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Biomechanics of the Edentulous State

Biomechanics of the Edentulous State. Dr Balendra pratap singh BDS, MDS, MAMS, FISDR, FPFA, FAAMP, ICMR-IF Assistant Professor Deptt. of Prosthodontics. Table of content. Support mechanism for natural teeth. Support mechanism for complete denture.

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Biomechanics of the Edentulous State

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  1. Biomechanics of the Edentulous State Dr Balendra pratap singh BDS, MDS, MAMS, FISDR, FPFA, FAAMP, ICMR-IF Assistant Professor Deptt. of Prosthodontics

  2. Table of content • Support mechanism for natural teeth. • Support mechanism for complete denture. • Functional and parafunctional considerations • Changes in Morphological face height and the TMJ. • Esthetic, Behavioural, and Adaptive responses. • Conclusion

  3. Support mechanism for natural teeth • The principal functions of the periodontium are supportand positional adjustment of teeth together with secondary and dependent function of sensory perception and osteogenetic regulation potential.

  4. Soft tissue: PDL +Gingiva Highly organized and oriented. Highly vascularized (three sources). Highly innervated( touch, pain &pressure). Contain elastic fibers. Approximately uniform thickness. Hard tissue: bone+ cementum Cementumresorbs rarely. Bone well vascularized. Normally bone receive tensile loads. Provide excellent medium for PDL attachment. Periodontium as a supporting element

  5. Support mechanism for complete denture Alveolar mucosa • Uneven thickness-thinnest in mid palatal region. • Uneven attachment &resiliency. • Less vasularization & innervations. • Diminished proprioceptive nerve endings. • Reduced elasticity.

  6. Viscoelastic behavior of the 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.

  7. Support mechanism for complete denture Alveolar bone • Receive vertical, diagonal & horizontal loads. • Undesirable and irreversible bone loss.

  8. Concepts of bone loss • As a normal sequalae of loss of PD structure-disuse atrophy. • Not necessary a consequence of tooth loss but depends on a series of poorly understood factors. Local bone resorbing factors-endotoxins from plaque, PGs, OAF etc. Systemic factors include all those that influence the balance b/w normal bone formation & bone resorption.

  9. Factors influencing mucosal support • Total surface area:22.96 cm2 edentulous maxilla 12.25 cm2edentulous mandible 45 cm2 PDL • Tolerance and adaptability:reduced by systemic and metabolic disease. • Masticatory loads:44Ib(20 kg) natural teeth 13 to 16 Ib(6 to 8 kg) complete denture.

  10. Function Parafunction DENTULOUS STATE Tooth support : PERIODONTIUM EDENTULOUS STATE CD 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

  11. Functional and parafunctional considerations • Functional: occlusion mastication& swallowing mandibular movements • Parafunctional: bruxism denture induced

  12. Occlusion The primary components of human dental occlusion: 1- dentition 2- neuromuscular system 3- craniofacial structures

  13. Developing dentition▼ Healthy adult dentition ▼ Deteriorating adult dentition ▼ The edentulous state

  14. Mastication, swallowing & other mandibular movements • Mastication consists of a rhythmic separation and apposition of the jaws and involves biophysical and biochemical processes including lips, teeth, tongue ,palate and all the oral structure to prepare food for swallowing.

  15. Important facts on Mastication 25% masticatory efficiency is adequate for complete digestion of food . Maximal biting force for complete denture wearers is 5-6 times less than natural biting force for complete denture :100N at molar region and 40N anteriorly. Tendency to chew at premolar-molar region.

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

  17. Parafunctions • Parafunctions related to complete denture • Tongue thrusting against denture. • Tendency to occlude teeth frequently. • Strong response of the lower lip and mentalis to lower labial flange • The main problem with the parafunctional habits are that they impose undesirable stresses on underlying mucosal tissues resulting in soreness due to interruption or diminution in blood flow which in turn upsets the metabolism of involved tissues.

  18. WHAT WE CAN DO? • All possible methods should be undertaken to ensure continued tissue health by minimizing the potential traumatic effects of complete dentures.

  19. CHANGE IN MORPHOLOGICAL FACE HEIGHT & TMJ CHANGES • The skeletal growth terminated 20-25y of age. • It is recognized that growth and remodeling continues throughout adult life and such growth accounts for dimensional changes in adult facial skeleton. • TALLGREN,1957 found that morphological face height (MFH)increases with age in persons with intact dentition. • However, a premature reduction in MFH occurs with attrition & abrasion of teeth and this reduction is even more conspicuous in edentulous and complete denture wearing patients.

  20. Any changes in MFH as result of teeth loss are inevitably transmitted to TMJs. • In CD wearers, mean reduction in height of mandibular process in ant.region is 6.6 mm,approx.4 times greater than mean reduction in maxilla. • This reduction in residual ridges tends to cause a resultant reduction in total face height & an increase in mandibularprognathism. • Longitudinal studies and cephalometric observations support the hypothesis that the vertical dimension of rest change throughout life. l

  21. Thus concepts of reproducible & relatively unchangeable maxillo-mandibular relationships may not identically apply to edentulous patients as they do to those with healthy dentitions. However ,the recognition that jaw relations are not immutable does not invalidate the clinical requirement of using CR record as a starting point for developing a prosthetic occlusion.

  22. Centric relation • CR is the most posterior relation of the mandible to the maxilla at the established vertical dimension. • The occlusion of complete denture is designed to harmonized with the primitive unconditioned reflex of swallowing, that is mandatory to prevent disharmonious occlusal contacts. • Centric occlusion position is the most functional and physiologic position for occlusion however it could not be recorded accurately in edentulous subjects. • The coincidence of CR &CO is the proper solution as well. • CR is subjected to change with alteration in face height, and morphological change in the TMJs.

  23. TMJ changes • Most of edentulous patients experience a spectrum variation as a result of mutilated dentition. • In the course of such periods, pathological and/or adaptive structural alterations may take place. • Appearance of cartilage cells and GAG occur as response of additional forces to TMJ by teeth loss. • Continued loading beyond adaptive capability of the articular tissues may lead to osteoarthritis. • TMJ could undergo degenerative joint disease, however other investigators consider it as a process rather than disease entity.

  24. COSMETIC CHANGES ANDADAPTIVE RESPONSES Esthetic changes : • Deepening of the nasolabial groove. • Loss of labiodental angle. • Narrowing the lips. • Increase in columellaphiltral angle. • Prognathic appearance. • Decrease in horizontal labial angle.

  25. Adaptability • Acceptance and usage of dentures require adaptation of learning, muscular skills and motivation. • Learning mean the acquisition of a new activity or change of an existing one. • Muscular skill refers to the capacity to coordinate muscular activity to execute movement. • As a result habituation process occurred.

  26. Habituation is the gradual diminution of responses to continued or repeated stimuli. • The oral cavity is richly innervated which receive various stimuli from the prosthesis as a foreign body. • After repeated stimuli ,the tissue response decrease due to information storage. • The habituation process reduced with advancing age due to progressive atrophy of elements in the cerebral cortex.

  27. The tactile stimuli should be specific and identical to achieve habituation. • Patient’ motivation dictates the speed with which adaptation to denture takes place. • Connection exists between emotional problems and denture problems. • Emotional and psychological factors also should not be neglected.

  28. CONCLUSION • The edentulous state represents a compromise in the integrity of masticatory system ,which is frequently accompanied by adverse functional, behavioural and cosmetic consequences, which are varyingly percieved by the patient. • So, when we are treating edentulous patients, we should take all the aspects into consideration and we should not only treat the patient for his dental condition but we should treat in the terms of totality of the individual.

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