TRANSFER OF TRANSVERSE HINGE AXIS TO AN ARTICULATOR

TRANSFER OF TRANSVERSE HINGE AXIS TO AN ARTICULATOR:

TRANSFER OF TRANSVERSE HINGE AXIS TO AN ARTICULATOR GUIDED BY: Dr. MANJULA DAS DEPARTMENT OF PROSTHODONTICS REGIONAL DENTAL COLLEGE GHY-32 . PRESENTED BY: SANGEETA BAYAN ROLL NO-10 FINAL YEAR B.D.S

CONTENTS:

CONTENTS INTRODUCTION DEFINITIONS AND TERMINOLOGIES MANDIBULAR MOVEMENTS HINGE AXIS TRANSVERSE HINGE AXIS HISTORY VALUE OF TRANVERSE HINGE AXIS SIGNIFICANCE OF TRANSVERSE HINGE AXIS IN MANDIBULAR MOVEMENTS. NEED TO LOCATE TRANSVERSE HINGE AXIS OF MANDIBLE KINEMATIC FACEBOW LOCATING THE TRANSVERSE HINGE AXIS. SELECTION OF ARTICULATORS TRANSVERSE HINGE AXIS TRANSFER TO THE ARTICULATOR CONCLUSION BIBLIOGRAPHY

INTRODUCTION:

INTRODUCTION . Theoretically a hinge movement (pure rotation )of the mandible can be generated from any mandibular position anterior to centric relation ,for this to occur condyles should be stabilised so that translation of the horizontal axis does not occur . This stabilization is difficult to establish except at the terminal hinge position. It is the only true hinge position of the mandible. The mandibular hinging movement around the transverse horizontal axis is repeatable. That makes this imaginary "hinge axis" around which the mandible may rotate in the sagittal plane. Facebows are used to record the anteroposterior and mediolateral spatial position of the maxillary occlusal surfaces relative to this transverse opening and closing axis of the patient's mandible. The facebow is then attached to the articulator to transfer the recorded relationship of the maxilla by ensuring that the corresponding cast is attached in the correct position relative to the hinge axis of the instrument. After the maxillary cast has been attached to the articulator with mounting stone or plaster, the mandibular cast is subsequently related to the maxillary cast through the use of an interocclusal record. If the patient's casts are accurately transferred to an instrument, considerable time is saved in the fabrication and delivery of high-quality prosthesis .

DEFINITIONS AND TERMINOLOGIES :

DEFINITIONS AND TERMINOLOGIES Hinge axis :- An imaginary line around which the mandible may rotate within the sagittal plane. (It is also called- Transverse horizontal axis). Hinge axis point/posterior reference points :- Two points, located on each side of the face in the area of transverse horizontal axis of mandible. Hinge bow/Kinematic face bow:- A face bow with adjustable caliper ends used to locate the transverse horizontal axis of mandible. Kinematic axis: - The transverse horizontal axis connecting the rotational centers of right & left condyles . Pantograph : n (1723) 1: an instrument used for copying a planar figure to any desired scale. 2: in dentistry,an instrument used to graphically record paths of mandibular movements and to provide information for the programming instead of adjustment of an articulator. The axis :” A line around which a body may rotate or about which a structure will turn if it could revolve “ (GPT-5)

Slide 5:

Hinge joint:- A ginglymus joint, a joint that allows motion around one axis. Hinge position :- The orientation of parts in a manner permitting hinge movement between them. Terminal Hinge axis: - An imaginary line around which mandible can rotate in sagittal plane & passes horizontally through the rotational centers of right & left condyles when they are in their most retracted/distal, unstrained position in their respective articular / glenoid fossa . Facebow: A caliper like device that is used to record the relationship of the jaws to the temperomandibular joints and to orient the casts on the articulator the relationship of the opening axis of the temperomandibular joint. Articulators: An Articulator may be defined as “a mechanical device that represents the Temperomandibular joints and jaw member to which maxillary and mandibular cast may be attached to stimulate jaw movement”. GPT . Centric relation : The maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the anterior-superior position against the shapes of the articular eminences. This position is independent of tooth contact. This position is clinically discernible when the mandible is directed superior and anteriorly . It is restricted to a purely rotational movement about the transverse horizontal axis (GPT 5)

MANDIBULAR MOVEMENTS:

MANDIBULAR MOVEMENTS ROTATIONAL MOVEMENT TRANSLATIONAL MOVEMENT

Plane Axis:

Plane Axis Fig. 4-6. Reference planes.

