Vertical Jaw Relations

1. Vertical Jaw Relations

2. Contents • Introduction • Vertical jaw relation • Determinants of vertical relations of mandible to maxilla • Physiologic rest position • Vertical jaw relation at rest • Recording rest position • Free way space/ interocclusal space

3. Discussion – review of literature • Vertical jaw relation of occlusion • Recording vertical relation at occlusion • What happens if vertical dimension is altered? • Summary • Conclusion • References

4. Introduction • Complete dentures must be used in most functions once served by natural dentition. • Mastication, speech and appearance all depend on specific vertical and horizontal relations of mandible to the maxilla. • Any horizontal jaw relation is valid only at a specific vertical dimension…..hence the importance of vertical jaw relation.

5. What is Vertical Dimension? • The vertical dimension is the length of the face as determined by the amount of separation of the jaws.

6. Vertical Jaw Relation • The vertical jaw relations are those established by the amount of separation of the two jaws in a vertical direction under specified conditions… Boucher. • May be recorded as: vertical jaw relation at rest vertical jaw relation at occlusion • Vertical jaw relation at rest in denture construction is used as guide to the lost vertical dimension at occlusion.

7. Determinants of Vertical Relations of Mandible to Maxilla • The masticatory musculature • The occlusal stops (teeth or occlusion rims)

8. Physiologic Rest Position • The postural position of the mandible when an individual is resting comfortably in an upright position and the associated muscles are in a state of minimal contractural activity…GPT 8. • The mandible is said to be in its physiologic rest position when all the muscles that close and open the jaws are in a state of minimal tonic contraction only to maintain posture….Boucher.

9. Importance of Physiologic Rest Position

10. If this space is not given, the tissues under the denture bearing area get their much needed rest by resorption of the underlying bone.

11. Methods to Establish the Vertical Jaw Relations • Many methods to establish the vertical dimension at rest and in occlusion have been put forth. • To use several methods and to compare the results is advised.

12. Categorisation of Methods to Determine Vertical Jaw Relations • According to Sharry : pre-extraction determination post extraction records • According to Boucher : mechanical methods physiological methods • According to Heartwell : to determine, vertical jaw relation at rest vertical jaw relation of occlusion

13. Vertical Jaw Relation at Rest • The habitual postural position of the mandible when the patient is resting comfortably in the upright position and the condyles are in a neutral unstrained position in the glenoid fossa . …Academy of Denture Prosthetics.

14. Vertical Jaw Relation at Rest VDR

15. Features of Vertical Rest Dimension • It is a bone to bone relation. • The position of the mandible is influenced by gravity… • Rest position is a relaxed position… • It may not be easy to record in patients with neuromuscular disturbances.. • This position can not be maintained for any amount of time… • Failure to establish rest position may lead to pain, discomfort and residual ridge resorption…

16. Recording Rest Position • Niswonger’s method • Facial measurements • Tactile sense • Phonetics • Facial expression • Radiographs – cephalometric method

17. Niswonger’s Method • Given in 1934 by Niswonger. • He defined the rest position as “the neutral position of the mandible where the opening and closing muscles are in a state of equilibrium.” • The method : - Patient seated such that ala tragal line parallel to floor. - Two marks are marked…. - Patient told to swallow and relax.

19. -The dimension is measured between the two points. -Occlusal rims are constructed so that they are 4/32 or 1/8 inch less than the original measurement. Disadvantages: soft tissue landmarks variability to obtain same measurements { Interocclusal space

20. Facial Measurements • Advocated by Pleasure (1951) • By using artificial landmarks on nose and chin. • photo

21. Tactile Sense • Patient asked to open mouth wide open until strain is felt in the muscles. • Then he is asked to close the mouth till it reaches a comfortable, relaxed position. • Measure the dimension between points of reference and compare with those got after swallowing.

22. Phonetics • Patient repeats any word which has the sound ‘em’ in it. till the lips contact. • Ask him to stop all jaw movements, measure between two points of reference. OR • Ask patient to pause in between normal speech and measure between two points.

