biomechanicsofedentulousstate-200719071419 (1).pptx

Gypsum (calcium sulphate dihydrate) is a naturally occurring mineral used in dentistry to fabricate models (Figure 12.1a), casts and dies (Figure 12.1b). Calcination is the process of heating the gypsum to dehydrate it (partially or completely) to form calcium sulphate hemihydrate. Plaster and stone are products of the dehydration process. It is the calcination process that determines the strength of the gypsum material. The differences in the types of gypsum are related to the amount of water removed, resulting in varying densities and particle sizes of the material.

Gypsum materials are combined with water and spatulated to create a slurried mixture that is poured into a dental impression (negative reproduction of the teeth and surrounding tissues). It is allowed to set, after which the gypsum and impression are separated, resulting in the positive reproduction of the patient’s tooth/teeth, arch and surrounding tissues. Many dental appliances and restorations are constructed extra-orally using models, dies (one tooth) and casts (replicas of the patients tooth/teeth and surrounding tissues).

It is desirable that all gypsum products are strong, compatible with impression materials and waxes and fluid at the time of pouring into the impression; they should also have good dimensional stability.

1. Biomechanics Of complete Edentulous State Presented by Mansi Agarwal Under the guidance of Prof.Shaista Afroz

2. Content s Introduction Reasons for edentulousness . Modifications in the area of support. i) biomechanical support mechanism for natural dentition ii) biomechanical support mechanism for complete denture Natural and prosthetic dental occlusion Changes in the morphological face height and tmj Esthetic changes Behaviouaral and adaptive responses Conclusion References

3. The edentulous state represents a compromise in the integrity of the masticatory system. It is frequently accompanied by adverse functional and esthetic sequelae, which are varyingly perceived by the affected patient. Perceptions of the edentulous state may range from feelings of inconvenience to feelings of severe handicap because many regard total loss of teeth as equivalent to the loss of a body part. B Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

4. Causes for Edentulism DENTAL Caries Periodontal Developmental anomalies Cyst, tumours etc NON-DENTAL Education Behaviour Attitude Occupational and financial status Social status Health care system Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

5. BIOMECHANICS AND DENTISTRY

6. The clinical implications of an edentulous stomatognathic system are considered under the following factors: Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

7. Modifications in areas of support N atural dentition Vs Complete denture

8. DENTULOUS vs EDENTULOUS Teeth are supported by the periodontium which consist of the PDL, lamina propria of gingiva (soft), bone and the cementum (hard). Dentures are supported by the residual ridge which consist of the denture bearing mucosa, sub mucosa, periosteum , and the underlying residual alveolar bone .

9. THE RESIDUAL RIDGES The edentulous ridge receives vertical, diagonal and horizontal loads on a much smaller surface area than the periodontium of healthy teeth. There is an undesirable and irreversible loss accompanied with denture wearing

10. The loss of teeth and their periodontal support results in the removal of an important sensory mechanism and a change in the loading pattern of the alveolar bone from tensile to compressive with forces being predominantly vertical as well as horizontal. Although unproven, it is tempting to conclude that the recurrent functional movements of removable prostheses may be a major factor contributing to residual ridge reduction .

11. The magnitude of this bone loss is extremely variable. So the dentist must take care for the preservation and protection of any remaining teeth to minimize or avoid advanced residual ridge reduction. The compromised support is further complicated because complete dentures move in relation to the underlying bone during function. So the construction of complete denture should be formulated to minimize the force transmitted to the supporting structure or to decrease the movement of the prosthesis in relation to them.

12. DENTULOUS vs EDENTULOUS The periodontium provides a resilient suspensory apparatus resistant to functional forces. Two principal functions are : Support and positional adjustment of the tooth alongwith a secondary function of sensory perception. Deprived of Periodontal support, and the entire mechanism of functional load transmission to the supporting tissues is altered.

13. DENTULOUS vs EDENTULOUS Teeth are in occlusion only during the functional movements of chewing and deglutition and during the movements associated with para function . Dentures come in contact even when the patient is not carrying out functional movements like speaking, smiling etc.

14. DENTULOUS vs EDENTULOUS Occlusal forces exerted on the teeth are controlled by the neuromuscular mechanisms of the masticatory system. Reflex mechanisms with receptors in the muscles, tendons, joints, and periodontal structures regulate mandibular movements. Patients are unable to gauge or sense the amount of occlusal forces exerted by the dentures and is deprived of the protective reflex mechanisms .

