[Study on changes of mandibular movement by aging. 1. Analysis of sagittal movements].

It is known that the temporomandibular joint changes with age. However, it isn't clarified yet how these changes affect mandibular movements. Therefore, I investigated the changes which occur in mandibular movement with aging. This study details 62 cases whose age ranged from 20 to 79 years, and whose dentition was either complete or nearly so, and whose intercuspal position was firm. First, I investigated the path of protrusive movement at representative points on the mandible, such as incisor, canine, first molar, second molar, the condylar center and the kinematic axis point. Results were as follows: 1) Data obtained from the 20 to 29 year old age group differed little from the results of previous investigations, 2) The sagittal inclination of the condylar path became less acute in subjects 60 years and over than in the younger subjects. Second, I evaluated the vertical mobility of the condyle by the gap between opening path and closing path of the condyle in sagittal border movement and the location of the kinematic axis point. The results showed that the gap between the two paths of the condylar center was slightly larger and the kinematic axis point was tended to locate more anteriorly in subjects 50 years and up than in the others.