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A Study on the Determination of Instantaneous Centre of Rotation in the Mandibular Movement 하악골 운동의 순간회전 중심결정에 관한 연구
Keun Su Kang, Chang Keun Yoon
강근수, 윤창근

For the determination of instantaneous centre of rotation in the mandibular movement, the
habitual opening path was recorded on the sagittal tracing plate by a Gnathorecorder attached on
the lower anterior teeth which was designed for this study. The opening path was demonstrated
mathematically and the instantaneous centre of rotation in the opening path were calculated and
plotted by computer programs, and then a computer graphic movement of the mandible was
obtained according to the opening path. The hinge path of posterior border movement was
graphied by the Gnathorecorder as well and demonstrated mathematically. This hinge path was
compared with the same obtained by Visitrainer to prove a reliability of the Gnathorecorder. The
results obtained from this study were as follows.
1.  The habitual opening path and hinge path obtained from the Gnathorecorder movement were
expressed mathematically as follows: y = 0.11x2
+ 0.66x + 3.09(equation of opening path), y =
0.04x2
+ 0.21x + 3.71(equation of hinge path), and a kinematic hinge axis was not shown in
the equation of hinge path.
2.  The early habitual opening movement of the mandible demonstrated almost a straight opening
path or an arc motion with the larger radius and it’ s centre of rotation moved parallelly in the
more rear and lower position than a kinematic hinge axis.
3.  Instantaneous centre of rotation occurred along with the translation of the condyle, and
Mandible was rotated around an axis in the close to the maximum opening and then moved
toward the forward and upward position.
4.  There were some similarities between the articular eminence and the movement pattern of a
special point, which was the kinematic hinge axis.

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