15. DENTULOUS vs EDENTULOUS Area of PDL support:- Tooth attachment apparatus has an approximate area of 45cm 2 in each arch. Area of mucosal support:- The mean denture bearing area of 22.96cm 2 in the edentulous maxillae and approximately 12.25cm 2 in an edentulous mandible .

16. T he mucosa demonstrates little tolerance or adaptability to denture wearing. This minimal tolerance can still be reduced further by the presence of systemic diseases such as anemia , hypertension, or diabetes, as well as nutritional deficiencies . In fact, any disturbance of the normal metabolic processes may lower the upper limit of mucosal tolerance and initiate inflammation .

17. DENTULOUS vs EDENTULOUS Occlusal forces act perpendicular to the occlusal plane. Alveolar bone subjected to tensile loads . Nature- Intermittent, rhythmic, and dynamic . Limited tissue support Dentures subjected to displacing forces in vertical, horizontal and diagonal directions and tend to move in relation to the underlying bone.

18. FORCES ACTING ON TEETH Greatest forces – during mastication and deglutition, which are vertical in direction. MASTICATION – thrust of short duration restricted to short periods during the day. DEGLUTITION – about 500 times/day ( Zemlin , 1998) , longer duration of contact.

19. Mastication Deglutition Duration per stroke- 0.3 sec 1800 strokes per day During meals Short duration Directed principally perpendicular to occlusal plane with some horizontal component Duration is 1 sec 500 times per day At meals and in between meals Tooth contacts for longer duration Mainly vertical in direction with slight horizontal component by surrounding musculature During peak forces – Tongue force > Labiolingual force During rest – Both forces are similar

20. Loads of a lower order but longer duration are produced throughout the day by the tongue and circumoral musculature . These forces are predominantly in the horizontal direction . Upper incisors may be displaced labially with each biting thrust, and these tooth movements probably cause wear facets to develop .

21. It has been calculated that within a 24-hour period the teeth are subjected to the functional forces of mastication and deglutition for a total of some 17.5 minutes. However , it must be emphasized that the collective forces acting on a prosthetic occlusion are unlikely to be controlled or attenuated as effectively as they appear to be by the natural dentition. Consequently , the time-dependent responses of tissues supporting complete dentures are likely to be different from those seen around natural teeth.

22. DENTULOUS vs EDENTULOUS Masticatory loads of 20 kg are exerted on natural teeth. Masticatory loads of 6-8 kg during chewing are recorded with complete dentures.

23. Masticatory loads Dentulous Person Edentulous Person Onto teeth Onto large periodontal ligament area Onto the bone Onto the small area of mucosa Directly onto the bone Boucher’s prosthodontic treatment for Edentulous patients;Eleventh edition Continually adapts to forces Cannot adapt well to forces

24. DENTULOUS STATE Tooth Support: Periodontium EDENTULOUS STATE CD Support: Mucosa Function Parafunction Cosmetic perceptions & adaptive responses Morphological face height & TMJ changes Interactions of the Components of Masticatory system

25. RETENTION The retention of complete denture are considered as either physical or muscular. Brill has described factors affecting denture retention. He has divided them into physical and muscular factors Physical factors 1. Maximal extension of the denture base. 2. Intimate contact of the denture base and its basal seat. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

26. Muscular factors The buccinator , orbicularis oris and the extrinsic & intrinsic muscles of the tongue are the key muscles that the dentist harnesses to increase retention and stability, by means of impression techniques.

27. Muscular factors can be used to increase retention and stability of dentures. Impression techniques, design of the labial buccal and lingual polished surfaces of the denture and arch form, all should be considered in balancing the forces generated by tongue and perioral musculature. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

28. Buccinator The buccinator muscle may be divided into superior, middle, and inferior divisions. The superior fibers act to seat the maxillary denture, M iddle fibers control the bolus of food, and I nferior fibers contribute to mandibular denture stability in th disto-buccal v e stibul e . J Prosthet Dent 1956:6(4):450- 64 .

