Dental arch morphology in south Australian twins.

Fourth-order polynomials were used to represent dental arch morphology in 29 monozygous and 19 dizygous like-sexed twin pairs, and in 45 unrelated individuals. The polynomial coefficients provided an accurate description of dental arch morphology with the quadratic (chi 2) and quartic (chi 4) terms reflecting arch shape and the linear (chi) and cubic (chi 3) terms summarizing asymmetry. There were no significant differences between the groups in either the quadratic or quartic terms. Values of correlations between polynomial terms indicated that there was no consistent relationship between maxillary and mandibular arch shape or asymmetry. Intraclass correlations between twins suggested that genetic factors contributed to variation in maxillary arch shape and to a lesser extent to variation in mandibular arch shape but not to arch asymmetry.