Generational cohort analysis of tooth loss in Japan

Objectives: The purpose of this study was to evaluate the percentiles and risk of tooth loss using comparative statistical analysis by age and the number of present teeth.

Methods: The percentiles were estimated using the cumulative frequency distribution of present teeth from two surveys undertaken by the National Survey of Dental Disease in Japan. The first was a survey of 3,272 subjects aged 46–75 in 1999, and the second was a survey of 2,399 participants aged 52–81 in 2005. The 1st to 100th percentiles of the number of present teeth were calculated for both age groups. Using these percentiles and a generational cohort from the two surveys, the projected number of teeth lost in the next six years could be calculated.

Results: The results revealed that the number of teeth lost per year was 0.13 for people who had 25 present teeth (PT), 0.32 for 20 PT, 0.51 for 15 PT, 0.56 for 10 PT, and 0.39 for 5 PT in the 46–60 age group. The peak of tooth loss was around 12 PT.In the 61–75 age group, the number of teeth lost per year was 0.25 for those who had 25 present teeth (PT), 0.58 for 20 PT, 0.79 for 15 PT, 0.73 for 10 PT, and 0.49 for 5 PT. The peak of tooth loss was around 15 PT.

Conclusions: The number of teeth lost for 15 PT in the 46-60 age group was twice as high as that of 20 PT in the 61-75 age group. This data provided proof that "tooth loss predicts tooth loss." This study suggested that there were a critical number of teeth that needed to be maintained to prevent further tooth loss.