treatment planning: force factors related to patient conditions chapter6 presented by:dr.ali beygi...
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Treatment Planning: Force Factors Related to Patient Conditions
chapter6
Presented by:Dr.Ali BeygiSupervised by: Dr. Mansour Rismanchian
And Dr.saied Nosouhian Dental of implantology
Dental implants research centerIsfahan university of mediacal science
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Treatment Planning: Force Factors Related to Patient Conditions
chapter6
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Biomechanical stress : significant risk factor in implant dentistry.
dental force factor : risk of stress-related complications
Different patient : different amounts of force in magnitude, duration, type, and direction
several factors may multiply or increase the effect of these other conditions
The initial implant survival, loading survival, marginal crestal bone loss, incidence of abutment or
prosthetic screw loosening, and unretained restorations, porcelain fracture, and component
fracture are all influenced by the force factors.
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NORMAL BITE FORCE The greatest natural forces exerted against teeth, and thus against implants, occur during
mastication
primarily perpendicular to the occlusal plane in the posterior regions, are of short duration, occur only during brief periods of the day, and range from 5 to 44 lb for natural teeth.
time of chewing forces on the teeth is about 9 minutes each day
The perioral musculature and tongue exert a more constant, yet lighter horizontal force on the teeth or on implants .These forces reach 3 to 5 psi during swallowing
A person swallows 25 times per hour while awake and 10 times per hour while sleeping, for a total of 480 times each day.
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• natural forces against teeth are primarily in their long axis, less than 30 psi, and for less than 30 minutes for all normal forces of deglutition and mastication (Box 6-2)
• Forces of mastication placed on implant-supported bridges have been measured in a similar range as natural teeth.
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The maximum bite force differs from mastication force, varies widely among individuals, and depends on the state of the dentition and masticatory musculature
More recent studies indicate normal maximum vertical biting forces on teeth or implants can range from 45 to 550 psi
The forces on the chewing side and the opposite side appear very similar in amplitude
there are conditions that increase our risks of occlusal overload on the implant prosthesis. Most noteworthy are the parafunctional forces of bruxism and clenching
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PARAFUNCTION are characterized by repeated or sustained occlusion
The lack of rigid fixation during healing is often a result of parafunction on soft tissue-
borne prostheses overlying the submerged implant
The most common cause of both early and late implant failure after successful surgical
fixation is the result of parafunction.
complications occur with greater frequency in the maxilla, because of a decrease in bone
density and an increase in the moment of force
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Nadler has classified the causes of parafunction or nonfunctional tooth contact into the following six categories:
1. Local 2. Systemic 3. Psychological 4. Occupational 5. Involuntary 6. Voluntary
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• Local factors include tooth form or occlusion, soft tissue changes such as
ulcerations or pericoronitis.
• Systemic factors include cerebral palsy, epilepsy, and drug-related dyskinesia
• Psychological causes occur with the greatest frequency and include the
release of emotional tension or anxiety
• Occupational factors concern professionals such as dentists, athletes, and
precision workers, as well as the seamstress or musician who develops altered oral
habits
• involuntary movement that provokes bracing of the jaws, such as during lifting of
heavy objects or sudden stops while driving
• Voluntary causes include chewing gum or pencils, bracing the telephone between
the head and shoulder, and pipe smoking.
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Bruxism
Bruxism is the most common oral habit.
horizontal, nonfunctional, significant excess forces
Bruxism may affect the teeth, muscles, joints, bone, implants, and prostheses. These forces may
occur while the patient is awake or asleep and may generate increased force on the system
several hours per day
A study on bruxing patients with implants showed 80% of sleep bruxism occurred during light
sleep stages but did not cause arousal.
rarely have muscle tenderness when they are awake; and are usually unaware of their oral habit.
In other words, nocturnal bruxism is sometimes difficult to diagnose."
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Diagnosis Bruxism does not necessarily represent a contraindication for implants, but it does
dramatically influence treatment planning.
The symptoms of this disorder, which may be ascertained by a dental history, may
include repeated headaches, a history of fractured teeth or restorations, repeated
uncemented restorations, and jaw discomfort upon awakening.
A lack of these symptoms does not negate bruxism as a possibility.
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The signs of bruxism include an increase in size of the temporal and masseter muscles (these
muscles and the external pterygoid may be tender), deviation of the lower jaw on opening, limited
occlusal opening, increased mobility of teeth, cervical abfraction of teeth, fracture of teeth or
restorations, and uncemented crowns or fixed prostheses.