29. MENTALIS MUSCLE These muscles take origin bilaterally from area above mental tuberosity and inserts to the highest point of origin, which lies superior to the position of the mucosal reflection of the natural teeth . When resorption of the residual ridge and body of mandible takes place, the level 0f the ridge crest falls below the level of the superior fibres of the mentalis muscle. In order to maintain its area of origin, the muscle attachment Folds over the alveolar ridge and lies on the superior Surface of residual ridge. the result of this is a backward movement , and reduction of neutral zone in anterior region . J Prosthet Dent 1956:6(4):450- 64 .

30. Fish (1948) and Wright (1966) in their attempt to describe approaches to occlusal plane determination have highlighted the importance of Modiolus. The food bolus is triturated while resting on the mandibular occlusal surface (occlusal table). This table is bound by the cheeks ( buccally ), tongue ( lingually ), pterygomandibular raphe (distally) and contraction of the corner of the mouth ( mesially ). The mesial boundary is a point of meeting of 8 muscles, called the Modiolus .

31. The modiolus becomes fixed everytime the buccinators contracts due to chewing efforts. This contraction presses the corner of the mouth against the premolars, closing the occlusal table from the front. Food crushed by the premolars and molars does not escape at the corner of the mouth unless facial nerve is damaged.

32. VISCOELASTIC BEHAVIOUR OF 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 .

33. NATURAL AND PROSTHETIC DENTAL OCCLUSION : FUNCTIONAL AND PARAFUNCTIONAL CONSIDERATIONS

34. The masticatory system appears to operate best in an environment of functional equilibrium . The substitution of complete denture for teeth/ periodontium alters this equilibrium . An analysis of this alteration is the basis for understanding the significance of the edentulous state. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

35. OCCLUSION The primary components of occlusion: Dentition lkijikjijijijk Neuromuscular system Craniofacial structures

36. Developing Dentition Healthy adult dentition Deteriorating adult dentition Edentulous state Development of motor skills & neuromuscular learning Dental, alveolar, craniofacial adaptability Dental adaptation (wear, drift, extrusion) Bone adaptation is reparative Learned protective reflexes Partial edentulism Periodontal disease Diminished dental reflex adaptation Residual ridge reduction Vastly diminished reflexes Increase in parafunctional movements Development and adaptation of occlusion After Moyers, R.E.: Dent. Clin . North Am. 13:523-536, 1969

37. FUNCTIONAL CONSIDERATIONS MASTICATION – Prepares food for swallowing. Tongue and cheek muscles keep the food bolus between the occlusal surfaces of the teeth. Teeth arrangement must be done within the confines of a functional balance of the musculature involved in maintaining the food bolus between the occlusal surfaces of the teeth.

38. The pronounced differences between persons with natural teeth and those with complete dentures, are conspicuous in the functional context: Mucosal mechanism of support as opposed to support by the periodontium. The movements of dentures during mastication. The progressive changes in maxillomandibular relations and eventual migration of dentures. The different physical stimuli to the sensory motor system.

39. Forces generated DIRECTION DURATION & MAGNITUDE MASTICATION (FUNCTION) Mainly vertical Intermittent and light Diurnal only PARAFUNCTION Frequently horizontal as well as vertical Prolonged , possibly excessive Both diurnal and nocturnal

40. Conclusion Reduction in the extension of upper and lower denture bases in different areas failed to affect the chewing ability of the subjects. Significant reductions in performance appeared only when an extensive reduction was made on the over-all border of the lower denture base. Subjects with a previous denture experience possessed significantly better ability to chew the test food than the subjects who had had no previous denture experience.

41. Conclusion Evidence of marked improvement in masticatory performance appeared among individual subjects with different denture forms. This would suggest that polished surface denture contour may be an important factor influencing the efficacy of the food transporting mechanism and thereby affecting masticatory function.

42. Conclusion The position of the food platform on the crest of the lower ridge at the height of the lower canine and parallel to the flat portion of the lower ridge was found to be most effective for the subjects to chew the two test foods. Significant reductions in chewing efficiency of subjects resulted when the food platforms were moved in dentures in a position buccal to the crest of ridges.

43. PARAFUNCTIONAL CONSIDERATIONS P arafunctional habits involving repeated or sustained occlusion can be harmful to the teeth and other components of the masticatory system. Teeth clenching is a common cause of soreness of the denture bearing mucosa. Such habits cause additional loading on the denture bearing tissues.

44. The initial discomfort associated with wearing new dentures is known to evoke unusual pattern behavior in the surrounding musculature. Complaint of sore tongue is related to a habit of thrusting the tongue against the denture and patient usually is unaware. Tendency to occlude teeth more frequently at first – to strengthen confidence in retention, until surrounding muscles become accustomed OR to provide some accommodation in the chewing pattern.

