Biomechanical considerations in edentulous state

1. AJAY YERRAMSETTI
BIOMECHANICS
IN
EDENTULOUS STATE

2. CONTENTS
 Introduction
 The clinical implications of an edentulous stomatognathic system
-Modifications in areas of support (natural dentition vs. Complete denture);
-Functional and parafunctional considerations;
-Changes in morphologic face height, and Temporomandibular joint
-Cosmetic changes and adaptive responses.
 Review of literature
 Conclusion
 References

3. INTRODUCTION
 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.
 Consequently, the required treatment addresses a range of biomechanical problems that involve a wide
range of individual tolerances and perceptions.
 Research has demonstrated that several non-disease factors such as attitude, behaviour, financial,
dental attendance and characteristics of the health care system play an important role in the decision to
become edentulous.

4. THE CLINICAL IMPLICATIONS OF AN EDENTULOUS STOMATOGNATHIC SYSTEM
ARE CONSIDERED UNDER THE FOLLOWING FACTORS
 Modifications in areas
of support (natural
dentition vs. Complete
denture);
 Functional and
parafunctional
considerations
 Changes in
morphologic face height,
and temporomandibular
joint
Cosmetic changes
and adaptive
responses

5. 1.SUPPORT MECHANISM FOR THE NATURAL DENTITION
 The masticatory system is made up of closely related morphological, functional, and behavioural
components. Their interactions are affected by changes in the mechanism of support for a dentition
when natural teeth are replaced by artificial or prosthetic ones.
 An understanding of the many subtleties associated with the transition from a dentulous to an
edentulous state demands a comparison of the mechanisms of both natural teeth and complete denture
support.

6.  Teeth function properly only if adequately supported, and this
support is provided by the periodontium, an organ composed of soft
and hard connective tissues.
 The patient who needs complete denture therapy is deprived of
periodontal support, and the entire mechanism of functional load
transmission to the supporting tissues is altered.

7.  The greatest forces acting on the teeth are normally produced
during mastication and deglutition, and they are essentially
vertical in direction.
 Each thrust is of short duration, and for most people, chewing is
restricted to short periods during the day. Deglutition, on the
other hand, occurs about 500 times a day, and tooth contacts
during swallowing are usually of longer duration than those
occurring during chewing.

8.  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.

9.  Estimates of peak forces from the tongue, cheeks, and lips have been made, and lingual force
appears to exceed buccolabial force during activity. During rest or inactive periods, the total
forces may be of similar magnitude.
 It has been calculated that the total time during which the teeth are subjected to functional forces
of mastication and deglutition during an entire day amounts to approximately 17.5 minutes.

10. 2.SUPPORT MECHANISM FOR COMPLETE DENTURES
 The basic challenge in the treatment of edentulous patients lies in the
nature of the difference between the ways natural teeth and their artificial
replacements are supported.
 On the other hand, the unsuitability of the tissues supporting complete
dentures for load-bearing function must be immediately recognized
because the mucous membrane is forced to serve an identical purpose as
the periodontal ligaments.

11. I.MUCOSAL SUPPORT AND MASTICATORY LOADS
 The area of mucosa available to receive the load from complete dentures is limited when compared with the
corresponding areas of support available for natural dentitions.
 Researchers have computed the mean denture-bearing area to be 22.96 cm2 in the edentulous maxillae and
approximately 12.25 cm2 in an edentulous mandible.
 It also must be remembered that the denture-bearing area (basal seat) becomes progressively smaller as
residual ridges resorb.

12.  Furthermore, the mucosa demonstrates little tolerance or adaptability to denture wearing.
 This minimal tolerance can be reduced still 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.

13.  Masticatory loads are much smaller than those that can be produced by conscious effort and are in the
region of 44 lb (20 kg) for the natural teeth.
 Maximum forces of 13 to 16 lb (6 to 8 kg) during chewing have been recorded with complete dentures,
but the average loads are probably much less than these.
 In fact, maximal bite forces appear to be five to six times less for complete denture wearers than for
persons with natural teeth.

14. II.RESIDUAL RIDGE
 The residual ridge consists of denture-bearing mucosa, the submucosa and periosteum, and the
underlying residual alveolar bone.
 A variety of changes occur in the residual bone after tooth extraction and use of complete dentures.
 Alveolar bone supporting natural teeth receives tensile loads through a large area of periodontal ligament,
whereas the edentulous residual ridge receives vertical, diagonal, and horizontal loads applied by a
denture with a surface area much smaller than the total area of the periodontal ligaments of all the natural
teeth that had been present.