ROTATIONAL MOVEMENT:

ROTATIONAL MOVEMENT The process of turning around an axis ;the movement of body about its axis ( dorland medical dictionary) In masticatory system ,rotation occurs when the mouth opens and close around a fixed point or axis within its condyle .

Slide 9:

Rotation movement of mandible can occur in all three reference planes : Vertical Sagittal Horizontal

FRONTAL (VERTICAL) AXIS OF ROTATION:

FRONTAL (VERTICAL) AXIS OF ROTATION It occurs when one condyle moves anteriorly out of terminal hinge position with the vertical axis of opposite condyle remaining in the terminal hinge position. The inclination of the articular eminence, dictates the frontal axis tilt of the orbiting condyle as it moves forward. This type of isolated movement doesn’t occur naturally

SAGITTAL AXIS OF ROTATION:

SAGITTAL AXIS OF ROTATION It occurs when one condyle moves inferiorly while other remains in the terminal hinge position. Ligaments and muscles prevent inferior displacement of the joint. This type of movement doesn’t occur naturally but occur in conjunction with downward and forward movement of the condyle

HORIZONTAL AXIS OF ROTATION:

HORIZONTAL AXIS OF ROTATION Mandibular movement around the horizontal axis is an opening and closing motion, referred to as Hinge Movement and horizontal axis around which it occurs is therefore referred to as “ HINGE AXIS ”.

HINGE AXIS :

HINGE AXIS Mandibular movement around the horizontal axis is an opening and closing motion, referred to as Hinge Movement and horizontal axis around which it occurs is therefore referred to as “HINGE AXIS ’’ This rotation averages about 12 degree with a range from 10-13 degree or 18-25mm of incisal opening according to Rahn , and occurs during centric relation. Hinge axis allows us to mount cast on an articulator with a bite at an increased vertical dimension. It allows us to orient the pantograph to the horizontal axis.

TRANSVERSE HINGE AXIS :

TRANSVERSE HINGE AXIS Definition: An imaginary line around which mandible can rotate in sagittal plane & passes horizontally through the rotational centers of right & left condyles when they are in their most retracted/distal, unstrained position in their respective articular / glenoid fossa .

HISTORY:

HISTORY Among the initial recorded evidences of hinge axis is that of Ferrien , in 18 th century & the first edition of Gray’s anatomy . The hinge like action of the TMJ has been described by anatomist for hundred of years. Its application to dentistry however, had to wait for the Gnathological society in 1920. It was gnathological society that developed the means of accurate location of the hinge axis. McCollum , Stuart (1921) reported discovery of first method of locating the axis. McCollum,”mandibular hinge axis and method of locating”; j.prosth dent:196 0

Slide 16:

Wadsworth (1925) Anatomist's view: first movement around transverse axis through condyles which remain seated in fossae . 2nd movement on eminentia . Lauritzen (1951) discussed the physiology of the TMJ. 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 was 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. Lauritzen and Wofford (1961) - Hinge axis location on an experimental basis - To study the accuracy of hinge axis location techniques. A special device was designed to test the hinge axis location at 5, 10, 15 degrees of movement .

Slide 17:

Credit for the idea of the mechanical location of an axis was given to Dr. Robert Harlan*. Snow recognized the importance of the hinge axis in the mandibular movements and developed a face-bow to be used to transfer to the articulators. Granger stated (1952): There is however one & only one position in which the hinge axis is constant to both maxilla & mandible. Centric relation, J. Pros. Den. 2:162, 1952 Kornfeld stated (1955 ): The hinge axis can be located accurately by trial & error. He also stated that the location of the hinge-axis was the basis of all articulator transfer. Problem of function in restorative dentistry : J. Pros. Den, 5:673. 1955

Slide 18:

Granger (1952) Centric relation is the only position where hinge axis is common to both mandible and maxilla. Trapozzano and Lazzari (1961) A study of hinge axis determination. To investigate whether there is a terminal hinge axis, and whether or not only one exists. 52% of the subjects showed more than one hinge axis point. These findings indicate that, since multiple condylar hinge axis points were located, the high degree of infallibility attributed to hinge axis points may be seriously questioned. Gordon (1984) Location of the terminal hinge axis and its effect on the second molar cusp position .

