forces as near up the long axis as possible, but contacts on

slight inclines are not as stressful as they may seem because the labial vector of

force is counteracted by inward pressure from the lips. Posterior support that is

harmonized to the anterior stops will also minimize the potential stress.

When all centric stops have been refined, each tooth should be checked

digitally to make sure it is not being moved by centric closure.

Step 2: Extend centric stops forward at the same vertical to include light

closure from the postural rest position:

This is when we determine how much long centric the patient requires. After

centric stops have been established by manipulating the mandible into terminal

axis closure, the patient should sit up in a postural position. The headrest is

removed and the patient is instructed to tap lightly with the lips relaxed. Red

silk ribbon is inserted between the teeth and the tapping is repeated. The mouth

should be held open while the patients returned to the supine position and a

manipulated centric closure into a darker marking ribbon made (green or blue

works fine). If the red marks extend onto inclines forward of the centric marks,

the centric stops should be extended at the same vertical so that the teeth can be

closed either into centric relation or slightly forward of it without bumping into

inclines. The amount of freedom from centric relation required rarely exceeds

0.5 mm. Regardless of the amount needed, it can be determined quite precisely

by following this procedure.

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Extension of the centric stops is accomplished nice!) with sharp inverted cone

carborundum stone. Care should be taken not to touch the centric stops them

selves. The results should be checked digitally to make sure that no teeth are

jarred when the patient taps.

Step 3: Establish group function in straight protrusion:

Before protrusive pathways can be established, the precise location of each

incisal edge must be determined. For simplicity's sake now, we will assume

that all the aspects of lip support, phonetics and esthetics that dictate incisal

edge position are correct. If so, all we need to do is selectively grind from the

centric and "long centric" stops forward to the incisal edges. In most cases the

four incisors fall right into group function as individual tooth interferences are

reduced. All reductions should be done on the upper teeth. Interferences are

marked by sliding forward on marking ribbon from centric to end-to-end. If

one tooth marks by itself, the marked area is hollow ground until the second

tooth shared the load and on until all four incisors have continuous contact

forward(fig-42).

At the completion of the protrusive movement, the incisal edges of the lower

central incisors should meet the incisal edges of the upper centrals. If the

lateral incisors can also meet edge to edge, so much the better, hut it is not

always possible without ruining the esthetics.

Step 4: Establish ideal anterior stress distribution in lateral excursions:

It is wrong to think that every mouth should have anterior group function in

lateral excursions. It is just as big a fallacy as giving every mouth cuspid

protection. However, if the cuspid is showing signs of hypermobiliiy.

accelerated wear, or loss of periodontal support, both stress and wear can be

diminished by bringing it into group (unction with other anterior teeth. While it

is often advantageous to change a cuspid-protected occlusion to anterior group

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function, there appears to be no sound reason for changing anterior group

function to cuspid protection.

The procedure for customizing the lateral anterior guidance starts with closing

the mandible into centric contact. With firm help from the operator, the patient

is asked to slide his jaw laterally and any movement of any teeth is noted. The

excursion is repeated with marking ribbon interposed between the teeth and the

marked lateral contacts selectively ground until there is continuous contact

from centric to the incisal edge of the upper cuspid.

To reduce the lateral stress on any tooth or teeth, the contacting surfaces must

be flattened from centric contact laterally. However, it is not necessary to

extend the flat surface all the way through the teeth, The cuspid is the key tooth

in lateral excursions, and as the jaw moves laterally on a fairly flat plane, teeth

in front of the cuspid begin to share more of the load. This permits the lateral

lingual inclines to be gradually steepened, forming concave pathway. The

downward excursion of the balancing condyle also contributes to a tendency

for a natural opening movement as the jaw moves laterally to form a concave

over-and-down pathway of the lower front teeth.

For best esthetics, protrusive inclines are almost always steeper than lateral

inclines.

Once the dentist and the patient have accepted the anterior relationship as

correct, we are ready to capture that relationship so that it cannot be lost. We

must duplicate it carefully.

There are a number of ways of accomplishing this. Making a customized

anterior guide table is a most effective yet simple method of transferring the

guidance pathways to an instrument. It can be used with any instrument that

has an anterior guide table.

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Customized anterior guide table(fig-43):

The customized anterior guide table is only needed when anterior teeth are

being restored. If anterior teeth are not being restored, the teeth themselves (on

the models) act to guide the front end of the articulator when the posterior teeth

are being fabricated.

If both the anterior and the posterior teeth are to be completely fabricated on a

fully adjustable articulator. the condylar guidances must all be set prior to

making the custom guide table.

If the border movements of the posterior teeth are to be recorded directly

through functionally generated path techniques, there is no need to precisely

duplicated condyle pathways on the instrument. The result of condylar

pathways will be captured three dimensionally by the functionally generated

path technique at the site of the teeth themselves.

If the functionally generated path technique for later fabrication of the posterior

teeth is chosen, the condyle paths may be set on the articulator arbitrarily. A

practical approach is to set the horizontal path at 20 degrees and the lateral

setting at 30 degrees. Condylar settings cannot be changed after the customized

anterior guide table is fabricated.

Method of Fabrication:

1. After the anterior guidance has been finalized in the mouth, upper and

lower impressions are made.

2. Using indentations in the bite record of posterior teeth only, a centric bite

record is taken. If the posterior teeth have be<*n prepared, the centric bite

record can be taken at the correct vertical dimension with the front teeth

touching.

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3. After the centric bite record and the impression of the harmonized anterior

teeth are completed, the preparation of the anterior teeth is begun. The model

of the prepared anterior teeth should fit into the same bite record made before

anterior preparations were completed. This will make the model of the

harmonized anterior teeth and the model of the prepared anterior teeth

interchangeable on ihe articulator.

4. With the model of the harmonized anterior teeth in place, the anterior

guide table is flattened to 0 degrees and the special guide pin is raised about 1

mm.

5. Special acrylic with dialomaceous earth added is mixed and placed on the

guide table and the articulator is closed. When the anterior teeth are in centric

contact, the guide pin should indent about 3mm, into the doughy acrylic. The

teeth on the upper model should then be slid over the lower anteriors from

centric relation through protrusive and lateral excursions. As the front of the

upper model is guided through all excursions from straight lateral to straight

protrusive, the guide pin forms its own pathways in the acrylic on the guide

table. The acrylic is then allowed to harden.

A customized guide table formed in this manner is in precise harmony with the

guiding lingual inclines of the upper anterior teeth. As long as the condylar

pathways are not changed, the anterior guide pin, sliding on the custom

guidance inclines, will produce the same movements of the upper bow of the

articulator whether the model is on it or not. If the model of the prepared

anterior teeth is mounted in exactly the same position as the model of the

harmonized teeth, its pathways will be identical. This is of course

accomplished by using the same centric bite record to mount both models.

When the customized guide table is completed, it should be checked for

accuracy by making sure that during excursions the upper teeth maintain

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contact with the lower teeth and that the pin maintains contact with the guide

table.

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THE PRINCIPLES OF OBTAINING OCCLUSION IN OCCLUSAL

REHABILITATION

The restoration of occlusion requires a correlation and integration of biologic

factors, mechanical principles, and esthetic requirements with treatment

procedures. The objectives of such dental service may be satisfied to a high

degree by several excellent methods of approach.

The unit area concept in the restoration of occlusion for the individual

rehabilitation problem should not be confused with segment of the arch

techniques. The construction of fixed partial denture restorations has been

influenced largely by the materials available through the years.

Within recent years, the segment of the arch procedure has been generally

discarded in favor of techniques with complete arch casts. This technical

improvement has been responsible for the elimination of many of the

inaccuracies which formerly complicated the restoration of occlusal harmony,

even in short-span restorations.

The unit area concept:

With this background, unit area concept in occlusal rehabilitation can be

differentiated from a mere technical procedure used in the construction of fixed

"bridges.'" Basically, the unit area concept is the original method of handling

the involved problems in occlusal reconstruction improved by many

refinements developed in clinical dentistry. The improvements have not been

all technical in nature since emphasis has continued to be placed on the value

of conservative dental treatment for the patient. Further, it is no* necessarily

the most direct approach to the treatment for the total restorative problem.

However, the benefits realized are the preservation and use of jaw relation

landmarks, the conservation of tooth structure in the choice of retainers, the

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construction of the restorations by the dentist even when auxiliary technical

assistance is not available, the simplified correction of inaccuracies, and the

more efficient management or complicated restorative problems.

Diagnosis:

Preoperative plan of treatmcnl is very important in any method of restoration,

but is indispensable in the unit area approach. While the lower arch may be

restored first for most patients, it is frequently of greater advantage and

necessary to initiate treatment many limes in the upper arch. The factors to be

considered in making this decision arc the existing occlusal plane, the amount

of freeway space (interocclusal distance), the size and location of edentulous

areas, the number, position, and quality of teeth in each arch, the health of the

supporting tissues, and the subjective symptoms.

The elimination and correction of occlusal disharmonies are prerequisites to all

restorative treatment. Harmony must be created between occlusal position and

centric relation, thus establishing centric occlusion. The information necessary

for this prerestorative mouth preparation is obtained from an analysis of the

existing occlusal relation. While it is possible to detect gross irregularities and

interceptive occlusal contacts clinically a detailed study of the occlusal contact

relations must be made on mounted complete upper and lower casts. It is very

important that a thin wafer-type centric relation record be used to relate the

casts. The mounting on an adjustable articulator requires a face-bow transfer

and the wax inter occlusal records to set the condylar guidances.

Questions:

The specific questions to be answered in this discussion are I) Do you use a

hinge bow to register &K hinge axis? Why? (2) How do you record the

occlusa! vertical dimension? (3j How do you record centric relation? (4) What

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eccentric interocctusal records do you record? (5) How do you establish the

occlusal plane? (6) How do you form cusps?

Summary:

The unit area concept in the application of fundamental principles in occlusal

rehabilitation provides a good practical approach to restorative treatment. Since

the total treatment can be extended over a long period of time while

masticatory comfort is being maintained for the patient, an opportunity to

observe tissue reaction in the restored region is provided.

The lerm "Functional Occlusion" refers to any tooth contacts made within the

functional size of opposing tooth surfaces, or as Schweitzer defined it, as. such

arrangement of teeth as will provide the highest efficiency during all of the

excursions of the mandible which arc necessary to the function of mastication.

In occlusal rehabilitation, we attempt to develop an acceptable functional

occlusion as our end result. Many articulators have been devised in an attempt

to record the many craniofacial, maxillomandibular, and muscle-tcndon-joint

relationships that influence and relate to the occlusal harmony of the

masticatory apparatus. Despite outstanding accomplishments in the articulaior

field, the claim that the mouth itself is the most accurate articulator is still

valid.

Principles and basic laws:

There are two important and basic steps, which must be recognized in FGP

technique and then should be recognized in any technique. These are (I) a

preliminary equilibration of the occlusion, and (2) the establishment of the

incisal guidance. The basic principles of occlusion must be understood and

observed, and definite objectives must be visualized and achieved wherever

possible.

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The objectives of the preliminary occlusal equilibration are: (I) to correlate .

centric occlusion with the unstrained centric relation, (2) to obtain the

maximum distribution of occlusal stress in centric relation, (3) to retain the

vertical dimension of occlusion. (4) to equalize the steepness of similar tooth

inclines in order to distribute eccentric occlusal stresses evenly, (5) to establish

smooth guidance tooth inclines, (6) lo reduce the steepness of inclines of

guiding tooth surfaces so that occlusal stresses may be more favorably applied

to the supporting tissues. (7)io retain the sharpness of cutting cusps, (8) to

increase number and size of food exits, and (9) to decrease the size of the

occlusal contact surfaces.

Classification and treatment:

There are four classifications of occlusal rehabilitation and situations, and each

requires a different type of treatment: (I) The curve of Spee (occlusal curvature

of the posterior teeth) and the incisal guidance are acceptable as presented by

the patient, but the posterior teeth need rehabilitation. The treatment plan

includes the restoration of the lower posterior teeth to the patient's curve of

Spee. as presented. Then the upper posterior teeth are restored by the

functionally generated path technique. (2) The curve of Spee (occlusal

curvature of the posterior teeth) is irregular, but the incisal guidance is

acceptable. The treatment plan involves the restoration of the lower posterior

teeth to a more desirable curvature with the use of the P.M. instrument. Then

the upper posterior teeth are restored with the functionally generated path

technique and the existing incisal guidance. (3) The curve of Spee (curvature of

the occlusal plane of the posterior teeth) and the incisal guidance are both

unacceptable. The treatment plan involves: (a) the correction of the incisal

guidance by restoring the upper anterior teeth by means of jackets or pinlays as

indicated, (b) the restoration of the lower posterior teeth to a more desirable

occlusal curvature, using the P.M. instrument, and (c) the restoration of the

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upper posterior teeth with the use of the functionally generated path technique.

(4) The curve of Spec (curvature of the occlusal plane of the posterior teeth)

and the incisal guidance are not acceptable, and the upper and lower anterior

teeth need rehabilitation. The treatment plan involves: (a) (he restoration of all

the lower anterior teeth, (b) the restoration of the upper anterior teeth and the

incisal guidance, (c) the restoration of the lower posterior teeth to a more

acceptable occlusal curvature with the P -M. instrument, and (d) the restoration

of upper posterior teeth with the use of the functionally generated path

technique

Diagnosis:

The diagnosis is made from all possible prediagnostic procedures, such as

intraoral and temporomandibular joint roentgenograms. two sets of diagnostic

casts mounted on a Hanau model H2 articulator, and one set of diagnoslic casts

mounted or. a P.M. instrument. All of these casts mounted with cast relator

(face-bow) registrations and wax interocclusal records.

The Class 4 rehabilitation siluation occurs most frequently. In these patients,

the incisal guidance and the curve of Spee both need changing. The upper

anterior teeth need crowns or pinlays to change the incisal guidance (usually to

make it less steep), and the upper and lower posterior teeth need occlusal

rehabilitation. In planning the incisal guidance, we can reduce its steepness by

reducing the length of both the lower and upper anterior teeth. If, for esthetic or

other reasons, this cannot be accomplished, the incisal guidance can be reduced

by making parallel vertical pinlays.

Treatment plan:

Plan the treatment before any tooth is prepared, just as an architect has his

plans finished before the building is started. Bliminatc any deflective or

interceptive occlusal contacts in centric occlusion. Prepare the upper anterior

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teeth first, and make complete arch reversible hydrocolloid impressions of the

upper and lower teeth. Mount the casts on a Hanau H2 articulator, which has

straight-line incisal guide table (not convex or concave), by means of a cast

relator (face-bow) transfer and centric and protrusive wax interocclusal records.

Wax patterns are formed and carved on the preparations to establish the

esthetics and the incisal guide factor. The lingual surfaces of these wax patterns

are carved to create a freedom in centric occlusion (what we, call a long centric

occlusion). Centric occlusion should be an area of contact rather than a point of

contact. Therefore if we establish :he area of contact simultaneously with the

incisal guidance, it will be reflected in posterior tooth restorations through the

functionally generated path technique.

Establishing centric occlusion, on anterior restorations:

Metal strips. 0.5 mm. thick, are inserted in front of the condyie balls of the.

instrument, or the protrusive retrusi\e adjustment (on some instruments) is

extended 0.5 mm. Either procedure will-change the relationship of the casts so

the lower one is protruded 0.5 mm. The wax patterns forming the incisal

guidance are first waxed to this position in all functional movements then, the

metal strips are removed, or the protrusive-retrusive adjustment is returned to

zero (centric relation), and the carvings arc extended lingually to establish the

contacts in centric relation. This procedure provides for uniform contacts of the

restorations in both the protruded relation and the centric relation.

After the anterior wax patterns are completed and cast, the castings are returned

to the articulator and gross adjustments are made. This is done even if full

coverage restorations are used. These adjustments are made prior to baking the

porcelain The finished restorations are sealed in the mouth, and different

colored silk ribbons are used to adjust the restorations until the ideal "long

centric" occlusion, occlusal vertical dimension, incisal guidance, and eccentric

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relationships have been established on all of the anterior castings. These

restorations are then cemented on the preparations and tested and adjusted

again, if necessary. When the lower posterior teeth are prepared, the anterior

teeth maintain the occlusat vertical dimension and the incisal-guidance, which

then influences the shape of the posterior preparation, the occlusal curvature,

and the cuspal inclines in the lower posterior wax patterns. These factors must

be in harmony with the, incisal guidance.

Summary:

1. The objectives of occlusal rehabilitation are optimum oral health,

functional efficiency, mouth comfort, and esthetics, and they can be

achieved by the technique described.

2. The posterior teeth maintain the vertical dimension while the anterior teeth

are being restored.

3. The anterior teeth maintain the occlusal vertical dimension while the

posterior teeth are being restored.

4. The incisal guide angle, the temporomandibular joints, and the

mandibular musculature register a functionally generated path.

5. The restorations exhibit a static occlusal contact of all teeth when the

mandible is in centric relation to the maxillae.

6. An area of centric occlusal contact is developed to provide freedom of

movement in a horizontal direction while the same vertical dimension is

maintained.

7. All centric movements, including the Bennet movement, can be exercised

without occlusal interferences.

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8. Working side contacts are coordinated with the incisal guide contour while

the potentially damaging nonfunctioning side contacts are eliminated.

Treatment of human beings is still a problem of human variables. There are

indications for cuspless teeth or balanced occlusion, and variations or

combinations of the two in treatment of occlusion for some patients. Whichever

is the treatment of choice, it must be capable of functioning within the pattern

of the patient's own individual functional requirements.

In order to construct such restorations with the knowledge that they will fit

these personal human variables, the restorations must be mechanically related

to the individual. The treatment of occlusion requires instruments and

techniques to determine these relations. The mouth is not a good articulator.

The nonfunctioning mouth which makes voluntary movements does not

necessarily function the same, as it will in the involuntary actions of

mastication. This difference is because.the icinporomandibular joints are

unique, being held together by muscle action and not by ligaments. The

ligaments serve to limit the condylar movements, and the glenoid fossae dictate

the paths which the muscles can make the condyles take. Regardless of

thinking to the contrary, clinical experience has shown that there is a relation

between the lemporomandibular joints and the occlusal form of teeth which the

mouth can tolerate. The purpose of instrumentation is to reproduce these

functional paths of the joints in order that occlusal surfaces which will permit a

benign harmony of teeth, joints, and muscles can be constructed for the

individual patient.

Proprioceptive mechanism and instruments:

The proprioceptive mechanism coordinates these structures so that they can

function in harmonious relation and avoid self-inflicted injury. But it cannot

compensate for disharmonious relationships. The problem in constructing

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harmonious occlusal surfaces is to transfer to a suitable instrument those

functional relations which will result in a benign action of all of the structures

involved. Therefore, the articulator used in the construction of the restorations

should reproduce the relations in which teeth may contact. The articulator does

not prescribe nor dictate the resloration. but it should enable the dentist to know

how the restoration will function in the mouth. Functional contact of the teeth

results from two simultaneous actions. The mandible rotates to closure around

the condyles, while at the same time the condyles glide from an eccentric

position toward their position in centric relation. It is vitally necessary that we

keep this basic problem in mind. In any involuntary muscular act of

mastication, these two actions always occur simultaneously. The patient cannot

rotate the mandible 10 closure without making bodily movements of the

condyles at the same time. Recent investigations point to the fact that the

reason for this is that the greatest muscle power is exerted in lateral excursions,

or. expressed in different words, the more muscle power required, the wider the

lateral excursion. With less resistance, the patient uses less lateral movement

with the same amount of vertical movement. Whenever the condyles are in the

glenoid fossae when the teeth do come into contact, they glide to and beyond

centric occlusion before opening to make the next lateral return stroke.

Opening and closing axes:

The hinge axis is located in the mandible, and since the mandible cannot rotate

to closure without the condyle gliding, the hinge axis moves when the

mandible moves. As the jaw opens, each condyle rotates on its meniscus and, at

the same time, the meniscus glides in its fossa. The mandible (jaw) opens down

and forward. The resultant of these two actions is an opening axis somewhere

near the angle of the mandible. The patient never opens his jaws successively

alike. Each opening is different from the one before. So this axis is neither

locatable nor reproducible. This axis results from rotation around the hinge axis

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as it is moving along the condyle path. Therefore, if we locate the axis and the

path it follows, we can reproduce the effect of the opening axis. More

important, the closing axis is not the same as the opening axis. The closing

movement is not the reverse of the opening movement; the action is the

reciprocal. The closing axis is a point in space above the skull. But this is still a

result of the same two simultaneous motions, rotation and gliding, so we can

reproduce the effect of the closing axis in closures of the teeth. Because these

are the changing axes of opening and closing, which result from eccentric paths

of the hinge axis, we must reproduce these eccentric paths in the occlusal

relations of the teeth.

We must differentiate between two terms which are often used A changing axis

is not the same as a moving axis. The opening axis and the closing axis are the

changing axis. They are different every time they operate. The hinge axis is the

moving axis, always moving with the mandible, yet unchanging its relation to

tooth closures. Regardless of how you may accomplish it. whether you locate

the axis or not teeth cannot make harmonious functional contact unless 'hey are

related to the hinge axis, it ;s the relation of teeth to this moving hinge axis

which determines cusp form and position for a given individual. This is a

human variable and this is the way cusps are formed.

Establishment of a correct centric relation, vertical dimension, and occlusa!

plane, all depend upon this relation. The joints do not, per se, directly

determine the shape of the cusps. Correct centric relation does determine the

changing relation of the occlusal plane at a given vertical opening, which will

result in cusps which are harmonious for a given individual. So the hinge axis

alone is not enough to restore an occlusion, but without it we cannot determine

the other relation, all of which are necessary for treatment of the mouth. There

are many techniques for obtaining a centric relation record, equally good in the

hands of various dentists, yet a full occlusal restoration made with a correct

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centric relation record is rarely seen. Therefore, a technique is not of much

value without an understanding of what is required.

Interocclusal records of centric relation:

Centric relation is the most posterior superior position of the hinge axis. A

centric interocclusal record involves two considerations one of which is the use

of a material in the mouth upon which the patient can bite with his own

muscular force, while maintaining the hinge axis in its posterior terminal

position. For reasons having to do with proprioceptivc mechanism, it is

desirable that the "bite" be made at an increased vertical dimension, with a

minimum of closing pressure applied between the teeth Therefore the "bite"

(inierocclusal record) must be made with a pure rotary closure and mounted on

the hinge axis so that the cast can be closed to the correct vertical! relation to

the maxillae. This is not a natural act. As soon as something is introduced into

the mouth for the patient to bite, the mandible attempts to move into a lateral

protrusive relation. Thus, there is the need for a soft material requiring little

muscular force to be applied on the teeth. To provide resistance so that the

muscles will elevate the condyles without moving into a lateral position, the

chin is glided down and back as the mandible is rising to a closed position, the

guidance provides the resistance to the. closure and does not help the closing.

The patient makes repeated closures against this resistance to elevate and

position the condyles. before lite soft recording material is introduced into the

mouth. A centric interocclusal record should never be made with a single

closure into a static position. The rotary ciosmg is continued as the teeth

penetrate more deeply into the material in which the interocclusal record is

made, but closure to the point of tooth contact is never permitted. If the patient

does "bite through" to tooih contact, the record is discarded and a new one is

made. Many materials and methods for making these records are equally good.

Some work better for some purposes than others in different hands, but all have

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the same objective; to elevate the condyles to their functional bracing position

and to avoid tooth proprioception and a lateral protrusive inlerocclusal record.

They all are intended to provide resistance to closure outside of the

proprioceptive area, so the muscle action will hold the temporomandibular

joints lightly together.

In the restoration of natural teeth, the dentist has little choice in positioning the

plane of occlusion. The occlusal vertical dimension, the plane of occlusion, and

the formation of cusps are all inseparably related. One factor cannot be

discussed without considering its relation to the others. The vertical relation

depends largely upon what is necessary lo position a plane of occlusion that

will permit the formation of cusps which are harmonious with the

temporomandibular joints and the muscles. The presence of teeth limits the

location of the plane of occlusion and may require a change in occlusal vertical

dimension in order to reduce the height of the cusps so they will be

harmonious, with the temporomandibular joints and still not exceed the

tolerance of the supporting structures.

Against this is the fact that an increased occlusal vertical dimension results in

increased crown-root ratio. One must be balanced against the other, and this, in

turn, may require some alteration in cusp form which will represent the best

balanee between the two. Indeed, balanced occlusion embodies many things

other than simple cross arch prosthetic balance. It means a balance of al of the

factors which enter into tooth contact to produce equilibrium of forces acting

upon all of the structures involved. There is no one, arbitrary cusp form and

relation which is best for all cases.

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RATIONALE AND TECHNIQUE OF BIOMECHANICAL OCCLUSAL

REHABILITATION

"A physiologic occlusion is one in which the relation between the teeth and the

periodontal tissues is such lhat under occlusal stress no injury is produced by

them and further, the tissues are best able to withstand the forces of occlusion,

without the initiation of pathologic changes in the periodontium."

All teeth are subjected to both vertical and horizontal stresses. The steeper the

cusp, the greater the horizontal loading. Vertical loading distributes the stress

over the entire alveolus and may be increased considerably without

overloading. Horizontal loading acts on the periodontal membrane and bone

regionally and frequently exceeds the normal limits of the tissues.