23. Facial Expression • Evidence of relaxation of maxillo mandibular musculature… • lips even antero-posteriorly. • Skin around eyes and chin relaxed. • Relaxation around nares.

24. Clinical Means of Measuring Vertical Dimension…how accurate?? • Made on soft tissues which are mobile…accuracy questionable. • Manipulation of face is necessary at the time of measurement. • Lack of a permanent reference point to return to, for checking subsequent measured dimensions.

25. Cephalometric Determination • Method by Atwood (1956). • Advantages: measured on bony landmarks. no manipulation of face needed. permanent record is available, even after months. • Disadvantages: measurements are made of shadow of the reference points. special equipment. radiographic exposure.

26. Electromyography.. to verify rest position • Shpuntoff and Shpuntoff(1956) • Principle : activity or lack of activity in muscle is measured as a change in its electric potential. muscle contracts electrical activity is measured and amplified. cathode ray oscilloscope • Disadvantages : not practical equipment expensive difficult to interpret tracing tracing

27. Discussion • Pre extraction records in determining vertical dimension: In spite of fallibility of most pre extraction recording instruments, some are more accurate than the post extraction aids. Measuring instruments like Willis gauge, Vernier calipers were used. But because of the soft tissue impingement, a more reliable method is to measure the distance between the upper and the lower frena with dividers when teeth are in centric occlusion.

28. Alternate methods are : Turner’s cut out method using a simple pantograph acrylic face mask plaster face mask • But these methods displace the skin when formed and applied to the face. may lead to inaccuracy.

29. Facial dimensions in establishing vertical dimension : • Goodfriend(1933) suggested that distance from the pupil of the eye to the junction of the lips equaled that from the subnasion to gnathion. • However,Willis(1935) has been said to popularise these measurements.

30. Dates to as early as 1771.. • In 1771,Hunter wrote “ in the lower jaws, as in all the joints of the body, when the motion is carried to its greatest extent, in any direction, the muscles and ligaments are strained and the persons made uneasy. The state, therefore, into which every joint naturally falls, especially when we are asleep, is nearly in the middle between the extremes of motion, by which means all the muscles and ligaments are equally relaxed.” • Using physiologic rest position as a guide to vertical dimension of occlusion:

31. According to Gottleib, Wallish was one of the first to define the physiologic rest position of mandible as “the position of the mandible where in all muscle action is eliminated and it is passively suspended.” • Sicher and Tandler(1920), stated “ the rest position of the articulation, the middle position is that in which the mandible is at a slight distance from the the maxilla. In this position the mandible is kept against gravity by the forces of the closing muscles”

32. Constancy of rest position in a strict sense is doubtful. • Niswonger(1934), designed an instrument called ‘jaw relator’ for use in measuring the distance that the mandible moves from rest position to centric occlusion • He studied 200 dentulous patients. He established that the interocclusal clearance measured 4/32 inch ( 3+mm ) in 87% of pt’s and that the other 13% varies from 1/32 to 11/32 inch.

33. He concluded that as the teeth slowly wear down, nature makes the necessary changes in bone and soft tissues to maintain this measurement of 4/32 • Niswonger’s work was the beginning of the dictum that the individual mandibular rest position remains constant throughout life. • This theory has since been referred to as concept of constancy of face height.

34. Gillis (1941) defined rest position of the mandible as that “ position from which all mandibular movements begin and to which they return” • Schlosser (1941) conducted a series of phonetic experiments and found a space of from 1-3mm between the upper and lower incisors with the lips in contact when natural teeth were present.

35. Thompson(1942) believed that the rest position is determined by a balance of tension in the musculature which suspends the mandible, & that the rest position is not affected by the presence or absence of teeth. He indicated that the interocclusal distance averaged 2-3mm in normal dentitions & may be 10mm or more in abnormal dentitions.