VALUE OF TRANSVERSE HINGE AXIS   :

VALUE OF TRANSVERSE HINGE AXIS Pure hinge movement. Starting point of lateral movement Landmark for jaw registration . Hinge axis allows us to mount cast on an articulator with a bite at an increased vertical dimension. It allows us to orient the pantograph to the horizontal axis. Constant point to both maxilla & mandible . To check the accuracy of the centric inter occlusion record . Permits vertical dimension to be changed Transfer of opening axis . Allows CR record in dentulous situation Benefit in diagnosis & treatment planning \

SIGNIFICANCE OF TRANSVERSE HINGE AXIS IN MANDIBULAR MOVEMENT :

SIGNIFICANCE OF TRANSVERSE HINGE AXIS IN MANDIBULAR MOVEMENT Every seconds during mandibular movement & maxillomandibular relationship changes Position of the hinge axis changes moving the mandible beyond the comfortable opening (18-25mm)(terminal hinge axis position). If hinge axis record has been properly transferred, an accurate centric relation record will orient the lower cast to the opening axis of the articulatorr in the same relationship as the patients mandible relates to his/her opening axis. For articulator to provide accurate interocclusal relationships, the cast on the articulator must relate to the hinge axis of the instrument in as nearly as possible the same way on the jaws relate to the patents are of closure.

Slide 21:

The hinge movement is probably the only example of mandibular activity in which pure rotation occurs. In all other movements rotation around the axis is accompanied by translation of the axis . It is only by means of hinge axis & centric relation that the teeth can be located to the terminal hinge position i.e. CR=Co. If permits to control the vertical dimension on the articulator. the vertical dimension can be raised up to (3-4)mm on the articulator when the hinge axis transferred. BROTMAN. If makes it possible to duplicate all the eccentric relations and all the possible contacts of the teeth in these relations

NEED TO LOCATE TRANVERSE HINGE AXIS OF THE MANDIBLE :

NEED TO LOCATE TRANVERSE HINGE AXIS OF THE MANDIBLE The relation of maxillary cast to the axis of rotation of the articulator must be the same that exist between the maxillae and the terminal hinge axis in the skull. Border movement in articulator will not be same as in patient’s mouth. If it is not the same there will be a disharmony of the arc of closure in the articulator and in the patient’s mouth, leading to occlusal discrepancies when the prosthesis is given to the patient.

Slide 23:

TMJ Instrument Axiograph Pantograph

Slide 24:

KINEMATIC FACE BOW QUICKMOUNT FACE BOW

Slide 25:

FACE BOW BY WHIPMIX FACE BOW BY ARTEX

Slide 26:

HANAU SPRING BOW SLIDEMATIC FACEBOW

Slide 28:

Electronic jaw recording system. The Axiotron is an electronic recording system that attaches to the Axiograph pantograph. (Courtesy Great Lakes Orthodontics.)

KINEMATIC FACE-BOW   :

KINEMATIC FACE-BOW DEFINITION : A facebow with adjustable calliper ends used to locate the transverse horizontal axis of mandible. The kinematic face bow locates the rotational points of the condyles by using mandibular opening and closing movement. Kinematic facebow are indicated when it is critical to precisely reproduce the exact opening and closing movement of the patient on the articulator.. The kinematic Facebow consist of three components: a transverse component and two adjustable side arms the transverse component is attached to the clutch that protrudes from the patient mouth. The side arms are than attached to the transverse member and adjusted so that syli are as close to the joint area as possible . Fig. Kinematic Face-bow

LOCATING THE TERMINAL HINGE AXIS OF THE MANDIBLE :

LOCATING THE TERMINAL HINGE AXIS OF THE MANDIBLE There are two methods to locate hinge axis , they are:- Kinematic or hinge method Pantograph tracing Geometric method

