Biomechanics of the Biomechanics of the Edentulous StateEdentulous State

Dr Balendra pratap singh

BDS, MDS, MAMS, FISDR, FPFA, FAAMP, ICMR-IF

Assistant Professor

Deptt. of Prosthodontics

Table of contentTable of content

Support mechanism for natural teeth.Support mechanism for natural teeth. Support mechanism for complete denture.Support mechanism for complete denture. Functional and parafunctional considerations Changes in Morphological face height and Changes in Morphological face height and

the TMJ.the TMJ. Esthetic, Behavioural, and Adaptive Esthetic, Behavioural, and Adaptive

responses.responses. ConclusionConclusion

Support mechanism for Support mechanism for natural teethnatural teeth

• The principal The principal functions of the functions of the periodontium are periodontium are supportsupport and and positional adjustmentpositional adjustment of teeth together of teeth together with secondary and with secondary and dependent function dependent function of of sensory perception sensory perception and and osteogenetic osteogenetic regulation potential.regulation potential.

Periodontium as a Periodontium as a supporting elementsupporting element

Soft tissue: PDL +GingivaSoft tissue: PDL +Gingiva

Highly organized and Highly organized and oriented.oriented.

Highly vascularized Highly vascularized (three sources).(three sources).

Highly Highly innervated( touch, pain innervated( touch, pain &pressure). &pressure).

Contain elastic fibers.Contain elastic fibers. Approximately uniform Approximately uniform

thickness.thickness.

Hard tissue: bone+ Hard tissue: bone+ cementumcementum

Cementum resorbs Cementum resorbs rarely.rarely.

Bone well Bone well vascularized.vascularized.

Normally bone receive Normally bone receive tensile loads.tensile loads.

Provide excellent Provide excellent medium for PDL medium for PDL attachment.attachment.

Support mechanism for Support mechanism for complete denturecomplete denture

Alveolar mucosa Alveolar mucosa Uneven thickness-Uneven thickness-thinnest in mid thinnest in mid palatal region.palatal region.Uneven attachment Uneven attachment &resiliency.&resiliency.Less vasularization & Less vasularization & innervations.innervations.Diminished Diminished proprioceptive nerve proprioceptive nerve endings.endings.Reduced elasticity.Reduced elasticity.

Viscoelastic behavior of the Viscoelastic behavior of the alveolar mucosa alveolar mucosa

• oral mucosa is displaced under load about 10 times more than the periodontium.

• mucosa has less elasticity than the PDL.

• A slower recovery rate to sustained loads.

• Time required for recovery increases with age.

Support mechanism for Support mechanism for complete denturecomplete denture

Alveolar boneAlveolar bone

Receive vertical, Receive vertical, diagonal & diagonal & horizontal loads.horizontal loads.

Undesirable and Undesirable and irreversible bone irreversible bone loss.loss.

Concepts of bone loss Concepts of bone loss • As a normal sequalae of loss of PD As a normal sequalae of loss of PD

structure-disuse atrophy.structure-disuse atrophy.• Not necessary a consequence of Not necessary a consequence of

tooth loss but depends on a series tooth loss but depends on a series of poorly understood factors. Local of poorly understood factors. Local bone resorbing factors-endotoxins bone resorbing factors-endotoxins from plaque, PGs, OAF etc. from plaque, PGs, OAF etc. Systemic factors include all those Systemic factors include all those that influence the balance b/w that influence the balance b/w normal bone formation & bone normal bone formation & bone resorption.resorption.

Factors influencing Factors influencing mucosal supportmucosal support

• Total surface areaTotal surface area:: 22.96 cm222.96 cm2 edentulous edentulous maxillamaxilla

12.25 12.25 cmcm22 edentulous edentulous mandiblemandible

45 45 cmcm2 2 PDLPDL

• Tolerance and adaptability:Tolerance and adaptability: reduced by reduced by systemic and metabolic disease.systemic and metabolic disease.

• Masticatory loads:Masticatory loads: 44Ib(20 kg) natural 44Ib(20 kg) natural teethteeth

13 to 16 Ib(6 to 8 kg) complete denture.13 to 16 Ib(6 to 8 kg) complete denture.