Optimum occlusion is one in which the relation between the teeth and the

periodontal tissues is such that under occlusal stress the most favorable loading

is achieved, thereby fostering the biologic maintenance of the periodontium.

Bilateral balance versus optimum loading:

The question of bilateral balance in the natural dentition is still a controversial

one. Those who are opposed argue that mastication is a unilateral process, that

bilateral balance rarely occurs in nature, that many healthy dentitions present

without bilateral balance and clinch their argument with the pithy comment of

Prime, "Enter bolus, exit balance."

Jankelson's recent work promises to resolve this hitherto academic question. He

concludes. "The evidence strongly suggests that centric occlusion is the only

tooth contact of any significance that occurs during stomatognathic function.

Evidence of eccentric tooth balance during eating was not found. There was no

evidence that balance of teeth eccentric positions is a physiologic necessity, or

that lack of eccentric balance is less conductive to masticatory function".

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Although bilateral balance is not essential to masticatory function, it is a most

desirable adjunct to occlusal reconstructions. Here we are dealing with

mutilated dentitions and periodontal breakdown, and bilateral balance serves to

distribute the occlusal loading over more teeth and greater saddle area. This

distribution of loading is probably more important during the nonchewing

movements than in actual mastication. We know that actual chewing function

occupies but one hour a day. and we have also' learned from the work of

Hildebrand. Jankelson, and others, that even in chewing, teeth make only

occasional contact. However, in the twenty-three remaining hours of the day,

the teeth contact innumerable limes: in swallowing, during conversation, and

intensional movements. Mow many of our patients requiring occlusal

reconstruction are completely free of emotional tension which frequently is

attended by clenching, tapping, or gritting of the teeth, although perhaps

unconsciously? It is during these twenty-three hours of nonchewing and

tensional contacts that the teeth are subjected to repeated stress, and it is during

this time that bilateral balance serves to mitigate that stress by wider

distribution of it.

Thus bilateral balance is essential to achieving optimum loading of our

reconstructed occlusion. (Note: Bilateral, balance, as it is used here implies

contact of all the posterior teeth and not a single balancing point or area.)

The optimum occlusa! pattern:

From the preceding it would follow that the optimum occlusal pattern for

rehabilitation is the most shallow intercuspation consistent with bilateral

balance.

What can we do to influence and achieve such an occlusal pattern? In virtually

every reconstruction case, we find it necessary to re-establish correct, centric

relation and/or to restore lost vertical dimension. Both of these changes cause

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the mandible to be brought downward, decreasing the vertical overlap. This

results in a decrease in the degree of inclination of the incisal guidance.

Judicious grinding and reshaping of the anterior teeth, or rebuilding the

anterior- teeth can achieve further reduction in the jangle of the incisal

inclination. Let us now see how by control of this single factor (the angle of the

incisal guidance) we can drastically influence cusp height. Fig.44 illustrates a

comparative study of two different incisal guide angles with the same condyle

angle, in Fig.44. A (with a 50 degree incisal guide angle) we find that in order

to achieve occlusal harmony, we must build upper lingual cusps (and

conversely, lower buccal cusps) ranging from 32.5 to 41 degrees, and; also we

must build upper buccal cusps (and, conversely, lower lingual cusps) ranging

from 15.5 to 32.5 degrees. In Fig. 44.B with a 0 degree incisal guidance and the

same condylar inclination, we find that we .\eed only build upper lingual cusps

(and conversely, lower bucca) cusps) ranging from 17.5 to 9 degrees, and aiso

that all the upper buccal cusps and all the lower lingual cusps require a 0

degree inclination.

Fig. 44.A is representative of an anatomic articulation. In Fig. 44.D, there is no

interdigitation of cusps, and in gliding from the centric position forward, the

teeth encounter a free path without cusp inclines. Fig. 44.B is representative of

a biomechanic occlusion.

Let us trace these lateral gliding movements in the mouth starting from centric

occlusion and ending in left lateral occlusion as illustrated in the schematic

drawing.

In fig. 44.A" (no Bennett movement present) the working condyle lying in the

mandibular fossa begins to pivot or rotate horizontally (on its vertical axis)

However, due to the upper buccal cusp inclines on the working side, the

condyle is now compelled to rotate on its horizontal axis, dropping the body of

the mandible vertically and allowing the lower buccal cusps to glide down

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along buccal inclines and assume their cusp-to-cusp relationship. The balancing

condyle glides down along the posterior slope of the articular tubercle, and

come to rest when the working side inclines achieve their lateral contacting

position. The balancing teeth have no influence on the movement of the

balancing condyle except where there is premature contact of these balancing

teeth. The balancing condyle in gliding down the articular tubercle drops the

mandible lower on the balancing side, and therefore the upper lingual cusps

must always be steeper than the upper buccal cusps to achieve bilateral

balance.

In Fig. 44,B'. the working condyle pivols on iti horizontal axis a^ In Fig.

L44.A, but: does not have tn rotate on its horizontal axis to permit the lower

buccal cusps for reach their lateral contacting position, because the upper

buccal cusp inclines, are at zero degrees. The balancing condyle travels as just

described but does not have to travel as far down on the articular tubercle to

achieve its balancing position.

In Fig. 44, A" (Bennett movement preseni). there is some clearance between

the condyle (on the balancing side) and the medial wall of the fossa; as the

mandible glides into left lateral position, the pull of the right external pterygoid

muscle draws the right (balancing) condyle toward the inner wall of the fossa

in the Bennett movement. This carries the mandible and left condyle further

laterally than in Fig. 44.A' where no Bennett movement is present. This shift in

the pivoting center of the mandibular gliding movement, does not appreciably

effect the cusp heights previously-established, but does affect materially the

curvature of all the cusps (upper and lower reorganization, may not the

articulation alter again? Certainly we are all aware of this phenomenon, either

consciously or subconsciously, when you recall your patient to check the

occlusion subsequent to completion of the restorations. You have experienced

this phenomenon when you have found it necessary to touch up or adjust the

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occlusion many months after the delivery of the restorations. Has there been a

slight depression of the teeth? Has there been a slight movement en masse of

all the teeth and prosthesis? And how about subsequent wear of the prosthesis?

Where the occlusal surfaces had been reconstructed to an anatomic articulation,

the paths of movement are closely bounded by interdigitating cusps. The

slightest change due to reorganization or wear may completely disorient the

articulation: There is no tolerance in the occlusal relationship of an anatomic

articulation; this would be contrary to its very concept. Correction in the mouth

would be extremely difficult if not impossible. Mutilation of the original

articulation would be inevitable.

With the shallow modified cusp as in Fig. 44.B, there is no interdigitation of

cusps. A slight change due to reorganization or wear can be easily compensated

for by a slight adjustment in the mouth. This tolerance factor an important and

added safeguard to the continued success of the rehabilitation.

Decalogue for occlusal rehabilitation:

1. Occlusal rehabilitation is a radical and serious procedure. It should

not be undertaken merely because the occlusal relationship existing does not

conform to preconceived concepts of the normal or ideal.

2. The ultimate standard of normal is functional adequacy. In the presence

of functional adequacy, conservative treatment is indicated.

3. Where pathologic changes in the periodontium are in evidence, and where

mutilation and/or occlusal disharmonies are present, mouth rehabilitation is

indicated.

4. Where extensive prosthesis is necessary, occlusal reconstruction is

indicated although no pathosis is evident. It will enhance the success of the

treatment.

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5. The final judgment of success must be in terms of how well and for how

long the remaining teeth and supporting structures are preserved.

6- There is no evidence that an anatomic articulation is a physiologic necessity.

Chewing efficiency can exist over a wide range of occlusal forms and types of

occlusion.

7. Bilateral balance, although not essential to masticatory function, is de-

sirable in that it serves to mitigate the stresses of nonchewing and tensional

tooth contacts by their wider distribution.

8. The optimum occlusal pattern for occlusal reconstruction is the most

shallow cuspation consistent with bilateral balance.

9. A reconstructed occlusion cannot be regarded as static; a tolerance factor

to permit simple correction for reorganization and wear is desirable to

safeguard the result.

9. Optimum occlusion {where the relation between the leeth and the

periodontal tissues is such that under occlusal stress the most favorable loading

is achieved thereby fostering the biologic maintenance of the periodontium) is

the goal of occiusal rehabilitation.

Classification and technique of treatment:

The conditions which require occlusal reconstruction may be classified in three

categories:

Class A -Condyles in normal resting position in the fossae, loss of vertical

dimension due to missing teeth, drifting of teeth or abnormal wear of teeth.

144

Class B-Condyles in inferior and anterior (mesial) relation in the fossae,

mutilation of the teeth, loss of vertical dimension or increase of vertical

dimension due to eccentric contact.

Class C- Condyles in superior and posterior (distal) relation in fossae with loss

of vertical dimension.

The technique of treatment is very much the same for all three classes.

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RESTORING LOWER ANTERIOR TEETH

When planning the restorative correction of any occlusal problem, the first

segment to be completed should be the lower interior teeth. Until the precise

location and shapes of the lower incisal edges are set, there is no practical way

to work out the lingual contours of the upper anterior teeth.

The first consideration in restoring lower anterior teeth should be to determine

the correct location of the incisal edges. While this would ideally be decided on

the basis of providing the most stable centric contact with the upper anterior

teeth.

It is a fairly safe assumption that problems are minimal if the lower anterior

teeth can be made to contact in centric relation at the correct vertical

dimension. It is ideal if the contact is on the cingulum of the upper anterior

teeth, but contact on any part of the upper lingual surface can usually be

adapted to the requirements of good function. Even an end-to-end relationship

can be made functional and stable with minor alteration. Shaping the lower

incisal edge back slightly may be all that is required to provide a protrusive

pathway against the upper anterior teeth.

Even a short horizontal path of the lower incisor teeth against the upper incisal

edges is sufficient to disclude the posterior teeth in protrusion if the occlusal

plane is correct. A flat lateral anterior guidance can disclude the balancing side

because of the downward movement of the orbiting condyle, if cusp-fossae

angles are coordinated.

Sometimes a too steep anterior guidance can be flattened by shortening the

lower anterior teeth and restoring the lingual surfaces of the upper teeth. The

cinguium is brought down into contact with the shortened lower anterior teeth,

making the angle flatter between centric contact and the upper incisal edge.

146

Any modifications of this nature should always be worked out on mounted

models and the changes duplicated in the upper temporary restoration for

refinement in the mouth and testing by the-patient.

Crowded lower anterior teeth present a variety of problems that can be solved

in a variety of ways. The first determination to make is whether the crowding is

really a problem. It is not an occlusal problem if the teeth are stable and

cleanable

and can function without interference in excursions. It may be an esthetic

problem if the crowding is too noticeable. However, a slight irregularity of

lower incisors is usually not the esthetic shortcoming that some patients may

think. It is most often better lo keep the slightly crowded condition that it

would be to do unnecessary restorative procedures.

If crowded lower anterior teeth need to be restored for any reason, minor tooth

movement can often be simplified by combining it with the restorative

procedures.

After the alignment is corrected, a temporary restoration can be used as an

esthetic yet very effective retainer for a few weeks while the bone and

periodontal fibers reorganize around the moved teeth.

Combining minor tooth movement with restorative preparation of lower

anterior teeth makes possible a myriad of simplified and practical approaches

to solving problems of irregularity or crowding.

Lower incisors that are locked lingually by a steep incline can frequently be

moved forward by tongue pressure if the upper lingual contour is shaped to

accept it. A single lower incisor that has erupted up such a steep incline into

soft tissue impingement may be corrected by shortening it back to the length of

147

the other lower incisors and then providing a concave stop on the upper tooth

that will allow the lower incisor to move forward.

A lower incisor that has supraerupted up above the incisal edge line of the other

incisors should never be shortened back to correct alignment unless a centric

stop is provided for it. If a centric stop cannot be provided, the tooth must be

splinted to another tooth that does have a centric stop. Otherwise the shortened

tooth will erupt right back up where it was.

Separated lower anterior teeth constitute another "problem" that should very

often be left as is. Separation in itself is not an occlusal problem if the teeth are

stable maintainable, and esthetically acceptable. If the spaces must be closed

for estheiics or stabilization, the corrections should first be made by waxing

against the study model.

If the space between lower anterior teeth is too great to be widened acceptably,

it may be necessary to move the teeth together orthodontically and add a fifth

incisor. The extra incisor presents no esthetic problems and is hardly noticeable

even with close observation.

Worn lower anterior teeth can present some difficult problems to solve if the

wear has shortened the teeth to an extreme degree. The usual tendency is to

assume thai vertical dimension has been lost and the treatment is merely a

matter of lengthening the teeth back to their original length to "restore the lost

vertical". This is a dangerous assumption, such treatment is clearly

contraindicated. As teeth wear, they erupt, taking the alveolar process with

them,

Frequently the cause of anterior wear is a posterior interference that deviates

the mandible forward into an acquired position that causes increased stress and

wear on the front teeth. If the interference is eliminated, it often permits the

patient to close 'on a more retruded arc to the same vertical dimension, with

148

ample room provided horizontally between the upper and lower incisors. The

lower anterior teeth can then be lengthened to regain centric contact and to

restore the worn incisal edges.

If full coverage is indicated, it should be either porcelain jacket or porcelain

veneer. Using acrylic on lower anterior teeth is absolutely contraindicated. The

shape and position of the incisal edges are critical to the anterior guidance, and

once precisely established, they should be maintained just as precisely.

Not all worn lower anterior teeth need to be restored. Even if the wear has

penetrated to the dentin. it may be possible to maintain the incisal edges

without restoration. Lower incisors make contact at their labioincisal line angle.

Even with worn edges, the contact will still be on enamel.

If the dentin is cupped out the enamel around it is intact, restoration of the

cupped area with one of the hard filled resin materials is sometimes a logical

choice of treatment. It is conservative, the esthetics is good, and it does not

preclude the later use of full coverage if it becomes necessary.

Hypermobility of lower anterior teeth frequently results from occlusal stress.

Occlusal correction often produces amazing results in eliminating

hypermobility completely.

Any hypermobility should be treated as an unhealthy situation and all

necessary steps should be taken to correct it. If mobility patterns cannot be

controlled by combined occlusal and psriodontal therapy, splinting may be

considered.

Lower incisors can be maintained with a higher degree of mobility than other

leeth. If restorative procedures are required on the lower incisors for other

reasons and hypermobility patterns are present, it would be practical to go

149

ahead and splint the restorations rather than having to destroy them at a later

time if the need for splinting was determined.

Lower incisors with extreme bone loss should not be splinted unless they offer

support to other teeth. It is more practical to replace lower incisors with a

fixed bridge than to splint them if the splinted teeth present problems of

maintenance and offer no advantages to the treatment plan.

The replacement of missing lower anterior teeth requires the same preplanning

as other anterior problems. The teeth should be set up or waxed up tentatively

on mounted models so that the incisal edges arc in the best relationship for

stable centric contact.

Esthetic considerations:

The incisal edges of the lower anterior teeth should form a horizontal line that

is either straight across or slightly bowed up in the middle(fig-45). Regardless

of the slant or shape of the ridge, the line of incisal edges should be horizontal

for the best appearance. An incisal edge line that curves down in the middle is

very unesthetic and is not compatible functionally with properly oriented upper

anterior teeth.

It is not difficult to decide how high the incisal edges should be. The anterior

teeth normally form a slightly convex curve that continues smoothly into the

concave curve of Spee. Simply noting the height of the posterior cusp tips and

relaling them to the anterior teeth is a rather uncomplicated clinical judgment.

The labiolingual position of the incisal edges is also very limited in its

flexibility. The direction of stresses must stay as close to the long axes as

possible, and the teeth must stay within the very narrow confines of the

alveolar ridge, so labiolingual positioning is usually rather clear-cut.

150

Duplicating correct incisal edge position:

Once the precise position of the incisal edges has been established, it should be

duplicated in, the permanent restorations. Preparing every other anterior tooth

and taking an accurate impression gives the technician a simple means of

duplicating not only the incisal edge position but also the exact contours of the

incisal edges. A second impression made after all the lower anterior teeth have

been prepared is used in combination with the model of every other tooth

prepared. Waxups or porcelain jackets made on the first model are transferred

to the second model. They are then used as the guide for completing the

remaining crov-ns on the model with all of the anterior teeth prepared.

In restoring lower anterior teeth, it is important to remember that the incisai

edges are not only the key to correct function and stability, they arc also the

key to natural appearance.

Regardless of the occlusal problem, the correctness of the anterior relationship

should be established before proceeding with the restoration of the posterior

teeth. Most often the lower anterior teeth do not require restoration, but

whatever modification is needed, if any. should be finalized before proceeding

to the next step. If the lower anterior teeth have been correctly analyzed and

needed improvements have been carefully made, it should not be necessary to

make any further changes in them through the completion of the entire

restorative procedures.

RESTORING UPPER ANTEIROR TEETH

No technician, including Ihe dentist who prepared the teeth, can consistently

shape anterior restorations precisely enough unless he is furnished the

necessary information.

151

In order to successfully restore upper anterior teeth, the correctness of the

following information must be verified in the mouth and it must be accurately

transferred to the laboratory bench.

Correct lip support: The tightness or flaccidity of the upper lip plays an

important role in positioning the upper anterior teeth. It plays an equally

important role in maintaining that position. Teeth that are not in harmony with

the lip are not only unstable, they are generally uncomfortable and unesthetic.

Precise incisal edge position: Location of the incisal edges establishes the

correct length of each tooth. In combination with correct lip support, the

labiolingual position of the incisal edges determines the pitch of each upper

anterior tooth. This is an extremely important factor to duplicate with

preciseness. It plays the dominant role in esthetics and is a critical determinant

of optimum function.

Labial contours: Some anterior teeth are fan shaped, some convex. Some are

square, some fan shaped, some have distinctive conlours tiiat give the patient's

smile its particular individuality. Good features should be faithfully preserved

and unesthetic features should be corrected. Position and contours of contact

areas demand careful attention to detail and should never be determined by

guesswork.

Lingual Contours: The anterior guidance cannot be finalized until the precise

incisal edge positions have been located because lingual contours are

determined from centric relation to the incisal edge positions. Evaluation of

lingual contours is the last step prior to preparation.

152

Esthetic consideration:

Esthetics and function go hand in hand. The better the esthetics, the better the

function is likely to be and vice versa. The best esthetic result is a natural

appearance. Conversely, close attention to achieving optimum function almost

automatically positions and shapes the teeth in the best relationship to the lips

and the muscles of facia! expression. Like phonetics esthetic considerations are

actually a helpful determinant in establishing the relationship of the anterior

teeth.

Phonetic considerations:

The relationship of the upper anterior teeth to the lower anterior teeth, the lips

and the tongue has a considerable effect on phonetics. The spatial relationships

used to form certain sounds are the result of long-standing muscle memory

patterns. In spite of patient's adaptability to change, a good rule to follow is:

unless there is a specific need to change inctsal edge position, it should be

meticulously duplicated in an\ anterior restorations.

Whenever any gross change of the anterior relationship is undertaken,

contouring and positioning of the teeth should be evaluated from a phonetic

standpoint. Frequently, minor changes make major differences.

Any decision to change the incisal edge position should be considered a major

decision. While necessary in many cases, it should never be done without full

awareness of the effects resulting from the change.

Changing the incisa! edge position affects the following.

Phonetics: The incisa! edges of the upper anterior teeth should lightly touch the

vermillion border of the lower lip when making V and V sounds. Any change

of incisal edge position changes the spatial relationship of the teeth to the lip.

153

Such spatial relationships are so consistent that they can be used an aid to

determine incisal edge position when it has been lost or destroyed.

Lip support: If the incisal edge position is moved either labially or lingually, lip

support is altered. Of course many times such alterations are an improvement,

but ^rteri lip support is changed, it must be consistent with the lip itself. If the

teeth are moved too far labially, pressure from the lip will try to move them

back. The lower "P w ill hang up under the incisal edges and magnify the

change.

For the sake of comfort, phonetics, and stability, any change of the incisal edge

toward the labial should be made only after thoughtful determination that it is

truly needed.

Moving the incisal edge toward the lingual frequently improves

both appearance and function, but carelessly or unnecessarily done it can be

disastrous.

The smile line: Minor changes in the incisal edge position can completely

change a person's appearance.

It is essential to the success of each anterior restorative case that the incisal

edge position be accurately determined and precisely duplicated.

Anterior guidance angles: Since functional movements at the front of the

mouth occur between centric contact and the incisal edge position of the upper

anteriors, shortening the teeth or moving the incisat edges labially would have

the effect of flattening the anterior guidance angle. Lengthening the teeth or

moving the incisal edges lingually has the effects of steepening the angle.

When there is sufficient overjet. it is possible to lengthen the upper anterior

teeth and lo compensate with concave lingual contours.

154

When there is minimal overjet. it is often not possible to lengthen the upper

anterior teeth without steepening the anterior guidance angle. If a sleeper

guidance angle is not compatible with function, the upper incisal edges will

have to be move labially as the teeth are lengthened. When longer anterior teeth

are desired, such changes should definitely be effected in the temporary

restorations first to evaluate the results before the permanent restorations are

completed.

THE PLANE OF OCCLUSION

The plane of occlusion refers to an imaginary surface that theoretically touches

the incisat edges of the incisors and the tips of the occluding surfaces of the

posterior teeth. Instead of flat surface, the plane of occlusion actually

represents the average curvature of the occlusal surface.

There are two basic requirements of a proper plane of occlusion:

1. It must permit the anterior guidance to do its job of discluding the posterior

teeth when the mandible is protruded.

2. It must permit the disclusion of all teeth on the balancing side when the

mandible is moved laterally.

It is possible for an occlusal plane to be flat and still fulfill the basic

requirements, but if optimum efficiency in function is the goal, the occlusal

plane will usually have curvatures to it. Better esthetics is in most cases also

dependent on curvatures of the occlusal plane, the perfectly flat plane of

occlusion often being the epitome of artificiality. A flat occlusal plane can even

be harmful, since it can actually create stressful crown-root ratios when the

curvature of the supporting alveolar bone is not matched to a reasonable degree

with the curvature of the occlusal plane.

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If the reasons for making each curve in the occlusal plane arc understood, it

will become evident that there are number of methods that can be used

effectively to establish a suitable occlusal plane for any given patient. Each

curvature is determined by ihe effects it should produce.

The curvatures of the anterior teeth are determined by establishment of the

esthetically correct "smile line" and its relationship to phonetics and the

functional aspects of the anterior guidance.

The curvatures of the posterior plane of occlusion are divided into (I) an

anteroposterior curve, called the "curve of Spee" and (2) a mediolateral curve,

referred to as the "curve of Wilson". Together, the composite of the curve of

Wilson the curve of Spec, and the curve of the incisal edges is properly referred

to as the curve of occlusion. Popular usage combines both the curve of

occlusion and its relationship to the cranium into the plane of occlusion.

Curve of spee<fig-46):

The curve of Spce refers to the anteropostcrior curvature of the occlusal

surfaces, beginning at the tip of the lower cuspid and following the buccal cusp

tips of the bicuspids and molars and continuing to the anterior border of the

ramus. The importance of this aspect of a correct plane of occlusion is more

easily understood if we note what problems occur with variations of an

incorrect curve of Spec. Curve of Spee too high in posterior: This is the most

common disharmony of the occlusal plane. It can be extremely deleterious to

the supporting tissues of the posterior teeth because it forces the most posterior

teeth to carry the full stress imposed on them by the musculature when the

mandible is protruded. Irregular occlusal plane caused by losl but imreplaced

posterior teeth: The result is a collapsed arch that does not permit protrusive or

lateral excursions without interfering with the tilled or elongated teeth. The

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effect is the same as a curve of Spee that is too high posteriorly. The protruding

mandible directs the stresses onto the teeth least able to resist it.

When an upper molar has supracrupted into a vacant space between two lower

posterior teeth, the upper tooth should be shortened to permit protrusion of the

mandible without posterior contact. This should even be done if it requires

devitalization of the elongated tooth. The same is true if a lower posterior tooth

has elongated into a space above.

If the terminal tooth on the upper has erupted down distal to the most posterior

lower tooth, it does not present a problem, even though it fails to conform to

the picture of an "ideal" occlusal plane.

Curve of Spee too low posteriorly: Making the distal end of the occlusal plane

too low presents no major problems since it cannot interfere with the basic

requirements of protrusive and balancing side disclusion. If it is grossly

overdone, however, it can create a poor esthetic result, can cause excessive

stress on upper teeth by requiring an unfavorable crown-root ration, and could

conceivably reduce function in some mouths by causing too much separation of

the posterior teeth in protrusion. Cune of Spee too high or low in front: If the

lower premolars are higher than the cuspids, they can interfere with the anterior

protrusive guidance by bumping into the upper cuspids. If the lower premolars

are considerably lower than the anterior teeth. the result is very poor

esthetically.

Curve of Wilson(fig-47):

Since upper posterior teeth normally slant outward and lower posterior teeth

are tilted inward toward the tongue, an imaginary line drawn mediolaterally to

touch cusp tips of similar teeth on each side of the lower arch would generally

be concave. This aspect of the occlusal plane is referred to as the curve of

Wilson.

