The aim of this study was to determine age- and sex-specific differences in the ratio of occluding pairs (OPs) to number of present teeth (PT). The data were obtained from a periodontal disease examination carried out under a health promotion law in a city located northeast of Tokyo, Japan, in 2005. Data from a total of 5,131 (1,735 male and 3,396 female) 40-, 50-, and 60-year-old participants were analysed in this study. Occluding pairs were counted by analysing dental charts. Sex-related differences in the ratio of mean PT to OPs were found at 30 PT in 40-year-olds, at 22 PT and 28 PT in 50-year-olds, and at 24 PT and 28 PT in 60-year-olds. Age differences were only found at 28 PT in males. These differences in the ratio of PT to OPs were influenced by the presence of third molars and the type of tooth loss pattern. In some cases the PT-to-OP ratio is influenced by age and sex, but these differences are very small. Age and sex need to be considered when using PT to estimate OPs.
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