45. Parafunction can cause increase in residual ridge resorption

46. What we can do ? Methods should be undertaken to ensure continued tissue health by minimizing the potential traumatic effects of complete dentures Function and parafunction generate Pressure = Force Time Tissue damage d by occluding local circulation Controlled by: Correct clinical techniques Use of permanent soft tissue liner Controlled partially by nocturnal tissue rest

47. CHANGES IN MORPHOLOGICAL FACE HEIGHT AND THE TEMPOROMANDIBULAR JOINTS

48. The growth and remodeling of the bony skeleton continue well into adult life and such growth accounts for dimensional changes in the adult facial skeleton. Neverthless , a premature reduction in morphological face height can occur as a result of occlusal tooth surface loss. (attrition , abrasion ) This reduction is even more prominent in edentulous and complete denture wearing patients. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition Pg:8-28

49. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition Loss of teeth causing edentulism Reduction in the facial height and jaw bones Overclosure and mandibular prognathism Change in the position of TMJ Congruity of the opposing articular surface is maintained due to growth and remodelling by the proliferative articular cartilages

50. Changes in morphological face height or the shapes of the jawbones due to tooth loss are inevitably transmitted to the TMJs . It is not surprising, then, that these articular surfaces undergo a slow but continuous remodeling throughout life .

51. Resorption of the residual ridges supporting complete dentures and the consequent reduction in the vertical dimension of occlusion tend to cause a decrease in total face height and a resultant mandibular prognathism . Indeed in complete denture wearers, the mean reduction in height of the mandibular process measured in the anterior region may be approximately four times greater than that in the corresponding maxillary process MANDIBULAR REDUCTION = 4 X MAXILLARY REDUCTION

52. Occlusion The occlusion of complete dentures is designed to harmonize with the primitive and unconditioned reflex of the patient’s unconscious swallow . Tooth contacts and mandibular bracing against the maxillae occur during swallowing by complete denture patients . This suggests that complete denture occlusions must be compatible with the forces developed during deglutition to prevent disharmonious occlusal contacts that could cause trauma to the basal seat of dentures .

53. I n the natural dentition, most functional tooth contacts occur in a mandibular position slightly anterior to centric relation, a position referred to as centric occlusion. However, in complete denture prosthodontics, the position of planned maximum intercuspation of teeth is established to coincide with the patient’s centric relation. Centric relation at the established vertical dimension has potential for change. This change is brought about by alterations in denture-supporting tissues and facial height, as well as by morphological changes in the TMJs .

54. Centric relation Most posterior position of mandible relative to the maxillae at the established vertical dimension. Recordable , reproducible , repeatable. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

55. Proprioceptive impulses guide mandibular movements. In dentulous patients the proprioceptive impulses are obtained from the periodontal ligament. Edentulous patients do not have any proprioceptive guidance from their teeth to guide their mandibular movements. The source of proprioceptive impulses is transferred to the TMJ. The Centric relation position acts as a proprioceptive centre to guide the mandibular movements. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition

56. Unconscious swallowing is carried out with the mandible at or near the centric relation position. Position of planned maximum intercuspation of teeth is established to coincide with the patient’s centric relation. The coincidence of CR and CO is consequently referred to as centric relation occlusion.

57. TEMPOROMANDIBULAR JOINT CHANGES The basic physiological relationships between condyles , disks, and glenoid fossae appear to be maintained during maximal occlusal contacts and during all movements guided by occlusal elements. It is therefore logical that the dentist should seek to maintain or restore these basic physiological relations when treating a patient with complete dentures.

58. Boucher’s prosthodontic treatment for Edentulous patients; Eleventh edition Pg:8-28 Reproducible border movements Within the confines of the envelope of motion Not reproduced effectively in edentulous patients due to pathological and adapative structural alterations May lead to incorrect prosthodontic treatment Leading to Degenerative joint changes and TMD’s Combination of prosthodontic , pharmacological, and supportive therapy should be used.

59. Researchers have concluded that the passive hinge movement tends to have a constant rotational and reproducible character. This reproducibility of the posterior border path is of tremendous practical significance in patients undergoing prosthodontic treatment, It also has been reported that impaired dental efficiency resulting from partial tooth loss, inappropriate prosthodontic treatment, or indeed its absence can influence the outcome of temporomandibular disorders (TMDs) .

