TERMINAL HINGE MOVEMENT OF THE MANDIBLE

TERMINAL HINGE MOVEMENT OF THE MANDIBLEUlf PosseltThe Royal Dental School,Malmo,SwedenVol 86 num1 JPDReprinted from JPD 1957;7:787-97

Terminal hinge movement is a typical opening and closing movements with the condyles remain in their most posterior(superior) positionsRemarkably consultantReproducibleRELATION OF HINGE AXIS TO CONDYLES-LITERARY REVIEWMccollum: Axis point fell within the outlines of either condyleBeyron and Good: Axis point of each condyle was located within the outline of the condyle but not in any static relationship to any definite part of condyle

AIM OF THE PRESENT INVESTIGATIONThe study was undertaken to further elucidate the terminal hinge movement upto 20mm of hinge opening by checking the relation of the axis point to the condyles and by recording the shift of the kinematically established hinge axisMATERIALS AND METHODSSUBJECTS 19 Male volunteers: Profile Roentgenogram 13 Male volunteers: Gnatho-thesiometer AGE : 20 TO 29 YEARS PROFILED ROENTGENOGRAMS were made in (1) The most posterior contact position (2) The most posterior position with the hinge opening of about 20mm (3) With maximal opening

TRACING OF THE PROFILE ROENTGENOGRAMX ray outline of the most important parts of the skull, with the mandible in the most posterior contact position, was traced onto a transparent paperError of double contouring if occurred can be eliminated by drawing and intermediate line between the double contoursThe accuracy of tracing method can be assessed by the following method

the apparatus for

The apparatus for checking tracings from roentgenograms. The degree of rotationaround the vertical axle can be read from the scale (a) on the base. Rotation around the sagittalaxle (b) can be read from the frontal scale at (c). roentgenogram of the mandible. At 5 degrees left rotation around the vertical axis(above) in right rotation# (below)

REPRODUCTION OF THE TERMINAL HINGE MOVEMENT WITH A CARDBOARD PATTERN

GEOMETRICAL CONSTRUCTION OF THE HINGE AXIS FROM PROFILE ROENTGENOGRAMS

AXIS POINT RECORDED BY MEANS OF A KINEMATIC FACE BOW AND CHECKED BY PROFILE ROENTGENOGRAMS

HINGE AXIS ESTABLISHED BY MEANS OF KINEMATIC FACE BOW AND CHECKED BY MEASUREMENTS IN THE GNATHO- THESIOMETER

RESULTS

The median section of the terminal hinge axis lies within the outline of condylesThe position slightly anterior to the mid point of condyle was recorded two of the four cases in which indicators had been attached to the axis pointThe standard deviation for sagittal shifts increases with increase in opening but within the confines of contour of condyles, so this suggests the terminal hinge movement with the recorded extension of 50 to 20mm can be recorded as rotation around an axis passing through condyles

DISCUSSIONThe hinge opening as measured on the roentgenograms corresponds to an angle of 15 degrees on the average( range: 12 to 18 degrees)Although the experiments presented here suggest that the mandible carries out its terminal hinge movement around an axis passing through the condyles, they do not per se imply that the axis can be precisely recorded by means of a kinetic hinge axis face bow , nor do they elucidate problems concerning the imitation on the instrument of the terminal hinge movementSUMMARYThe terminal hinge movement was analysed by means of the following methods: (1) geometric constructions from profile roentgenograms; (2) axis points recorded by means of kinematic face bow and checked by profile roentgenograms; and (3)hinge axis established by means of kinematic face bow and checked by gnatho-thesiometeric measurements17The results obtained were similar in so far as they showed the axis of the terminal hinge movement to pass through both condyles or make only minor shifts.This is true for hinge openings of 15 upto 20mmThank you