Introduction: Studies in rodents and humans have suggested that masculinisation of females and feminisation of males can occur between fetuses in utero due to hormonal diffusion. Opposite-sex twin pairs provide a useful model to study the effects of prenatal hormone diffusion on tooth size.
Aim: To determine whether primary and permanent tooth size is altered in females and/or males from opposite-sex dizygotic (OSDZ) twin pairs compared with same-sex monozygotic (SSMZ) or dizygotic (SSDZ) twins.
Methods: Female sample: 43 OSDZ females, 48 SSDZ females, 50 MZ females; and male sample: 49 OSDZ males, 53 SSDZ males, 54 MZ males; ages from 4.1 to 16.5 years. Serial dental models of primary, mixed and permanent dentitions were used. Mesiodistal (MD) and buccolingual (BL) crown diameters of upper central incisors were measured to an accuracy of 0.1mm using calipers.
Results: OSDZ females were consistently larger by approximately 1-3% in MD and BL dimensions of permanent upper central incisors compared with other groups. However, no systematic trend was found in either dentition of the male groups.
Conclusion: This preliminary analysis shows a tendency for permanent central incisors to be larger in OSDZ females than in the other female twins. This may be related to circulating male hormones in utero. Incisor crown size of OSDZ males does not seem to differ from values for other male twins. It is intended to explore these associations further by measuring all primary and permanent teeth, including intercuspal distances, using a 2D image analysis system.