Abstract
Purpose: The shift of condylar position was three-dimensionally measured to clarify the effect of repeated opening and closing movements without any teeth contact on the condylar position when the mouth was closed, and the relationship between that movement and the condylar position was evaluated.
Methods: Thirty-two dentulous subjects were enrolled. Prior to the measurement, they were examined for muscle tenderness. Then, bilateral deviations of condylar points were measured after repeated opening and closing movements by the “Win Jaw System®”. Mouth-opening range was classified into three levels: “maximal voluntary opening”, “intermediate opening”, and “slight opening”. The number of times of opening and closing movements was classified into 12 levels: 0, 1, 2, 4, 6, 10, 12, 14, 16, 18 and 20 times.
At each time, three-dimensional shifts of condylar point were measured and were evaluated according to each condition such as presence of muscle tenderness or not, mouth-opening range, and number of times of mouth opening and closing movements.
Results: The positional deviation of condylar point was significantly different in the number of times of mouth opening and closing at “maximal voluntary opening”. A significant difference was found on the vertical shift in the group without muscle tenderness, and in the group with muscle tenderness that was found on anteroposterior and vertical shift. The degree of these shifts grew larger in accordance with the number of times of opening and closing movements.
Conclusions: The shift of condylar position was caused by the repeated maximal opening and closing movements without any tooth contact, and its degree increased according to the number of that particular movement. These results will be useful for occlusal treatment.