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When the mandible moves toward the working side with such a flat anterior

guidance, the rotating, translating condyle permits the posterior teeth on that

side to move almost horizontally toward the check. The lower lingual cusp

must be lowered to prevent it from interfering with the upper lingual cusp.

On the balancing side, the orbiting condyle moves downward as it moves

forward and permits lateral movement without interference to the upper lingual

cusps. The result in the lower arch is buccal cusps that are higher than lingual

cusps and consequently a concave curve of Wilson.

There are two ways of effectively changing the curve of Wilson. The first way

is to change the lateral anterior guidance angle. The steeper the lateral anterior

guidance angle, the higher the lower lingual cusps may be on the opposite side.

One may wonder why we even worry about the height of these lower lingual

cusps if they serve neither as a holding contact nor as a functioning incline, but

they do act as useful grippers of coarse of fibrous foods and consequently they

serve a useful purpose even though they need never be in actual contact.

The second way we may change the curve of Wilson is by changing the length

of the upper lingual cusps. By shortening the upper lingual cusps and flattening

the cusp-fossae angles, we can actually make a flat curve of Wilson. Such an

occlusion can still function without interference and without losing the upper

lingual cusps as centric holding contacts. All that would be lost is the

maximum gripping effect that goes with closely approximating cusps in

excursions.

Establishing the plane of occlusion:

There are three practical methods for establishing an acceptable plane of

occlusion:

1) Analysis on natural Iccth through selective grinding

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2) Analysis on models with fully adjustable instrumentation

3) Use of Pankcy-Mann-Schuyler methods of occlusal plane analysis

Analysis through selective grinding: if it is possible to eliminate excursive

interferences without losing stable centric holding contacts, the plane of

occlusion is acceptable as it is. There is no need to change an occlusal plane

that permits the anterior guidance to do its job of discluding the posterior teeth

in protrusive and balancing excursions unless centric stops are lost in the

process.

Fully adjustable instrument analysis: Any instrument that can duplicate

condylar border movements can be used to analyze or establish a correct

occlusal plane. Selective grinding and or preliminary waxup of models on such

an instrument will clearly show the outer limits of occlusal plane curvatures as

long as the anterior guidance and condylar guidances are correctly programmed

into the instrument.

Pankey-Mann-Schuyler(P.M.S-) analysis of mounted models: If models are

properly mounted with an accurate facebow record on either a fully adjustable

or a semi-adjustable instrument, an acceptable plane of occlusion can be

determined with extreme simplicity. It should be made very clear that the

P.M.S. technique should not be used to determine whether a tooth should be

restored. It is simply a technique for determining the occlusal plane when all or

most of the posterior teeth have already been diagnosed as needing restoration.

When it has been determined that restoration of all or most of the posterior

teeth is necessary, the P.M.S. technique provides an excellent and practical

method for determining an occlusal plane that will fulfill all of the

requirements of a correct occlusion. The simplest method of implementing this

part of the technique is through the use of the Broadrick Occlusal Plane

Analyzer.

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Broadrick Occlusal Plane Analyzer:

For mouihs requiring restoration of all or most of the posterior teeth, proper use

of the occlusal plane analyzer will accomplish the following: ] Preliminary

determination of an acceptable plane of occlusion on the study models as an

aid in treatment planning.

2. Preliminary determination of the amount of reduction that will be required

when each tooth is prepared.

3. Extremely simple transfer to the mouth of predetermined preparation

height for each tooth

4. In the laboratory waxup. simple determination of the height of each cusp

tip. Through such a determination, the curve of Spee and the curve of Wilson

arc automatically established according to the predetermined plan of the

demist.

5. Predetermination of both the cusp height of the finished restoration and

also the height of each prepared tooth. Thus room for a sufficient thickness of

gold or gold and porcelain can be assured in advance. The technician never

need be restricted in his occlusal carving because of insufficient tooth

reduction.

6. A properly predetermined plane of occlusion on the lower arch, which

enables the dentist to select virtually any type of acceptable occlusal

contour scheme (posterior disclusion. group function, and so on) with

complete assurance that the established plane of occlusion will permit it.

Using the Broadrick Occlusal Plane Analyzer:

The so-called flag instrument can be adapted to almost any type of articulator

that will accept a facebow mounting of the upper model. The lower model must

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be mounted with a centric bite record. By using a scribing caliper, a survey

center is located on the plastic sheet attached to the flag. From that survey

center, an acceptable plane of occlusion can be drawn on the lower model. The

technique was adapted for restorative dentistry by Pankey from original

anthropologic research by Monson. The "Monson curve" was originally

applied to complete denture fabrication, but the practicality of the concept

makes it especially useful for patients needing restoration if it has been

predetermined that all or most of the posterior teeth need to be restored.

The technique consists of the following steps:

1. After the upper model has been oriented to the articulator by a carefully

taken facebow registration, the mounting is completed and the lower model is

then related lo the upper by means of a centric bite record. When the lower

model has been mounted with stone, the upper model should be removed and

set aside for later use.

2. The "flag" is secured to the upper bow of the articulator and the plastic

sheet is snapped onto one side.

3. The pencil lead is inserted into one end of the caliper and it is set a! a radius

of 4 inches from needlepoint to lead point. The width of the "flag" is 4 inches,

so it can be used as a convenient guide. The selection of a 4-inch radius may

seem to be a very arbitrary setting. The radius could be varied a little either

way. but the change has so little effect on the occlusal plane that there is

nothing to be gained by it except in unusual cases where there is an extreme

curve to the occlusal plane occurring naturally in an extremely small arch.

4. The point on the lower cuspid from which an cstheticaih pleasing occlusal

plane would emanate is located. This will vary slightly according to the shape

of the lower cuspid, but it is a matter of simple judgment. It will fall

somewhere between the tip of the cuspid and the distoincisal line angle.

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Generally speaking, the flatter the cusp tip. the closer the point will be to the

line angle. The more pointed the cuspid, the closer the survey point will be to

the cusp tip. The needlepoint of the caliper is placed against the selected

point on the cuspid and an arc scribed on the flag. This arc will be referred to

as the anterior survey line (fig«48). The survey center that will be used to

determine the occlusai plane will be located somewhere on this line.

5. Without varying the radius of the calipers, the point is held againsi the

condyle ball of the arliculator so that it aims through the center of the ball and

another arc that will interest the anterior survey line is scribed. This will be

referred to as the condvlar survey line(fig-49). The "survey center for scribing

the occlusal plane on the lower model is usually at the point where the lines

intersect but the point may be moved up to 1 cm. from the intersect if necessary

to favor either the upper or lower posterior tooth as long as it remains on the

anterior survey line. To determine the acceptability of the intersect as a survey

center, the calipers are turned around, the point pul at ihe intersect, and the

height of the pencil mark, which would be made on the last lower tooth,

checked(fig-50). If too much reduction would be required to make the lower

molar fit into such an occlusal plane, the survey center is moved forward on the

anterior survey line up to 1cm. The occlusal plane may be lowered in the hack

by moving the survey center backward up to 1 cm.

If it appears necessary to move the survey center more than lem forward or

backward to establish an acceptable plane, the faccbow mounting is incorrect.

An error can also occur from an incorrect transfer of the intercondylar distance.

6. When an acceptable height has been established for the most distal lower

tooth, a line is scribed on the model from that tooth forward to the cuspid.

This line will represent the height of the buccal cusp tips.

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7. To determine the preparation line, the calipers are opened an amount equal

to the desired occlusal thickness of the proposed restoration (usually about 1

'/2mm) and a second line scribed. This will represent the height of the buccal

cusps after the teeth have been prepared.

8. Some softened base plate wax is adapted to the buccai surfaces of the

model and the preparation line scribed on the wax. The wax is cut carefully

back to this line and also trimmed along the mucobuccal fold line so that the

wax can be fitted accurately in the mouth against the teelh. Extra hard base

plate wax is used so that it will not distort when it is chilled and placed in the

mouth. This is called the occlusat plane cutting guide.

9. When the lower posterior teelh are to be prepared- the cutting guide is

placed snugly against the buccal surfaces of the dried teeth and a pencil line is

drawn on the teeth according to the guide.

10. The wax is removed and an inverted cone diamond is used to cut into the

teeth along the line. The entire occlusal surface of each toolh is reduced down

to the preparation line. The preparation should be about 1 Vimm lower on the

lingual than it is on the buccal to accommodate for the curve of Wilson. It is

possible to make a lingual cutting guide to determine the lingual preparation

line precisely. but it is more practical to just visualize the curve of Wilson and

prepare the teeth sufficiently lower on [he lingual than on the buccal.

1. The occlusal plane cutting guide represents only the preparation height for

the buccal cusps. The lingual cusp preparation is 1 ½ mm lower. After

reduction for correct cusp height has been completed, il is still necessary to

reduce the central groove area to permit correct cusp-fossae contouring of the

restorations. One must note the steepness of the lateral anterior guide angle to

get a general idea of the steepness of the cusp-fossa angle. The steeper the

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lateral anterior guidance. The deeper one should hollow-grind the central

groove part of the teeth.

The same procedure that is used for determining the plane of occlusion can also

be used most effectively to establish the correct occlusal plane on the wax

patterns. By using a special wax cutting blade in the calipers, the overwaxed

patterns can be cut back to the correct height. The angle of the blade

automatically produces an acceptable curve of Wilson, making the lingual

cusps lower than the buccal cusps.

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DETERMINING THE TYPE OF POSTERIOR OCCLUSAL

MORPHOLOGY

There is no one type of occlusal form that is optimum for all patients.

Techniques oriented concepts may work well for the majority of patients, but

the varied problems of stress associated with sick mouths can be solved better

by flexibility of form that enables us to vary the direction and distribution of

forces.

The first objective of occlusal form is proper direction of forces. Teeth can

withstand tremendous force if it is directed up or down the long axis of each

tooth when force is directed parallel to the long axis, it is uniformly resisted by

all of the supporting periodontal ligaments except those at the apex. If the force

is directed rurally, the tooth loses the support from about half of the ligaments

that are compressed and puts almost the entire load on the half under tension.

So the starting point in designing occlusal contours is to shape and located the

centric contacts so that the forces are directed as nearly parallel as possible to

the long axes of both upper and lower teeth.

A perfectly flat occlusal surface contacting another flat surface could be

made :o fulfill this first requirement, but it would not be a very good design for

penetrating or grinding fibrous foods. Proper placement of a sharp cusp against

a flat surface could penetrate foods easily and still direct the forces correctly,

but a single sharp cusp against a flat surface would lack resistance to the lateral

forces that come from the cheeks versus the tongue. The addition of more

contacts is often needed to fulfill the second requiicment of occlusal form:

stability.

The back teeth must do more than simply penetrate food: they must crush it

2nd grind it. To enable them to fulfill their role as grinders they must be able to

work one surface against another in either direct contact or a near miss as the

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jaw moves laterally and protrusively. To accomplish this, the sharp cusps are

broadened at the base and rounded at the tips.

Since the lower back teeth move as the mandible moves, their contours and the

contours of the teeth they contact must be in harmony with the mandibular

movements. The contours of the back teeth are controlled by the same

determinants that control the border movements of the mandible, namely the

condylar pathways in the back and the anterior guidance in the front. The

condylar pathways are referred to as the posterior determinants and the anterior

guidance is referred to as the anterior determinant of occlusion.

Any posterior tooth can create stress in the entire' mechanism if it interferes

with cither the path of the condyles or the path of the lower anterior teeth

against the lingual inclines of the upper anterior teeth.

In the planning of occlusal contours for each individual patient, a major

determination that must he made is concerned with the distribution of lateral

stresses. There are three basic decisions to make regarding the design of

posterior occlusa! contours:

1. Selection of the type of centric holding contacts

2. Determination of the type and distribution of contact in lateral excursions

3. Selection of most practical method of providing stability to the occlusal

form. Types of centric holding contacts:

There arc three basic ways by which centric contact is usually established. !.

Surface - to - surface contact

2. Tripod contact

3. Cusp tip-to-fossa contact.

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Surface-to-surface contact(fig-51): We refer to this as 'mashed potato

occlusion". It is the form that results if the articulator is simply closed together

when the wax on the dies is soft. There is never any valid reason for using this

type of contact. It is stressful and it produces lateral interferences in anything

other than near vertical chop-chop function.

Tripod contact(fig-52): In tripod contact the tip of the cusp never touches the

opposing tooth. Instead, contact is made on the sides of the cusps that are

convexly shaped. Three points are selected from the sides of the cusps and each

point in turn is made to contact the side of the opposing fossa. Contacts of the

stamp cusps must be made el the brim of the fossa wall so that all posterior

teeth can disengage from any contact immediately upon leaving centric

relation. Lateral and protrusive disclusion of posterior teeth is essential

whenever tripod contact is used because convex tower cusps cannot follow

normally concave border pathways against upper teeth which are also convex.

Tripod contact is difficult to accomplish but it can be done as long as the

anterior teeth are capable of discluding the posterior teeth in all excursions.

Tripod contact should not be used when lateral stress distribution is best

served by including posterior teeth into group function to help out weak or

missing anterior teeth or when the arch relationship docs not permit the anterior

guidance to do its job.

With tripod contact, any degree of shifting of any tooth produces incline

interference. Since upper and lower arches are usually restored together, even a

minute error in recording or transferring centric relation causes loss of

tripoidism on all teeth.

Tripod contact is extremely difficult or impossible to equilibrate without losing

tripoidism and ending up with contacts on inclines.

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If tripod contact is so difficult to achieve and has so many limitations, why is it

used? Probably the main reason for the popularity of tripoidism is the

impression that it is so stable if it is properly done. This certainly has been one

of the main reasons for advocating its use. However, there is no scientific

evidence to show that tripod contact is more stable than proper tip-to-fossa

contact.

There are no actual indications for tripod contact. While it can be used

successfully in a large number of patients, it has definite limitations in many

others. It offers no advantages over proper cusp tip-to-fossa contact and since it

is more difficult to achieve, is hard to adjust, and is limited in its use, we would

probably do well to thoughtfully evaluate its practicality.

Cusp tip-to-fossa contact(fig-53): If cusp tips are properly located in the most

advantageous fossae, this type of occlusion offers excellent function and

stability with the flexibility Lo choose any degree of distribution of lateral

forces that is warranted. It is the easiest occlusion to equilibrate. Resistance to

wear is excellent since the centric stops are on the cusp tips, while in working

excursions, contact is on the side of the cusp tips as they travel along the

inclines of the opposing teeth. If disclusion of any tooth is desired in any

eccentric excursion, it is accomplished easily by adjusting Ihe fossa inclines

without disturbing the centric holding contacts.

With cusp tip-to-fossa contact, it is not necessary to restore upper and lower

teeth together.

Cusp tip-to-fossa conlact is not a by-product of any specific technique. It serves

the goal of function rather than form. It can be accomplished with the aid of

gnathologic instrumentation, functional path procedures, or a myriad

of other instrumentation techniques. The one essential for accomplishing it

correctly is an understanding of what we are after. ProperK done, it can be

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beautiful as well as functional and stable. Variations of posterior contact in

lateral excursions:

As the mandible moves laterally, the lower posterior teeth leave their centric

contact with the upper teeth and travel sidc-\\a\s down a path dictated by the

condyles in the back and by the lateral anterior guidance in the front. Each

lower posterior tooth is limited to these border pathway, meaning that they

cannot follow a path from centric relation that is any Hatter or more concave

than the condyles and the lateral anterior guidance permits.

In order to make meaningful judgments about the distribution of lateral stress.

we must first distinguish the difference between the rotating condyle and the

orbiting condylc. Each side has physical characteristics that are important to

understand before and occlusal scheme can be planned with any degree of

dependability. In discussing lateral excursions we divide the movements

accordingly into working side occlusion and nonfunctioning side occlusion

(also referred to as the balancing side).

Working side occlusion refers to the contact relationship of lower teeth to

upper teeth on the side of the rotating condyle. The side toward which the

mandible moves is the working side. The condvle on the working side can be

braced against bone or ligament throughout the working excursion, so it is

possible and quite practical to accurately record and restore the posterior teeth

to precise working side-border movement contacts.

Nonfunctioning side occlusion is the side of the orbiting condvle. When the

condyle leaves its braced position and slides forward down the slippery incline

of the eminentia. it is no longer solidly feed against the unyielding bone and

ligament. Rather, it can move up a little since the mandible bends slightly

under firm muscle pressure. Consequently, tooth contact during non-

functioning side excursions should not be allowed. Because of the flexibility of

169

the mandible, it would not be possible to harmonize occlusal contours to all the

variations resulting from the differences in muscle force from light to heavy.

Hence we have the rule: wherever lower teeth move toward the tongue, they

should not contact.

The job of discluding the nonfunctioning side is always the responsibility of the

working side.

The dentist must decide how all this is done by selecting one of the following

choices for working side occlusion:

1. Group function

2. Partial group function

3. Posterior disclusion

Group function refers to the distribution of lateral forces to a group of teeth

rather than protecting those teeth from contact in function by assigning all the

forces to one particular tooth.

To paraphrase a law of physics - the more teeth that carry the load, the less load

any one tooth must carry. We must decide which teeth are capable of carrying

how much load and assign the load accordingly.

Group function of the working side is indicated whenever the arch relationship

does not allow the anterior guidance to do its job of discluding the

nonfunctioning side. The anterior guidance cannot do its job in the following

situations:

1. Class II occlusions with extreme overjet.

2. Class HI occlusions when all lower anterior teeth are outside of the upper

anterior teeth

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3. Some end-to-end bites

4. Anterior open bite cases

When using posterior group function the following rule applies: contacting

inclines must be perfectly harmonized to border movements of the condyles

and the anterior guidance. Convex-to-convex contacts cannot be used to

accomplish this.

Partial group function refers to allowing some of the posterior teeth to share

the load in excursions while others to share the load in excursions while others

contact only in centric relation. As an example, a second molar may be very

firm vertically but be hypermobile buccoiingually. Such a tooth should touch

only in centric relation and be discluded immediately.

Anterior teeth with post orthodontic root rcsorption or congenital!; poor crown-

root ratios should very often be harmonized to group function with the working

side.

Whether or not any tooth should share the lateral stresses should be decided on

the basis of each tooth's resistance to lateral stress. There is no good reason

why such a decision cannot be made on a tooth-by-tooth basis. If a tooth is

weak laterally, it should contact in centric relation only.

Problems with group function result from improper harmony of the contacting

inclines.

For group function to be effective in reducing stress, the cusp inclines must be

in perfect harmony with the lateral border movements of the jaw. Incline

interferences on posterior teeth get closer to the condyle fulcrum, so a slight

interference on a second molar would probably be more stressful Irian a more

noticeable interference on a cuspid.

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Posterior disclusion refers to no contact on any posterior teeth in any position

but centric relation. It can be accomplished easily tt ith cusp tip-to-fossa

morphology. It must be accomplished with tripod or surface-to-surface

morphology to prevent lateral interferences in any case with centric contact on

inclines that are steeper than the lateral border movements of the mandible.

There are two methods of accomplishing posterior disclusion:

1. The anterior guidance is harmonized to functional border movements first

and then the lateral inclines of the posterior teeth opened up so that they are

discluded by a correct anterior guidance.

2. The posterior teeth are built first and then discluded by restricting the

anterior guidance. This method is backward. Anterior guidance is a proper

determinant of posterior occlusal form and thus should be done first. When

posterior occlusal form determines the anterior guidance, the correctness of the

anterior guidance is a product of chance.

Posterior disclusion can be achieved by two different types of anterior

guidance: anterior group function and cuspid protected occlusion. Neither is

applicable for all cases.

Anterior group function is the most practical method for discluding the

posterior teeth when arch relationships and tooth alignment permit it. Anterior

group function is beneficial in three ways:

1. It distributes wear over more teeth

2. It distributes the stresses to more teeth

3. It distributes stress to teeth that are progressively farther from the

condyle fulcrum.

172

Anterior group function is extremely comfortable and efficient. It improves the

efficiency of incising movements by providing lateral as well as protrusive

shearing contacts.

When it is impractical to distribute the lateral guidance stresses over several

teeth, disclusion of the posterior teeth can be accomplished by using the

cuspids in one form or another of cuspid-protected occlusion.

Cuspid - protected occlusion refers to disclusion by the cuspids of all other

teeth in lateral excursion. It usually serves as the cornerstone of what is called

mutually protect occlusion. Mutually protected occlusion has been defined in a

number of ways, but the usual connotation refers to an occlusal arrangement in

which the posterior teeth contact in centric relation only, the incisors are the

only teeth contacting in protrusion, and the cuspids are the only teeth

contacting in lateral excursion.

Predominant prerequisite for its use is the capability of the cuspid to withstand

the entire lateral stress load without any help from other teeth. Lateral stress

becomes insignificant if the mandible functions normally within the lingual

inclines of the upper cuspids.

It is impossible to exert excessive stresses against the cuspids in centric relation

because the posterior teeth also resist the stresses in that position, if the

occlusion is correct.

In natural cuspid-protected occlusions, the pattern of function is rather vertical,

so the mandible does not use lateral movements that would subject the cuspids

to stress in that direction either.

Any attempt at lateral movement is felt by the pressoreceptors around the

cuspids. Within limits, these exquisitely sensitive nerve endings protect the

cuspids against loo much lateral stress by redirecting the muscles to more

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vertical function. As long as the pressoreceptors can keep the muscles

programmed to a vertical envelope of function, there is insufficient lateral

stress generated to harm the cuspids.

Some clinicians have reported that the cuspids have the distinction of being

protected by a greater number of pressoreceptor nerve endings than is found

around any other tooth. This alleged density of proprioceptors is supposed to

impart a unique capacity to the cuspid to redirect any functional pattern that

would be destructive. If. for example, a horizontal chewing cycle would exert

too much lateral stress against

The cuspids, their special proprtoccptive protectors would simply change the

chewing cycle to a vertical, chop-chop function rather lhan let harm come to

the cuspids or their supporting structures. But further research has failed to

substantiate the report [hat there are more proprioccptors around the cuspids

than there are around other teeth. Furthermore, clinical results over a period of

time have shown that the cuspid, just like other teeth, is also subject to the

usual problems of excessive lateral stress if it interference with normal

functional movements. There does not appear to be any valid support for the

cuspid-protection theory on the basis of special proprioceptive capacity to

radically after habitual patterns of function.

However, there are other valid reasons why cuspid-protected occlusion works

well for many patients. The cuspids have extremely good crown - root ratios,

and their long fluted roots are in some of the densest bone of the alveolar

process. Furthermore, their position in the arch, far from the fulcrum, makes it

more difficult to stress them. In short, they are very strong teeth. If their upper

lingual inclines are in harmony with the envelope of function, they are usually

quite capable of withstanding lateral stresses without help from other teeth.

174

The natural cuspid-protected mouth is easily distinguished by convex or very

steep lingual inclines on the upper cuspids. For simplicity, cuspid protection

can be divided into two categories:

1. Posterior disclusion by cuspid inclines that are in harmony with functional

border movements.

2. Posterior disclusion by cuspid inclines that restrict mandibular movements

within habituai functional border movements.

Restrictive cuspid protection is usually used as an attempt to avoid stressful

posterior contact in lateral excursion by forcing the patient into a changed

pattern of function.

Selecting occlusal form for stability:

Assuming that cusp-fossae relationships are correctly placed for ideal direction

of stress, we still must make decisions regarding the number of contacting

cusps that are needed for maximum stability under differing conditions. We

generally have four basic types to choose from in normal arch relationships.

Type l(fig-54): Lower buccal cusps contact upper fossae. There are no other

centric contacts. Working side excursive function is limited to the lingual

inclines of upper buccal cusps.

If desired, continuous contact can be maintained in working excursions on the

lingual incline of the upper buccal cusps, or if disclusion of posterior teeth is

desired, it can be easily accomplished by modifying the upper inclines.

Disclusion of balancing inclines can be easily accomplished.

The only apparent disadvantage to this type of occlusal relationship is its lack

of dependable buccolingual stability. Pressure from the tongue can tilt the teeth

toward the buccal with very little resistance.

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Type 2{fig-S5): Centric contact on the tips of lower buccal cusps and upper

lingual cusps. Working side excursive function is limited to the lingual inclines

of the upper buccal cusps. There is no excursive function on any lower incline.

The addition of the upper lingual cusps as centric holding contacts contributes

greatly to the stability of the posterior teeth. Lateral stress toward the buccal is

resisted by the contact of the upper lingual cusps against ihe lower fossae.

Stress to ward the lingual is resisted by the lower buccal cusps against the

upper fossae.

From every clinical standpoint, the performance of this type of occlusal contour

is unsurpassed. It is comfortable and functional and its stability is as good or

better than any other type of occlusal relationship. Because it fulfills all the

requirements of good occlusal form and can be accomplished with clinical

practically.

Type 3{fig-56): Centric contact on tips of lower buccal cusps and upper lingual

cusps. Working excursion contact is limited to the lingual incline of upper

buccal cusps and buccal incline of lower lingual cusps.