1.KINEMATIC OR HINGE METHOD:

1.KINEMATIC OR HINGE METHOD It is essentially same for the dentulous and the edentulous patient , except the method of attaching clutch (mechanical device to which hinge axis bow is attached )to the mandible are different for the two case. Once the clutch has been attached to the mandible and hinge bow is attached to it, patient is asked to lie in a semi-supine position, with head tilted slightly in backward . Guide the patient in making hinge opening and closing movement. Stylus present on he either side of the hinge axis locator move bodily in an arc form when the stylus is not at the hinge axis which is demonstrated onto the flags attached to it. Fig 2-11. Hinge axis recording: Left and right styli are attached via a facebow to a clutch affixed to the mandibular teeth. When the mandible makes a strictly rotational movement, the stylus will remain stationary if aligned with the actual axis of rotation. If the stylus is positioned forward or backward, above or below the actual axis, it will travel one of the arcs indicated by the arrows when the mandible makes a rotational movement. Thus, the arc indicates in what direction an adjustment should be made to the stylus position

Slide 32:

When styli are present on the hinge axis there will be no arcing of the styli rather there will be only rotation of the styli onto a single point with out arcing , this point is marked onto the patient , and is the true hinge axis This hinge axis is transferred to the articulator for the mounting of the maxillary cast in the same relation to the hinge axis of the articulator as that of maxillae to the temporomandibular joint. 80% of the kinematic axis points were located below a reference line drawn from the superior border of the tragus to the outer canthus of the eye, and posterior to a point 13 mm anterior to the superior border of the tragus on the same reference line. Schalhorn , R. G. A study of the arbitrary center and kinematic center of rotation for facebow mounting. J Prosthet Dent 7: 162-169, 1957.

Slide 33:

Fig. 2-10. Kinematic hinge axis facebow . A, Mandibular clutch. The clutch separates for removal into two components by loosening the screws on left and right sides. B, Transferring the position of the mandibular hinge axis. C. pointers aligned with the previously marked hinge axis location. D.Kinematic facebow aligned on the articulator.

PANTOGRAPH TRACING:

PANTOGRAPH TRACING The pantograph consist of two facebows . One is affixed to the maxilla and other to the mandible, using clutches that attach to the teeth in respective arches. Recording styli are attached to one member of the instrument and small tables upon which the tracing are made are attached to the other member of the instrument, opposite the styli. Mandible goes through a opening and closing movement within the range of 18-25mm of interincisal opening. The styli of one facebow produces arching movement on the recording table as the mandible moves. When the stylus rotates on a single point on the recording table , that point is transferred to the skin. This point is the terminal hinge axis point . The axis formed by joining this two point is the terminal hinge axis. After locating the hinge axis the pantograph is attached to the articulator , various adjusments are made until the movement of the articulator follow the same path scribed on the tracing by the stylus on the patient. Pantographic tracing can only utilized full advantage when used with a fully adjustible articulator.

PANTOGRAPHIC TRACING :

PANTOGRAPHIC TRACING

GEOMETRIC METHOD :

GEOMETRIC METHOD Getz (1988) Application of a geometric principle for locating the mandibular hinge axis through the use of a double recording stylus. Theorem #1 . A line drawn through the centre of a circle perpendicular to a chord meets it as its midpoint and bisects the arcs determined by the chord; Theorem#2: The line joining the center of a circle to the midpoint of a chord is perpendicular to the chord. Using a modified Satellite Bow with double recording styli at a distance of 2 to 4 inches from the estimated axis area, 12 determinations on 2 subjects were made. It was possible to define the axis point between 0.1 to 1.0 mm. Getz, E.H. et al. Application of a geometric principle for locating the mandibular hinge axis through the use of a double recording stylus. J Prosthet Dent 60:553-559, 1988

SELECTION OF ARTICULATORS :

SELECTION OF ARTICULATORS Articulators can simulate the movement of the condyles in their corresponding fossae . Most articulators use mechanically adjustable posterior controls to simulate these movements, although some use plastic premilled or customized fossa analogs . If an articulator closely reproduces the actual border movements of a given patient, this will significantly reduce chair time because the dental laboratory can then design the prosthesis to be in functional harmony with the patient's movements. In addition, less time will be needed for adjustments at delivery .

