Monitoring time-related trends in dental caries in permanent teeth in Japanese national surveys

Objectives: According to dental examinations of 3- and 12-year-old children conducted throughout Japan, the prevalence of dental caries in children is decreasing. However, little is known about changes in the prevalence of dental caries in adults. This study analysed past and present prevalences of dental caries in permanent teeth and predicted future trends in dental caries in adults. Methods: Data were sourced from nine national dental surveys conducted in Japan at 6-year intervals from 1957 to 2005. Data from oral examinations were recorded as indices of decayed, missing and filled teeth. Results: The mean number of filled teeth increased markedly, whereas mean numbers of decayed teeth and missing teeth decreased substantially in people aged 40 years. By contrast, the mean number of filled teeth first increased and then decreased in groups aged 5-39 years. Conclusions: Among Japanese respondents sampled in a series of cross-sectional studies between 1957 and 2005, the incidence of dental caries in young adults decreased, suggesting a decrease in prevalences of dental caries in future generations. However, this tendency was not observed in respondents aged 40 years. The results suggest adults will experience less dental caries in the near future.