This type of occlusal contour is identical to type 2 except thai the buccal incline

of the lower lingual cusp becomes a functioning incline.

There is no clinically discernible advantage in making the upper lingual cusps

contact in lateral function.

The major difference between this type of occlusal form and type 2 is the

difficulty of accomplishing it. In order to bring the upper lingual cusps into

working excursion contact, the buccal inclines of the lower lingual cusps must

be precisely contoured to the exact lateral border movement of both the

condyle and the anterior guidance.

Type 4(fig-57): Tripod contact

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There are two types of tripod contacts: contact on the sides of cusps and the

walls of fossae and contacts on the brims of fossae and on top of wide cusp

tips.

Contact on the sides of cusps and the wall of fossae: Contact on the sides of the

cusps does not permit any lateral or protrusive movement on a horizontal plane,

so if the anterior guidance has been flattened even for a short distance from the

centric stops to permit a lateral side shift of the mandible, this type of occlusat

form will be contraindicated. It is also contraindicated for any patient who

requires a "long centric".

It may be used in vertical or near vertical functional cycles with either cuspid-

protected occlusion or anterior protected occlusion.

Tripod contact is the most difficult of all occlusal forms to fabricate. Centric

contact on the brims of fossae and the top of wide cusp tips with no contact in

eccentric excursions. This type of tripod contact can be made to function with

any type of anterior guidance because it permits horizontal lateral movement

without interference. It is automatically discluded by any anterior guidance

effect other than flat plane, so it cannot be used when posterior group function

is indicated.

There are several types of" occlusal form that can be used to restore posterior

teeth. Whatever contour is selected should be chosen because it:

1. Directs the forces as near parallel as possible to the long axis of each toolh

2. Distributes the lateral stress to maximum advantage in varying situations

of periodontal support

3. Provides maximum stability

4. Provides maximum wearabUJty

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5. Provides optimum function for gripping, grinding and crushing

RESTORING LOWER POSTERIOR TEETH

The lower cup-fossae inclines are determined by the anterior guidance and the

condylar guidance. If the lower lingual cusp is 10 have functional contact in

working excursions, its buccal incline must be the same as the lateral anterior

guidance, with some modifications to maintain simultaneous conformity to

condylar paths. If the lower lingual cusp is to be discludcd in working

excursions, its buccal incline must be Halter than the lateral anterior guidance.

So from a practical standpoint, lower cusp-fossae angles should be Hatter than

ihe lateral anterior guidance.

Posterior teeth in the lower arch can be accurateK restored with cusp tip-to-

fossa contact if the following determinations can be made:

1. Correct height and placement of bucca! cusps

2. Correct height and placement of lingual cusps

3. Correct placement of fossae

4. Correct inclines for fossae walls

5. Fairly accurate ridge and groove direction

The starting point for determining lower occlusal contours should be the buccal

cusps.

Placement of lower buccal cusps

Placement of lower buccal cusps is determined on the basis of providing the

optimum effect for buccolingual stability, mesiociistal stability, and

noninterfering excursions.

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Buccal cusp placement for buccolingual stability: The correct bcation of

each lower bucca! cusp should be one of the first determinations made when

the original treatment plan is outlined. Preparation for restorations should not

be made until the lower teeth are in their most acceptable relationship to the

upper teeth.

The buccolingual position of lower buccal cusps is determined in the

following manner on mounted models: 1. Upper central groove position is

analyzed. On each upper occlusal surface, a line is drawn from mesial to distal

in the central groove. The ideal contact point for each lower buccal cusp tip

should usually be located somewhere on this line.

How ever, the correctness of the central groove should be analyzed on each

tooth.

In some lilted teeth, it is advantageous to move the central groove to gain better

direction of forces through the long axis. If moving the central groove will

enable the stresses to be directed more nearly through the long axis of any

upper tooth, the improved central groove position should be so noted on the

upper model by drawing a new line.

2. Optimum contact for stress direction on lower posterior teeth should

be determined. While disregarding the upper central groove1 position, the

buccal cusp position that would most nearly direct stresses down through the

long axis of each lower posterior tooth is determined.

A mark is made on each lower tooth to indicate the position of the buccal cusp

that would be optimum for buccolingual stability and direction of force.

3. The alignment of the optimum lower buccal cusp position against optimum

upper central groove position is evaluated. If the marks do not line up

precisely, the positions of both the upper central groove and the lower buccal

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cusp tip are equally changes. The new cusp tip positions are rcevaluated to

make certain that they are compatible with acceptable stress direction through

the long axis of each lower tooth. The upper groove position is similarly

evaluated.

If the altered buccal cusp tip position does not provide acceptable stress

directioning for both upper and lower posterior teeth, the arch relationship is

unacceptable and the treatment plan should be designed to correct the problem.

The basic rule to follow regarding the buccolingual position of the lower buccal

cusp is: the lower buccal cusp must be positioned so that its contact directs the

stresses through the long axis of both upper and lower tecth(fig-58).

Mcsiodislal placement of lower buccal cusps:

Two considerations should determine the mesiodislal position of lower buccai

cusps: mesiodistal stability and nonintcrfering excursions.

Attaining mesiodistal stability: The best mesiodistal stability is attained by

placing the lower buccal cusps in upper fossae.

There is no tendency for cusp tips to migrate out of properly contoured fossae.

There will be times wheit it is not practical to place the lower buccal cusp in an

upper fossa, and it will be necessary for it to contact on the marginal ridges of

two upper teeth. Plunger cusp food impact ion can be avoided by proper

design. The upper marginal ridges should be conioured with sluiceways from

the adjacent fossae that permit the crushed bolus to slide away from the

contact. The contact itself should be wide enough to protect the interdental

papilla.

Incline contacts in centric relation should be avoided. While acceptable tooth-

to-iwo teeth contact can be accomplished, it is usually rather simple to warp the

lower buccal cusp mesially or distally the 1 or 2 mm required to place the cusp

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tip into an upper fossa. Whenever ii can be done with practicality, this is what

we try to do. Locating the lower buccal cusps for no n interfering excursions:

The mcsiodistal placement of each lower buccal cusp is determined by locating

it in the fossa that permits excursions from centric relation without interference.

By first selecting appropriate fossae on the upper mounted model, the paths of

the lower cusps from each fossa can be quickly determined since they will

travel at right angles to the rotating condyle(fig-59).

It is not necessary at this time to consider the side shift of the mandible. Its

effect will be primarily on ridge and groove direction and fossae contours that

will be compatible with this method of selecting cusp tip position.

If stress direction is acceptable to both teeth, the paths of movement from the

selected fossa should be evaluated. If the lower bucca! cusp can move out of

the fossa in protrusive working and balancing excursions without colliding with

another cups, its position is acceptable.

Placement of the lower cusp tip directly between the upper buccal and lingual

cusps is not only unstable, it also necessitates the destruction of upper occlusal

anatomy to permit excursions.

It is usually best to place the lower buccal cusps of bicuspids in a mesial fossa

when possible. This aliows egress from centric relation through all excursions

with the least chance of destroying tooth anatomy in the process.

Molar cusp tips should be placed so that they will not collide with upper cusps.

They may be placed in the mesial fossa the same as bicuspids, or in the distal

fossa with nonfunctional egress through the transverse groove. Molar cusp tip

placement is also permissible in the jipper central fossa since it can pass to the

mesial of the upper mesiolingual cusp in its nonfunctioning excursion and it

can pass between the buccal cusps in working excursion.

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Contouring cusp tips:

For cusp tip-to-fossa contact, the tip of each lower buccal cusp should be small

enough to fit into a normally contoured fossa. If the anterior guidance permits a

lateral side shift, the cusp tip should be able to contact the base of the fossa

with out touching the fossa walls in centric relation. If the anterior guidance is

steeper than the fossa walls and no lateral side shift is permitted, the side of the

cusp may contact the fossa walls.

When the tip of the cusp serves as the centric contact, it should be wide enough

to provide optimum wear resistance. It is difficult to be specific about the size

of a cusp tip that would be suitable for all fossae because contours vary as

border palhways vary, but in general the tip of the cusp should have a fairly flat

area about 1mm or so wide. In lateral excursions, if group function is desired,

the side of the cusp contacts the wall of the fossa rather than the tip.

If a cusp tip is to be placed in a fossa, the tip must not be wide mesiodistally.

This is a common fault, and it should be remembered that each cusp must

follow border pathways from its point of centric contact. If a cusp is too wide,

the path that must be cleared for its excursive movements will destroy the

anatomy of the opposing tooth.

Wide cusp tips require more force for bolus penetration and therefore they put

more stress on the supporting structures. Narrow cusps require less force and so

they produce less stress.

Placement of lower lingual cusps:

In normal tooth-to-tooth relationships, the tip of the lower lingual cusp never

comes in contact with the upper tooth. Even though the buccal incline of the

lower lingual cusp be made to contact in working excursions, there is no

apparent advantage in doing so.

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The lower lingual cusp has another job to do. since it is primarily responsible

for keeping the tongue from getting pinched between the posterior teeth. The

position and contour of the cusp tip should reflect this responsibility without

causing irritation to the tongue. The cusp tip should be rounded and smooth on

its lingual aspect. The position of the tip should have enough lingual overjet to

hold the tongue out of the way, but it should always be located over the root,

within the long axis,

The distance between the lower buccal and lingual cusp tips is the same as the

distance between upper cusp tips, so once the lower buccal cusp tip has been

located, this measurement can be applied to position the lingual cusp. The

measurement between buccal cusp tip and lingual cusp tip should not be much

greater than half the total buccolingual width of the tooth as its widest part. .

Generally the lower lingual cusp height should be about a millimeter shorter

than the buccal cusp. Cusp height can be lowered further in the first premolar.

Contouring the lower fossae:

When it serves as the lateral anterior guidance, the lingual incline of each upper

cuspid dictates the fossa contour of each lower incline that faces it{fig-6O).

• The lateral guidance incline of each upper cuspid dictates the fossa contours

of the buccal inclines of each lower lingual cusp on the same side and the

lingual inclines of each lower buccal cusp on the opposite side. When the

cuspid is not in position to function individually or in group function as the

lateral anterior guidance, the lingual incline of the most anterior upper tooth

that can assume the role becomes the dictator of the lower fossae inclines

facing it.

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From the contact point of each upper lingual cusp, the lower fossa inclines

should be no steeper than the lateral guidance inclines they face. Any incline

that is steeper discludes the lateral guidance and adds to its own lateral stress.

The simplest and most practical approach is to open up the lower fossae by

providing more than enough freedom for a lateral side shift and making the

cusp-fossa angle flatter than the lateral anterior guidance angle.

Contouring ridges and grooves:

Ridges and grooves give beauty and naturalness to the occlusal scheme. It is

the action of ridges and grooves against their opponent counterparts that grasps

the food and then crushes, tears, and shreds it as the lower teeth follow their

cyclic paths of function against upper inclines.

The arrangement of ridges and grooves is to permit the cusps to pass close

enough to each other to mangle the food between the grooved surfaces without

actual need for tooth contact.

Fairly accurate determination of ridge and groove direction is all that is needed.

Extreme preciseness is not required because in tip-to-fossa contact only the

base of the lower fossa contact the upper lingual cusp. The walls of the fossae

never contact and grooves can be opened out just as fossae are opened out lo

avoid contact.

We must not make the mistake of designing grooves that are slotted so a cusp

can pass precisely through the slot on a given border path. As an example, the

walls of such a groove may allow passageway of the cusp in a lateral working

excursion, but the groove would not accommodate the cusp in a protrusive

lateral path.

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The direction of any ridge or groove is determined by the path of the lower

tooth as it moves with the mandible. Lateral excursion grooves are at right

angles to a line drawn from the rotating condyle.

WAXING TECHNIQUE FOR LOWER POSTERIOR TEETH

When lower cusp location and fossae contours have been correctly established

on an acceptable occlusal plane, the upper occlusal surfaces may be accurately

restored using a number of different methods including stereographic or

pantographic techniques. Functionally generated path procedures, however, can

be used against such lower occlusal contours with extreme accuracy in the full

range of border movements without loss of the upper lingual cusp as a centric

contact. The correctly placed and contoured cusps of the lower teeth used

against functionally generated pain wax determine not only upper fossa

contours but ridge and groove directions as well.

After the tower posterior teeth have been prepared, the anterior guidance

should be checked for correctness. Impressions should then be made for the

upper opposing model and the lower die models. They should be properly

mounted with a facebow and centric bite record.

Procedure for locating (he buccal and lingual cusp tips:

1. A line is drawn along the central groove of the upper posterior teeth. If

some of the upper teeth are badly broken down or missing, it is often helpful to

reshape the upper teeth by carving the stone model or reshaping the teeth with

wax before finalizing the best cusp tip placement.

2. Now, noting the mesiodistal relationship of each lower tooth to its opposing

upper, the most advantageous placement of each lower bucca! cusp is selected.

We should try to select fossae for cusp tip placement whenever possible. Each

spot should be marked. Buccal cusp top placement will be where each line

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intersects (FlG-61). The selection of cusp tip placement should be checked by

noting the direction of excursions from each point.

3. Using a No. 6 round bur, a hole is drilled at each cusp tip location to the

depth of the bur head.

4. Dark-colored 14 - gauge wax sprues should be cut into 3mm lengths and

inserted into each drilled hole(FlG-62). The articulator should be closed to be

sure the sprue wax does not in interfere with opposing lower dies.

5. With the articulator closed, red inlay wax is flowed around the occlusal part

of the die to engage the dark sprue was.

6. The articulalor is opened and more wax flowed around the dies until the

crowns are overbuilt. Interproximal contacts between teeth should be as close

to correct as practical in ihis early waxup stage.

7.. The flag instrument (Broadrick Occlusal Plane Analyzer) should be used to

determine the heights of the buccal and lingual cusps through the establishment

of the curve of Wilson (buccolingual curve). The correct occlusal plane must

be determined prior to preparation of the teeth to ensure sufficient occlusal

thickness for all the lower posterior restorations. When the overbuilt wax

patterns arc reduced to the proper line and plane of occlusion the precise

position of each lower buccal cusp tip will show up in the dark wax. After the

plane of occlusion is established, that dark cusp tip is never touched. When this

step is completed, there is no further need for keeping the lower model on the

articulator. All the steps that follow can be accurately carried out with the

lower model off the instrument.

8. Buccal anatomy is carved easily now the crest of contour should be

established at about the junction of the gingival and middle third. In waxing

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full crowns, the contour of the gingival third should start with a concavity

before becoming convex at the junction of the middle third.

9. Lingual cusp tips are located. The distance between the buccal and lingual

cusps of the lower teeth is generally the same as mat of the upper posterior

teeth. It is a practical procedure to simply measure the upper teeth and transfer

to the lower. A double - pointed caliper can be used to measure the upper lip-

to-tip distance. One point of the caliper is then placed in the center of the

bucca! cusp tip is noted by making a slight depression in the wax with the other

caliper point(fig-63).

10. Lingual contours can now be carved using the lingual cusp tip location as

one reference and the gingiva! margin as the other. The crest of contour

should be with in the middle third.

Determining and carving lower fossa contours:

It has one purpose: to ensure a noninterfering accommodation for the upper

lingua! cusps.

The procedure involves making a fossa contour guide that can be used in any

stage of waxup or even porcelain application. The guide should accompany the

articulated die model.

Normally the guide is made before waxup is started but it not used until the last

stage of pattern contouring.

1. The anterior guide table is flattened to 0 degrees and the incisal guide pin

removed. The special pin for making the fossa contour guide is inserted in its

placer It must not touch the metal.

2. A mound of softened wax is made on the flat guide table. Bosworths Tacky

Wax works fine.

187

3. The special pin is lowered into the wax and the upper model moved into

left and right excursions. The articulator must not go into protrusion. As the

upper bow of the articulator is moved right and left, the lingual surfaces of the

upper cuspids guide the upper model over the incisal edges of the lower

cuspids and carry the special wax cutter pin through the wax on the same path

as the lateral anterior guidance. The resultant angulations or curvatures in the

wax will be in direct relationship to the correct fosse contours.

4. When the lateral guidance pathways have been cut sharply into ihe wax on

the guide table, the special pin in raised and the wax painted with a separating

agent.

5. The tip is cut off the small end of a plastic protector that comes on

disposable syringe needles. The large end will fit snugly on the raised special

pin.

6. a. Mix of self-curing acrylic is made and some is poured into the indentation

in the wax.

b. Some of the acrylic is wiped up into the hole in the bottom end of plaslic

needle protector.

c. The pin is lowered so that the acrylic is joined. The needle protector will

become the handle for the fossa contour guide.

d. When the acrylic has set, the pin is raised and the guide removed.

7. Because of the design of the special wax cutter pin. the lateral anterior

guidance angle will be evident as a sharp line running along the bottom edge of

the acrylic.

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The ridges should be contoured to reflect food away from the contact which

means directing it into the fossae.

Porcelain occlusal veneers:

Porcelain veneers are much stronger if the veneer thickness is kept fairly

uniform. Waxing the teeth to contour first and then cutting the patterns back

about 1 to- 1.5mm. wherever porcelain is to be applied results in the strongest

possible porcelain application.

To make certain that the porcelain cusp tips are in the correct position, a simple

procedure can be followed that utilizes an easily made stone matrix. The

patterns are cast and prepared for porcelain application. With a marking pencil,

a mark is put in each indentation, which represents the exact tip of each buccal

cusp. The matrix is trimmed back on a model trimmer to the center of each

cusp tip mark. The matrix will fit back on the model, indexed to the front teeth,

and will serve as a series of reference points so the ceramist can build the

porcelain buccal cusp tips to the correct position.

The bottom edge of the guide is marked with a pencil and any excess acrylic

ground off in front of the line. One may actually hollow-grind the front surface

down to the line to make a scoop-shaped guide, which is excellent for shaving

out wax from the fossae.

There are just three basic rules for using ihc fossae contour guide(fig-64).

t. .Always hold the handle perpendicular

2. Never destroy a predetermined cusp lip

3. Locate fossae in proper relations to cusp tips

The front of the guide always faces front, and in that position it is correct for

either the right or the left side. When the handle is held perpendicular, it

189

exactly reproduces the lateral anterior guidance. Flattening the bottom of the

guide will provide extra room for a lateral side shift. F.ven though the side shift

is usually built into the anterior guidance (and consequently duplicated in the

fossae contour guide), it is a good practice to give a little extra lateral freedom

as insurance, especially since to do so takes away nothing that is needed in the

first place.

Modifications in using the fossae contour guide:

The fossae contour guide may be used before supplemental grooves are placed

or it can be used to refine fossae wall inclinations after all the occlusal carvings

have been completed. Carving the patterns with fairly deep grooves and

slightly convex inclines will usually require an opening out of the fossae, but

the result is an unusually natural looking occlusa! contour since it simulates

normal wear.

The fossae contour guide can be used in combination with dropped wax

techniques and gnathologic mountings.

Finished castings and porcelain occlusals can be checked by the dentist and

modified by selective grinding. The fossae contour guide is an easy tool to

use. A quick analysis of each fossa can be made when the restorations are

received from the laboratory.

Carving the marginal ridges:

When all cusp tips have been properly located and the fossae correctly placed

and contoured, the marginal ridges seem to fall right into place.

The most common error noted in marginal ridge contouring is failure to evenly

line up the marginal ridges of contacting teeth would create considerable lateral

torque in the extremely stressful position near the condylar fulcrum.

190

More definitively, the anterior guidance contact should be maintained during ,

posterior contact in working excursions.

Balancing excursions:

The term "balancing excursion" is a remnant of full denture terminology. It

originally referred to actual balancing contact to stabilize the dentures on the

side of the downward moving, orbiting condyle. It is a part of the three-point

contact concept, which for denture stability is a good concept.

Bilaterally balanced occlusion docs not work because there is no way to

harmonize the "balancing" inclines of the teeth to all of the variations of muscle

force against the unbraced orbiting condyle. "Balancing" inclines must be

relieved on all restorations regardless of the method used to record the border

movements. The relief can be accomplished rather simply by slight hollow

grinding of the buccal inclines of the upper lingual cusps between the centric

contact in the fossae and on the tips of lingual cusps.

Since balancing incline interferences are so stressful, extra care should be taken

to make sure such inclines are never allowed to contact,

When applied to natural teeth, the term "balancing side" is obviously not a

correct connotation. Stuart and Thomas refer to the orbiting condyle side as the

"idling side". It is certainly a better term, since it correctly indicates a lack of

contact.

If the occlusion must be grossly adjusted on the finished restorations, one or

more of the following errors has probably been committed: Improper recording

of centric relation Errors in mounting Improper fit of finished restorations

Errors in cementation

191

FUNCTIONALLY GENERATED PATH TECHNIQUES FOR

RECORDING BORDER MOVEMENTS INTRAORALLY

In spite of its simplicity, the functionally generated path technique (FGP) can

be an extremely sophisticated method of capturing in a usable way the precise

border pathways that ihe lower posterior teeth follow. The technique has the

distinct advantage of being able 10 record all dimensions of such border

movements at the correct vertical as they are directly influenced by both

condylar guidances and anterior guidance.

Like any other technique for recording border pathways, the value of functional

path procedures is directly proportionate to the operator's understanding of

what he is trying to accomplish and why. When properly used, FGP procedures

are unsurpassed in accuracy and they require no compromise whatever in the

finishing of occlusal contours.

If the following facts are understood, the value of FGP as a logical method of

achieving precisely accurate occlusal contours will be obvious. 1. Border

pathways of the lower posterior teeth are dictated by two different

determinants:

a. The anatomic limits of movement of the condyle - disc assemblies (posterior

determinant)

b. The anterior guidance (anterior determinant)

c, Functionally generated path procedures, properly used on upper posterior

teeth. record directly all possible border pathways of the lower posterior teeth,

as they are influenced by both the anterior and posterior determinants. 3. The

shape of the occlusal surfaces of the lower posterior teeth has a profound

influence on the type of occlusion that is dictated by moving said shapes along

the border pathways through the functional wax.

192

Obviously, any dentist who does not wish to reproduce an incorrect existing

occlusion would not use FGP procedures until he has made certain that both ihe

anterior guidance and the lower occlusal contours are correct. However, if

either the anterior guidance or the lower occlusal contours are incorrect, there is

no technique that can produce correct upper posterior teeth.

193

RESTORING UPPER POSTERIOR TEETH

The upper posterior teeth should be the last segment to be restored. It is the

fixed posterior segment, and its cusps, inclines, grooves, and ridges are placed

and contoured to accommodate the many border movements of the lower

posterior teeth.

While it is possible to fabricate upper and lower posterior restorations together

on a fully adjustable instrument, upper posterior restorations should never be

fabricated against lower posterior teeth that require correction of their occlusal

plane cusp tip placement, or fossa contours. If it is absolutely necessary to

restore upper posterior teeth first, the lower teeth should be corrected as close

to optimum as possible with selective grinding or temporary restorations.

Preparing upper posterior teeth for occlusal restoration:

When upper posterior teeth are being prepared, they should be checked in all

excursions to make certain that there is room for a sufficient thickness of metal

or metal and porcelain.

Most important centric record:

Of all the interocclusal records that are made during occlusal reconstruction.

(he most important one of all is the one for articulating the upper posterior die

model.

Whenever possible, this final centric record should be taken at the correct

vertical dimension. Taking the centric record at the correct vertical dimension

eliminates any error thai would have been associated with a missed axis of

closure and provides the operator with a means of verifying the accuracy of the

centrically articulated models.

194

All of the occlusal inclines on the upper posterior teeth are related to the border

pathways that the lower posterior teeth follow. Whether it is desirable to have

excursive contact on certain inclines or a near miss, it will still be essential to

record the border pathways with extreme preciseness. Upper contours can only

be planned when we know exactly where the lower cusps will be traveling.

The effect of the border movements of the condyles must be recorded at least to

the extent that they can function within the envelope permitted by the anterior

guidance.

The important thing to remember about capturing border movements of the

lower teeth that determine upper occlusal contours. Whether condylar and

anterior guidance determinants are captured directly to then reproduce tooth

movements on an instrument or whether the tooth movements are captured

directly at their site makes no difference, as long as the final upper tooth

inclines are in harmony with the functional pathways that the lower teeth

follow.

One of the most accurate methods of capturing border movements is the

functionally generated path technique.

The dentist must decide whether the upper occlusal inclines are to be in group

function, partial group function, or total disdusion in excursive movements.

Whichever decision is made, it is accomplished by contouring and angulations

of the inclines themselves. Supplemental grooves cut into inclines add to the

natural appearance and increase the gripping and shredding ability of the tooth

surfaces.

Logical approach to first develop the incline surfaces according to type of

function desired and hen carve into that surface the supplemental anatomy.

The grooves are carved smaller than the cusp tips. The tips will just pass over

195

the grooves with no effect on the actual contact through the excursive

movement.

Length of group function contact in working excursion:

If we elect to provide group function on the working side, we should be aware

that all teeth do no stay in excursive contact for the same length of stroke. As

the mandible starts its move to the working side, all the posterior teeth may

contact in harmony with the anterior guidance and of course the condyle. As

the mandible moves further to the side, the first teeth to dis-engage from

contact are the most posterior molars. The disengagement is progressive,

starting with the back molar, which has the shortest contact stroke, forward to

the cuspid, which has the longest contact(fig-65).

