[Prediction of mandibular movement by observation of facial skin markers].

Purpose: Various methods have been used for observation of mandibular movement. However, many methods disturb physiological movement as the subject must wear a sensor. Therefore, to predict mandibular movement from the motion of facial skin, the correlation between the movements of mandibular incisor-tooth point and facial skin markers was evaluated by multiple regression analysis.

Methods: Nine retro-reflective markers were placed on the lower facial skin of 8 dentulous subjects and three markers on the wire frame attached to the mandibular tooth, respectively. Movement of markers was repeatedly recorded by 6 video cameras from centric occlusion to maximal opening position. Data was analyzed and the movements were constructed in 3D. In order to predict movement (opening, vertical, anterior-posterior) at an incisor-tooth point, multiple regression analysis was performed by making the 27 amounts of 3D movements (X, Y, Z components) of nine facial skin markers as explanatory variables. The difference between the actual value and the predicted value by multiple regressions was calculated, and compared in the 5 ranges of analysis (0-5 mm, 0-10 mm, 0-15 mm, 5-10 mm, 10-15 mm).

Results: The movements of mouth opening and vertical direction could be predicted with the accuracy of 0.76 mm (3.7%)and 0.69 mm (4.9%) in the range of 0-15 mm with nine variables, respectively. However, the accuracy of movements in the anterior-posterior direction was 0.40 mm (9.7%) with ten variables. The ratio was larger than these in the movements of mouth opening and vertical direction.

Conclusions: It was suggested that movement of mandibular incisor-tooth point in mouth opening and vertical direction to 15 mm could be predicted from the facial skin markers.