15.  One of the few firm facts relating to edentulous patients is that wearing dentures is almost invariably
accompanied by an undesirable and irreversible bone loss.
 Two concepts have been advanced concerning the inevitable loss of residual bone:
1. Direct consequence of loss of the periodontal structures, variable progressive bone reduction occurs.
2. Residual bone loss is not a necessary consequence of tooth removal but depends on a series of poorly
understood factors.

16.  There are two physical factors involved in denture retention that are under the control of the dentist and are
technique driven.
1. Maximal extension of the denture base;
2. Maximal intimate contact of the denture base and its basal seat.
 Muscular factors can be used to increase retention (and stability) of dentures. In fact, the buccinator, the
orbicularis oris , and the intrinsic and extrinsic muscles of the tongue are key muscles that the dentist harnesses
to achieve this objective by means of impression techniques.
 Furthermore, the design of the labial, buccal, and lingual polished surfaces of the denture and the form of the
dental arch are considered in balancing the forces generated by the tongue and perioral musculature.

17.  As the form and size of the denture-supporting tissues (the basal seat) change, harnessing muscular forces in
complete denture design becomes particularly important for denture retention.
 Following full mouth extractions, the alveolar ridges undergo significant bony changes, with the largest
changes seen on the mandibular arch. Studies indicate that the mandibular ridge resorps approximately four
times as much as the maxillary arch.
 The direction of mandibular resorption is downward and outward, while maxillary resorption is upward and
inward. The results of this resorptive pattern often force a crossbite of the posterior dentures in order to
maintain the dentures over the residual ridges.

18. OCCLUSION: FUNCTIONALAND PARAFUNCTIONAL CONSIDERATIONS
 The masticatory system appears to operate best in an environment of continuing functional equilibrium.
 The substitution of a complete denture for the teeth/periodontium mechanism alters this equilibrium. An
analysis of this alteration is the basis for understanding the significance of the edentulous state.

19.  Dentition development is characterized by a
period of dental alveolar and craniofacial
adaptability, which is also a time when motor
skills and neuromuscular learning are
developing.

20.  If and when an adult dentition begins to deteriorate, the dentist resorts to fixed or removable prosthodontic
therapy in attempts to maintain a functional occlusal equilibrium.
 This period is characterized by greatly diminished dental and reflex adaptation and by bone resorption.
 Obviously, the presence of tooth loss and disease and the depletion of reparative processes pose a major
prosthodontic problem. Finally, in the edentulous state, there are few natural adaptive mechanisms left.

21.  The prosthesis rests on tissues that will change progressively and irreversibly, and the artificial occlusion
serves in an environment characterized by constant change that is mainly regressive.
 Design and fabrication of prosthetic occlusions have led to fascinating controversies. Dental occlusion
was studied first in the field of complete dentures and then in other disciplines.
 Early workers encountered enormous mechanical difficulties in constructing reasonably well-fitting
dentures that would be both durable and esthetic. Inevitably, these dentists had to be mechanically
minded. Because anatomy was the first of the biological basic sciences to be related to prosthodontic
services, its application dominated prosthodontic protocol.

22.  Later, histology, physiology, and bioengineering were recognized as having essential roles in the treatment
of edentulous patients.
 The emphasis on and application of these basic sciences lifted prosthodontics from the early mechanical art
to the applied clinical science it is today.
 The modern complete denture service is characterized by an integration of biological information with
instrumentation materials and clinical techniques. Complete dentures are designed so that their occlusal
surfaces permit multidirectional contact movements of the mandible.

23. • Orofacial and tongue muscles play an important role in retaining
and stabilizing complete dentures.
• This is accomplished by arrangement of the artificial teeth to
occupy a “neutral zone” in the edentulous mouth so the teeth will
occupy a space determined by the functional balance of the
orofacial and tongue musculature.

24. FUNCTION: MASTICATION AND OTHER MANDIBULAR MOVEMENTS
 During masticatory movements, the tongue and cheek muscles play an essential role in keeping the food
bolus between the occlusal surfaces of the teeth.
 The teeth must be placed within the confines of a functional balance of the musculature involved in
controlling the food bolus between the occlusal surfaces of the teeth.
 Because mastication results in the mixing of food with saliva, it facilitates not only the swallowing but the
digestion of carbohydrates by amylase as well.

