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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

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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).

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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."

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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

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• 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

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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.

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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.

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• 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.

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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

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• 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.

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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

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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).

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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)

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• Bidez and Misch evaluated the effect of a cantilever on an implant and its relation to crown height.

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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.

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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

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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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surgical techniques

• block onlay bone grafts

• particulate bone grafts with titanium mesh or barrier membranes

• Interpositional bone grafts,

• distraction osteogenesis

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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

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• 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)

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• 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

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• 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

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• 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.

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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).

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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."

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• 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).

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• 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

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• 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.

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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

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• 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).

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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.

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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

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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

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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.

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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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