2016 Volume 31 Issue 1 Pages 39-50
Using data from The Surveys of Dental Diseases, conducted by the Ministry of Health, Labour, and Welfare from 1957 to 2011, variations in the number of permanent teeth in the Japanese population were descriptively and epidemiologically observed by performing a cohort analysis using a Bayesian age-period-cohort model.
Between 1957 and 1975, the number of teeth among 65-year-old Japanese males and females ranged from 13 to 15 and 9 to 10, respectively. In 2011, the number of teeth exceeded 20 for both sexes. Similarly, in other groups over the age of 40, until 1987, the number of teeth was 3 to 5 higher among males than among females；however, such differences between the sexes were rarely observed in 2011.
In the cohort analysis, the age effect, when compared with the two other effects, ranged more markedly indicating a close association between the number of teeth and age. The period effect, which was the smallest between 1975 and 1987, subsequently increased. This tendency of the period to increase was more marked among females. The cohort effect was small among those born before 1900, and generally, large among those born between 1930 and 1975. Females also showed a higher level of improvement than males in this respect.
To summarize, while decrease in the number of teeth was associated with aging in most cases, there was a tendency for it to improve in all age groups from 1993, with the pace of such improvement being higher among females. Sex differences in the number of teeth in adults were not observed in 2011. If this tendency continues, the situation will probably reverse, and the number of teeth will be higher among females than among males. In order to promote dental health on a nationwide basis under these circumstances, it may be necessary to provide population-based approaches, particularly the ones to enhance the interest of males in dental health and to guide them to take measures to maintain a sufficient number of teeth.
To increase of the number of teeth of the elderly, we should start quantitative changes as well as qualitative ones for their oral health care and dental treatment.
