Volume 118 (2010) Issue 2 Pages 141-149
Permanent tooth emergence was examined in a sample of 114 Japanese children (63 girls and 51 boys) born in Tokyo in 1914 and 1924. Subjects were enrolled as young infants from households spanning a wide range of socioeconomic conditions, without regard to parental income or occupation. The children were prospectively examined up to age 20 years with observations of permanent tooth emergence recorded to the nearest two or three months. Parametric logistic-survival analysis was used to estimate the distribution of tooth emergence and, simultaneously, an agenic proportion. The effects of infant and childhood health status (good, medium, poor), breastfeeding type (full, partial, not), child’s sex, and birth cohort (1914, 1924) were modeled on the hazard of permanent tooth emergence and the fraction of agenic teeth. Controlling for other covariates, males exhibited a shorter time to emergence for three (PM1, PM2, M3) of the 16 permanent teeth, compared to females. Breastfeeding significantly affected time to emergence for seven teeth (I1, M1, M2, I2, PM1, M1, M2), although the direction of the effect was not consistent among teeth. Poor infant health consistently delayed emergence relative to children in good health for the earliest emerging teeth. Children of medium or poor child health showed delayed emergence for six permanent teeth (I2, PM2, M1, I2, PM1, M3). The strongest and most consistent relationship was a delay in emergence for children born in the 1914 cohort. This cohort effect may reflect changes in health resulting from declining socioeconomic conditions in Japan during this period. The probability of a tooth being agenic was generally unaffected by infant and childhood health status, breastfeeding type, child’s sex, or birth cohort.