[Development of mandibular movements associated with growth and development of stomatognathic system]

In order to clarify the development of mandibular movements associated with growth and development of the stomatognathic system, we compared the mandibular movements of children with normal occlusion at different Hellman's dental age between IIA and IIIB, during tooth tapping movements using the following 7 different kinds of frequency; ad lib.; 1 time/sec, 2 times/sec and 3 times/sec movements with reguration; 1 time/sec, 2 times/sec and 3 times/sec movements without reguration. Then, we determined the correlation between the results and the subjects' chronological age and obtained the following findings. 1) During 5 strokes between the 3rd and 7th strokes after the start of the tooth tapping movements, mandibular movements were not very diversified among 30 tooth tapping movements using the 7 different kinds of frequency, and the mean values were almost consistent. 2) In the 5 strokes between the 3rd and 7th strokes at all dental age, each determined item showed minimal dispersion during the 3 times/sec unregurated movements. 3) In the following items, changes related to age were noted during the 3 times/sec unregurated movements. (1) Cycle time decreased and became closer to the calculated value (333.33 msec), and maximum velocity in closing increased as age advanced. (2) Although there was no significant correlation with the subjects' chronological age, degree of mandibular opening, duration of opening phase, duration of closing phase, duration of occluding phase and velocity peak time in opening decreased, and maximum velocity in opening increased as age advanced. (3) Velocity peak time in closing was only slightly influenced by age. 4) These results indicate that mandibular movements develop in the course of growth and development of the stomatognathic system.