However, the best and easiest way to diagnose bruxism is to evaluate the wearing of teeth
Not only is this the easiest method to determine bruxism in an individual patient, it also allows the
disorder to be classified as absent, mild, moderate, or severe (Figures 6-1 to 6-3).
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No anterior wear patterns in the teeth signify an absence of bruxism.
Mild bruxism has slight wearing of anterior teeth but is not a cosmetic compromise.
Moderate bruxism has obvious anterior incisal wear facets but no posterior
occlusal wear pattern.
Severe bruxism has absent incisal guidance from excessive wear, and posterior
wearing of the teeth is obvious.
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Nonfunctional wear facets on the incisal edges may occur on both natural or replacement
teeth, especially in the mandible and maxillary canines, and there may be notching of the
cingulum in the maxillary anterior teeth.
Isolated anterior wear is not much of a concern if all posterior teeth contacts can be
eliminated in excursions.
Tooth wear is most significant when found in the posterior regions and changes the intensity
of bruxism from the moderate to the severe category.
Posterior wear patterns are more difficult to manage, because this usually is related to a
loss of anterior guidance in excursions; once the posterior teeth contact in excursive jaw
positions, greater forces are generated
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With incisal guidance and an absence of posterior contact, two thirds of The masseter and
temporalis do not contract and, as a consequence, the bite force is dramatically reduced.
posterior teeth contact the bite forces in excursions = during posterior biting.
In severe bruxism, the occlusal plane, the anterior incisal guidance, or both may need
modification
Bruxing patients often repeat mandibular movements, which are different from border movements
of the mandible and are in one particular direction("pathway of destruction“). As a result, the
occlusal wear is very specific and primarily on one side of the arch, or even on only a few teeth
(Figure 6-4).
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This engram pattern usually remains after treatment.
Establishment of incisive guidance on teeth severely affected by an engram bruxing pattern:
complications on these teeth
The most common complications on teeth restored in this "pathway of destruction" are
porcelain fracture, uncemented prostheses, and root fracture.“
When implants support the crowns in the pathway of destruction the implant may fail,
fracture, or have crestal bone loss, abutment screw loosening, porcelain fracture, or
unretained restorations.
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Bruxism changes normal masticatory forces
magnitude (higher bite forces), duration (hours rather than minutes), direction (lateral rather than
vertical), type (shear rather than compression), and magnification (four to seven times normal).
anterior teeth wear + eruption overall occlusal vertical dimension remains unchanged. In
addition, the alveolar process may follow the eruption of the tooth.
As such, when the anterior teeth are restored for esthetics (or to obtain an incisal guidance), the
reduced crown height cannot be increased merely by increasing the height of the crown to
an average dimension.
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Instead, the following guidelines are suggested:
1. Determine the position of the maxillary incisor edge of the anterior teeth
acceptable (if eruption occurred as they wore)
or need greater coronal length to correct related incisal wear.
2. Determine the desired occlusal vertical dimension.
facial measurements, closest speaking space, physiologic rest position, speech, and
esthetics.
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• The accelerated occlusal wear may cause a loss of occlusal vertical dimension (OVD).
• The OVD is rarely decreased when incisal guidance is still present, as the posterior teeth
maintain the dimension and the anterior teeth have time to erupt because the forces are less and
the wear rate is slower.
3. Evaluate and restore the position of the lower anterior teeth where necessary.
In the past, several authors have stated that a reconstruction begins with the lower anterior teeth.
The mandibular arch cannot be restored until the maxillary anterior teeth and occlusal vertical
dimension are established.
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• Incisal guidance must be greater than the condylar disc assembly (the angle of the eminential) so
the posterior teeth will separate during mandibular excursions.
• In patients with moderate to severe bruxism, the height of the vertical overjet and the angle of
incisal guidance should not be extreme, as the amount of the force on the anterior abutments,
cement seals, and porcelain is directly related to these conditions (Figure 6-5).
• In patients with severe bruxism, the intensity of the force should be reduced, because the
duration of the force is increased.
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• When anterior tooth wear is accompanied by tooth eruption and maintenance of the occlusal
vertical dimension , alveolar bone and cervical regions should be reduced and crown
lengthening should be performed on the teeth before their restoration.