25.  As mentioned previously, the maximal bite force in denture wearers is five to six times less than in
edentulous subjects. Edentulous patients are clearly handicapped in masticatory function, and even
clinically satisfactory complete dentures are a poor substitute for natural teeth.
 The results of studies of mandibular movement patterns of complete denture patients indicate that these
movements are similar in denture-wearing patients and persons with natural teeth.

26. The pronounced differences between persons with natural teeth and
patients with complete dentures are conspicuous in this functional
context:
The mucosal mechanism of support as opposed to support by
the periodontium
The movements of the dentures during mastication
The progressive changes in maxillomandibular relations and the
eventual migration of dentures
The different physical stimuli to the sensor motor systems

27. PARAFUNCTIONAL CONSIDERATIONS
 Non-functional or parafunctional habits involving repeated or sustained occlusion of the teeth can be
harmful to the teeth or other components of the masticatory system.
 Nevertheless, clinical experience indicates that teeth clenching is common and is a frequent cause of the
complaint of soreness of the denture-bearing mucosa.
 In the denture wearer, parafunctional habits can cause additional loading on the denture-bearing tissues.

28.  It is a very complex area of research and has been shown to result from psychosocial factors (such as stress
or anxiety) or to be a reaction to strong emotions (e.g., anger, frustration).
 It may be associated with specific medical conditions (oral tardive dyskinesia, Parkinson’s disease) or with
sleep parasomnia (e.g., bruxism [tooth grinding], rapid eye movement [REM] behaviour disorders,
oromandibular myoclonus) or sleep disorders (apnoea).
 It may also be found concomitantly with certain intraoral conditions such as pain, oral lesions, xerostomia,
and discomfort with prostheses or occlusion.

29.  The initial discomfort associated with wearing new dentures is known to evoke unusual patterns of
behaviour in the surrounding musculature.
 It is feasible and probable that the tentative occlusal contacts resulting may trigger the development of
habitual non-functional occlusion.

30. • Functional contact of the opposing teeth has been estimated at only 17.5 minutes per day, Therefore
many clinicians believe that the effort necessary to create a balanced occlusion is not justified by this
minimal daily occlusal contact time.
 However parafunctional, potentially destructive, occlusal contact time has been estimated at 2–4 hours
per day.
 Therefore, even though the maximum occlusal force of complete denture patients only averages 35
pounds, functional and para-functional contacts should be considered when selecting a posterior
occlusal scheme.

31.  Direction , duration and magnitude of forces generated during function
and parafunction

32. CHANGES IN MORPHOLOGICAL FACE HEIGHT AND THE
TEMPOROMANDIBULAR JOINTS
 The terminal stage of skeletal growth is usually accepted as being at 20 to 25 years of age.
 It is also recognized that growth and remodelling of the bony skeleton continue well into adult life and
that such growth accounts for dimensional changes in the adult facial skeleton.
 Nevertheless, a premature reduction in morphological face height occurs with attrition or abrasion of
teeth. This reduction is even more conspicuous in edentulous and complete denture wearing patients.

33.  In the facial skeleton, any dimensional changes in morphological face height or the jawbones because of
the loss of teeth are inevitably transmitted to the TMJs.
 The reduction of the residual ridges under complete dentures and the accompanying reduction in vertical
dimension of occlusion tend to cause reduction in total face height and a resultant mandibular prognathism.

34.  In fact, 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 the mean reduction occurring in
the maxillary process.
 Furthermore, longitudinal studies support the hypothesis that the vertical dimension of rest position of
the jaws (which is allegedly not teeth related) does not remain stable and can change over time.

35. TEMPOROMANDIBULAR JOINT CHANGES
 The basic physiological relationship among the condyles, the disks, and their glenoid fossae appears to be
maintained during maximal occlusal contacts and during all movements guided by occlusal elements.
 It seems logical that in the treatment with complete dentures, the dentist should seek to maintain or restore
this basic physiological relation.
 The border movements of the mandible are reproducible, and all other movements take place within the
confines of the classic “envelopes of motion.”

36.  Researchers have concluded that the passive hinge movement tends to have a constant and definite
rotational and reproducible character.
 In the course of such periods, pathological or adaptive structural alterations or changes of the TMJs may
have occurred.
 It has also been reported that impaired dental efficiency resulting from partial tooth loss and absence of
or incorrect prosthodontic treatment can influence the outcome of temporomandibular disorders (TMDs).
This is thought to be particularly the case when arthritic or degenerative changes have occurred.