The reason for giving the cuspid such a long contact ride and a progressive

shorter contact as we go distally is based on factors of geometry and stress. As

the working condyle rotates, the path traveled around the center of rotation

lengthens as the distance from the condyle increases, While the cuspid is

traveling the full length of its incline from centric to its incisal edge, the second

molar is traveling about half that far. When the cuspid reaches its incisa! edge,

the molar still has some incline left on which it could ride out. However, if the

molar continued its contact after the cuspid was disengaged, the stress would

be no longer shared by the proiective anterior guidance. It would instead be

loaded entirely onto the outer incline of the molar and

Use of acrylic and other hard materials for fabricating the base: Any

material that can maintain accuracy through all the procedures is acceptable as

a base. It must not be flimsy, and it must be stable and retentive. Furthermore

the base must fit the master die model as accurately as it fits the mouth, and it

should not damage the dies when it is seated on and taken oft the master model.

196

Acrylic bases because of the distortion of the acrylic during or after setting and

the damaging effect of the acrylic on the dies.

Cross arch stabilization of the base: A common cause of error in FGP

techniques is hypermobility of the teeth. Cross-arch stabilization can be

affected by the base. Cast bases: When there are missing teeth, bases can be

cast in scrap gold or other metals. 'The functional wax table needs to be only

wide enough to represent the upper occlusal surface with a little extra to hold

the wax. Tables that arc too wide interfere with the cheeks.

The buccal and lingual edges of the cast table can be turned back to grip the

wax or holes can be drilled in the cast table.

Recording the border movements:

After all posterior contact is cleared, the following procedure is performed:

1. The base is returned to the model and softened functional wax added for

recording the FGP. The functional wax is heated with a flame to make sure it is

quite soft and sticky enough to securely adhere to the base. It may be sealed to

the base with a hot spatula, but the base should not be softened too much or it

will distort. A common problem is using too much functional wax. We want

only enough to be impressed by about one third or less of each lower tooth. If

too much wax is used, the excess bulk is too easily moved by the cheeks and

tongue during the FGP recording and the path is useless.

Bosworths Synthetic Tacky Wax is an ideal functional wax because of its good

working qualities and ideal plasticity at mouth temperatures. A little of the

patient's saliva maybe picked up on the tip of the finger and applied to the

functional wax as a lubricant to prevent it from sticking to the lower teeth.

2. Using the same manipulative technique that was used for recording centric

relation, a closure is manipulated into the wax until the anterior teeth contact.

197

The patient should be told in advance to hold that position and then slide

forward until the anterior teeth are end to end.

Technique steps for bilaterally recording the fgp:

After the anterior guidance has been harmonized according to the patient's

functional, esthetic, and periodontal support requirements and after the lower

posterior occlusal contours (fossae contours in particular) have been

harmonized to the anterior guidance and the fossae have been freed for possible

side shift of the .mandible. The technique for recording the FGP is as follows:

Making the base for the FGP

1. Upper posterior teeth are prepared

2. An impression is made of the upper prepared arch and, while the patient

waits it is poured immediately in hard stone. The impression material used for

this step should have a soft consistency so that it will not distort the soft tissues.

A smooth creamy mix of alginate is acceptable.

3. When the model has set, extra hard base plate wax is used to make a base

for the functional wax. The wax used for this step should be brittle hard so the

base will not bend without breaking. The wax is softened over a flame and

folded into three layers. While it is still soft, it is adapted around each tooth on

the model. It is pressed down very firmly over each tooth so that it will be thin

enough to see through on the occlusal portion. Then the wax is adapted down

around each tooth to completely cover all prepared teeth down 10 the gingival

margins. The wax wafer should not be adapted to the palate. It should go

straight across. It should cover only the posterior teeth but should be extended

right up to the unprepared cuspids(fig-66).

4. The chilled base is removed from the model and inserted in the mouth. This

base must be perfectly stable in the mouth. The base is seated firmly and

198

watched carefully for any spring back. If there is any movement whatever of

the base, the wax is trimmed back on the underside wherever it touches soft

tissue.

5. When it is certain that the base is stable, the patient should close his mouth.

There should be no tooth contact on the base. Contact in all excursions as well

as centric relation closure should* be checked. There must be no interferences

that will restrict the anterior guidance from functioning in its normal manner.

When there are fairly extensive edentulous areas (as an example) it may be

necessary to cast the base of metal. Regardless of what is required, the base

must fit the teeth and be absolutely stable.

3 The patient should close back inio centric relation and the mandible is guided

into lateral excursions. The dentist must guide the mandible through all

excursions to ensure capturing of all border movements. If the excursive

movements are left entirely to the patient, they will usually move in a protruded

lateral direction and the mandible will not move the lower posterior teeth as far

into the Bennett shift as it is really capable of doing in forceful movements. If

the condyles arc not forced to their outermost border positions during the

generation of the path in the wax. tooth interferences to the extreme border

positions will result in the restorations. These arc the same interferences that

usually go undetected by many dentists who do not use correct manipulative

techniques in equilibration. They are potent triggers for bruxism and are the

frequent cause of posterior looth hypermobility.

4. When all excursive movements have been recorded by manipulation of the

mandible, the patient should be allowed to slide around however he wishes.

This is the step that records the movements between straight lateral and straight

protrusive. If there are any interferences to any movement of the jaw. the

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functional wax will simply be moved out of the way to record the outer limits

of all functional movements(fig-67).

5. The KGP should. be checked for any movement during excursions and to

make sure all pathways have been recorded in sufficient functional wax. If

everything appears to be in order, the wax is chilled with ice water to make it

quite firm. A creamy mix of stone is mixed by the assistant. When the stone

is mixed, she should help hold the cheeks out again while the patient quickly

goes through one last set of excursions. The cheeks should be held out while a

creamy mix of stone is jiggled into all the depressions of the functional wax.

Vibrating the stone on the tip of the index linger while jiggling the mix ahead

of the fingertip works quite well. The fast-setting stone must cover at least one

unprepared tooth in front, and. if present, at least one distal to the prepared

ones. The stone index over the unprepared tooth on each side will serve a

definite vertical stop and a positive key to the master dies when the functional

model is being used in the laboratory.

The stone will stiffen the entire base and protect the functional wax. It also will

make it easier to seat the FGP on the model without distorting the functional

wax(fig-68).

Application of the stone mix in the mouth has another important advantage. It

enables the dentist to check for any distortion that may have occurred during

the intraoral procedures.

Checking for distortion: When the FGP is removed from the mouth, it should

be placed back on the same model that was used to adapt the base. The stone

that covered over the unprepared tooth or teeth on each side should fit the same

teeth on the model without any distortion whatsoever, that is. no space should

be in evidence between the functional stone and the model stone, liven a slight

200

crack between the model and the FGP stone should not be accepted since it is

an indication thai the base has been distorted.

If the FGP stone, now called the stone core, fits perfectly against the

unprepared teeth in front and the wax base fits the model or unprepared teeth

perfectly in the back, we may assume that ihere has been no distortion of the

base.

A wax base should not be used when there are many missing teeth unless it can

be thick enough to ensure strength.

Laboratory Procedures:

Many technicians prefer 10 wax the patterns against the anatomic model in the

same manner they are used to. and then they refine the inclines against the

functional model. This is a logical procedure. However, the skilled technician

can soon "'read'" the functional model as effectively as the anatomic model.

Mounting the FGP:

1. The opposing anatomic model is removed from the articulator and the FGP

base placed on [he mounted master die model. It should fit perfectly with no

rock. The functional stone core should fit against the cuspids (or an unprepared

tooth in front) without any crack showing. As long as the FGP base fits the first

model perfectly any discrepancies on the master die model can almost always

be resolved by removing soft tissue contact on either the model or the

underside of the base.

2. An inverted plastic cup with the bottom cut out makes a good form for

pouring the lower stone platform.

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The stone core and the platform should be dampened and the two neatly joined

together with another mix. The guide pin should be set the same as it is for the

anatomic model.

There are a number of ways to check the accuracy of the FGP recording, and

fade accuracy checks are made at each step of the procedure from the intraoral

steps through the completion of the mounting. None of the checks is

complicated or time consuming, but each is important: Using the functional

model:

The articulator is always locked in the position that allows absolutely no lateral

movement when the functional model is in use. The articulator simply serves as

a device to position the functional core in its proper relationship to the dies.

Since the pathways of the lower teeth are recorded three dimensionally in the

solid stone core, moving the articulator laterally produces an error. It must be

kept locked in centric relation position.

The technician has three options for using the functional model. He may:

1. Wax the restorations directly against the functional model.

2. Wax against the anatomic model, then refine the occlusal inclines and

check for interferences against the functional model (stone core)

3. Complete the castings against the anatomic model, then adjust the metal or

porcelain occlusal surfaces against the functional model.

Making adjustments against the functional model:

When the restorations are in place on the upper die model, it should be possible

to close the articulator so that there is no crack between the "key" teeth and the

functional stone core. All restorations should be in contact with the functional

202

core. If there is any separation between these "key" teeth and the stone index, it

is an indication of an occlusal interference.

Group function is attained by adjusting the lingual inclines of the upper buccal

cusps to contact against the functional core (fig-69). Disclusion is attained by

taking the inclines out of contact with the functional core and leaving only the

selected centric stops in contact. The amount of space between the inclines and

the functional model will represent the exact amount of clearance between the

lower cusps and the upper inclines during excursions(fig-70). Balancing

inclines:

All excursions made during the recording of the FGP represent actual contact.

This includes balancing excursions. Since balancing side contact is undesirable.

balancing side disclusion must be effected by reducing balancing inclines on

the restorations so that they do not contact the functional stone at any point.

FGP checkbite technique:

The FGP technique can be used as outlined to check out castings that are

already complete, after the castings have been tried in. checked for accuracy of

fit. and then removed. To make sure the castings fit the mouth the same as they

fit the model, they should be tried in and a stone matrix made along the

occlusal surfaces. Fast setting stone is ideal for the matrix because of its rapid

setting time. The castings are then removed from the mouth and relumed to the

die model.

The stone matrix is trimmed back to the tip of the buccal cusps and placed on

the castings. The matrix should fit the castings on the model as perfectly as it

fit them in the mouth. Castings that have been checked in this manner and pass

the test can be adjusted against an FGP model with complete assurance of

accuracy,

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FGP for quadrant dentistry:

The real value of functional path procedures is more practically realized when

it is used bilaterally because of the stabilizing effect on the teeth and FGP base

when it is attached to both sides of the arch. Nevertheless funciional paths can

be recorded unilaterally if great care is exercised to assure the stability of the

base and if hypermobility of the teeth in the quadrant is not a problem.

A single quadrant may be prepared and FGP procedures may be used to

advantage if the base can be stabilized. In a unilateral quadrant ii is often

necessary to make a cast base in order to get enough stabilization.

When preparing a single quadrant, special care should be taken to make sure

the opposite side is perfectly equilibrated so that there are no deviating

interferences to influence the functional paths.

FGP for a single tooth:

One of the most common uses for functional path procedures is the restoration

of a single tooth. As a practical clinical approach, however, FGP for a single

tooth has minimal value. Using FGP for restoration of a single tooth involves

unnecessary extra procedures that require longer chair time, and in many

instances it produces unwanted results.

If there are occlusa! interferences present, the FGP will perpetuate them in the

restoration. If tooth inclines limit the movement, the FGP can be done directly

on the models.

The biggest shortcoming of single tooth FGP occurs in mouths with posterior

disclusion. Even it all other posterior inclines are discluded in working and

balancing excursions, restoring against a functional model will put the restored

inclines in full lateral contact.

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If FGP is used in posterior disclusion cases, the restoration should be relieved

on the working and balancing inclines. If full arch hand-held models are used

instead of FGP. the disclusion of both working and balancing inclines will be

perfected right on the models, a decided advantage.

There is another potential disadvantage for single tooth FGP. If adjacent teeth

have any hypermobility they can move during generation of the path and the

path will be flatter in the wax than it is on the adjacent teeth.

If FGP is used, the tooth being restored must be stabilized during generation of

the path.

If full arch models are used, the position of the teeth stays the same as when the

impression was made. If the other occlusal inclines are correct in the mouth,

they will be correct on the models. Rubbing such models together with wax on

the die will produce the same inclines in the wax that exist on the adjacent

teeth, so thai the wax pat'.crn will also be correct.

Posterior inclines on each side of the die must be permitted to contact in order

to have their working and balancing inclines duplicated in the soft wax on the

die.

The Johnson-Oglesby Spring Arliculator is a practical device for holding full

arch models together while still permitting a full range of movement, including

contact of the balancing inclines on the model. The three essentials for a good

result are:

1. Occlusal correction before restoration

2. Full arch models

3. Reduction on the model of steep anterior inclines that prevent full

excursive contact against the posterior inclines being copied.

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Clinical procedure for single tooth FGP:

1. The occlusal reduction for the preparation is completed.

2. Before doing any proximal reduction the tooth is stabilized with softened

slick compounded the same compound formed into a broader occlusal table to

receive the functional wax.

3.. The surface of the compound is roughened so that the functional wax will

not slide off.

4. Using a flame, the functional wax is softened (Bosworth's Synthetic Tacky

Wax is a favorite) and stuck to the prepared occlusal table. The occlusal

portion is lubricated with saliva.

5. The patient should close into centric relation and move through all possible

excursions.

6. A creamy mix of Healey's Fast Setting Gray Rock of Whipmix Bite Stone

is made and vibrated into the FGP indentations. The stone is extended onto at

least one tooth on each side of the prepared tooth.

Note: FGP can be done on a terminal tooth if the base and the wax can be

made stable. On a terminal tooth, the fast-setting stone should be extended over

at least three teeth in front of the prepared tooth.

7. The hardened stone is removed and set aside. The compound and the wax

are removed and discarded, and the preparation is completed. An impression

of the prepared tooth is made, including all teeth that will be covered with the

stone functional core. An opposing model is not necessary.

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Laboratory procedure:

1. The impression with removable dies for the prepared tooth and each

adjacent tooth is poured. The functional core is positioned against the die

model. The unprepared teeth on the die model should fit perfectly into the stone

index.

3. Any instrument that can repeatedly reposition the functional model with

accuracy is acceptable for mounting the two models. They can be mounted in

the joined position on a simple hinge aniculator, because the only requirement

of the instrument is to permit the models to be separated and then returned to

the same closed position. The arc of opening and closing has no importance,

and of course no lateral movement is permitted. All pathways are represented

on the functional model itself when it is closed. Instruments that have been

especially designed for relating the functional model to the die model include

the following.

a. The verticulator (fig-71) is a device that permits only an up or down

movement. It is precision-made with a sturdy metal stop that permits the

functional model to be struck forcefully against the die model without danger

of model breakage. The verticulator is spring loaded so that with each closure it

springs open to give access to the die or pattern.

b. The twin stage occludcr is simple hinge articulator that will articulate both

a functional core and an anatomic model interchangeably against the same die

model(fig-72).

4. When using FGP for a single tooth, the pattern is generally waxed directly

against the functional core. The pattern should contact the functional model but

should not interfere with its closure. If the restoration is to be in group function,

the lingual inclines of the upper buccal cusps should be in continuous contact

with the functional model. If the inclines are to be discluded. they must be

207

reduced so that there is no contact, but centric relation contacts must not be

tost. In all cases, the balancing inclines should be relived from any contact with

the functional core.

FGP for lower teeth:

Functional path procedures are not generally used on lower teeth. For KGP to

work on the lower teeth, the upper inclines would have to be perfected first. If

the lover tooth is not in contact, it can be built up with compound or a well-

made temporary restoration and the occlusion refined prior to taking the

functional record. This is referred to as cup-fossae analysis.

Cusp-fossae analysis can be accomplished very effectively on the stone

models. It is safer to adjust the occlusion against the finished restoration than to

take the chance of wiping away the lower buccal cusp in FGP wax against

upper inclines that may be in interference.

FGP can be used on lower teeth, but only if the upper occlusal contours have

been perfected first. This is true for a single tooth or for multiple teeth. For

multiple teeth there is the added problem of stabilizing of lower base against

tongue and cheek action. It usually must be a cast base. In lower teeth the

dentist is not interested in having any inclines in function, only functioning

contacts on the buccal cusp tips and centric contact in the base of fossae. This

can be accomplished in more practical

Ways that using

Using FGP for cross bites Posterior cross bites can be restored using FGP if

lower cusp tip placement and cast fossae contours have been perfected in

advance. In all cases, the balancing inclines must be additionally reduced

when FGP is used.

208

PROCEDURAL STEP IN RESTORING OCCLUSION

Restoring posterior teeth before the anterior guidance is finalized is an

example of a common error of sequence.

Two of the best rules to follow for staying out of trouble with restorative

procedures are: 1. Sever begin any restorative procedure unless all the

procedures that follow are outlined in advance and properly related to one

another in correct sequence. 2. Never begin any restorative procedure unless

the end result is perfectly visualized and understood.

Preliminary mouth preparation:

1. Mouth hygiene instructions should be given

2. Caries control should be achieved

3. Periodomal therapy should be completed.

J. Minor tooth movement should be complete. Stabilization of the occlusion

following any orthodontic procedures should have occurred. When teeth have

been moved ample lime should be given for reorganization of the periodontal

fibers and bony support before final impressions are made for restorations.

5 Necessary extractions should be done and tissues healed before permanent

placement of fixed prostheses.

6. Equilibration should be completed prior to preparation of the teeth. The

temporomandibular joints should be comfortable prior to finalizing any

restorative treatment.

209

Sequential steps for restoring different combinations:

Following is a general list of the variations in restorative needs of different

patients. A suggested sequence of restorative procedures is outlined for each

type of case. The outline is general and it may be necessary to vary the

procedures or the sequence for particular needs of certain patients.

210

RESTORING ALL UPPER POSTERIOR TEETH ONLY

RESTORING ALL UPPER TEETH BUT NO LOWER TEETH

RESTORING ALL POSTERIOR TEETH BUT NO ANTERIOR TEETH

RESTORING ALL UPPER AND LOWER TEETH

PREPARING ALL UPPER TEETH AND LOWER POSTERIOR TEETH

ONLY

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REVIEW OF LITERATURE

HINGE AXIS

Campion(1902,1905) produced probably the first graphic record of mandibular

movements on a patient, he used a basic form of pantograph which produced a

succession of dots on the skin of the side of the face as the condyles moved

during function, the slope of the condyle path in different individuals was

demonstrated by comparison with an imaginary line from the external auditory

meatus to the lower border of the nose, from his work he concluded ' ... there is

and can be no one axis about which the mandible moves in opening the mouth,

but that the movement is a complex one. consisting first of a rotation of the

bone on an axis passing approximately through the centers of the two condyles,

and secondly of a forward and downward movement of the condyles as they

slide over or with the meniscus-shaped inter articular cartilage along the curve

of the eminentia articuiaris".

Bennett (1908) in his classical paper on movements of the mandible, stated

that no single fixed center of rotation for the mandible existed since the center

of rotation constantly shifted (for movements in the sagittal plane). However,

he did point out that the mandible was capable of two independent movements;

one. an angular rotation about the condyle, the other a translation movement

produced by the gliding of the condyle along its path. Using geometrical and

mechanical theories, based on work carried out on himself when undertaking

mandibular movements, he demonstrated the instantaneous centre about which

the mandible was at any moment turning, for every position of the mandible.

He accepted the criticism that the experiments were carried out on one

individual (himself) as that no general conclusions could be drawn from them.

Gysi(19lO) presented a treatise on the history of articulators and described

instruments used for determining the slope of the condyle path. He stated that

212

the natural condyles could not b£ considered as true rotation points or axes

above which the various movements of the mandible occurred, but should be

regarded only as fixed guides of the mandible in its movements. He stated ',.,

The mandible in opening and closing rotates around anther center, which,

however has no influence in the setting up of the teeth for articulations, and

therefore need not be considered in the construction of an articulator.

Needles (1923) carried out experiments to test the accuracy of articulators and

came to the same conclusion as Bennett, viz. there were two fundamental joints

between the mandible and the maxilla. One was a hinge joint with the axis

through the heads of the condyles; the other was a sliding joint between the

fibrocartilage and the articular eminence. He said that any movement of which

the mandible was capable was the result of the movement in one or both of

these joints.

In a further paper (Needles 1927) he again discussed the two parts of the

temporomandibular joint. He though the only logical method of studying

mandibular movements was to divide them into their two elementary

components and refer each movement to its respective part of the joint. With

regard to articulators he said that, with any type, the axis of the opening

movement should be so placed as to correspond lo the heads of the condyles.

The articulator could then be opened or closed a considerable distance without

producing any error is the occlusion of dentures or prosthetic appliances.

Bennett (1924) discussed mandibular movements in relaiion to prosthetic

dentistry and again stated that there was no center of rotation in the

temporomandibular joint itself. Movements of the mandible in the sagittal

plane were composed of rotation about the line of the condyles and translation

213

in the direction of the condyie paths giving instantaneous or constantly shifting

centers.

VVadsworth (1925) referred to the anatomists conclusions. He stated that the

first movement of the mandible occurred around a transverse axis passing

through the condyles. the condyles themselves remaining sealed in the fossae.

The second movement was a sliding movement, the condyles gliding forward

onto the articular eminence.

Stansbery (1928) was^dubious about the value of face bows and adjustable

articulators. He thought that since an opening movement about the hinge axis

took the teeth out of contact, the use of these instruments was ineffective

except for the arrangement of the teeth in centric occlusion. In his opinion, the

plain line hinge type of articulator was jus as effective.

Hall (1929) reviewed early work on articulators and the investigation of

mandibular movements. He credited Balkwill with describing practically all the

movements of the mandible then known. He quoted Balkwill, who had stated in

1866. A side view shows that the condyle articulates with the glenoid cavity so

as to allow of a simple hinge like motion, and a forward and backward motion.

When the teeth are shut, the condyle lies at the back of the glenoid cavity,

where, the front of the lower jaw being depressed, it turns like a hinge. The

work of lace was also reviewed by Hall. He had concluded, as a result of his

(Luce's) investigations, that the condyle advanced even if an effort was made to

it back. Hall stated: "It is noted that the question of whether or not the condyle

is the centre of the opening movement in slight movement was a point of

contention in Luce's time, just as it is today. I believe, as Luce did, that it is

not".

214

McLean (1937) stated:

The hinge functions of the lower portion (of the temporomandibular joint) are

still disputed and little understood. The hinge portion of the jaw has two

functions of great importance to Prosthodontists.

First, the hinge portion of the joint is the great equalizer for disharmonies

between the gnathodynamic factors of occlusion... When occlusions are

synthesized on articulators without accurate hinge axis orieniation. there may

be minor cuspal conflicts, which must be removed by selective spot grinding.

Regarding the satisfactory construction of full dentures, he said that opening or

closing the bite on an articulator with an incorrect hinge-axis location would

result in unsatisfactory occlusion of the dentures when they were placed in the

mouth. When the hinge axis on the articulator was too far forward compared

with a location on a patient, closing the interocclusal distance would result in

the dentures meeting prematurely posteriorly. If the axis was too far

posteriorly, premature contact would occur anteriorly. If the axis was too low,

the lower denture would be forward of centric relation. If too high, the lower

denture would be posterior to centric relation. The conclusion was that any

alteration in the interocclusal distance must either be made in the mouth or by

the use of a hinge-axis articulator. If the latter were to be used, then the hinge

axis must be determined as a stationary point (i.e. rotatory but not translatory)

over the head of the condyle during hinge-axis movements and not by palpation

or anatomical location.

McCollum (1939) published a very important series of articles concerning

restorative remedies. Since he was one of the leading advocates of the "hinge-

axis theory", it is important to quote a large part of his work:

Prominent anatomists have insisted that there is no true hinge joint in the body

only because they have understood the mechanistns of a hinge. Some

215

anatomists seem to believe that a hinge-action is a total movement between an

edge and a surface such that the axis of rotation lies on the surface. They are

confusing pivotal action with hinge action and do not realize that door hinges

work by one surface gliding over another, the amount of gliding depending on

the size of the pin, but the centre of action is an imaginary axis through the

centre of the pin.

In 1921, I became convinced that the opening and closing centre of the

mandible was a most important factory in dental articulation and that it

determination was preliminary to the transferring to an articulating instrument a

record of jaw relations. Snow and others, in a gross way, had recognized an

importance and thirty years previously had invented the face bow and a method

for its use. Gysi definitely recognized the importance of the opening and

closing axis to articulation, as is evidenced by the statement that the raising or

lowering of the bite is a chair operations. Bui he failed to grasp the necessity

for its being recorded in instruments as accurately as he tried to record the

other phases of jaw motions. His experiments wore so inaccurate that he

concluded that a hinge-axis, if it did case was down below the condyles near

the lower border of the tragus and he actually made an articular accordingly.

However, his latest articulators has the hinge axis in the condylar region, but so

far as know he does not ascribe much importance to it; changing vertical

dimensions with him is still a chair operation... Now it must be obvious to the

siudious that, if the articulator absolutely duplicates as jaw relation, it is

possible to alter the vertical dimension by either raising or lowering the bite on

ihe articulator and have the same conditions prevail in the mouth as existed on

the instruments.

