hinge axis

1. Hinge axis

2. Contents Introduction Definitions Mandibular movements History Theories of hinge axis Method of locating hinge axis Clinical value of hinge axis Summary Reference

3. Definition “ Imaginary line between mandibular condyles around which the mandible can rotate within the sagittal plane” GPT—8 Terminal hinge axis = Transverse axis = Transverse horizontal axis = Transverse hinge axis Pure rotation of condyles prior to translation

4. Mandibular Movements

5. Rotation - the movement of a rigid body in which the parts move in circular paths with their centers on a fixed line called the axis of rotation. Translation - that motion of a rigid body in which a straight line passing through any two points always remains parallel to its initial position. Hinge axis point = posterior reference points - two points, located one on each side of the face in the area of the transverse horizontal axis, which together with an anterior reference point, establish the horizontal reference plane.

6. Rotational movement can occur in all the three reference planes: Frontal Horizontal Sagittal In each plane occurs around a point called the axis

7. Frontal (Vertical) Axis of Rotation

8. Horizontal axis of rotation

9. Sagittal Axis of Rotation

10. Sagittal view Frontal view Horizontal view Posselt`s border movements

11. Posselt’s Figure MP MO ICP RCP HA MP = Maximal protrusion ICP = Intercuspal position RCP= Retruded Contact position HA = Hinge axis MO = Maximum opening

12. History Campion ( 1902-1905 ) – No axis, but movement is complex one. Consisting first of rotation and secondly of a forward and downward movement Bennett ( 1908 ) - no single fixed rotation, since center of rotation constantly shifted for movements in sagittal plane, mandible was capable of two independent movements 1. Angular rotation 2. Translation movement

13. Gysi ( 1920 ) – Natural condyles are not considered as true rotation points, but as fixed guides of the mandible " The mandible opens/closes and rotates on another rotational center which has no influence in the setting up of the teeth on articulators. Therefore, need not be considered in the construction of an articulator .” Needles ( 1923 ) - agrees with Bennett: Hinge Joint + Sliding Joint. No center of rotation in temporomandibular joint itself . Instant and constantly shifting centers

14. Wadsworth (1925) – Anatomist's conclusion 1 st movement around transverse axis passing through condyles which remain seated in fossae . 2 nd movement on articular eminence Hall ( 1929 ) – concluded that “ condyle is not center of rotation” `

15. McCollum ( 1939 ) Leading advocate of the hinge-axis theory Definite opening and closing axis by using facebow External landmarks are of little use. Rotation occurs during 0.5 inch at incisors for most people, some can open 1 inch.

16. Stuart ( 1939 ) Completed work of McCollum Pioneers of gnathology Movements were reproduced on articulator to duplicate the jaw movements McLean ( 1944 ) " The diagnosis of pathological occlusion depended on the fact that the final phase of jaw closure was pure hinge movement.“

17. Lauritzen ( 1951 ) He thought articulation would be understood more easily if the joint were regarded as two separate joints The only movement which could take place in the 'menisco-condylar' part of the joint while opening and closing - a purely rotational movement. In all patients, the anterior teeth could be separated by at least 12 mm in the rotational hinge relation.

18. Posselt (1952) Hinge opening is obtained if patient is in passive, or trained active motion . He could not prove this movement was habitual. Hinge-axis opening = 19.2mm ± 1.9mm. Kornfield & Granger ( 1955 ) The only position at which it was possible to locate & reproduce the hinge axis was at centric relation

19. Trapozzano ( 1955 ) Hinge-axis represented a border movement that could be recorded repeatedly with unfailing accuracy

20. Theories Of Hinge axis

21. Aull ( 1963 ) Four schools of thought

22. The hinge axis is a component of every masticatory movement and can not be disregarded . If the hinge axis of the articulator is not the same as the hinge axis of the patient then the mechanical reproduction of jaw motions are impossible. Believe that there is a definitive transvers axis and should be located Absolute location of the axis

23. The value of actually locating the exact hinge axis is not worth the effort. This group fails to recognize that if the hinge axis of the articulator does not coincide with the hinge axis of the patient, the paths of closure will not be the same. Arbitrary location of axis

24. This group does not believe the hinge axis can be accurately located or believes other movements are involved and can not be reproduced by an articulator simulating one axis Non-Believers in the transverse axis location