• most often necessary in the mandibular anterior region but may be observed in any region of
the mouth after long-term severe bruxism
• endodontic therapy may be required to allow proper anterior tooth preparation.
• when the vertical dimension has been reduced Crown lengthening and associated procedures
are not necessary : The restoration restores the occlusal vertical dimension and reestablishes
anterior incisal guidance.
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4. Determination of posterior plan of occlusion.
This may be accomplished by using first the maxillary arch or the posterior mandibular
arch.
it is best if the same bilateral posterior quadrants are addressed at the same time, so
that the posterior plane may be parallel to the horizontal plane. The maxillary
posterior region is most often determined first in the completely edentulous patient.
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Fatigue Fractures
The increase in duration of the force
fatigue curve
number of cycles and the intensity
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• A bruxing patient is at greater risk of fatigue fractures for two reasons: magnitude of the forces increases over time as the muscles become
stronger number of cycles increase on the prosthetic components.
incisal guidance -
higher forces with posterior contact during excursions,
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elements able to reduce stress
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Occlusal Guards• bruxism and occlusal disharmony
• Premature and posterior contacts during mandibular excursions increase stress
conditions
• elimination of eccentric contacts recovery of periodontal ligament
health and muscle activity within 1 to 4 weeks
• No study demonstrates an increase in parafunction after occlusal adjustment.
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night guard as a useful diagnostic tool
Michigan night guard even occlusal contacts in centric relation occlusion posterior disocclusion with anterior guidance. may be fabricated with 0.5 to 1 mm colored acrylic resin on the occlusal surface.
• After 4 weeks of nocturnal wear, if the patient wears this device for an additional month or more, the influence of occlusion on the bruxism may be directly observed.
• the colored acrylic is still intact : the nocturnal parafunction has been reduced or eliminated occlusal reconstruction or modification may proceed
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• If the colored acrylic on the night guard is ground through, an occlusal adjustment will have
little influence on decreasing this parafunctional habit.
• The night guard is still indicated to relieve stresses during nocturnal parafunction, but the
treatment plan should account for the greater forces
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• If the opposing arch is a soft tissue-supported removable prosthesis, the effects of the
nocturnal habit may be minimized if the patient removes the prosthesis at night.
• night guard and fixed prosthesis : in order to transfer the weakest link of the system to the
removable acrylic device
34
Unlike teeth, implants do not extrude in the absence of occlusal contacts
in partially edentulous patients, the maxillary night guard can be relieved around the implant crowns so the remaining natural teeth bear the entire load.
When the restoration is in the mandible, the occluding surfaces of the maxillary night guard are relieved over the implant crowns so no occlusal force is transmitted to the implants (Figure 6-8).
35
A mandibular posterior cantilever on a full-arch implant prosthesis may also be taken out of
occlusion with a maxillary night guard.
implant supported fixed prosthesis in posterior maxilla opposing mandibular teeth:
a soft reline material is placed around the implant crowns
When full-arch implant restorations are opposing each other, the night guard provides solely
anterior contacts during centric occlusion and mandibular excursions. Thus the parafunctional
force is reduced on the anterior teeth/implants and eliminated in the posterior regions.
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Treatment Planning• The implant treatment plan is modified primarily in two ways when implants are inserted in
the posterior region:
(1) additional implants that are wider in diameter
(2) the anterior teeth may be modified to recreate the proper incisal guidance and avoid posterior interferences during excursions
(opposing natural teeth or an implant or tooth supported fixed prosthesis)
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(1) the elimination of posterior contacts effect of angled forces during bruxism
(2) the presence of posterior contacts during excursions
almost all fibers of the masseter, temporalis, and the external pterygoid muscles contract
place higher forces on the anterior teeth/implants
in the absence of posterior contacts : forces applied on the anterior implant-teeth system are reduced
by as much as two thirds
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Clenching constant force , Without any lateral movement
habitual clenching position does not necessarily correspond to centric occlusion
The jaw may be positioned in any direction before the static load; therefore a bruxing and
clenching combination may exist
The clench position most often is in the same repeated position and rarely changes from one
period to another
The direction of load may be vertical or horizontal
are similar to bruxism in amount and duration; however, several clinical conditions differ in
clenching.