36. He related variations in rest positions to hypotonicity and hyper tonicity of muscles and described them as short term variations- stress,respiration long term variations- debilitated patients, mouth breathers.

37. Leof(1950),took issue with the doctrine that physiologic rest position is not constant throughout life. • He pointed out that muscle tone rather than muscle length controls the rest position, and that muscle tone can and does vary. Leof further stated that we must never eliminate the interocclusal distance. • Oslen (1951) studied physiologic rest position radiographically, his findings suggested that the resting position was not rigidly stable.

38. Sicher (1954) felt that the mandibular rest position was completely dependent on the tonicity of the musculature and that only in disturbed muscle tonus as in disease, overwork, or nervous tension the rest position varies from normal. He also pointed out that “constancy in a living organism means simply that the range of variation or variability is negligible”.

39. Atwood( 1958) performed a longitudinal radiographic analysis of face height before and after extraction on 42 subjects. This study demonstrated variability within a sitting, between sittings, and between readings with and without dentures.

40. Duncan & Williams(1960) studied the rest position as a guide in prosthetic treatment. Lateral roentgenographic cephalometric measurements were made on 10 patients for whom complete dentures were constructed. They found instability in rest position & hence concluded that, rest position is a poor guide for establishing the pre-extraction occlusal vertical dimension.

41. Tactile sense in establishing vertical dimension: Lytle(1964) adopted a refined technique using a central bearing device fixed to upper and lower occlusal rims. McGee stated that methods which relied on patients’ neuromuscular perception transferred the responsibility of registering the occlusal dimension from the dentist to the patient.

42. Phonetics in establishing vertical dimension: • This theory is dependent upon the correlation during speech of the inter occlusal distances and position of the occlusal plane. • Silverman (1953) maintains that it is easier and more accurate to record a measurement which relies upon muscular phonetic enunciation…

43. Deglutition in establishing vertical dimension: • Shanahan (1956) indicated that mandibular pattern during deglutition dictates the eruption of teeth so that they are maintained at the occlusal plane by the act of swallowing. this establishes the vertical dimension.

44. Ward and Osterholtz (1963) concluded that swallowing may be used only as a guide to the vertical dimension of occlusion. • They advised the dentures should be removed for sometime before recording the occlusal vertical dimension to obliterate the memory of acquired neuromuscular patterns.

45. Ismail and George (1968) conducted a study to test the accuracy of the swallowing technique for determining and recording the occlusal vertical relation of jaws as compared to occlusal vertical relation in the same patients before extraction. • They concluded that with the swallowing method, the occlusal face height showed an increase of mean 2.8mm before and after extraction.

46. Acceptance of clinical assessment of vertical dimension of occlusion established by different methods • Under the guidance of Dr.N.P.Patil sir, • Objective : to evaluate the most acceptable method of establishing vertical dimension. • 3 methods: physiologic rest position phonetics swallowing threshold • Results : swallowing threshold method is the most acceptable and comfortable to the patients as compared to the other two.

47. Free- Way Space/ Interocclusal Space • The difference between the vertical dimension at rest and the vertical dimension while in occlusion…GPT 8.

48. Average of 2 – 3mm. Depends on position of head. Is 2 – 3mm of free-way space a scientific average for rest position of mandible?....can it be a static entity at any time?

49. A study ‘the free-way space and its significance in rehabilitation of masticatory apparatus’ was done by J.S.Landa (1952). • Four methods, the clinical method, measurement by mechanical devices, radiography and registrations by means of extra oral needle point tracers were used to determine inter occlusal space. • Conclusions: Average free way space was 3.07 to 3.67mm. Complex architectural structure of the freeway space cannot be incorporated into an articulator. It cannot be used as the only criterion… It is effected by mandibular movement and by gravity.

50. Vertical Dimension of Occlusion • The relationship of the mandible to the maxillae when the jaw is closed and the teeth are in contact, this position may or may not coincide with centric occlusion…GPT 8.