Function

Parafunction

DENTULOUS STATE Tooth

support : PERIODONTIUM

EDENTULOUS

STATECD support :

MUCOSA

Morphological face height& TMJ changes

Cosmetic perceptions & adaptive responses

DIAGRAM OF MASTICATORY SYSTEM SHOWING THE POSSIBLE INTERACTIONS OF ITS COMPONENTS IN THE CONTEXT OF CHANGE IN OCCLUSAL SUPPORT MECHANISM

Functional and parafunctional considerations

•Functional:Functional: occlusion occlusion

mastication& mastication& swallowingswallowing

mandibular mandibular movementsmovements

•Parafunctional: Parafunctional: bruxism bruxism

denture induceddenture induced

OcclusionOcclusionThe primary components of The primary components of human dental occlusion:human dental occlusion:

1-1- dentition dentition

2-2- neuromuscular neuromuscular systemsystem

3- 3- craniofacial craniofacial structuresstructures

Developing Developing dentitiondentition

▼▼

1-development of motor skills& 1-development of motor skills& neuromuscular learning.neuromuscular learning.

2- dental , alveolar, craniofacial 2- dental , alveolar, craniofacial adaptability adaptability

Healthy adult Healthy adult dentitiondentition

▼▼

Deteriorating adult Deteriorating adult dentitiondentition

▼▼

The edentulous stateThe edentulous state

1-dental adaptation (wear, drift, 1-dental adaptation (wear, drift, extrusion)extrusion)

2-bone adaptation is reparative.2-bone adaptation is reparative.

3-learned protective reflexes.3-learned protective reflexes.

1-partial edentulism.1-partial edentulism.

2-periodontal disease.2-periodontal disease.

3-diminished dental reflex 3-diminished dental reflex adaptation.adaptation.

1-residual ridge reduction..1-residual ridge reduction..

2-compromised reflex.2-compromised reflex.

3-increase in parafunctional 3-increase in parafunctional movements.movements.

Mastication, swallowing & Mastication, swallowing & other mandibular other mandibular

movementsmovements•Mastication consists of a Mastication consists of a

rhythmic separation and rhythmic separation and apposition of the jaws and apposition of the jaws and involves biophysical and involves biophysical and biochemical processes including biochemical processes including lips, teeth, tongue ,palate and all lips, teeth, tongue ,palate and all the oral structure to prepare the oral structure to prepare food for swallowing.food for swallowing.

Mastication Mastication DeglutitionDeglutition

• duration per stroke duration per stroke 0.30.3 sec. sec.• 18001800 stroke/ day stroke/ day• occur during mealsoccur during meals•Each thrust is short Each thrust is short duration.duration.•stress transmitted stress transmitted through bolus of food to through bolus of food to the opposing teeth. the opposing teeth. These forces increase These forces increase steadily , reach a peak steadily , reach a peak and abruptly to zeroand abruptly to zero• directed principally directed principally perpendicular to occlusal perpendicular to occlusal plane with some plane with some horizontal component.horizontal component.

• duration is duration is 11 sec. sec.• 500500 times/day times/day• occur at meals & in-occur at meals & in-between ( daytime between ( daytime 400400sec, sleep sec, sleep 8080 sec) sec)• tooth contacts are tooth contacts are usually of longer usually of longer duration than chewing duration than chewing and are fleeting in and are fleeting in nature.nature.• mainly vertical in mainly vertical in direction with slight direction with slight horizontal component by horizontal component by surrounding musculaturesurrounding musculature

Important facts on Important facts on Mastication Mastication

• 25% masticatory efficiency is adequate 25% masticatory efficiency is adequate for complete digestion of food for complete digestion of food ..

• Maximal biting force for complete Maximal biting force for complete denture wearers is 5-6 times less than denture wearers is 5-6 times less than natural biting force for complete natural biting force for complete denture :100N at molar region and denture :100N at molar region and 40N anteriorly.40N anteriorly.

• Tendency to chew at premolar-molar Tendency to chew at premolar-molar region.region.

MANDIBULAR MOVEMENTS

The mandibular movement patterns in denture wearing patients are similar to those with natural teeth .

ParafunctionsParafunctions• Parafunctions related to complete Parafunctions related to complete

denturedenture Tongue thrusting against denture.Tongue thrusting against denture.Tendency to occlude teeth frequently.Tendency to occlude teeth frequently.Strong response of the lower lip and mentalis to Strong response of the lower lip and mentalis to

lower labial flange lower labial flange

• The main problem with the parafunctional The main problem with the parafunctional habits are that they impose undesirable habits are that they impose undesirable stresses on underlying mucosal tissues stresses on underlying mucosal tissues resulting in soreness due to interruption resulting in soreness due to interruption or diminution in blood flow which in turn or diminution in blood flow which in turn upsets the metabolism of involved tissues.upsets the metabolism of involved tissues.