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Diagnosis
the signs for clenching are often less obvious
The forces generated during clenching are directed more vertically to the plane of occlusion, at
least in the posterior regions of the mouth
Wearing : usually not evident; therefore clenching often escapes notice during the intraoral
examination
Many of the clinical signs of clenching often resemble bruxism
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clinical signs of clenching
Tooth mobility muscle tenderness or hypertrophy deviation during occlusal opening limited opening stress lines in enamel cervical abfraction material fatigue (enamel, enamel pits, porcelain and implant components)
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• All these conditions may also be found in the bruxing patient.
• enamel wear has such a strong correlation to bruxism that it is the primary and
often the only factor needed to evaluate or bruxism
• The clenching patient has the "sneaky disease of force."
42
Hyperactive muscles are not always tender
tender muscles in the absence of trauma or disease is a sign of excess use or
incoordination among muscle groups
The lateral pterygoid muscle is more often overused by the bruxing or clenching patient
but is difficult to palpate
The ipsilateral medial pterygoid muscle : antagonist to the lateral pterygoid in
hyperfunction and, when tender, provides a good indicator of overuse of the lateral
pterygoid
43
• Muscle evaluation for clenching also includes :
deviation during opening the jaw, limited opening, and tmj tenderness
• Deviation to one side during opening indicates a muscle imbalance on the same
side
44
Limited opening : muscular imbalance or degenerative joint disease
normal opening : at least 40 mm from the maxillary incisal edge to the mandibular
incisal edge in an Angle's Class I patient ( taking into consideration an overjet or
overlap)
horizontal overjet or overlap value in millimeters is subtracted from the 40-mm
minimum opening measurement
The range of opening without regard for overlap or overjet
38 to 65 mm for men
36 to 60 mm for women, from incisal edge to edge.
45
Increased mobility : force beyond physiologic limits, bone loss, or their combination
The rigid implant may receive more occlusal force when surrounded by mobile teeth
Fremitus is often present in the clenching patient
is symptomatic of local excess occlusal loads.
To evaluate this condition, the dentist's finger barely contacts the facial surface of
one tooth at a time and feels for vibrations while the patient taps the teeth together.
46
• Cervical erosion is primarily a sign of parafunctional clenching or bruxism (Figure 6-10)
Black analyzed the eight most popular theories for gingival ditching of the teeth,
finding all inconclusive.
47
Other signs of enamel or occlusal material fatigue include
occlusal invaginations or pits, stress lines in enamel, stress lines in alloy restorations
or acrylic (lines of Luder), and material fracture (Figures 6-11 and 6-12).
Fremitus can be noticed clinically on many cervically eroded, nonmobile teeth
48
• A common clinical finding of clenching is
a scalloped border of the tongue (Figure
6-13).
• The tongue is often braced against the
lingual surfaces of the maxillary teeth
during clenching, exerting lateral
pressures and resulting in the scalloped
border.
• This braced tongue position may also be
accompanied by an intraoral vacuum,
which permits a clench to extend for a
considerable time, often during sleep.
49
Fatigue Fractures
clenching creep fracture of
components
Creep: increasing deformation related
to constant load
This condition may also occur in bone,
which may result with implant mobility and
failure
50
clenching versus bruxism
Clenching affects the treatment plan in a
fashion similar to bruxism.
vertical forces are less detrimental than
horizontal forces, and alteration of the
anterior occlusal scheme is not as critical
as with the bruxing patient.
Night guards are also less effective. a
hard acrylic shell and softer, resilient liner
night guard, which is slightly relieved
over the implants, is often beneficial to a
clenching patient.
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parafunction in a patient wearing a soft tissue supported prosthesis over a submerged
implant
premature loading micromovement of the implant body compromise
osteointegration.
pressure necrosis causes soft tissue dehiscence over the implant.
prosthesis over the implant should be generously relieved during the healing period
whenever parafunction is noted.
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6-mm diameter hole through the
metal substructure should be
prepared (Figure 6-17).
53
Prosthetic Considerations
progressive bone-loading techniques produce load-bearing bone
Anterior implants submitted to lateral parafunction forces require further treatment
considerations: Additional implants are indicated, preferably of greater diamete
The excursions are canine guided if natural, healthy canines are present.
Mutually protected occlusion : implants are in the canine position or if this tooth is restored as a
pontic
centric vertical contacts aligned with the long axis of the implant
narrow posterior occlusal tables to prevent inadvertent lateral forces and to decrease the occlusal
forces
Enamoplasty of the cusp tips of the opposing natural teeth : direction of vertical force
Clenching increases the risk of mechanical failure, such as porcelain fracture, uncemented
restoration, abutment screw fracture, implant body fracture, and crestal bone loss (Figure 6-18).
