Abstract
The trajectory of the incisal point has been used as a parameter by many studies concerning jaw movements during mastication. Little information, however, is available regarding the movements of molars, in which area masticatory movement is actually performed. Our previous studies reported that sagittally-viewed masticatory patterns are different among incisal and molar points, while frontally-viewed patterns are same within the individual. However, these findings were based on the analysis of only masticatory envelopes. The purpose of this study was to clarify the movements of molars as related to those of incisor, especially close to the intercuspal range.
Using chewing gum as foodstuff, masticatory movements were measured on 50 normal young adults (22 males & 28 females, 19-35 yrs, mean 22.3 yrs) using the 3-D mandibular movement analyzing system. The analyzing points were medial edge of the left lower incisor and distobuccal cusp of the working-side and non-working-side lower 1st molar. Their 3-D position at every 0.1mm level was calculated for each stroke at each analyzing points from ICP to 3.0mm opening level. After averaging the data from 10 strokes on each subject, the individual averaged anteroposterior and lateral positions of incisal, working-side and non-working-side molar points were obtained. Difference in the antero-posterior and lateral locations of the opening and closing paths were tested statistically among 3 analyzing points. Statistical significance was set at 5% and determined by Post-Hoc test and Fisherman's PLSD test. The results were as follows:
1. Frontally-viewed opening and closing path was consistent in location among 3 analyzing points.
2 . Sagittally-viewed opening path was also consistent among 3 analyzing points, while closing path were different among each point, i.e, the closing path of working-side molar points located posteriorly and non-working-side molar points located aoteriorly, compared to that of incisal point.
It was concluded that the masticatory closing path of the molar points were different in location from incisal point close to the intercuspal range.