DIRECTION OF FORCE

DURATION AND MAGNITUDE OF FORCE

MASTICATION

Mainly vertical

Intermittent and light.Diurnal only

PARAFUNCTION

Frequently horizontal as well as vertical

Prolonged and excessive. Both diurnal and nocturnal

WHAT WE CAN DO? WHAT WE CAN DO? • All possible methods should be undertaken to ensure All possible methods should be undertaken to ensure

continued tissue health by minimizing the potential continued tissue health by minimizing the potential traumatic effects of complete dentures.traumatic effects of complete dentures.

FUNCTION AND PARAFUNCTION GENERATE

NOT UNDER DENTIST’S CONTROL

PRESSURE =

FORCE *

TIME

CONTROLLED BY:1)ADEQUETE PREPARATION OF SUPPORTING HARD AND SOFT TISSUES.2)COMPLETE DENTURE BASE EXTENSION WITHIN MORPHOLOGIC AND FUNCTIONAL LIMITS.3)REDUCTION OF THE AREA OF OCCLUSAL TABLE.4)USE OF RESILIENT DENTURE BASE LINING MATERIALS.5)DEVELOPING OPTIMAL DENTURE OCCLUSION6)PATIENT INSTRUCTED TO HANDLE PARAFUNCTIONAL HABITS BTHROUGH EDUCATION AND UNDERSTANDING.

CONTROLLED PARTIALLY BY NOCTURNAL TISSUE REST

CHANGE IN MORPHOLOGICAL FACE HEIGHT & TMJ CHANGES

• The skeletal growth terminated 20-25y of The skeletal growth terminated 20-25y of age.age.

• It is recognized that growth and remodeling It is recognized that growth and remodeling continues throughout adult life and such continues throughout adult life and such growth accounts for dimensional changes in growth accounts for dimensional changes in adult facial skeleton.adult facial skeleton.

• TALLGREN,1957 found that morphological TALLGREN,1957 found that morphological face height (MFH)increases with age in face height (MFH)increases with age in persons with intact dentition.persons with intact dentition.

• However, a premature reduction in MFH However, a premature reduction in MFH occurs with attrition & abrasion of teeth occurs with attrition & abrasion of teeth and this reduction is even more and this reduction is even more conspicuous in edentulous and complete conspicuous in edentulous and complete denture wearing patients.denture wearing patients.

l

• Any changes in MFH as result of teeth Any changes in MFH as result of teeth loss are inevitably transmitted to TMJs.loss are inevitably transmitted to TMJs.

• In CD wearers, mean reduction in height In CD wearers, mean reduction in height of mandibular process in ant.region is 6.6 of mandibular process in ant.region is 6.6 mm,approx.4 times greater than mean mm,approx.4 times greater than mean reduction in maxilla. reduction in maxilla.

• This reduction in residual ridges tends to This reduction in residual ridges tends to cause a resultant reduction in total face cause a resultant reduction in total face height & an increase in mandibular height & an increase in mandibular prognathism.prognathism.

• Longitudinal studies and cephalometric Longitudinal studies and cephalometric observations support the hypothesis that observations support the hypothesis that the vertical dimension of rest change the vertical dimension of rest change throughout life.throughout life.

• Thus concepts of reproducible & Thus concepts of reproducible & relatively unchangeable maxillo-relatively unchangeable maxillo-mandibular relationships may not mandibular relationships may not identically apply to edentulous patients identically apply to edentulous patients as they do to those with healthy as they do to those with healthy dentitions.dentitions.

• However ,the recognition that jaw However ,the recognition that jaw relations are not immutable does not relations are not immutable does not invalidate the clinical requirement of invalidate the clinical requirement of using CR record as a starting point for using CR record as a starting point for developing a prosthetic occlusion.developing a prosthetic occlusion.

Centric relationCentric relation• CR is the most posterior relation of the mandible CR is the most posterior relation of the mandible

to the maxilla at the established vertical to the maxilla at the established vertical dimension.dimension.