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TONGUE THRUST AND SIZE
• A force of approximately 41 to 709 g/cm2 on the anterior and lateral areas of the
palate has been recorded during swallowing
• Six different types of tongue thrust
anterior, intermediate, posterior, and either unilateral or bilateral may be in most any
combination
• A common question is which came first , the aberrant tongue position or the
misalignment of teeth
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force of tongue thrust : lesser intensity than in other parafunctional forces
horizontal in nature and can increase stress at the permucosal site of the implant.
most critical for one-stage surgical approaches : implants are in an elevated position at
initial placement and the implant interface is in an early healing phase.
The tongue thrust may also contribute to incision line opening, which may compromise
both the hard and soft tissues
If the teeth exhibit increased mobility, the implant prosthesis may be subject to
increased occlusal loads
Evaluation of anterior tongue trust
the patient is unable to swallow while the lower lip is withdrawn.
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Evaluation of posterior tongue thrust
The posterior tongue thrust may occur in patients wearing a maxillary denture opposing
a Kennedy Class 1 mandibular arch, without a mandibular prosthesis replacing the
posterior
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lateral tongue thrust :complaint of inadequate room for the tongue once the
mandibular implants are restored
A prosthetic mistake is to reduce the width of the lingual contour of the mandibular teeth
(often increases the occurrence of tongue biting )
The lingual cusp of the restored mandibular posterior teeth should follow the curve of
Wilson and include proper horizontal overjet to protect the tongue during function
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• loss of teeth (Even in the absence of tongue thrust) tongue size increase
• This patient complains of inadequate room for the tongue and may bite it during
function
• usually short-lived
• the patient eventually adapts to the new intraoral condition (Figure 6-22).
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CROWN HEIGHT SPACE• Definition
• ideal CHS needed for a fixed implant prosthesis : 8 - 12 mm
• Includes : biological width, abutment height for cement retention or
prosthesis screw fixation, occlusal material strength, esthetics, and hygiene
considerations around the abutment crowns
• Removable prostheses
• often require greater than 12 mm
• denture teeth , acrylic resin base strength, attachments, bars, and oral
hygiene considerations.
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Biomechanic Consequences of ExcessiveCrown Height Space
Mechanical complication rates for implant prostheses are often the highest
of all complications reported in the literature
Implant body fracture may result from fatigue loading of the implant ,but
occurs at less incidence than most complications.
Crestal bone loss ,often occurs before implant body fracture
Porcelain and occlusal material fracture
Clips or attachment fractures
Fracture of the framework or substructure
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Force magnifiers
• situations or devices that increase
the amount of force applied
and include a screw, pulley,
incline plane, and a lever
• CHS is a vertical cantilever when
any lateral or cantilevered load is
applied and, therefore, is also a
force magnifier • Direction of forces
vertical
contilevered or lateral forces • (direct relationship to the CH)
63
• Bidez and Misch evaluated the effect of a cantilever on an implant and its relation to crown height.
64
A cantilevered force may be in any direction: facial, lingual, mesial, or distal.
Forces cantilevered to the facial and lingual direction are often called offset loads.
edentulous ridge resorption :
more lingual implant facial cantilevered restoration
An angled load to a crown will also magnify the force applied to the implant.
A 12-degree force to the implant will be increased by 20%. This increase in force is
further magnified by the crown height( as in Maxillary anterior teeth that are
usually at an angle of 12 degrees or more to the occlusal)
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Most forces applied to the osteointegrated implant body are concentrated in
the crestal 7 to 9 mm of bone, regardless of implant design and bone
density.
Therefore implant body height is not an effective method to counter the
effects of crown height.
The implant does not rotate away from the force in relation to implant
length. Instead, it captures the force at the crest of the ridge.
66
The greater the CHS, the greater number of implants usually required for the prosthesis, especially in the presence of other force factors.
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crestal bone loss
CHS increases
screw loosening, crestal bone loss, implant fracture, and implant failure
68
69
Excessive CHS
greater than 15 mm
causes may include long term edentulism ,genetics, trauma, and implant failure
Treatment of excessive CHS before implant placement includes orthodontic and
surgical methods.
