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This lecture is about Occlusion.

The reference for this script was the record of the lecture.

Occlusion

Occlusion is a force transmitted to the oral structures via muscles to the teeth, this force is in the form of load → functional load because it’s associated with direction which is not always axial. ( axial direction of load is the most preferable type of force application).

Factors affecting occlusion:

-Structures in the oral cavity resist these forces to prevent their damage, so the healthier the teeth and periodontium were the better the resistance is.

-The direction, frequency and magnitude of the applied force

-The number of contacts: the number of teeth available in the oral cavity that make contact with an opposing tooth.

*The dentist needs a balanced view on occlusion so that the patient can have a balanced occlusion.

*Physiological occlusion doesn’t necessarily mean ideal occlusion, it depends on the adaptive capacity of the patient himself. there may be one or two criteria deviated from ideal but the patient still can function and be happy with the esthetics of his teeth. If these non-ideal things are beyond the adaptive capacity of the patient then problems start to appear.

The masticatory system is composed of:

1- teeth

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2- the articulatory system ( TMJ, muscles and occlusion)

3- the periodontium ( gingiva, bone, periodontal membrane) .

* all elements of this system are related to each other and controlled by nerves through neuromuscular control or neural pathway feedback.

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TMJ

MusclesOcclusion

This is the articulatory system :-

1)TMJ represents the hinge.

2) Muscles of Mastication are the motors, they are the parts responsible for the motility ( the ability to move) of the other two parts.

3)Occlusion represented by the contact between teeth.

It’s a system as well because all the elements are interrelated.

Temporomandibular Joint:

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Disk Attachments

Mandibular Fossa

Articular eminence

Articular Disk

Lateral Pterygoid

Mandibular Condyle

Muscles of mastication:

Muscle Origin Insertion Nerve Supply ActionMasseter Zygomatic

archLateral surface of the ramus

Mandibular division of Trigeminal nerve

Elevates mandible to occlude teeth

Temporalis Floor of temporal foosa

Coronoid process

Mandibular Division of Trigeminal nerve

*Ant.+sup. Fibers elevate the mandible.

*Pos. fibers retract the mandible

Medial Pterygoid(two heads)

Maxillary tuberosity and lateral pterygoid palte

Medial surface of the angle of mandible

Mandibular Division of Trigeminal nerve

Elevates the mandible

Lateral Pterygoid(two heads)

Greater wing of sphenoid and lateral pterygoid plate

Neck of mandible and articular disk

Mandibular Division of Trigeminal nerve

Pulls the neck of condyle forward to protrude the mandible.

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Occlusion:

Static Dynamic

→ Static occlusion: when the mandible is contacting the maxilla and they are stationary

( not moving).

→ Dynamic occlusion: when the mandible and maxilla are moving together against the

surfaces of teeth.

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Static Occlusion :

- Centric occlusion

- Centric relation

- Freedom in centric

- Overbite

- Overjet

- Cusp to fossa contact

- Cusp to marginal ridge contact

Dynamic Occlusion:

-Protrusive and Retrusive movements

-Lateral or excursive movements

- Envelope of motion

Centric occlusion: maximum intercuspation of teeth, contact between upper and lower

jaws when teeth are maximally intercuspating, irrespective of the position of the

condyle.

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Static Occlusion

* Other terms for it: intercuspal position, bite of convenience, habitual bite ( because

the patient is habituated to bite in this position, and it is a functional (convenient)

position because most of the teeth are intercuspating together).

* It is the most easily recorded bite.

* Functional forces are applied axially not obliquely.

* Contact on posterior teeth is usually heavier than on anterior teeth.

* to know that you have stable occlusion, you should see a tripod: two contacts

posteriorly and one contact anteriorly.

Centric Relation : The position of the condyle in relation to the maxilla in which it’s in the uppermost anterior position, the muscles are least restrained and the disc is relaxed in its place.

*So, it doesn’t depend on teeth but on the position of the condyle and status of muscles, it’s a bone to bone contact.

*It’s the most reproducible position that’s why it’s used for edentulous patients.

* when you try to manipulate the jaw of a dentate patient to achieve centric relation,

after the first tooth contact happens ( which is not necessarily the same as centric

occlusion) , the patient shifts to centric occlusion because he can’t function on one or

two teeth only and needs maximum intercuspation for function to happen.

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Sometimes when you are dealing with a partially edentulous patient with no posterior

support, you need to do deprogramming for the muscles which will keep resisting you

every time you try to manipulate the jaw to record the centric relation, this is done by

letting the patient bite on a piece of cotton roll or green stick for a few minutes until the

muscles become strained and relaxed then you manipulate the jaw easily to centric

relation position.

Freedom in Centric (long centric) :

*does centric relation equal centric occlusion?

Only 10% of people have them coinciding together , 90% of people have a difference of

1-2 mm between them.

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In figure (a) the cusp tip is interlocked between the two fossae , and there is a deep bite in the anterior region. So, here there is no freedom in occlusion.

In figure (b) the cusp is not interlocked and the anterior teeth have a space between them which allows some sort of movement . So ,here there is freedom in occlusion.

*Freedom in centric occlusion occurs when the mandible is able to move anteriorly for a

short distance in the same horizontal and sagittal plane while maintaining tooth contact.

** Mandibular Movements**

1- Centric relation: occurs in static occlusion.