McCollum described how; he came to demonstrate conclusively the existed of

a definite opening and closing axis by using a face-bow rigidly attached to the

lower teeth with orthodontic appliances. The development of accurate and rips

216

clutches, and adjustable face bows, led to the determination of the hinge axis

easily. He also demonstrated, by means of diagrams showing exact locations

nine pairs of hinge axis points that external landmarks were of little use

location of the axis. In addition to wide variation in anatomical location of

these points, he also found great variation between sides on the same

individual. He gained the impression, however, hinge axis point remained

constant in the tattoo dot on the skin throughout life.

Further work on cadavers showed that the hinge axis bore no Constance's

relationship to ouiside landmarks and that the only satisfactory method of

locating the axis was by trial and error. Although it was necessary to open the

jaw slightly to avoid cuspal interference when determining the hinge axis, he

was quite satisfied that the mouth could be opened by as much as one half inch

in the incisor region in every individual, and in some individuals by as much as

one inch without the condyle heads moving forward in the fossae.

Stuart (1939) complemented the work of McCollum in his discussions on the

articulation of human teeth, the relationship of the mandible to the maxilla, and

the cuspal interdigitation of the teeth. These two workers were the pioneers of

'gnathology' as it is practiced today. Their early work led to the publication of a

research report (McCollum and Stuart 1955). which formed the basis of the

postgraduate teaching in the subject.

Higley (1940) discussed controversies surrounding the temporomandibular

joint including the manner of its development, adaptive changes in the joint, the

importance of the joint to articulation, muscles controlling mandibular

movement, and movement patterns of the mandible and condyle. Referring to

McCoHum's work, he stated; No matter what may finally be proved regarding

these movements of the condyle it would seem that the Gnathological Society

(of Lee Angeles, headed by McCollum) has developed an excellent technique

217

and one that will always be of value, because, clinically it has seemed

adequate.

In an attempt to clarify the contradictory statements regarding movements of

the mandible, and particularly the question of whether it was possible for the

condyle to exhibit hinge action only, and retain its centric relationship, Higley

Logan (1941) analysed condyle action as shown by radiographic examination.

The results showed that, in all the subjects studied, as the mandible dropped

from occlusion to an opening of 15 mm, there was a rctrusive movement of the

chin point, and the head of the condyle dropped progressively. The majority of

the subjects (70.6%) showed a forward shift of the head of the condyle from

occlusion to physiological rest position.

With an opening of I Omm. 95% of case showed a forward shift of the head of

the condyle. When the mandible was opened 15 mm all the subjects showed a

forward movement of the condyle.

McCollum (1943) reiterated his ideas concerning the hinge axis concept. He

said that in simple opening movements (if the mandible, the joint acted as a

common axis. This action took place anatomically by rotation of the head of

the condyle in the lower surface of the meniscus. It was possible for the

mandible to the simple opening to the extent of separating the incisors from

half an inch with individuals, lo 1.5 inches with some individuals. He though

that one of the confusing ideas about this opening component was that it could

accompanied by a contraction of the external pterygoid muscles which pulled

the condyles and menisci forward in the temporomandibular fossae. The

combined action was a natural elements of the chewing motions, especially the

prehensile or biting capsule. Therefore, when the individuals were told lo open

his mouth he would automatically combine these movements. He pointed out

that in order lo determine the true opening component it was necessary lo

ensure the individuals did not combine these movements.

218

McLean (1914) said that the diagnosis of "pathological occlusion" dependent

on the fact that the final phase of jaw closure was a pure hinge movement.

This movement, he said, required rehearsal or guidance from the hand of the

operator of the chin.

Branstad (1950) dealt with the problem of function in periodontal disease and

though! most of the emphasis in the treatment of traumatogenic occlusions or

to articulation had been placed on selective grinding performed directly in the

mouth. This, according to some authorities, merely moved the disease from one

both to another. This led him to think, therefore, that a description of the

biological factors, which should be understood in order to create and maintain a

physiological articulation, was called for. He said thai the only practical way to

diagnose what type of corrections or restorations were necessary to enable the

south lo function physiological, was to record maxillomandihular relationships

as an instrument capable of reproducing mandibular movements. In his

opinion, as adjustable articulator was as important in oral diagnosis as a

microscope was in pathological or bacteriological

In a further paper (Sloane 1952) he staled; "One component of mandibular

function, the mandibular axis, is of pre-eminent importance. The mandibular

arc is not a theoretical assumption, but a definitely demonstrable

biomechanica! fact. It is the axis upon which the mandible rotates in an

opening and closing function when comfortably, not forcibly, retruded. He said

that if the mandibular axis as recorded . and transferred to an anatomical

articulator the casts could be mounted so thai they opened and closed on the

articulator in the same fashion as patient's jaws. A method of locating the

mandibular axis and transferring it to modified llanau instrument was

described.

Clapp(1952) was in agreement with Gysi's (1910) ideas concerning

mandibular movement. He considered that there were a number of axes for

219

opening movements of the mandible and that they were all located outside the

mandible except the one for extreme opening. The infrahyoid muscles were the

activators of the straight opening movement rather than the external pterygoid

muscles. This article was published at a time when the hinge-axis theory had

been accepted by a number of authorities following the work of McCollum

(1939. 1943) as Granger (1952). It is interesting to note that Clapp was the

first American pupil of Gysi at Zurich in 1912.

Granger (1952) pointed out that each lemporomandibular joint consisted of

two joints. The one between condyle and meniscus was a pure ball and socket

joini capable of rotational movements in a vertical and horizontal plane. The

ball and socket could function in this way while the joint itself was gliding

bodily in the glenoid fossa. In use. gliding and rotation usually occurred

together, and this together with bodily movement of the mandible, gave rise to

complex mandibular movements. Granger stated that all rotations responsible

for mandibular movements had axes. which met at a common point within each

condyle. If these two points were joined by an imaginary line this would give

the transverse hinge axis. He said that the hinge axis was constant to the

mandible since gliding movement did not alter the relationship between

condyle and meniscus but ihc relationship of the hinge axis to the glenoid

fossa. There was only one position where the hinge axis was common to both

mandible and maxilla and that was centric relation.

Craddock and Symmons (1952) stated that in normal subjects, and for small

opening movements, the horizontal axis of rotation did pass through the

condyles and that in wider opening movements the axis became progressively

displaced downwards. They considered that the accurate determination of the

hinge axis was only of academic interest since it would never be found to be

more than a few millimeters distant from the assumed centre in the condyle

itself. The assumed centre could be found by palpation or by measurements one

220

centimeter anteriorly along a line drawn from the upper free margin of the

tragus of the ear to the corner of the eye. They concluded that a difference of a

few millimeters in the location of an axis which is about 100mm distant from

the point being observed could have little influence on the axis generated.

Posselt (1952) in his extensive studies, was concerned with the problem of

whether hinge opening around an inter condylar axis was typical of habitual

opening. He thought that hinge opening was better performed as a passive

movement, or as an active movement after suitable training. However, he could

find nothing to support ihe view that this type of movement was performed as a

habitual movement. Posselt's registrations showed the possibility of performing

a posterior hinge opening of the mandible during a posterior opening

movement of a certain extent and this he confirmed by postmortem registration.

He presumed this took place in the lower compartment of the

temporomandibular joints. The extent of the hinge opening betw cen the upper

and lower incisor teeth was found to be i 9.2 mm + 1.9 mm, although he said

this was not necessarily the maximum.

Page (1952) described the hinge bow, developed by McCollum in 1936. and

said... it was one of the most important contributions made to dental science.

He pointed out that although the hinge axis was entirely theoretical, the jaw

must revolve upon such an axis since it could carry out rotary movements.

Lucia (1953) stated that movements of the mandible was accomplished by a

simple rotation of the condyles on the lower surfaces of the menisci and that

this hinge motion could take place at any point along the condyle path as the

menisci moved along the glenoid fossa. He questioned the practical application

of the hinge action of the joint and whether it was possible to locate this centre

in a practical way. In answer he said: "The practical importance of the hinge

axis and hinge axis transfer

221

of casts to an articulator is of tremendous importance. Without a hinge axis

transfer he thought it is impossible lo diagnose an occlusal problem because the

teeth on the models would not meet in the same way as they would in the

mouth, a centric relation record could not be verified, an articulator could not

be produced which would have the cusps meeting in the same are of closure as

thai of the patient.

Brandrup-Wognsen (1953) discussed the theory and history of face bows. He

quoted the work of Beyron who had demonstrated that the axis of movement of

the mandible did not always pass through the centers of the condyles. Although

the mandible did not always pass through the centers of the condyles. Although

they rarely coincided they were always close to each other and Brandrup-

Wognsen concluded that complicated forms of registration were rarely

necessary for practical work.

Granger (1954) gave an account of the hinge axis and mandibular movements.

He stated thai the mandible was capable of an infinite variety of paths of

movement; one condyle could be undergoing only rotational movement while

the other condyle was both rotating and gliding, or both condyles could be

undergoing both rotational and gliding movements simultaneously.

In conclusion. Granger stated thai successful treatment depended upon the

correct orientation of the teeth to each other and to the hinge axis. Functional

movements of the mandible started and ended at centric relation (terminal

hinge relation). Correct orientation of the teeth in centric occlusion, therefore

dependent upon the correct relationship of the teeth to the hinge axis recorded

with the teeth orientated to each other in the most retruded position of the

mandible.

Sicher (1954) thought that some of the misunderstandings about mandibular

posilions and movements were due to problems of terminology, and he opened

222

his paper with a number of definitions of which that concerning the hinge axis

is quoted: Hinge, or terminal hinge, position is the position of the mandible

from which the mandibular hinge axis is determined or registered. It is the most

retruded position of the mandible that the individual can assume under the

action of his mandibular musculature and is. therefore, an unstrained position.

He slated that every person could move the lower jaw in hinge movement to an

opening of O.5-O.7S of an inch, or even more, bul what he wanted to know

was whether his movement was unnatural, forced, or learned. He concluded

that the hinge position was the most retruded position of the mandible achieved

by the action of a patient's own musculature.

Thompson (1954) was concerned with full mouth reconstruction ofthe natural

dentition. He described his modification of a face-bow so that accurate hinge

axis location could take place. This enabled him to mount the models of a

patient on an articulator so that the same relationship which existed between

the dental arches and the hinge axis ofthe patient was recreated on the

articulator.

Page (1955) criticized the report ofthe official Nomenclature Committee

Meeting of 1952 for its definition and explanation of hinge opening position.

He said that it was a misconception and had failed to recognize that none ofthe

groups who used kinematic location ofthe hinge axis considered this a

significant component of mandibular opening. These groups stressed thai the

important mandibular movement to be recorded was functional hinge closing.

Page also stated that the jaw did not rotate open to rest position on the hinge

axis, but that the whole jaw relaxed with the condylcs dropping into the

hammock and capsular ligaments. This view differed somewhat from that of

Eberle (! 951).

Colled (1955) stated; "There is not agreement on ihe existence ofthe hinge axis.

It is importanl to those who believe in its existence, because by using it we can

223

record centric relation at a level above the place where the proprioceptive

reflex occurs, transfer our recording to an articulating instruments, and on the

instrument, close down to the occlusal level. Hw said that the recording ofthe

opening axis and the transference of it to an articulator were of considerable

value in the diagnosis and treatment of occlusal malfunction.

Korn field (1955) discuSsed the anatomy of the temporomandibular joints and

outlines the technique of recording the hinge axis and its transfer to the

articulator. He stated that the location ofthe hinge axis was the basis of all

articulator transfers. and made the study and treatment of masticator disease

easier and more intelligible. If hi models of the mouth were not mounted on the

hinge axis, then restorations would not meet correctly in the moulh. a centric

relation record could not be verified, an articulator could not be adjusted to

reproduce jaw movements accurately, an occlusion could not be formed with

cusps which were in harmony with the arc of closure of the mandible, and any

changes in vertical dimension would produce occlusal disharmonies. He

concluded that most problems encountered with restorations could be traced to

the failure to maintain a correct relationship to the hinge axis. The importance

placed upon centric relation by Granger was also echoed by Korn field when he

said that the only position at which it was possible to locate and reproduce the

hinge axis was at centric relation, and that centric relation was only one

position of the hinge axis.

Lcvao (1955) staled, as have many workers previously, that mandibular

movements were a combination of rotation and / or translation in either or both

condyles. He described how hinge axis records were obtained on both cadaver

and patients, but said; there is a possibility that the hinge axis does exist, but is

may not be necessarily located within the condyles. Depression of the mandible

is a hinge like opening may cause the condyle to traverse a radial arc. Of its

own. due to the influence of the external pterygoid musculature.

224

Although the interference drawn appeared to negate the value of hinge axis

recordings, he assumed that it was possible to demonstrate a valid hinge axis

passing though or near both condyles. Levao's (1955) article was an important

contribution to the literature, as many of the statements had not previously been

nonarcon type articulators. Levao pointed out the nonacron type articulators

were unsatisfactory for reproducing eccentric pathways when their use was

based on hinge axis transfer since. with these types, the condylar axis moved

backwards. This increased the condylo-incisal distance and consequently a

change in he radius of the rare of closure took place with such movements.

Trapozzano(l955) gave an excellent dissertation on the subject of occlusion

including many clear definitions. He said that the presence of a terminal hinge

axis and centre of rotation from occlusal position through, and in may instances

greatly beyond, the next positional level, had been demonstrated repeatedly.

The fact that the registration of the hinge axis involved a learned movement he

thought in no way invalidated its accuracy or usefulness. He said it was

precisely because the hinge axis represented a "border" position that it was

capable of being recorded repeatedly with unfailing accuracy.

Beck and described the Bcrgstrom arcon articulator and pointed out, as Levao

(1955) had done, that with a non-arcon articulator the beginning and end points

were the same as the beginning and end points of mandibular movements.

However, only the arcon-type of articulator would reproduce mandibular

movements accurately between these two points. He stated that a constant

relationship existed between the occlusal plane on the arcon guides of the

instrument at any position of the upper member, making the reproduction of

mandibular movements more accurate. One interesting factor which the authors

discussed, and which has always been recognized but seldom mentioned, was

that there is a possibility of incorporating multiple errors into articulators of

complex design because of the increased number of measurements and

225

adjustments. The total of these errors may exceed the errors introduced by

assigning fixed values to some adjustments.

Cohen (1956) carried oul experiments on a patient using a Gnathoscope and

Gnathoyraph and found that, within the ranye of opening of the vertical

dimension used, there was conclusive evidence for Morrison (1956) the

existence of a hinge action of the mandible.

Nevakari (1956) investigated the nature of mandibular movement from rest

position to occlusal position using ccphalometrics. He found it impossible to

determine whether the movement actually occurred around a stationary axis or

whether it was composed of rotatory and translatory movement taking place at

different times.

Schallhorn (1957) discussed the advantages and disadvantages of an arbitrary

hinge axis location for face bow Transfer compared with kinematic locations.

Experiments were undertaken to compare kinematic hinge axis location with an

arbitrary location 13 m anterior to the tragus on a line from the tragus to the

outer canthus of the eye. In over 95% of subjects with normal jaw

relationships the kinetic centre was found to be within a radius of 5mm from

the arbitrary centre. Schallhorn said this was within the limits of negligible

error.

Woelfel, Hickey and Rinear (1957) demonstrated electromyographcially that

hinge opening could be accomplished when a trained subject made this type of

opening, since no increase of electrical activity was recorded from the normally

functioning external pterygoid muscles. The results indicated that the

ncuromuscular system was so arranged that hinge movement of the mandible

was possible. This did not, however, preclude the possibility of the bony

structures of the temporomandibular joints interfering with a true hinge

movement. When the bony struciure of the temporomandibular joint and shape

226

of the meniscus would permit, the neuromuscular system was such that a

significant amount of hinge movement could be accomplished. However, they

said that for most individuals this was not a normal opening pattern.

So far little discussion has taken place regarding the split hinge axis theory. A

type of articulator called a Transograph was developed in an attempt to

overcome the problem of irregular condyles. which made it impossible for the

various individual axes (including the transverse hinge axis) to be constant,

even in simple rotation. This instrument made use of a transverse split hinge

axis. Trapozzano (1957) disagreed with the theory and practical aspects of this

technique and stated thai to have two separate axes, or a split axis, then the

mandible would have to bend or the continuity of the mandible would have to

be broken.

Posselt (1957) carried out the following experiments

1. Geometric constructions from a profile radiographs

2. Axis points recorded by a kinematic face bow and checked by profile

radiographs;

3. Hinge axis established by a kinematic face bow and verified by

gnathothesiometric methods.

His results showed that the axis of terminal hinge movement passed through

both condyles. and made only minor shifts, for openings of 15-2Omm.

In further studies to demonstrate mandibular movements Posselt (1958)

showed that the envelope of sagittal movement he said was pure hinge

movement around an inter condylar axis. He also stated that extreme opening

movements differed from habitual opening and closing movemenis and this

could be seen clearly in his diagram of the envelope of sagittal rotation of the

mandible.

227

Borgh and Posscli (1958) reported on their experiments relating to the hinge a\

is of the mandible using a Hanau model H articulator. They concluded that a

hinge movement could not be recorded accurately without error, although there

was some doubt about the accuracy of the machining of this articulator. The

findings on the -whole confirmed those of Kurth and Feinstein (1951).

In determinations of the hinge axis, clutches are used, attached to the upper and

lower teeth (or to the ridges in edentulous cases.) Sheppard (1958) undertook.

experiments to see what effect the presence of clutches in the mouth had on the

position of the condyles, using radiographs for comparison. He found the

clutches immediately altered the closed position of the condyles in most of the

joints studied and could also limit the extent of condylar movement. These

effects obviously have an important influence on the accuracy of such a precise

technique as hinge axis location.

Page (1958) stated that there were at least twelve hinge axes in every head,

three in each temporomandibular joint and three in each mandibular angle.

These, he said, were responsible for movements in all three planes.

Beck (1959) carried out experiments to compare the relative positions of the

following axes of rotation.

1. Bergstrom's axis. This was an arbitrary axis located automatically by his

face bow !0mm anteriorly to the centre of a spherical insert for the external

auditory meatus, and 7 mm below the Frankfurt plane.

2. Gysi's arbitrary axis. This was on a line from the upper margin of the

external auditory mealus to the outer canthus of the eye. 13mm in front of ihe

anterior margin of the meatus.

228

3. Beyron's arbitrary axis. This was located 13mm anteriorly to the posterior

margin of the iragus on a similar line to Gysi's. i.e. along the line from the

tragus to the outer canthus of Ihe eye.

4. Kinematic axis. This was determined using the method developed by

McCollum.

The kinematic centre of rotation for each of twelve subjects was found in the

accepted way using clutches and then the other axes were determined by

measurement. Small metal balls were placed over each axis point and

radiographs taken so that the relative positions could be seen and compared.

The Bergstrom points compared most favorably with the kinematic points, the

majority lying within a radius of 5mm. Beyron's axis points compared well

with the kinematic points, while the Gysi points showed a greater difference

from the kinematic points.

The existence of a fixed axis of rotation for the mandible was questioned by

Beck who postulated that it was impossible to determine with the face bow

alone whether the linear displacement of the condyle point tip was due to

rotation alone and due to rotation and translation. He used a modified Hanau

articulator to demonstrate how it was possible to locate a seemingly stationary

point when translation as well as rotation occurred. In conclusion he felt that

the selection of an arbitrar\ axis was justified.

A review of the literature concerning the hinge axis would not be complete

unless the work of Weinberg was discussed. Since Weinberg is one of the

leading authorities on this subject, adequate space must be given to summarize

his investigations and findings. Weinberg (1959) attempted to clear up any

misunderstanding concerning the hinge axis in the following way. He

1. Described the hinge axis

229

2. Described geometrical and clinical methods for finding it:

3. Described its use;

4. Determined whether there were one or two transverse hinge axes:

5. Discussed the mandibular movement pattern for the opening and closing

movement

6. Gave clinical evidence of the transverse hinge axis

7. Determined if pin point accuracy in the location of the transverse hinge

axis was necessary and

8- Related these factors to clinical practice.

Further reports by Weinberg (I960, 1961) were concerned with articulators and

face bows and reinforced the above findings. One important factor which was

not stated, but was obvious, in the earlier work was that marked deviation of

the hinge axis resulting from arbitrary location could cause marked antero-

posterior mandibular displacement, even with small changes in vertical

dimension.

A series of article by Weinberg (1963) evaluated several articulalors and their

basic concepts. These arc now recogniz.ed as some of the most important

dissertations on articulator design. It is worthwhile repeating Weinberg's

findings especially concerning the hinge axis. He stated that the transverse

hinge axis passed through both condyles and was associated with rotation of

the mandible in the vertical (sagittal) plane. It was of clinical importance for

orientation of the maxillary cast on the aniculator and the subsequent accurate

transfer of the centric relation record, With regard to recon and non-arcon

articuiators. he disagreed with Levao (1955), and Beet and Morrison (1956)

and stated that both instruments produced the same movement because

230

condylar guidance was the result of interaction of a condyle ball on an inclined

plane. Reversal of the relationship would not affect the guidance produced.

Shanahan and Leff (1959,1962) published an important series of reports on

their studies of mandibular and artieulator movements. Initially, they recorded

opening and closing movements, graphically, on a hinge axis artieulator by

attaching a pencil to the incisal guide post. Photographs were then taken using

pin point illumination in a darkened room. These results wee compared with

photographs taken of a subject making similar movements. They concluded

that the normal opening and closing mo\ements of the mandible did not

coincide with tne opening and closing movements of an artieulator. Shanahan

and Lcff (1959. 1962) stated that the There is w wciv>re3d belief that the

mandible opens and closes on an axis and that the mandibular teeih open and

close into centric occlusion on arcs with centers of rotsLkwi in the region of the

condyles. "Their later studies of tracing of natural opening, closing, and

masticating movements of the mandible did not show the presence of a

mandibular axis in the region of the condyles. but they did say that an artificial

mandibular axis could be produced during opening and closing movements by

forcing the chin backward. However, this was not a normal physiological

movement.

Brotman (I960) was of the opinion ihat the hinge axis theory was surrounded

by groups of research workers with strongly differing views. He attempted to

clarify the subject b\ discussing the clinical and geometrical significance of it.

He stated that

'The hinge axis position of the mandible is the most retruded position of the

mandible from which opening and closing movement can be made. When a

mandible is opened and closed in hinge axis position, it is possible to locate a

centre of rotation - the transverse hinge axis. He went on to question whether

the hinge axis position was the correct maxillomandibular relationship, but

231

since fixed occlusal restorations made to this position had functioned

satisfactorily he concluded it was a physiologically acceptable position.

In a further paper (Brotman 1960) he showed mathematically that if the hinge

axis interocclusal records were made at relatively small degree of opening (not

more than 5mm) and if the maxillary model was not far from its correct

position relative to the hinge axis (not more than 5mm), the maximum error

introduced by closing the articulator to occlusal contact would be the number

of mm of articulator close (from the vertical dimension at which the lower

model was mounted) multiplied by the error in the hinge axis location (in mm)

and divided by 100. He concluded that there was no simple way to determine if

the maxillary model had been improperly related to the hinge axis of the

articulator. The only way to avoid or reduce errors was to use a hinge bow, a

suitable articulator. and a precise technique.

Further work by Lucia (1960) supported opinion held previously. He said that

although he jaw could open and close in a hinge manner, it was not a normal

movement, but one that patients could be taught. The centre of this movement

could then b reproduced on the articulator. Lateral movements of the mandible,

he also stated, had centers in the condyles on the hinge axis. When these

centers were located on an articulator. all the patients' mandibular movements

could be very easily duplicated. The method of findings these rotation centers

was described.

Cohen (1960) described an instrument he had devised to train patients to open

and close the mandible in a hinge manner. The position of the condyle when

this movement occurred was not a retruded position or a forced position but a

position when the condyles were seated in the glenoid fossa as far posteriorly

as they would go by their own muscular power. This position but a position

when the condyles were seated in the glenoid fossa as far posteriorly as they

would yo by their own muscular power. This position was centric relation.

232

Cohen further stated that once the hinge axis points had been located and

marked permanently it was never necessary lo repeal the procedure since the

anatomic structures they represented never changed during life. The following

benefits were derived from a hinge axis record;

1. Study models could be mounted to determine if the patients own centric

occlusion was in harmony with centric relation

2. Working models could be mounted in the best relationship for the teeth

or denture bases.

3. The vertical dimension could be increased or decreased on the instrument

tt ithout disturbing centric relation.

A later article by McCollum (1960) reviewed early work on the hinge axis.

discussed his personal investigations (including the development of an

articulator). and commented upon the hinge axis and mandibular movements in

detail.

Lauritzen & Bodnre (1961) used fifty patients to determine variations in

hinge axis location when compared with arbitrary methods. They found that

their method of hinge axis location gave 67% of the points at a distance of 5 -

13mm from the arbitrary points. When the arbitrary centre was changed to an

area of 5 mm radius. ony76% of the hinge axis locations were within this.

