Chronological comparison on the occurrence of tooth germs of the maxillary and mandibular third molars in the orthodontic patients

Abstract

It has been recognized that the third molars effect the posterior discrepancy and the stability of the dental arch after orthodontic treatment. We investigated the chronological changes of the occurrence of the third molar germs and the relationship between those occurrence and the malocclusions. The selected subjects were 283 patients less than fifteen years old at the orthodontic clinic of Hokkaido University Dental Hospital. The congenital deformities such as cleft palate were excluded from the subjects. The subjects were divided into two groups. The one group was 147 patients who were initially examined between April 1981 and September 1982 (80s group), and the other group was 136 patients examined between February 1993 and November 1994 (90s group). Panoramic radiographs were used as materials. The following results were obtained : 1 .The frequency of the patients having all four third molars in the 90s group was slightly higher than that in the 80s group. The frequency of the existence of the mandibular third molars was significantly higher than that of the maxillary ones in both groups. 2. The frequency of the Class II patients having all third molars was significantly higher than that of the Class III. These results suggest that the orthodontic patients having all third molars slightly increase and this is related with the increment of Class II patients.