Orthodontics in partially edentulous patients is the method of choice, as other surgical or
prosthetic methods are usually more costly and have greater risks of complications
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71
surgical techniques
• block onlay bone grafts
• particulate bone grafts with titanium mesh or barrier membranes
• Interpositional bone grafts,
• distraction osteogenesis
72
surgical techniques
• A staged approach to reconstruction of the jaws is often preferred
• Distraction osteogenesis has several advantages
Vertical bone gains are not limited by factors such as graft size or expansion of the
existing soft tissue volume
There is no donor site morbidity
• Distraction osteogenesis requires patient compliance, and bone volume gains are
unidirectional
• secondary bone augmentation procedures are often required for dental implant
placernent.
surgical techniques
73
• Misch presented a unique approach combining vertical distraction and horizontal onlay bone grafting to reconstruct the deficiency threedimensionally. Osseous distraction is performed first to vertically increase the ridge and expand the soft tissue volume. Secondarily an onlay bone graft is used to complete the repair of the defect (Figure 6-29)
74
• In case of excessive CHS, bone augmentation may be preferred to prosthetic
replacement.
• reduce the CHS improve implant biomechanics
• Augmentation wider body implants with the associated benefit of increased
surface area.
• when restoring excessive CHS
gingival colored prosthetic materials (pink porcelain or acrylic resin)
removable restoration
• In the maxilla, a vertical loss of bone results in a more palatal ridge position. As a
consequence, implants are often inserted more palatal than the natural tooth
position.
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removable prosthesis
does not require embrasures for hygiene.
may be removed during sleep to decrease the effects of an increase in CHS on
nocturnal parafunction.
may improve the lip and facial support, which is deficient because of the
advanced bone loss.
may have sufficient bulk of acrylic resin to decrease the risk of prosthesis fracture
76
• A rigid overdenture : identical requirements to a fixed prosthesis, because it is rigid
during function.
• Misch describes the "hidden cantilever" beyond the cantilevered bar with a rigid
implant overdenture.“
• When the overdenture has no movement during function, the cantilever does not
stop at the end of the cantilevered substructure but ends at the last occlusal contact
position on the prosthesis, often the distal of a second molar
• The position and type of overdenture attachments may render an overdenture rigid
during function :when three anterior implants are splinted together and a Hader
dip is used to retain the prosthesis if the Hader clips are placed at angle to the
midline
• angles to the midline limited movement rigid overdenture
77
• Misch suggests the prosthesis movement, not the individual attachment movement,
should be evaluated.“
• The ideal CHS for a fixed prosthesis is between 8 and 12 mm
• 3 mm of soft tissue, 2 mm of occlusal material thickness, and a 5-mm or greater
abutment height.
• a CHS greater than 12 mm may be of concern in fixed restorations.
78
The greater impact force on implants combined with the increased crown height,
creates increased moment forces on implants and risks of component and material
fracture.
These problems are especially noted when associated with less favorable
biomechanics on cantilevered sections of fixed restorations
a CHS greater than 15 mm means a large amount of metal must be used in the
substructure of a traditional fixed restoration to keep porcelain to its ideal 2-mm
thickness (figure 6-31).
79
Controlling surface porosities of metal substructures after casting as their different
parts cool at different rates becomes increasingly difficult.
when the casting is reinserted into the oven to bake the porcelain, and the heat is
within the casting at different rates, so the porcelain cools in different regions at
different rates.“
risk of porcelain fracture
considerable weight of the prosthesis (approaching 3 oz of alloy)
Noble metals must be used to control alloy's heat expansion or corrosion; increases
the costs
Proposed methods to produce hollow frames to alleviate these problems, including
the use of special custom trays to achieve a passive fit will double or triple the
labor costs."
80
• An alternative method of fabricating fixed prostheses in situations of CHS of 15
mm or greater is the fixed complete denture or hybrid prosthesis, with a smaller
metal framework, denture teeth, and acrylic resin to join these elements together
(figure 6-32).
81
• The reduced metal framework compared with a porcelain-to-metal fixed
prosthesis exhibits fewer dimensional changes and may more accurately fit the
abutments, which is important for a screw-retained restoration.
• less expensive, is highly esthetic (premade denture teeth),
• easily replaces teeth and soft tissue in appearance, and is easier to repair if
fracture occurs.
• Because resin acts as an intermediary between the teeth and metal substructure, the
impact force during dynamic occlusal loading may also be reduced.