• The occlusion of complete denture is designed to The occlusion of complete denture is designed to harmonized with the primitive unconditioned reflex harmonized with the primitive unconditioned reflex of swallowing, that is mandatory to prevent of swallowing, that is mandatory to prevent disharmonious occlusal contacts.disharmonious occlusal contacts.

• Centric occlusion position is the most functional Centric occlusion position is the most functional and physiologic position for occlusion however it and physiologic position for occlusion however it could not be recorded accurately in edentulous could not be recorded accurately in edentulous subjects.subjects.

• The coincidence of The coincidence of CR &COCR &CO is the proper solution is the proper solution as well.as well.

• CR is subjected to change with alteration in face CR is subjected to change with alteration in face height, and morphological change in the TMJs.height, and morphological change in the TMJs.

TMJ changesTMJ changes• Most of edentulous patients experience a Most of edentulous patients experience a

spectrum variation as a result of mutilated spectrum variation as a result of mutilated dentition.dentition.

• In the course of such periods, pathological In the course of such periods, pathological and/or adaptive structural alterations may take and/or adaptive structural alterations may take place.place.

• Appearance of cartilage cells and GAG occur as Appearance of cartilage cells and GAG occur as response of additional forces to TMJ by teeth response of additional forces to TMJ by teeth loss.loss.

• Continued loading beyond adaptive capability of Continued loading beyond adaptive capability of the articular tissues may lead to osteoarthritis. the articular tissues may lead to osteoarthritis.

• TMJ could undergo degenerative joint disease, TMJ could undergo degenerative joint disease, however other investigators consider it as a however other investigators consider it as a process rather than disease entity. process rather than disease entity.

COSMETIC CHANGES ANDCOSMETIC CHANGES ANDADAPTIVE RESPONSESADAPTIVE RESPONSES

Esthetic changes :Esthetic changes :• Deepening of the nasolabial groove.Deepening of the nasolabial groove.• Loss of labiodental angle.Loss of labiodental angle.• Narrowing the lips.Narrowing the lips.• Increase in columella philtral angle.Increase in columella philtral angle.• Prognathic appearance.Prognathic appearance.• Decrease in horizontal labial angle.Decrease in horizontal labial angle.

Adaptability Adaptability • Acceptance and usage of dentures Acceptance and usage of dentures

require adaptation of learning, require adaptation of learning, muscular skills and motivation.muscular skills and motivation.

• Learning mean the acquisition of a new Learning mean the acquisition of a new activity or change of an existing one.activity or change of an existing one.

• Muscular skill refers to the capacity to Muscular skill refers to the capacity to coordinate muscular activity to execute coordinate muscular activity to execute movement.movement.

• As a result habituation process As a result habituation process occurred.occurred.

• Habituation is the gradual diminution of Habituation is the gradual diminution of responses to continued or repeated responses to continued or repeated stimuli.stimuli.

• The oral cavity is richly innervated which The oral cavity is richly innervated which receive various stimuli from the receive various stimuli from the prosthesis as a foreign body.prosthesis as a foreign body.

• After repeated stimuli ,the tissue After repeated stimuli ,the tissue response decrease due to information response decrease due to information storage.storage.

• The habituation process reduced with The habituation process reduced with advancing age due to progressive atrophy advancing age due to progressive atrophy of elements in the cerebral cortex.of elements in the cerebral cortex.

• The tactile stimuli should be specific and The tactile stimuli should be specific and identical to achieve habituation.identical to achieve habituation.

• Patient’ motivation dictates the speed Patient’ motivation dictates the speed with which adaptation to denture takes with which adaptation to denture takes place.place.

• Connection exists between emotional Connection exists between emotional problems and denture problems.problems and denture problems.

• Emotional and psychological factors also Emotional and psychological factors also should not be neglected.should not be neglected.

CONCLUSION• The edentulous state represents a The edentulous state represents a

compromise in the integrity of masticatory compromise in the integrity of masticatory system ,which is frequently accompanied by system ,which is frequently accompanied by adverse functional, behavioural and adverse functional, behavioural and cosmetic consequences, which are varyingly cosmetic consequences, which are varyingly percieved by the patient.percieved by the patient.

• So, when we are treating edentulous So, when we are treating edentulous patients, we should take all the aspects into patients, we should take all the aspects into consideration and we should not only treat consideration and we should not only treat the patient for his dental condition but we the patient for his dental condition but we should treat in the terms of totality of the should treat in the terms of totality of the individual. individual.