IADR Abstract Archives
Tooth Exfoliation Timing and Patterning in a Cohort of Australian Twins
Objectives: This study quantified the timing and sequence of tooth exfoliation in a cohort of Australian twins, and explored the modifying roles of sex, zygosity, gestational age, and primary tooth emergence timing.
Methods: Participants were 550 pairs of twins and their parents enrolled in a longitudinal Australian birth cohort study (HREC H-78-2003). Exfoliation dates were recorded by parents. Exfoliation dates were examined for reliability and internal validity. Descriptive statistics and inter-tooth correlations were calculated. Mixed linear models explored the roles of sex, zygosity, gestation length and primary tooth emergence timing. Principal Components Analysis for tooth emergence timing was used to extract a whole-mouth emergence component for subsequent modelling. A mixed linear model of raw exfoliation time was fitted, incorporating tooth, sex, and emergence time PC1, with twin nested within family fitted as a random effect.
Results: Descriptive statistics for tooth exfoliation corresponded to accepted population norms, with greater per-tooth variability. Antimeres and isomeres teeth were highly correlated. Correlations between emergence and exfoliation were low, with none exceeding 0.31. Females exfoliated on average 98 days earlier than males. Initial models demonstrated a marginal relationship with tooth emergence. Principal component 1 (PC1) for emergence timing was subsequently fit as a covariate. The slope of the relationship was 15.8±3.2, indicating a sixteen day increase in exfoliation time for each unit increase in PC1, which ranged from -10 to 13.
Conclusions: Primary tooth exfoliation is a biological process that, while predictable, showed significant temporal variation in this population. A non-linear relationship between primary tooth emergence and exfoliation timing was observed. This may have arisen from differences in the duration of the two processes, in which exfoliation timing had a much greater range on a whole-mouth basis. The next phase of this project will explore the contribution of genetic and environmental factors to covariation.
Methods: Participants were 550 pairs of twins and their parents enrolled in a longitudinal Australian birth cohort study (HREC H-78-2003). Exfoliation dates were recorded by parents. Exfoliation dates were examined for reliability and internal validity. Descriptive statistics and inter-tooth correlations were calculated. Mixed linear models explored the roles of sex, zygosity, gestation length and primary tooth emergence timing. Principal Components Analysis for tooth emergence timing was used to extract a whole-mouth emergence component for subsequent modelling. A mixed linear model of raw exfoliation time was fitted, incorporating tooth, sex, and emergence time PC1, with twin nested within family fitted as a random effect.
Results: Descriptive statistics for tooth exfoliation corresponded to accepted population norms, with greater per-tooth variability. Antimeres and isomeres teeth were highly correlated. Correlations between emergence and exfoliation were low, with none exceeding 0.31. Females exfoliated on average 98 days earlier than males. Initial models demonstrated a marginal relationship with tooth emergence. Principal component 1 (PC1) for emergence timing was subsequently fit as a covariate. The slope of the relationship was 15.8±3.2, indicating a sixteen day increase in exfoliation time for each unit increase in PC1, which ranged from -10 to 13.
Conclusions: Primary tooth exfoliation is a biological process that, while predictable, showed significant temporal variation in this population. A non-linear relationship between primary tooth emergence and exfoliation timing was observed. This may have arisen from differences in the duration of the two processes, in which exfoliation timing had a much greater range on a whole-mouth basis. The next phase of this project will explore the contribution of genetic and environmental factors to covariation.