Trapozzano & Lazzari (1961) discussed the opinions of workers such as

Komfield( 1955). Granger (1952. 1954). Sloanc (1951). Collett (1955) and

Kurth and Feinstein (195 I) during the report of their studies into hinge axis

determination. In view of the differences of opinion they decided to re-

examine two problems (i) whether there was a terminal hinge, and (ii) if there

was whether or not only one existed. The investigators located what they

thought to be the terminal hinge axis is fourteen subjects, but left the final

233

decision to a group of neutral observers. They found that 57.2% of the subjects

had more than one condyle hinge axis pint on cither one or both sides and

concludcdihat the high degree of infallibility attributed to hinge axis points

should be seriously questioned. It is interesting that this conclusion differed

somewhat from early statements made by Trapozzano (1955) concerning the

hinge axis.

This work was followed up by the same investigators (Trapozzano and Lazzan

1967) when they again found the presence of multiple hinge axes. They also

thought it essential that the technique of hinge axis location should be

undertakes by two operators; one to observe the opening and closing of the

mandible and the other to examine for rotation or translation of the stylus.

Relaxation of the patient during hinge axis determination was also considered

essential. Any alteration in vertical dimension was contra indicated unless a

new interocclusal record was taken because of the presence of more than one

hinge axis. The investigators also confirmed what had been stated often, viz.

they found a number of hinge axis points along tracings of condylar inclination

which showed that rotation could occur in protruded positions of the mandible.

Using a modified hinge axis locator, with two styli, they also found that both

styli remained stationary on a hinge axis during opening and closing. Since it is

not mathematically possible fora rotating body to have two different axes of

rotation at the same time, these results of Trapozzano and Lazzari (1961,

1967) must throw doubt on the accuracy of hinge axis location as it is practiced

today.

The subject of transographics appeared again when the secretary to the Mid-

states Odonto-occlusal symposium (Slavens 1961) asserted that there was no

single, inter condylar transverse axis common to and passing through both

condylcs. He said that articulation methods based on such assumptions usually

lead to poor results and that the Transograph was the only articulator to

234

duplicate essential jaw functions accurately, according to views expressed in

the symposium.

Schweitzer (1961) used still and motion picture photography to study

masticatory function. One of his findings was that posterior border or hinge

closure about the transverse axis in the condylcs did not appear to be reached in

functional chewing when viewed in the sagittal plane.

LauriUcn and Wolford (1961) carried out experiments on apparatus they had

designed to determine the accuracy of hinge axis location. In so doing, they

hoped to reduce errors in the machining, which Borgh and Posselt (1958) had

found had affected their results. A number of operators of differing

backgrounds carried out hinge axis locations on the apparatus, each person

having five attempts.

Group I were all people unfamiliar with the technique and they used 10 degrees

of mandibular opening. Group 2 were dentists who had seen hinge axis

locations carried out and had some slight experience of the technique. They

also used 10 degrees of opening. Group 3 were members of a study group

experienced in hinge AXIS location. They used the same degree of opening,

then 15 degrees of opening, and finally 5 degrees of opening- They found that,

of the 190 locations, all were within an area of diameter no longer than 1.5 mm.

and three were in an area of diameter greater than Imm. In the first group, 40%

of the locations were within an area of 0.2mm. in the second group 57% were

within an area of 0,2mm,and in the third group (10 dearees of opening) more

than 95% were within 0.2mm. With the latter group the same results were

obtained at !5degreesof opening for hinge axis location (with experienced

operators). With 5degrees of opening it became much more difficult to locate

thecorreel point but nevertheless 75% of the locations of group 3 were within

0.2mm of ihe axis. These results, where mechanical errors were reduced as

235

much as possible, were an improvement of 7% over Borgh and Posselt's (1958)

results and 4°/ over the results of Kurth and Feinstein (1951).

De Pietro (1963) stated that the only rotational centre which could function

independently in mandibular movement were the horizontal centers of rotation.

In a limited degree of mandibular opening, the condylar element, owing to the

limiting effect of the inferior surface of the glenoid fossa and the

temporomandibular ligaments, could brace itself superiorly and posteriorly and

thereby enable the horizontal centres of rotation to be located. Kurhter opening

led to translation as well as pure rotation which gave rise to different

instantaneous centers of rotation. He considered that, since rotational centers

did exist in mandibular movement, if they could be located in their natural

environment the possibility of a mechanical device «hich could simulate

mandibular movements was feasible. Much of De Pictro"s work was carried

out on an isolated mandible however, and as such this is nothing more ihan a

mechanical device.

Hickey et al(1963) used a pin inserted directly into the condyle and pin

attached to the lower incisors teeth for comparison when using motion picture

photograph} to record mandibular movements. Although they did not

deliberately locate the transverse axis of rotation of the mandible on the subject

under invesiigation. they found that during hinge opening the condyle pin

remained in a fixed position and rotated 5 degrees while the incisor pin moved

downwards 18mm without lateral deviation, and posteriorly 9mm. A lateral

deviation of 2.5mm occurred as the mandible reached its maximum opening.

The centre of rotation for the arc made by the incisor pin during the retruded

opening was not in the region of the condyle. They thought that the small

deviations over the tracing of the incisor pin during hinge opening may have

resulted from the irregularities of the surfaces of the cond>le and the disc as

rotation between the two surfaces occurred.

236

Aull (1963) published a paper in which he described four main schools of

though regarding the hinge axis.

1. The absolute location of the hinge axis school, as practiced by Lucia (1953).

McCollum(1939. 1943). Granger (1952. 1954) etc;

2. The arbitrary axis school as practiced by Graddock and Symmons (1952)

3. The non believers, such as Beck (1959). who thought the axis to be

theoretical) possible but not practically acceptable;

4. The split hinge axis school who believed in the transgraphic theory, such as

Stevens (1961).

Aull performed experiments to show the relative accuracy of the method used

to locate the terminal hinge position and demonstrated the fallacy of the split

axis theory. A simple but effective idea was to use two sets of flags and two

styli. Once set was positioned near each condyle and the other set was

positioned 4-5 includes normal way. Holes were drilled through the flags at the

rotation centers after the apparatus had been removed from the patient) and it

was then found to be possible to shine a light which passed through all four

holes. The points of all four styli also corresponded to a piece of elastic

stretched through all four holes. A colleague of Aull made a model of the lower

jaw with a Meccano set and showed that even when the axes were at different

levels there was still one common axis line through which the "mandible"

opened, even though this was not in the sagittal plane bul was at an angle to it.

La Pera (1964) stated; 'The hinge-axis expresses a relation of border

movements which involve or include the limits of all physiologic movements.

The hinge axis represents to the occlusal vertical dimension what the needle

point tracing docs to centric relation. He stated that there was no great

difference between human hinge axis movements and those of ihe articulator.

237

The hinge axis is though to be key to jaw movements. Once this had been

determined, its relationship to the anatomic elements of articulation could help

in the understanding of the physiology of the lemporomandibular joint. A

distinction was made between the kinematic hinge axis and the inter condylar

axis, the latter being above and in front of the former.

Schweitzer (1969) was of the opinion that hinge axes did exist and that it was

possible to locate them using a hinge bow. He disagreed with the idea that the

hinge axis was constant to the mandible and accompanied it no matter what

position the mandible assumed in function. He thought that translating

condyles had constantly changing axes once they left the hinge position. With

regard to articulators, he said that 'semi adjustable' ones and simple techniques

in his hands gave results equally as satisfactory as those obtained with fully

adjustable articulators and more complex techniques.

Long (1970) described an intra oral technique for locating he terminal hinge

axis by using two accurate centric relation records at two different degree of

jaw separation. Criticizing this paper, Naylor (1970) stated; they also claim thai

a trained hinge movement is possible and that the patient can be trained to keep

the condyles stationary in the fossae during rotation of the mandible. This is not

true.' He explained this by stating that a fixed axis of rotation could not change

its position in relation to a rigid body.

Ramfjord and Ash (1971) stated that hinge axis movement in the

tcmporomandibular joint could occur, theoretically, ai varying degrees of

protrusion, but that reference was usually made to the stationary hinge axis

movement with the mandible in centric relation. The relrusive opening

movement around the terminal hinge axis could be performed only to about 20-

25mm of anterior opening. Although the posterior part of the temporal muscle

held the jaw back during such movement. the pattern could also be duplicated

by manipulation of the jaw provided the patient was relaxed and pain or

238

muscular dysfunction was absent. This position of the mandible which gave a

hinge opening was also called by them centric relation, terminal hinge position,

or retruded contact position. Since it was determined by the ligaments or

structures of the temporomandibular joints, it could also be called the

ligamentous position. For this centre of rotation and mandibular movement

path to be constant and reproducible, they said that the condyles had to be

sealed against the menisci within he glenoid fossae. This assumed normal

function of the ligaments and jaw muscles. They also pointed out that

continued opening below the limit of hinge opening would lead to the centre of

rotation changing to a position slightly behind the mandibular foramen as the

condyies moved downwards and forwards.

Knap, Espinoza and Ziebert (1973) carried out studies to

1. Compare the hinge locating range as seen on a sagittal tracing plate with

the clinical hinge locating range as observed at the hinge bow stylus point:

2. To determine the amount of clinical hinge locating range that was lost by

the use of the closed occlusal clutch;

3. "To calculate and analyse the actual distance of the hinge locating range at

infradentale.

They stated that the optimum range available using a closed occlusal clutch and

metal flags attached to the maxillary rod was 12.5mm; the optimum hinge

locating range available using a closed occlusal clutch and graph paper

attached to the skin was 3.4 mm and the amount of hinge locating range

occupied by the closed occiusal clutch at infradentale was 5.2mm.

Rani (1973) made a comparison of the biomechanics of the human masticatory

muscles using a stationary axis of rotation located at the centre of the condyte

and a moving instantaneous centre of rotation.

239

Yohn (1974) used cinefluorography lo determine a new anatomical reference

point on the skin surface which could be used when transferring maxillo-

mandibular relationship to an articulator. However, the determination of this

position was made when the teeth were in the position of centric occlusion and

this could lead to error if this position did not coincide with centric relation.

Smith (1975) compared three methods of determining centric jaw relation to

determine which would consistently register the most retruded position, how

much variation there was between the methods, and the clinical significance of

this variation. The three methods compared were the terminal hinge axis.

Gothic arch apex, and an empirical method. He concluded that the empirical

method gave a centric relation point anterior to that of the other two methods,

and that the Gothic arch apex and the terminal hinge axis gave substantially the

same position. Te gothic arch method was the most precise and the empirical

method the least precise.

HiHoowala (1975) was the opinion, based on his radiographic studies, that

hinge movement took place in the upper compartment of the temporomadibular

joint as well as in the lower compartment.

Weinberg (1975) reported at length on his radiographic investigations into

temporomandibular joint function. The results of studies on a small group of

patients showed that, wiih half of them, condylar translation occurred during

hinge opening. This casts doubts on the validity of such recordings.

Rentier and Lau (1976) described a method of overcoming some of the

problems associated with hinge axis location on edentulous patients, such as

the resiliency of the soft tissue and the instability of clutches.

Jaarda, Clayton and Myers (1978) stated that, historically, the terminal hinge

axis has been ihe cornerstone of pantography as used in dentistry. The said that

the hinge axis of the articulator must be a duplicate of the hinge axis of the

240

patient otherwise there could be no mechanical reproduction of jaw motions.

The purpose of their study was to determine if the use of the terminal hinge

axis in transferring the pantograph to the articulator resulted in statistically

different cusp pathways and differences in ridge and groove direction and cusp

height who compared to the use of an arbitrary hinge axis. They used a linear

variable differential transformer mounted within a Denar D5 articulator to

measure cusp pathways. The studies were carried out on two patients and

showed statistically different cusp pathways when compared with the use of an

arbitrary hinge axis.

Preston (1979) discussed the history and development of the hinge axis

concept, particularly in relation to collinear and non collinear theories. He

outlined research which he had carried out on himself which showed

colineariiy of the contra-lateral styli in only four out of nineteen valid

measurements.

Winstantey(1979) carried out experiments to determine the accuracy of hinge

axis location using clinical methods on articulator. He found errors occurring

up to an area 2.4mm in diameter, although most results were most accurate. An

opening of 15 mm in the anterior region of the articulator gave better results

than I Omm opening.

Walker (1980) carried out 444 hinge axis locations in an attempt to correlate

the true hinge axis with various arbitrary or average locations. 1 le concluded

that an arbitrar> hinge axis does not exist, that any average position chosen

may lead to an inaccuracy of 6mm or more, and that very few individuals have

the same true hinge axis points on both sides of the face.

Razek (1981) determined the reliability of five methods used to locate the

arbitrary hinge axis when compared with compared with the kinematic hinge

241

axis. Although he thought none of ihe methods ideal, he found that palpation

gave resuils closest as the kinematic location.

Beard and Clayton (1981) carried out experiments to ascertain the reasons for

the discrepancy between the results of Trapozzano and Lazzari (1961. 1967)

(that more than one terminal hinge axis exists) and those of Aull (11963) (thai

only one lerminal hinge axis exists). They used improved recording apparatus

which they said eliminated some of the errors in previous work caused by

visual perceptions and concluded that there is online terminal hinge axis.

Lupkiovicz SM, Gibbs CH, Mahan PE, Lundccn HC, Ariet M, Sinkewiz

S14I982) This study investigated irregularities in hinge movement in 113

subjects.

These irregularities were analyzed by computer with an instantaneous three-

dimensional "screw1 axis method." The variation in hinge movement was

measured by ihe dispersion of the hinge axis instant centers. Dispersion of

instant centers was greater for muscle pain patients than for the normal,

indicating that instant center data could make a contribution to diagnosis and

treatment planning.

Gordon SR, Stoffer WM, Connor SA(1984) Incorrect location of the terminal

hinge axis of 5 and 8 mm to the anterior, posterior, superior, and inferior was

examined. With jaw relation records 3 and 6 mm thick at the incisors, the errors

in cusp height at the second molar ranged from 0.15 mm open space to 0.4 mm

excess height. The mesiodistal error ranged from 0.51 mm toward the distal to

0.52 mm toward the mesial. While the mesiodistal component to the error has

been calculated in the past with some accuracy, the values obtained have varied

because different anatomic dimensions were used. In addition, the vertical

component of the error in cusp height as illustrated in Fig. 2 was not considered

and/or not subjected to in-depth calculation.

242

Tsao DH(1986) On the basis of Newtonian principles of applied mechanics,

rotation around the mandibular hinge axis has been explored by separating this

rotation from translation of the mandibular hinge axis. After quantitative

comparison, it appears that hinge rotation is the primary physiologic movement

of the mandible, and that the Hanau qutnl provides compensatory factors in

facilitating hinge jaw movement. However, an unguided opening and closing of

the mouth usually consists of rotation and translation that are six-dimensional

in nature and very difficult to solve quantitatively without idealization and

differentiation. With an accurate three-dimensional image-measuring system,

such as computerized axial tomography, it should be possible to apply this

hypothesis clinically.

Abdal-Hadi L0989) A proposed arbitrary method of recording the hinge axis

based on the correlation between the profile width of the face and the kinematic

axis was compared with three commonly used arbitrary methods. The

investigation was carried out on 5 I individuals. The kinematic point was

recorded by the use of a kinematic locator. The different points of emerging

axes were photographed at a fixed distance by using a magnification

photoapparatus. The proposed method showed a regular distribution around the

kinematic axis. Furthermore, ihis method clearly illustrated that its highest

concentration was in the posteriosupcrior quarter around the true axis. The

proposed technique was found to be more accurate than the other techniques.

Vustin DC, Ricger MR, McGuckin RS, Connelly ME(1993) This study showed

that opening dynamics of the mandibular condyle could be studied by cine-MR|

and that an opening hinge axis appears to be located in the anatomic center of

the ccnd\lar head.

243

Degrees of freedom optoelectronic jaw movement recording system OKAS-3D

was used to record open/close movements in 10 asymptomatic subjects and 30

subjects with a clicking joint. Movement paths of the hinge axis and the

kinematic axis were calculated. A t-test was used in the analysis of the

locations of the two condylar movement reference points. Variances between

the values of the hinge and the kinematic axes were compared with the F-test.

Locations of the hinge axis and the kinematic centre on the average did not

differ significantly for the asymptomatic subjects at the group level (P>0. 05).

while individually the locations differed 4.96 mm on the average. The

difference between the hinge axis and the kinematic axis was significant for the

group of subjects with clicking joints (P<0.01), with the average individual

level difference of 9 mm. Variances differed significantly between the

coordinates of the hinge and the kinematic axes between the two groups of

subjects (P<0. 01). The study shows the importance of the choice of a condylar

movement reference point for the study of condylar movements and suggests

the use of the kinematic centre in such studies.

Hatzi P, Millstcin P, Maya A(20Gl):

STATEMENT OF PROBLEM: It has been reported that articulators are

interchangeable, which means that a clinician should be able to use one

articuiaior and send casts to a dental laboratory with the assurance that the casts

will be remounted with positional accuracy on a similar articulator. PURPOSE:

The purpose of the study was to determine whether mounted casts could be

transferred from 1 articulator to another with positional accuracy and whether

the hinge axis was reproducible in each of the articulators tested. MATERIAL

AND METHODS: This study compared left and right second premolars and

first molar occlusal contact areas with respective contact areas of like-mounted

casts. Five calibrated Whip Mix 3040, 5 calibrated Girrbach Artex AL. and 5

calibrated KaVo Protar articulators were tested, impact-resistant resin casts

244

mounted in occlusion on I articulator were transferred to 4 like articulators.

Each of the 5 articulators of each brand was opened and closed 10 times. Ten

vinyl polysiloxane right and left posterior interocclusa! records of the occluded

casts were made for each articulator. The use of a computerized image analysis

program provided quantitative measurements of light transmitted through the

occlusal records. A Kruskal-Wallis test was used for each of the 4 independent

variables of the study (molar differences, premolar differences, left differences,

right differences). By using a calibrated grid, a numerical assessment of

positional changes was made in millimeters. RESULTS: None of the articulator

systems was found to be exact, and no single articulator was an exact duplicate

of another (P<.01). The Whip Mix articulator showed greater deviation both in

hinge axis repeatability and in articulator interchangeabilUy than the KaVo.

The Artex articulator provided the most consistent hinge axis repeatability and

interchangcability of the 3 brands of articulators. CONCLUSION: The Artex

brand reproduced dental cast positions more consistently than the other

articulators tested.

CENTRIC RELATION

Philip Pfaff et al in 1756. the dentisl of Frederick the Great of Germany, was

the first to describe this technique of "taking a bite". This is known as the

"mush", "biscuit", or "squash" note.

Christenscn in 1905 was one of the early authors to use "impression wax" for

"bite" records.

In 1910, Greene described a mush bite made from modeling compound in

which he used a plaster wash to achieve a more accurate record.

Functional records were described in dental literature as early as 1910. Greene

used pumice and plaster mixture in one of the rims and instructed the palient to

grind the rims together. The denture teeth were set to the generated paths.

245

In 1923, Hanau wrote. "The most naive of our geniuses had intuitions, molded

into metal, attached a decorative theory onto their accomplishment and. it must

be admitted, they found a goodly number of fanatical believers and blind

followers, whose mental inertia probably did not care to penetrate even the

polish of the nickel-plated instrument under consideration.

In 1927, Hanau concluded that the Gysi tracing was satisfactory to check

records, but that universal usage was not good.

In 1929, Slansbery introduced a technique, which incorporated a curved plate

with a 4-inch radius (corresponding to Monson's curve) mounted on lhe upper

rim. A central bearing screw was aitached to a lower plate was injected to a

lower plate with a 3-inch radius curve (reverse-Monson curve). After the extra

oral tracing was made, plaster was injected between the plates to form a

biconcave centric registration. Hall (929) used Stanbery's method but

substituted compound for the centric relation record.

Kingery, R.H. in 1952 concluded that there are many excellent methods or

techniques all of with are capable of producing acceptable results. However,

the criteria for final acceptance of their accuracy, 1 feel, are and always will be

dependent upon the honesty, judgments and intelligent vision of the operator.

In 1954, Brown recommended repeated closures into softened wax rims.

Greene had his patients hold their jaws apart for 10 seconds to fatigue the

muscles and then had them snap the rims together. He then made lines in the

rims to orient them after removal from the mouth.

Shildkraut's paper was strongly criticized by Rinchuse (1955) who believed

CR and CO are like apples and oranges and, thus, not comparable. He wrote in

this regard, the Shildkraut et al. Article appears to be an ill-founded attempt to

relate a lot of nonsense of orthodontic diagnosis. Shildkraut believed that,

assuming CR and CO are different in all patients, this is not indicate of TMD or

246

any other problem in orthodontic diagnosis. Richuse objected to the idea of CR

mourning in orthodontics and believed that gnalhology in a thing of the past

that should not be applied to the principles of orthodontics.

Uinchusc (1955) had an opposing view again, and repeated his claim that these

two positions are not comparable and thus, the basis of the study is flowed. Me

summarized is criticism as follows "Because the study by Dr. Utt is descriptive

rather than experimental (Longitudinal/Prospective) or observational (cross-

sectional/retrospective), it must have a "sound" theoretical basis. I found the

basic premise for this study faulty. Furthermore, the methodology of this study

is tenuous. In addition 1 am still not certain what Dr Utt's study was about.

Since he did not directly define CR and CO. I do not know for sure what was

actually recorded and measured in the study.

Hodge and Mohan (1967) investigated the mandibular movement between

what we call today CR and CO even though the title of the study was "A study

of mandibular movement from CO and Ml". One hundred and one adults were

examined to determine whether there were any CR-CO slides and, in the

presence of a slide, the extent and direction was measured. It was found that

almost half the subjects did not have either antero-posterior or vertical

mandibular movement from CR to CO. As for lateral movement. 15 subjects

showed this component of movement.

Atwood D.A. in 1968 said that there still is a need for a simple terms with

describes the jaw relation in with the teeth, joints, ligaments and muscles are in

functional hormones and the teeth are in maximal occlusion.

Glickman 1 el al in 1974 concluded that "two complete fixed prosthesis built

with the occlusion in centric relation and with occlusion in the subjects existing

centric occlusal position were tested with telemetry under conditions of actual

use. The findings indicate that the subject did not use the centric relation

247

position but accepted the prosthesis built to her pre-existing centric occlusion.

These findings were consistent with their previous results of telemetric studies

conducted on patients with 3 unit fixed prosthesis.

McNamara and Henry (1974) titled their study "Terminal hinge contact in

dentitions", although the aim was to investigate the number of tooth contacts in

CR and CO. Cephalometric radiography was used to compare the positional

differences between CR and CO qualitatively. Eleciromyography was also used

to compare muscle contraction between the two positions. A positional

difference between CO and CR was demonstrated in all 15 subjects. However,

temporal and masseter muscle activity during maximal isometric contraction

did not differ significantly at these two positions.

One of the most often quoted studies in the field of CR-CO is by Glickman et

al. (1974). In this study a completely reconstructed, natural dentition was

studied under conditions of actual function to determine which of the two

occlusal relationships the patient used during chewing and swallowing. Multi-

frequency radio transmitters were constructed and inserted into the pontics of

full mouth restorations. Two fuil mouth restorations were made for the patient,

one in CO and the other in CR. Telemetric testing with the patient chewing and

swallowing was performed and the resultant tooth contact patterns were

recorded before ad after preparing the restorations. They found that the

prosthesis with intercupsalion in CR did not alter the tendency for tooth

contacts to occur in the patients CO. The patient had difficulty in achieving Ml

when allowed to close freely with the prosthesis designed to inter cuspate in

CR. They concluded that the use of the terminal hinge (the term 'lerminal hinge

position' was used as a synonym for CR in this study) in oral rehabilitation is

subjected to question since it appears that the patient would not function in this

position. It was suggested that the use of CR as a reference position is doubtful

because ihc distance to the existing CO position is variable and unpredictable.

248

Shafagh I. et al in 1975 conducted a study to investigate diurnal changes in

centric position within a period of one day. They made the following

conclusion, a. Sequential registration of centric position was exactly repcatable

in a few patients, but for most, a dispersion pattern resulted which varied

among individuals. The greatest variability registered at the level of condyles

was mostly supero-inferior, with little mediolaieral variability. There was no

single time of minimum variability common to most subjects.

b. in many subjects, records obtained in the morning showed the most antero

inferior position of the condyles and these made at night showed the most

postero-superior positioning the condyles. This indicates that centric relation

follows a diurnal rhythm with might be due to varying shapes and varying fluid

content of the temporomadibular joint.

c. If the most retruded and superior position of the condyles is desired, the

evening seems to be a belter time for making centric relation to records.

This study supports the theory of incorporation of some degree of freedom in

centric position in prosthetic restorations. It appears conceivable that diurnal or

periodicity analysis of centric relation will open a new dimension in dentistry

and prosthodontists.

Guichet, N.R(1977) in his study of biological lows governing functions of

muscles that move the mandible has drawn following conclusions.

Many factors, other than the proprioceptive inputs originating from occlusal

contacts on teeth, program jaw position and ihe functions of the muscles that

move the mandible. However, once the mechanisms by which specific occlusal

contacts program specific muscle functions in clearly understood, it becomes a

relatively simple matter to make an accurate diagnosis and select the most

direct approach io treatment.

