Third Molar Emergence in a Modern Japanese Population

The emergence ages of third molars in a modern Japanese population were examined, and the results were compared with those for other ethnic groups. The subjects of the study consisted of 983 individuals (539 males and 444 females) aged 18 to 40 years. The family backgrounds of all of the individuals studied were presumed to be of the middle-class socioeconomic group. In each case, a third molar was judged to have erupted if any part of the tooth crown had pierced the gingiva. The median emergence age was estimated by probit analysis of the incidence of eruption, measured as the number of persons at each age level with one or more third molars erupted. The median emergence age was 19.59 years for males and 20.67 years for females. More third molars had erupted in males than in females at any given age. Also, mandibular molars tended to have erupted earlier than their maxillary counterparts, especially in females. Viewed from a global perspective, the Japanese population was characterized as experiencing third molar emergence at a relatively late age.