School of Dentistry, The University of Adelaide
Friday 10, Plaza Level
Improving our understanding of factors that contribute to variation in dental arch form is important for modelling change in craniofacial structures, both developmentally, and within and between populations.
As part of a longitudinal study of dentofacial variation in a cohort of Australian twins, our aim was to apply curve-fitting methods to serial dental casts, and subsequently to estimate the contribution of the genotype to arch form at different developmental stages.
Longitudinal dental records were available for monozygotic same-sex pairs, dizygotic same-sex pairs, and opposite-sex dizygotic pairs. Standardised model photographs were obtained, landmarks digitised, and fourth-order orthogonal polynomials fitted to Cartesian data. Descriptive statistics were generated, and a series of structural equation models of individual polynomial coefficients were developed. Final models used a genetic simplex framework, allowing the contribution of genetic and environmental factors to change over time, both quantitatively (e.g. heritability) and qualitatively (e.g. different genes acting at different times).
Arches tended to be parabolic in the primary dentition, and square in the permanent dentition. Asymmetry provided a small contribution to variation at all stages of development. Genetic analyses confirmed the variable influence of a single ‘core’ group of genes on arch shape over time. There was also evidence of specific genes that were unique to individual developmental stages, although their relative contributions varied significantly. There was some degree of sexual heterogeneity for shape, particularly in the permanent dentition. Heritability was generally high, both for individual developmental stages, and over the course of development.
Components of this work were funded by the National Health and Medical Research Council of Australia, and it was resourced in-part by the Australian Twin Registry.