249

Azarbal (1977) compared three occlusal positions; CR. CO and Myo-monitor

positions. Bxtra-oral clutches were used io compare the three positions antero-

posteriorly and laterally. The study indicated that the Myo-monitor position

was almost always anterior and lateral to CR and CO. The author rejected the

use of the Myo-monilor as a suitable method for jaw positioning because the

method was not capable of locating the jaw as far posteriorly as possible.

Today such a conclusion based on these findings cannot be drawn.

Williamson, E.H. in 1978 conducted laminar graphic study of mandibular

condyle position when recording centric relation and concluded that "the

condyles to be significantly more superior in glenoid fossae when anterior

guidance was used. The difference in antero-psoterior positioning of the

condyles appeared to occur randomly

Guichet N.F. in 1978 staled that

a. A model to quantify muscle response to occlusal contacts is useful in

developing an under standing of the mechanisms by with the occlusion

programs muscle function. Knowledge of how occlusion programs muscles

function enables the dentist to develop manipulative skills of the mandible with

are necessary for diagnosis and effective occlusal treatment.

b. The character of the occlusal surfaces of the teeth programs the functions

of muscles that move the mandible and imposes specifications upon the dentist

with in with he must work in manipulating the patient's mandible. If he exceeds

those specifications, protective responses that inhibit his efforts are elicited in

the patient's musculature.

Numerous studies have reported that the majority of patients with a natural

definition show a discrepancy between the occlusal position of the mandible in

CR and MI (Posselt. 1952; Hodge and Mahan 1967; Rieder, 1978). This

discrepancy is present in least 90% of dentitions, and Posselt (1952) indicated

250

(hat the antcro-posterior distance between the retruded (now CR) and the ICP

position was about i .25 mm (+ 1.00) on average. This discrepancy was found

to remain constant even following successful orthodontic treatment. In

children, the distance was smaller (0.85 +0.6 mm).

Rieder (1978) authored an epidcmiological study of 323 adult patients to find

the prevalence and amount of mandibular displacement from retruded contact

position (RCP) (CR) to inter cuspal position (IP) (CO). Direct clinical

measurements revealed that 86% of the subjects had mandibular displacement

from CR to CO in one or more directions of movements. All of the patients

with mandibular displacement demonstrated a vertical component or

movement, nearly as exhibited an anterior component, and a third showed

lateral movement.

Rosner and Goldberg (1986) designed a study to investigate three-dimensional

difference between CR and CO. A custom made Buhnergraph on a Whip-mix

articulator was used to indicate the differences. Records of 75 patients

indicated that 60% of the CO records were placed anterior and inferior to CR.

There was no CO marking on the posterior superior quadrant suggesting that

CO is unlikely to be posterior and superior to CR.

G. Newell wood in 1988 discussed a physiologic clinical approach to

developing an optimum mandibular posture and clinical methods of recording

this posture when rehabilitating complete occlusion. Its theme is stabilization

and education before registration.

Shildkraut et a) (1994) were among the orthodontists who strongly believed

that hand held articulated casts used routinely in orthodontic treatment planning

should be replaced with the so called proslhodontic mounting with face bow

and CR records. They also criticized the use of conventional lateral

cephalometric radiographs for orthodontic diagnosis because such radiographs

251

are taken with the patient in CO. They commented that cephalomelric

radiographs should be transferred to CR radiographs and the treatment planning

and tracing of the radiographs be based on the modified CR radiographs. They

designed a study to determine if there was a significant difference between 24

cephalometric measurements of mandibular position derived from a CO tracing

compared with those of a converted CR tracing. They hypothesized that:

providing statistically significant differences exist between CR and CO, this

could affect the diagnosis and treatment planning necessary to correct the

malocclusion. A radiographic conversion method, devised bySlavicek (1988)

was used to modify CO cephalometrics. A SAM articulator and mandibular

position indicator was used to indicate the differences in the models. CR and

CO tracing on radiographs were also compared by computer soft ware. It was

found that mandibular positions were significantly different between a CO

tracing and the same tracing converted to CR. The condyle was always

vertically displaced and most often positioned distally when the teeth were in

CO. It was concluded that, to avoid errors in diagnosis, treatment plans should

be formulated from lateral cephalograms that have been convened to CR.

Later, Rolh (1995), Williams (1995a, b). Carter (1995), Chubb (1955), Hew

(1966) and Alpern (1996) defended Utfs position and emphasized that a

requirement in orthodontics is the necessarily of accurately mounted study

casts. Williams said; there is no way you can evaluate condylar position and

functional occlusion without the use of an articulator. I challenge any one on a

clinical level to disprove that statement. The academicians must get their heads

out of the scientific clouds and come back, to reality. The fact that one is astute

at doing research does not makes one a good clinician. In fact it is usually the

opposite. That is why they are in research.

252

INCISAL GUIDANCE

Clyhde H. Schuyler in 1963 staled "in the hands of most demist, complete oral

rehabilitation can be more satisfactorily accomplished by functionally

generated path technique than by the use of complicated articulating

instruments. It can be accomplished in less time with fewer problems and

failures and with less strain on the patient and the dentist. The coordinating of

the occlusion is recognized as one of the most important and most complicated

facts of practice of dentistry. Many articulating instrument and techniques have

been confusing to practicing dentists less complicated procedures for

developing occlusal coordination add to the pleasure and happiness of both

patient and demist.

Robert R. Scaife J.R in 1969 from the results of this study, it can be said tha the

natural occurrence of a cuspid protective mechanisms is relation large (57%)

but by no means over whehningly predominant. Thai it occurs in the majority

of subject studied would indicate that this type of occlusion is ideal. The huge

(91.5%) number of subjects with cuspid contact in CO. would be a negative

factor in the decision of the idealism of a cuspid protected occlusion, if in fact

proprioceplor abilities our lost through continuous contact. The faceting

statistics seem to be favorable to the cuspid protection theory,

J. Marvin Reynolds in 1971 proposed an occlusal pattern which organizes the

teeth to permit group function as well as mutual protection. The main load to

centrically related jaw closure is borne by the posterior teeth. The anterior teeth

protect the posterior teeth in centric closures. The incisors, canine or posterior

teeth mav function in dependent of each other. All the teeth remain just outside

the routine functional arena of cyclic motions. The muscles are permitted to

move the condyles to an> position in the joint compartment in eccentric

occlusal positions without guidance or interference from the teeth.

253

Timothy..]. O' Lealy in 1972 stated, "The mobility of teeth was assessed in 30

ma.\i11ar> quadrants of each of two groups of subjects. One group had a

cuspid-protected type of occlusion in the test quadrants of each of two groups

of subjects.

One group had a cuspid-protected type of occlusion in the test quadrants while

the second group had a group function type of occlusion. The mean mobility

was higher in the presence of a cuspid protected occlusa! pattern for each type

of tooth. The difference was statistically significant for the maxillary first

premolars. the first molar, and over all mean of the seven tooth types studied.

D. Blake. M.C.Adam in 1976 concluded

1. Tooth loading with cuspal guidance in canine and group function occlusions

has been discussed.

2. Canine guidance and group function guidance occlusion are considered

normal; the latter occurs naturally due to occlusal wear.

3. When an entire occlusion is to be restored, either occlusal scheme will serve

adequately.

4. Where only a portion of the occlusion is to be restored, the restoration must

be consistent with existing occlusal scheme.

5. Regardless of with occlusal scheme is used, the dentist must maintain it

during regular post operative appointments.

Arthus Edward Kahn in 1977 stated. "Organized disclusion by the canines

should find the canines paired in proper rotated stances so that in any of the

possible movements of laterotrusion. the tip of the lower canine engages the

mesial groove of the upper canine. In effect, this means that a cl.-I centric

relation occlusion is requisite to such a rotated stance of the canines; other

254

wise, wear of the teeth may occur. Thus, the importance of properly executed

orthodontics in the preservation of stomatognathic system becomes critically

apparent.

Walter Donald Heinlein 1980 The lack of more specific instrumentation in

rebuilding anterior teeth still leaves much to the individual dentist in making

value judgements. However, this apparent failing is the same reason that makes

this part of resloram e dentistry so exciting.

Torster Jemt and Jundquist in 1982 concluded that the chewing pattern may

be influenced by the type of occlusion irrespective of the existence of maxillary

canines

E.H. Williams in 1983 stated that only when posterior disclusion in obtained

by an appropriate anterior guidance can the elevating activity of the temporal

and masseter muscles be reduced. Further, it is not the contact of the canines

that decreases the activity of the elevator muscles, but the elimination of

posterior contacts.

Shoji KoKuo in 1987 concluded that "The inclination of the sagittal incisal

path, with is transferred to the incisal table of an articulator as anterior

guidance, should be equal to the inclination of the patients condylar path. It is

of course possible to make the incisal. Path steeper then the condylar path to

some extent; however, it should not be more than 25°steeper. Similarly the

incisal path should not be much flatter than the condylar path.

Sumiya Hobo in 1991 concluded that molar disclusion is determined by the

cusp shape factor and the angle of hinge rotation. A new twin table technique

has been introduced for developing molar disclusion by use of two incisal

tables. It is relatively in complicated technique and does not require special

equipment. The final prosthesis by use of the twin tables techniques results in a

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restoration with a predictable posterior disclusion and anterior guidance in

harmony with the condylar path.

256

FUNCTIONALLY GENERATED PATH

By Fredrick S.Mcycr (195?) This article discussed the use of the generated

path technique in FPD construction. If all procedures have been completed

correctly. the finished fixed partial denture will fit the dies on the aniculator

with no tension or distortion. It will fit the patient's moulh in a similar manner,

and correct balanced occlusion and function are insured.

By William L. McCrackan, (1958) It is not expected that the silver plating of

a wax occjusal record will receive wide acceptance because of the added step

of electroplating. Bui just as there are those who prefer to work with

electroformed dies. So there may be some who would prefer to set teeth to an

initial template. It is hoped lhai this procedure will contribute something

toward better RPD occlusion.

Robert G. VIG (1964) A technique has been described by which the patient

chews in a centric record of his own jaw movement in gliding and masticatory

mandibular excursion. The technique is most advantageous for the construction

of complete dentures against natural or mixed dentitions. The technique, with

modifications, is of value in numerous partial and immediate denture situation

in which articulator movements can not duplicate natural movement with in a

range of movements and harmony that is with in the accommodative ability

limits of the patient.

Fred S. Meyer (1954) We believe that any one can use it with equal success. It

requires no special skills. It will work in any man's hands.

Clyde H. Schuyler (1959) functional coordination of the occluding surfaces of

the tceih has been spoken of as one of the most important sciences in the

practice of dentistry. The incisal guidance, and is normally the inclination.

257

RECORDING VERTICLE DIMENSION

In 1771, Hunter wrote "In the lower jaw. as in all the joints of the body, when

the motion is carried to its greatest extent, in any direction, the muscles and

ligaments are strained and the persons made uneasy.

In 1906, Wailisch described mandibular rest position an that position of the

mandible where in alt muscles action is eliminated and the mandible is

passively suspended. I le reported that in this positive the opposing teeth do not

contact.

In late 1920's Sichcr and Tandlcr restated the role of the musculature in

controlling the posture of the mandible. They stated, "the rest position of the

articulation, the "middle position" is that in with the mandible is at a slight

distance from the maxilla.

In 1946, Thomson reported on the cephlometric analysis of the rest position in

edentulous and semiedentulos adults. He stated that the rest position was stable

and that it could not be permanently altered by prosthetic restorations.

However, in 1954 Thompson, somewhat qualified his earlier statement of the

immutability of the mandibular rest position of a given individual. He

recognized that the rest position is related to the variation in tonicity of the

involved musculature.

Farhad Fayz in 1958 concluded that the variations in the measurements of

different teeth conformed the anatomic individuality of each patient.

Nevertheless the finding of this study will be helpful as guides in the initial

placement of the maxillary and mandibular anterior teeth and in the initial

determination of the vertical dimension of occlusion of the lingual surfaces of

six upper anterior teeth, might be considered an the key to a harmonious

functional relationship of the natural dentition or the key to functional

258

occlusion and finally roentgenogram of TMJ should be made. Some badly

disorganized occlusal problems present as abnormal positioning an a very

necessary protection for the dentist of discomfort and complication should arise

following a complete oral rehabilitation

Boucher (1959) The registration of closing force with the Boss Biometer

cannot be classed as an objective method for determining vertical dimension.

Yahia H. Ismail (1968) The roentgcnographic cephalometric investigation

done to evaluate the swallowing technique for determining the occlusal vertical

relation in edentulous patients. The findings are

1. The occlusal face height after prosthetic treatment showed an increase

ranging between 0 and 5 mm. with a mean increase of 2.8mm, as compared to

occlusal face height before the extraction of teeth. This increase was

statistically significant.

2. A significant co-relation was found between the number of posterior teeth

missing before extraction and increase in occlusal face height as determined by

the swallowing technique after the patient becomes edentulous.

The swallowing technique presented a direct approach to the problem of

establishing the occlusal vertical dimension in edentulous patients

Allyn G. Wagner (1971) The rest method, based on natural relaxation to be an

acceptable method to determine the rest position, because the measurements

presented less high and low reading. The M. M. M method tended the produce

a large rest vertical dimension and the swallowing method a smaller one. The

instability of ihe mandibular rest position was of similar magnitude for all of

the methods tests .

A.J. W. Turrel in 1972 concluded that many methods of assessing and

recording vertical jaw relation in edentulous patients have been presented and

259

evaluated. When no accurate pre-extraction records exists, the dentist must rely

upon esthelic appearance supplemented by aids with an after misleading.

Sidney I. Silverman(1985) concluded that ; dentist measure the anticipated face

height of a patient when a mandibular trial base and occlusion rim simulating

the form of finished denture is placed in the mouth wiihout a maxillary trial

base and occlusion rim. This measurement can be an appropriate guide for the

vertical dimension recorded lo generate a trial arrangement of prosthetic teeth.

SUMMARY

Objective of treatment

Having decided that a mouth requires the full treatment, what is our objective?

All these patients have one problem in common: stress and strain. Usually the

stress and strain is due to malfunction or to poorly related parts of the oral

mechanism. Occasionally, undue stress and strain on the oral mechanism is the

result of an emotional disturbance. Whatever the cause, whatever the reason,

the common denominator seems to be stress. Our problem, then, resolves itself

into one of minimizing these stresses so that, they are not destructive. The

stresses should fall within'the capability of the tissues to withstand them and

maintain a state of health. To accomplish this objective to the fullest degree

possible, it is essential to have an intimate knowledge and a very clear

understanding of the masticatory mechanism, of certain principles and forces. It

requires knowledge of how the oral mechanism is built and how it functions. If

excessive stresses are involved, we must reduce or minimize them so that they

will not be destructive. Granted that the muscles of the oral mechanism can

exert a certain amount of force, in order to prevent this stress from being

destructive the best thing to do is to distribute it evenly over as great an area as

possible: over as many teeth as possible, over the ternporomandibular joints,

over as much tissue as possible, and over as many cells as possible. This

260

approach makes sense. A given force distributed over as great an area as

possible reduces the stress per unit so that it can be tolerated by the tissues.

Aging tissues may not be able lo withstand the same stress as younger tissues.

This is why a malfunction is frequently tolerated at a younger age. Our

problem, then, becomes one of how best to distribute this given force or stress.

The oral mechanism consists primarily of the ternporomandibular joints, the

teeth and their supporting structures, and the muscles of mastication. We arc

concerned with the joints and the supporting structures. The teeth are the

means by w hich the stresses are going to be directed or transmitted. We know

from our anatomy and physiology that the temporomandibular joint is a siress-

bearing joint know \hat the supporting structures (bone) of teeth are designed to

withstand stress. Our objective is to distribute these stresses equally between

the joint, tissues and the supporting structures. Teeth will be the means by

which the forces are distributed.

Harmony of form and function

The tcmporomandibular joint has a definite pattern of function. If, in the

execution of this pattern of function, the teeth interfere, there is a clashing of

stresses in the mechanism. This will be true whether the stress is used to

masticate food or just to. "Punctuate" a swallow. If the tooth contact is not in

harmony with the temporomandibular joint pattern, then the entire stress or the

greatest part of it will be transmitted through the poorly related tooth to its

supporting structures. It may be more than those cells can endure. It would be

much better to have the tooth contact its antagonist at the same lime the

temporomandibular joint is in its best bracing position so that the force could

be evenly distributed between the supporting structures of the tooth and the

temporomandibular joint. Therefore, in centric closure (patients exert the

greatest force in this position) all the upper and lower posterior occlusal

surfaces should come together simultaneously. In addition, ideally, the cuspal

261

design would be one with a tripod arrangement. This stabilizes teeth by putting

stress in the long axis of each tooth where it is best resisted. The anterior teeth

barely come together in this position (centric closure). In all other positions,

when teeth are in contact, only the anterior teeth come together for incision.

The posterior teeth are discluded. preventing any rubbing of posterior occlusal

surfaces. Thus, the anterior teeth protect the posterior teeth in the excursions,

and the posterior teeth protect anterior teeth in centric closure.

The question frequently asked is: "Why do you need cusps?"

The main reason we need cusps is to be able to stabilize the teeth in the long

axis. Only with cusps is it possible to have tripodization, that is, a cusp making

contact with the sides of a fossa in opposing directions when in centric

occlusion. If this is properly done, in most cases, it is possible to avoid the

necessity for splinting weak teeth. However, the cusps must be correctly

placed. This brings up another often asked question: "Why do we heed the

accuracy of a pantograph tracing if teeth disclude in the excursions?"

Disclusion does not mean missing by several millimeters: ideal disclusion is

the passing of cuspal elements close together without rubbing. The cuspal

elements should operate like the blades of a pair of scissors -very efficiently

without self destruction. This means that the cuspal elements must be very

carefully placed. In order to correctly place the cusps, we must know the

character of the individual's jaw movements, and the most accurate method of

capturing and duplicating an individual's jaw movements is by use of the

pantograph and a fully adjustable articulator that will reproduce the jaw

movements. A very minor dividend to all the effort involved in restoring the

occlusal surfaces is that they look like natural teeth

In cases where there are no end teeth in the arches and removable restorations

must be used, it is very important that every effort be made to continue to

262

distribute the stress over as great an area as possible. This is accomplished by

means of mucostatic bases and well-articulated chewing surfaces. Rather than

putting additional stress on the already endangered abutment teeth, it may be

possible to give some stability'to weak teeth by using a good removable

denture. The use of precision attachments helps to minimize the strain on

abutment 'teeth. A mucostatic base is the only means by which a removable

case can be kept in proper function for any length of lime.

Wherever feasible, fixed bridges are preferable to removable bridges. The

possibility of maintaining an equal distribution of stress is greater with fixed

work than with removable: the distribution can be maintained longer with less

adjustment.

Method of Treatment

We must be able to treat the entire mouth at one lime to manipulate all the

chewing surfaces at the same time so that they can be the true mates they were

intended to be. "At the same time" does, not mean in an interval of hours, days,

or weeks: it means that before anything is completed, we would be able to

adjust or alter any of the surfaces if necessary. Extreme skill is necessary if

total treatment is to be accomplished by the quadrant dentistry method. Very

careful equilibration of the existing occlusion must be completed first. This

may be difficult to expedite, because teeth shift, making it necessary to repeat

the procedure several times. Then each quadrant of dentistry must be perfectly

executed. When all four quadrants are completed, further equilibration is

usually necessary. Any adjustment in the mouth is difficult and cannot be

accomplished as accurately or as easily as on an articulator.

The patient's temporomandibular movements must be accurately recorded and

duplicated in minute detail. This is tantamount to having the patient's head to

work on in the laboratory without the distracting factors of saliva, cheeks, and

263

tongue. Some dentists attempt to accomplish this directly in the mouth, but this

is almost an impossible task.

Before the preparations are made, it is necessary to determine which cusps are

essential and approximately where they will be located. This is extremely

important because it will influence the type of preparations to be used. How the

teeth interdigitate will determine whether full coverage or onlays are indicated.

Of course, onlays are by far the best choice. The veneer materials available

today arc a poor substitute, for nature's enamel and will never take its place.

The best-made restorations that are adjacent to gingival tissue can only be

irritants. However. sometimes the amount of cusp warpage that is necessary

will produce too great a display "of gold. In these cases, a compromise may

have to be made whereby we will resort to full coverage with its drawbacks.

The practical treatmenl of a case necessitates ihe completion of all the

preparations of the teeth involved. Usually this cannot be accomplished at one

sitting; nor should it be done thai way. So. we have to construct temporary

restorations for each quadrant as we proceed. When all four quadrants are

prepared, the master impressions are taken, and these casts are accurately

related to the articulator by means of a face-bow and a centric interocclusal

record. The prepared teeth will have the exact relation on the articulator that

they have in the patient's mouth. Quadrant impressions are taken as each

quadrant is prepared, and the quadrant casts made from these impressions will

be used for fina! margin and contact adaptation of the wax patterns. The

temporary restorations are usually made of good scrap gold and are in one

piece for easy handling during their frequent removal and insertion. Splinted

together, they also tend to maintain the status quo in the interim required for

laboratory procedures.

264

Because of improvements in our techniques and materials, it is now possible to

temporize most cases with acrylic splints -either processed or auto

polymerized.

An articulation is developed in wax on the master casts on the articulator. The

characteristics of ihe articulation will be a harmonious arrangement of the

occlusal surfaces mat will follow the movement of the temporomandibular

joint. The anterior teeth -overbite and over-jet will be coupled with the

posterior occlusal surfaces. Ihe wax patterns will be separated, transferred to

the quadrant dies, and the margins adapted. The patterns will then be cast in

hard partial denture gold and prepared for trial in the mouth.

Regardless of how carefully and accurately we work or think we work, these

castings are far from the finished product that the patient will wear. The errors

incorporated in cutting the wax patterns and transferring them to individual

dies, the investing and casting errors, the material errors -all add up

unbelievably. It therefore becomes necessary to correct the restorations before

they can be worn, liach restoration is carefully fitted to each tooth and lo each

other restoration. After the restorations have been fitted satisfactorily, we do a

"remounting," This means that accurate casts containing the restorations are

placed on the articulator in the same relation that they had in the mouth. This

step is accomplished by means of a face-bow transfer and a centric

interocclusal record. The restorations are the carefully adjusted until they

exhibit the same characteristics and relation to each other as the wax patterns

on the master casts. When this has been accomplished, the restorations are

ready to be worn temporarily by the patient.

There are several reasons for temporary wearing of the restorations, i lealing of

the supporting structures of periodontally involved teeth will frequently

produce a slight change in the positions of the teeth (and their restorations).

Malfunctioning joints often heal after proper function, with the result that there

265

is a slightly different relationship. Patients, after overcoming long-imposed

neuromuscular patterns of malfunction, will more readily give us accurate joint

relationships. If the restorations are temporarily cemented, they can be removed

without difficulty for slight adjustments to perfect the case. One needs but a

single experience of having to cui out a permanently cemented case to be cured

of being has in permanently cementing restorations! In very bad pcriodontal or

joint cases, it is often necessary have half a dozen remountings over a period of

several years before real success can be achieved.

Splinting -A Last Resort

Temporary restorations are splinted together both for convenience in handling

and because this tends to maintain the status quo.. In contrast, permanent

restorations are almost never splinted. Experience has shown that splinted teeth

never respond to treatment so quickly nor so well as individual restorations do

(provided the articulation is correct). There is one exception to this rule: only

after repeated efforts at stabilizing the teeth by means of individual restorations

have failed may we, as a last resort, solder these restorations in a splint. We

recognize this as a tlnal resource and a definite compromise, something to be

undertaken when it is the only way to maintain the teeth for a while longer. It

is never the ireatment of choice. When splinting is routinely used, it is only a

"cover-up" or a compromise for improper articulation.

Periodontal Therapy

Full mouth rehabilitation is performed to produce a healthy, esthetic, well-

functioning, self-maintaining masticatory mechanism. It is often necessary to

institute good periodontal therapy to produce a healthy oral mechanism.

It is possible to eliminate pockets by periodontal therapy (conservative and/or

surgical). However, unless the function is corrected, pocket-free teeth can still

bounce around during function. Complete pocket elimination is less important

266

than stability in function. Experience has shown that pockets do not necessarily

get worse if not complete!) eliminated, provided that proper function is

established. Nevertheless, pockets should be carefully treated by frequent

curettage and adequate home care.

If the periodontal condition is not severe, it usually can be taken care of at the

time of tooth preparation. Curettage, electrosurgery, and even slight bone

contouring nay be performed when a quadrant is anesthetized for tooth

preparation.

When more sophisticated therapy is necessary and is to be performed by a

periodontist. cooperation by the prosthodontist is advantageous. The teeth can

be partial!) prepared and temporarily splinted. The periodontist can remove the

splint and do his or her periosurgery with greater ease and obtain better results.

After healing, the preparations are finalized. When the soft tissues are healed

and all the teeth prepared, then the reconstruction can be completed. When the

ultimate ideal is sought, definitive periodontal therapy should be protected by

definime occlusal therapy such as gnathology. However, bear this in mind:

unless the patient exercises diligent home care after treatment, even the best

therapy will fail.

267

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