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We have compared 10 occlusal traits in 358 monozygous and dizygous twin pairs in 4 different samples and estimated genetic variances for these features. Variable and frequently nonsignificant genetic variance was noted across samples for incisal overbite and overjet, sagittal molar relationship, posterior crossbite, and rotations and displacements of anterior teeth. Heritability estimates (when appropriately calculated) were low in magnitude (0-40%) and erratic, emphasizing the importance of environmental influences on occlusal variation and the variability of apparent genetic determinants with respect to the environm ent or population in which they are measured.