37.  The hypothesis has been advanced that degenerative joint disease is a process rather than a disease entity.
 The process involves joint changes that cause an imbalance in adaptation and a degeneration that results
from alterations in functional demands on or the functional capacity of the joints.
 However, because the onset of degenerative conditions is frequently encountered in the adult years, and
because the greater number of denture wearers are older patients who are edentulous, the treatment of
such conditions is very much the concern of the dentist.

38.  Clinical experience and long term studies indicate that a combination of adjunctive prosthodontic protocols,
and appropriate pharmacological and supportive therapy, are usually adequate to provide these patients with
comfort.
 One of the difficulties in managing degenerative joint involvement is achieving joint rest. Because of the
necessity for mastication and for the avoidance of parafunctional habits, voluntary or even enforced rest may
be difficult to achieve.
 Loss of teeth also disturbs the forces across the joint and also causes degenerative changes.

39. MORPHOLOGICAL CHANGES ASSOCIATED WITH THE
EDENTULOUS STATE
Deepening of nasolabial groove
Loss of labiodental angle
Narrowing of lips
Increase in columella-philtrum angle
Prognathic appearance

40. ESTHETIC, BEHAVIORAL, AND ADAPTIVE RESPONSES
1.AESTHETIC CHANGES
 There is little doubt that tooth loss can adversely affect a person’s appearance. Patients seek dental
treatment for both functional and aesthetic or cosmetic reasons, and dentists have been successful in
restoring or improving many a patient’s appearance.
 Patients should be asked to provide photographs of their pre-edentulous appearance, and relevant
details from these photographs should be carefully analysed and discussed with the patient.

41.  If this is not possible, photographs of siblings or of children who resemble the patient may be helpful.
Careful explanation of prosthodontic objectives and methods is the basis for good communication with all
patients.
 This is the case when the patient’s cosmetic desires exceed morphological or functional realities.

42. 2.BEHAVIOURALAND ADAPTIVE RESPONSES
 The process whereby an edentulous patient can accept and use complete dentures is complex.
 It requires adaptation of learning, muscular skill, and motivation and is related to the patient’s expectations.
 The patient’s ability and willingness to accept and learn to use the dentures ultimately determine the degree of
success of clinical treatment.

43.  The presence of inanimate foreign objects (dentures) in an edentulous mouth is bound to elicit different
stimuli to the sensorimotor system, which in turn influences the cyclic masticatory stroke pattern.
 Both exteroceptors and proprioceptors are probably affected by the size, shape, position, pressure from,
and mobility of the prostheses.
 The acceptance of complete dentures is accompanied by a process of habituation, which is defined as a
“gradual diminution of responses to continued or repeated stimuli.

44.  The insertion of a new denture introduces a new environment for the tongue, and the intrinsic tongue
musculature reorganizes the shape of the tongue to conform to the altered space available. A degree of
retraining tongue activity also takes place.
 Edentulous patients expect, and are expected, to adapt to the dentures more or less instantaneously. That
adaptation must take place in the context of the patient’s oral, systemic, emotional, and psychological
states.
 Successful management begins with identification of anticipated difficulties before treatment starts and
with careful planning to meet specific needs and problems.

45.  Dentists must train themselves to reassure the patient, to perceive the patient’s wishes, and to know how
and when to limit the patient’s expectations.
 An essential accompaniment of a denture design that is physically compatible with the oral complex is a
good interpersonal relationship between dentist and patient.
 Dentists must train themselves to reassure the patient, to perceive the patient’s wishes, and to know how
and when to limit the patient’s expectations.

46. REVIEW OF LITERATURE

 There will be swallowing function deterioration as a result of decline in tongue-palate contact on
removing complete dentures in edentulous older adults.
Effect of complete denture wearing on tongue motor biomechanics during swallowing in edentulous older adults.geratr
gerontol int.2015.jugo kondoh et al

47.  TOOTH LOSS AND BITING FORCE
 Changes in the biting force of a group of patients who underwent immediate denture treatment are reported for
a period of four years.
 Force increased with time and was independent of dental state. After two years the average biting force
approached that recorded for dentate individuals.
 The periodontal membrane does not appear to play an essential part in force production during mastication.
Atkinson , h. F, Ralph, W.J Tooth loss and biting force in man

48. CONCLUSION
 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 behavioural
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 together with the biocompatibility and physical properties of the materials used
in their construction.

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53. AJAY YERRAMSETTI
BIOMECHANICS
IN
EDENTULOUS STATE