A study of occlusal variation in the primary dentition of Australian twinsand singletons

In this study. we quantified the extent of variation in different occlusal features of Australian children of European descent with complete primary d entitions, but no permanent teeth present in the mouth. The study group con sisted of 412 individuals, aged between 3 and 7 years, including 70 monozyg ous (MZ) twin pairs, 68 same-sexed dizygous (DZ) twin pairs, 11 opposite-se xed DZ twin pairs, and 114 singletons, Occlusal traits, including inter-den tal spacing, incisal overbite and overjet, arch breadth and arch depth, wer e obtained directly from dental casts or indirectly from photocopies or imp ressions of the casts. Descriptive statistics summarised the data and indic ated that distributions were similar to those published for other populatio ns. Univariate genetic analysis, using the structural equation modelling pa ckage Mx, was carried out on the quantitative data using the normal assumpt ions of the twin model. Genetic modelling indicated that a model incorporat ing additive genetic (A) and unique environmental variation (E) was the mos t parsimonious for interdental spacing, overbite, overjet and arch dimensio ns. Estimates of heritability for interdental spacing ranged from 0.62 to 0 .81. Estimates for overbite and overjet were 0.53 and 0.28, respectively, a nd estimates for arch dimensions ranged from 0.69 to 0.89. These results in dicated a moderate to relatively high genetic contribution to observed vari ation. (C) 2001 Elsevier Science Ltd. All rights reserved.