25. This group believes there are two axis of rotation ( one in each condyle) and they parallel each other. The horizontal axis is a hypothetical line connecting the two horizontal rotation centers of the two condyles of the mandible. 2 . There is one hinge location ! Split axis theory

26. METHOODS OF LOCATING HINGE AXIS

27. Arbitrary methods Kinematic methods Modified methods loma-linda hinge axis device and method Buhnergraph intraoral method Technique using geometric principle to locate hinge axis Abdal-Hadi’s method for locating arbitrary hinge axis

28. Beryon point : 13mm anterior to posterior border of center of tragus on a line joining outer canthus of eye Bergstrom point : 10mm anterior to center of spherical insert for external auditory meatus and 7mm below FH plane Gysi point : This was on a line from the upper margin of the external auditory meatus to the outer canthus of the eye, 13 mm in front of the anterior margin of the meatus Commonly used today Arbitrary Method

29. Dejoyuex point : 10-11 mm anterior to ear on line to canthus and 5mm below it Dawson palpatory method Lauritzen boundner axis : 12mm anteroir and 2mm below portion of FH plane

30. Two theorems of geometry are used in this technique 1. A line drawn through the center of a circle perpendicular to chord meets it at its midpoint 2 . The line joining the center of a circle to the mid point of a chord is perpendicular to the chord . Kinematic methods

31. I nstruments Buhnerberg instrument Pantograph Transograph Electronic mathematical method Stereognathography Axitron-computerised axiograph Digital recording system

32. Step wise method of recording Recording hinge axis points Transfer to the articulator Mounting of upper casts and Mounting of lower casts with centric record

33. T.M.J instrument Hinge axis locator Hinge axis bow

34. Attach the clutch to lower teeth The clutch is a device, which relates the face-bow to the mandibular residual alveolar ridge. It is nothing but an occlusal rim made of impression compound with a bite fork attached to it the clutch resembles a cap splint with a bite fork attached to it. It is usually fabricated and cast in aluminum. Axis location

35. Axis transfer

36. Loma-linda hinge axis recording device and method The opponents of use of a kinematic hinge-axis location for edentulous patients point to its unreliability because of the resiliency of the oral mucosa. the added weight of the recording clutch which tends to shift the denture base Modified method

37. D entist called Buhnergraph Buhnergraph instrument consists of a U-shaped piece of aluminum Attached to the underside of the lower member of a Whip Mix articulator. On each side is attached an adjustable arm containing a pointed shaft which moves in and out . Buhnergraph intraoral method

38. New arbitrary method Y = 9.5 c 0.95 (X ) Y = width profile of the face measured from the ectocanthion to the center of the external auditory meatus X = anterioposterior position Abdal-Hadi's technique

39. Clinical value of Hinge Axis

40. Allows for correct recording of centric relation and its transfer to the articulator Starting point of lateral movements Permits a change in vertical dimension If transferred to articulator—teeth contact each other in the articulator exactly as they do in the mouth Helps in diagnosis and treatment planning

41. Variables affecting hinge axis location

42. Patient variables affecting the T.H.A . locations Condyle Asymmetry Inability to locate a true hinge axis Myospasm or joint pathosis Emotional conditions of patient Factors of the recording system affecting THA Right angle non-right angle system of the bow Length of stylus arms and sharpness of styli

43. A minimal error of 5 mm can be expected no matter what arbitrary position might be chosen. Placement of the tragus-canthus line at the superior border of the tragus of the ear will contribute to greater inaccuracy in most patients. The largest percentage of true axis locations will be inferior to the tragus-canthus line at the superior border of the tragus of the ear summary

44. In the final analysis, the true value of our individual work can be measured only by the degree of fineness with which we practice the art of dentistry rather than by the particular school of thought to which we adhere. conclusion

45. Jeffery P. Okeson . Management of temporomandibular disorders and occlusion, 5th edition Zarb bolender -prosthodontic treatment for edentulous patients-12 th edition Shillingberg Heartwell Terminal hinge movement of the mandible J Prosthet Dent 1957;7:787-97 . Winstanley , R. B. The hinge-axis: A review of the literature . J Oral Rehabil 12:135-159, 1985. Hinge axis overview ; ashu sharma int journal of clinical dentistry Vol 5, no, 3 : 2012 reference

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