2- Eccentric relation ( excursive movements): occurs in dynamic occlusion.

Overbite : vertical overlap between upper and lower anterior teeth.

Overjet: horizontal overlap between upper and lower anterior teeth.

Cusp to fossa contact: when the cusp tip contacts the fossa . It’s one tooth to one tooth contact. ( figure B)Cusp to marginal ridge contact: when the cusp tip contacts the marginal ridge. It’s one tooth to two teeth contact. (figure A)

** the functional cusp for upper teeth is the palatal and for lower teeth is the buccal.

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Protrusive , Retrusive , Lateral Movements.

-Protrusive movement: the buccal surface of the lower sliding against the palatal surface of the upper in an anterior direction. When this happens, teeth are in centric occlusion, sliding ,and there’s a space in posterior teeth. ( christensen’s phenomenon)

-Lateral (excursive) movements: moving the mandible to one side ( right or left).

** The side that the mandible moves to is called the working side , the other side is the

non- working side ( balancing side).

** Canine guidance: dynamic occlusion that occurs on the canines during lateral

excursion of the mandible. [When we are moving towards the working side if the

canine contacts only, this is called canine guidance]

**Group Function: the contacts are shared between several teeth on the working side during a lateral excursion. [the patient moves the mandible to one side and more than one tooth ( for example: canine, premolar, mesiobuccal cusp of molar) are contacting.

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Dynamic Occlusion

Canine Guidance.

**In the lever system, when the distance from the center increases, the force

decreases. The center of our lever is the TMJ, so when I put the oblique forces on an

anterior tooth I won’t cause damage as if I’m applying this force on the posterior teeth.

This explains why canine guidance is more preferred than group function. But if the

patient has group function and he’s satisfied with it, we don’t change it for canine

guidance, because it all depends on the adaptive capacity of the patient.

Question: if you want to do a class 4 on a central incisor , what are the things that

you need to assess to decide if you can do it or not?

→ if I have enough space to put a composite restoration, because if the tooth is

broken since a long time ago there may be supra eruption of the opposing tooth.

Envelope of motion

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Group Function

*Movements done to open and close the mandible.

The first act of movement is rotation along an imaginary axis ( terminal hinge axis, or

transverse horizontal axis)

It’s called transverse because it passes through the center of both condyles in the

horizontal plane an it’s the axis where rotation happens.

*After rotation, translation happens and the condyle is going against the surface of

the glenoid fossa along with the disc.

Look at the figure below:-

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**From CR downward to HAT this is rotation ( and here this is not the maximum

opening, only a few mm)→ from that point to MO , the condyle slides over the

glenoid fossa to reach MO (translation)

**from CR→MI ( centric occlusion) there’s 2 mm between them in 90% of people

(the space between them in the figure)→ then I do protrusion ( sliding) to maximum

protrusion MP→ then maximum opening MO→ then closure happens on two

stages: 1- translation (from MO to HAT) 2- rotation ( from HAT to CO)

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These are the same movements:

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CR

CO

Rotation

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Translation →

MO

Edge to edge

Maximum Protrusion

How do we assess the occlusion?

1- Articulating paper , comes in different thicknesses (20,40,60 microns) , we

hold the articulating paper with miller’s forceps, and there should be a dry

field, to obtain good results. (ps. Don’t fold the articulating paper when you

are checking occlusion)

2- Shim Stock: it’s like foil paper ,very thin ( 8 microns thickness) .it doesn’t give you the actual contact points. It shows the contact itself, whether it’s there or not ( for example you use it when you are doing a crown, you check

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Millers forceps with articulating paper.

Mandibular opening from MP→ MO

occlusion with it before and after putting the crown to make sure the occlusion didn’t change)

** Balanced Occlusion: balanced equal contacts on entire arch in centric and eccentric movements, we use it in complete denture fabrication.

Occlusal Interferences:

→Causes:

1-high restoration ( premature contact): it hinders smooth guidance in excursion or closure into centric occlusion.

2-Extraction and migration of teeth.

3-Tooth movement due to migration or periodontal problems.

4-Teeth wear, we don’t have interlocked cusp contact anymore.

5-Overeruption as a consequence and as a cause.

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→Consequences:1- Damage to the teeth2- Fracture of the restoration or the tooth3- Migration of teeth and mobility4- De-cementation of extracoronal restoration5- MIGHT cause TMJ disorders.6- Increased muscle fatigue.7- Tooth Wear.

*** If you are doing a simple restoration (class 1,2..) it’s easier to use centric occlusion not centric relation because it’s the easiest way to record the occlusion( provided that it’s stable) , it’s the most predictable, and the patient has got used to it.

In case of an extensive restoration or where the vertical dimension is changed, that’s a different story.

In the clinic you should follow the IDIC principle , which is:1-examine: examine the patient, check the Occlusal contact before you start.2-Design: design the restoration, the cavity, the restorative material you are going to use.3-execute4-Check

*Neither infraoccluded Nor supraoccluded restoration is good, they will both cause problems to occlusion. You should have a balanced restoration.

**After you are done with a class 4 restoration, what are the movements you ask the patient to do to check occlusion?1- Lateral excursive 2- protrusive 3- Centric

** If you have a heavily restored canine with canine guidance occlusion and you can change it to group function, then it’s preferable to change it.

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This is the end of the script

GOOD LUCK

Nagham Ayman Rabi

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