Slide 39:

Example: Gariot Articulator, slab articulator They are simple articulator and capable of accepting a simple static registration and only vertical motion is possible These articulators are used to diagnose dental occlusal conditions. These instruments do not have the capacity to reproduce the full range of mandibular movement. SMALL NON ADJUSTIBLE ARTICULATOR

SEMI-ADJUSTABLE ARTICULATOR :

SEMI-ADJUSTABLE ARTICULATOR Example: Dentatus series, Hanau-H 2 , Artex series They are most used articulator as they attempt to reproduce jaw movements of each patient’s jaw by trying to reproduce anatomy of jaw joints and related structures. There are two basic designs of the semiadjustable articulator: the arcon (for articulator and condyle ) and the nonarcon . Fig. . Semiadjustable arcon articulators. A, The Denar Mark 11. B, The Whip Mix model 2240. (A Courtesy Dmar Corporation.) minimal Advantages: Semiadjustable instruments do not require an inordinate amount of time or expertise. Safe and easy operation and offers better performance and precision. Its innovative design permits a better access and visualization of operating field from lingual side .

FULLY ADJUSTABLE ARTICULATORS:

FULLY ADJUSTABLE ARTICULATORS A fully (or highly) adjustable articulator has a wide range of positions and can be set to follow a patient's border movements. Advantages: They are capable being adjusted to follow the mandibular movements in all directions. These articulator have numerous adjustable readings, which are customized for each patient as recorded by a PANTOGRAPH. Because of their complexity they are used for Gnathologic studies and occlusal rehabilitation through full mouth crowns and restorations. Limitations: They are not commonly used because of their complexity. Cost effective Time consuming and requires a high level of skill and understanding. Fig. Fully adjustable articulators. A, The Stuart..B, The Denar D5A.

TRANSVERSE HINGE AXIS TRANSFER TO THE ARTICULATOR.   :

TRANSVERSE HINGE AXIS TRANSFER TO THE ARTICULATOR . The transverse hinge axis of the mandible recorded using a kinematic facebow is transferred to an articulator by the following techniques.

Slide 43:

Fig. 2-23. Mounting the maxillary cast articulator.A , Remove the incisal pin. B, Adjust the condylar inclination to the facebow setting. C, Set the sideshift to zero. D, Attach a mounting plate. E, Attach the facebow earpieces to the condylar elements. F, Facebow attached to the articulator.G , Position the scored maxillary cast on the bitefork and prewet the cast. H, Mounting stone is applied to the cast and the mounting plate.I , Close the upper member of the articulator until it contacts the cross bar of the facebow . J, Add additional stone as needed. (Courtesy Whip Mix Corporation.)

CONCLUSIONS:

CONCLUSIONS There is much in the prosthodontic literature that transfer of TRANSVERSE HINGE AXIS to an articulator using a facebow is essential for avoiding errors in the occlusion of finished dentures. The elimination of errors that can be produced by failure to use the face bow where indicated justifies the time required and procedures involved in face bow transfer. Though various methods have been proposed to record transverse hinge axis ,reliability of any of the method is questionable, reason being, the concept of hinge axis and its importance during articulation is still controversial. Many workers still believe that there is not significant benefits to record hinge axis, whereas other believe that arbitrary recording of the hinge axis is reliable enough to transfer to the articulator.

BIBLIOGRAPHY :

BIBLIOGRAPHY Temporomandibular Disorders & occlusion : Okeson 5 th edition. Shilliburgs Fundamentals of Fixed Prosthodontics . Rosentiels Contemporary fixed Prosthodontics Zarb,Bolender, Boucher’s Prosthetic Treatment For Edentulous Patient , E td . 11, biological and clinical consideration in making jaw relation 12:197-219. Heartwell Textbook On Complete Edentulism , Etd.4,maxillomandibularrelation 11:277-305. ESSENTIAL OF COMPLETE DENTURE PROSTHODONTICS- SHELDON WINKLER (2 ND EDITION). INTERNET SOURCES.

THANK YOU:

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