Tooth size and morphology in twins

Objective. To assess concordance of tooth size and occlusal morphology in monozygotic (identical) and dizygotic (non‐identical) twins compared to unrelated controls in order to determine how much these dental traits are related to inheritance. Methods. Mesiodistal and bucco‐lingual dimensions of tooth size in 34 pairs of twins were measured with dial callipers. In addition, the occlusal morphology of nine pairs of teeth was assessed using a co‐ordinate measuring machine with a non‐contact laser probe. Results. The results showed greater concordance in tooth size for both mesiodistal and bucco‐lingual dimensions within twin pairs compared to twin and unrelated controls. Furthermore, monozygotic (MZ) twins showed greater concordance than dizygotic (DZ) twins for all permanent teeth with statistically significant variance for the mesiodistal dimension (P = 0·01) but not bucco‐lingual dimension. Superimposed computer models of the digitized occlusal surfaces showed a high degree of similarity for MZ twins compared to DZ twins. The mean intrapair deviation was 147 µm for MZ, 209 µm for DZ and 258 µm for unrelated controls. Conclusions. The remarkable similarity in the tooth size and morphology of monozygotic twins suggests a strong inheritability factor to tooth size and shape and that these may be useful as additional tools for zygosity determination along with other dental traits.