• hybrid prosthesis is often indicated for implant restorations with a large CHS
82
• On occasion, under contoured interproximal areas are designed by the laboratory in
such restorations to assist oral hygiene and have been referred to as "high water"
restorations.
• This is an excellent method in the mandible; however, it results in food
entrapment, affects air flow patterns, and may contribute to speech problems in
the anterior maxilla.
83
stress reducing options
1. Shorten cantilever length
2. Minimize offset loads to the buccal or lingual
3. Increase the number of implants
4. Increase the diameters of implants
5. Design implants to maximize the surface area of Implants
6. Fabricate removable restorations that are less retentive and incorporate soft tissue support
7. Remove the removable restoration during sleeping hours to reduce the noxious effects of nocturnal Parafunction
8. Splint implants together, whether they support a fixed or removable prosthesis
84
• the greater the crown height, the shorter the prosthetic cantilever should
extend
• In CHS greater than 15 mrn , no cantilever should be considered, unless all
other force factors are minimal.
• The occlusal contact intensity should be reduced on any offset load from
the implant support system.
• Occlusal contacts in centric relation occlusion may even be eliminated on
the most posterior aspect of a cantilever.
• In this way, a parafunction load may be reduced, as the most cantilevered
portion of the prosthesis is only loaded during functional activity (such as
chewing).
85
diagnosis and treatment of bruxism and clenching are in some ways different.
Bruxism and clenching are the most critical factors to evaluate in any implant
reconstruction.
No long-term success will be obtained with severe parafunction of bruxism or
clenching.
This does not mean that patients with moderate and severe parafunction cannot be
treated with implants.
86
MASTICATORY DYNAMICS
• Masticatory muscle dynamics amount of force exerted on the implant system
patient size ,gender, age, and skeletal arch position , muscle mass, exercise, diet,
state of the dentition, physical status
• In general, the forces recorded in women are 20 lb less than those in men.
• The brachiocephalic, with may generate three times the bite force compared with a
regular head shapea
87
The skeletal Class III patient is primarily a vertical chewer and generates vertical forces
with little excursive movement.
However, some patients appear "pseudo- Class III" as a result of anterior bone resorption or
loss of posterior support and collapse of the vertical dimension with an anterior rotation of the
mandible.
These patients do exhibit lateral excursive movements when the incisal edge position
is restored to its initial position
88
masticatory musculature dynamics :
treatment plan should reduce other force magnifiers
cantilever length
crown height by bone augmentation.
The prosthesis may be made removable so nocturnal bruxism is reduced (if they do not
wear their prosthesis).
The implant number, size, and design may also be increased to increase the surface
area of load.
89
Arch position ( position in arch )
• Maximum bite forces in the
anterior incisor region correspond
approximately 35 to 50 psi;
• canine region :47 - 100 psi
• molar area :127 - 250 psi
• bone loss
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• The anterior biting force is decreased in the absence of posterior tooth contact
and greater in the presence of posterior occlusion or eccentric contacts.
mechanical properties of a Class III lever function
Greater contraction of large masticatory muscles
• implants in the posterior regions should often be of greater diameter, especially in
the presence of additional force factors
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the edentulous bone density is inversely related to the amount of force
generally applied in that arch position
The posterior maxilla is the most at-risk arch position, followed by the
posterior mandible, then the anterior maxilla. The most ideal region is the
mandibular anterior.
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OPPOSING ARCH
• Natural teeth transmit greater impact forces than soft tissue-borne complete
dentures
• the maximum occlusal force of patients with complete dentures is limited and may
range from 5 to 26 psi
• A complete implant fixed prosthesis does not benefit from proprioception as do
natural teeth, and patients bite with a force four times greater than with natural
teeth. Thus, the highest forces are created with implant prostheses
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• premature contacts in occlusal patterns or during parafunction on the implant
prostheses do not alter the pathway of closure, as occlusal awareness is decreased
with implant prostheses when compared with natural teeth.
• Partial denture patients may record forces intermediate between that of natural
teeth and complete dentures, depending on the location and condition of the
remaining teeth, muscles, and joints.
• In the partially edentulous patient with implant-supported fixed prostheses, force
ranges are more similar to those of natural dentition, but lack of proprioception
may magnify the load amount during parafunctional activity
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Rarely should the opposing arch be maintained in a traditional denture to decrease the
stress to the implant arch.
Instead, the implant arch should be designed to compensate for the higher stresses
expected from an implant-supported opposing arch (Figure 6-38).
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