Association between third molar agenesis patterns and agenesis of other teeth in a Japanese orthodontic population

The purpose of this study was to investigate the patterns of third molar agenesis and incidence of agenesis of other permanent teeth in a Japanese orthodontic patient group. A total of 417 Japanese subjects (134 males and 283 females) with agenesis of one or more third molars were divided into four groups according to the agenesis pattern, and 874 other Japanese subjects (302 males and 572 females) without third molar agenesis were assigned to a control group. Panoramic radiographs and medical and dental records were used to examine for tooth agenesis. The Chi-square test and odds ratio were used to make statistical comparisons. The prevalence of third molar agenesis worked out at 32.3% with no statistically significant gender difference. A high prevalence rate of agenesis of third molars, unilateral or bilateral, could be considered characteristic of the Japanese orthodontic population. Significant increases in occurrence of oligodontia, and unilateral or bilateral agenesis of other teeth, including maxillary lateral incisors and maxillary and mandibular second premolars, were observed in all or almost all of the third molar agenesis groups, compared with the controls. A significantly increased prevalence rate of mandibular lateral incisor agenesis was observed in almost all of the third molar agenesis groups. The Japanese patients with third molar agenesis had a significantly increased occurrence of oligodontia, and unilateral or bilateral agenesis of maxillary and mandibular lateral incisors and second premolars, except for bilateral agenesis of mandibular lateral incisors.