60. ESTHETIC CHANGES

61. In most cultures it is thought highly desirable to appear to be dentate, and socially evident tooth loss is thus considered unacceptable. Patients seek dental treatment for functional, esthetic , or cosmetic reasons and dentists have been quite successful in restoring or improving many a patient’s facial esthetics .

62. Photographs of pre edentulous appearance should be carefully analyzed and discussed with the patient

63. BEHAVIO U RAL AND ADAPTIVE RESPONSES

64. Requires the interpretation of new sensory inputs by CNS and acquisition of additional motor skills so as to use the dentures when speaking and eating. Foreign objects tend to elicit different stimuli to the sensorimotor system. Exteroceptors and proprioceptors are affected by the size, shape, position, pressure and mobility of the prostheses. This influences the cyclic masticatory stroke pattern.

65. Acceptance of complete dentures is accompanied by a process of habituation which is defined as “ gradual diminution of responses to continued or repeated stimuli ”. Tactile stimuli that arise from the contact of prosthesis with the richly innervated oral cavity are ignored after a short time. Each stage of decrease in response is related to the memory trace of the previous application of the stimulus. Habituation becomes difficult with older age. Thus, adaptability also becomes difficult.

66. Stimuli must be specific and identical to achieve habituation. This probably prevents the transfer of habituation evoked by an old familiar denture to a new denture. See! The old denture is much better than this new denture

67. Successful management begins with identification of anticipated difficulties before treatment starts and with careful planning to meet specific needs and problems . Dentists must train themselves to reassure the patient, to perceive their wishes , and to know how and when to limit the patient’s expectations.

68. Jamieson wrote that “fitting the personality of the aged patient is often more difficult than fitting the denture to the mouth .” Success in geriatric dentistry _ can be the result of building up the patient’s confidence in the dentist, regardless of the quality of the final prosthesis .

69. The role of prosthodontists is to gain an understanding of the changes in the form and function of the mouth and jaws, brought about by the total loss of teeth and the possible social and behavioral consequences of tooth loss. They should be able to critically evaluate the influence of complete dentures on the remaining soft tissues and the underlying bony structures so that it helps in understanding the scope and limitations of complete dentures.

70. Conclusion The application of biomechanical principles to clinical prosthodontics is what make it a science. Prosthodontists should not only possess manual dexterity but also have a scientific approach with the basis of structural engineering to aid in design of a restoration and enhance its longevity.

71. REFERENCES Boucher’s Prosthodontic treatment of edentulous patients, 9 th edition Winkler’s Essentials of Complete denture After Moyers, R.E .: (1969) Dent . Clin . North Am. 13:523-536 Kumar L, (2014) Biomechanics and clinical implications of complete dentulous state, Journal of Clinical Gerontology & Geriatrics Nimonkar S, Godbole S, Belkhode V, Nimonkar P, Pisulkar S. Effect of Rehabilitation of Completely Edentulous Patients With Complete Dentures on Temporomandibular Disorders: A Systematic Review. Cureus . 2022 Aug 14;14(8):e28012. doi : 10.7759/cureus.28012. PMID: 36134066; PMCID: PMC9470537. Alsaggaf A, Fenlon MR, (2020) A Case Control Study to investigate the effects of denture wear on residual alveolar ridge resorption in edentulous patients, Journal of Dentistry Szilvia E. Mezey , Magdalena Müller- Gerbl , Mireille Toranelli , Jens Christoph Türp , The human masseter muscle revisited: First description of its coronoid part, Annals of Anatomy - Anatomischer Anzeiger , Volume 240, 2022, Nakasato A, Kobayashi T, Kubota M, Yamashita F, Nakaya T, Sasaki M, Kihara H, Kondo H. Increase in masseter muscle activity by newly fabricated complete dentures improved brain function. J Prosthodont Res. 2021 Oct 15;65(4):482-488. doi : 10.2186/jpr.JPR_D_20_00038. Epub 2021 Mar 25. PMID: 33762505 . S J & M T Cristhian & T A Lesbia . (2013). SALIVA AND ALTERNATIVE ADHESIVE SYSTEMS FOR COMPLETE DENTURES , Revista Facultad de Odontología 25(1 ): 208-218