Is tooth size altered in opposite-sex dizygotic twin pairs, reflecting possible hormone diffusion in utero?

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. The aim of this study is 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: 44 OSDZ females, 39 SSDZ females, 52 MZ females; and male sample: 44 OSDZ males, 42 SSDZ males, 56 MZ males; aged 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, crown heights (CH) and intercuspal distances (IC) of upper central and lateral incisors, canines, second premolars, first and second molars and lower central and lateral incisors, canines, second premolars, first and second molars were measured to an accuracy of 0.1mm using 2D image analysis system. OSDZ females were consistently larger by approximately 1-3% in MD and BL dimensions for permanent teeth compared with other groups but CH and IC dimensions did not show the same pattern. No systematic trend was found in either dentition of the male groups. This effect may be related to circulating male hormones in utero. [ABSTRACT FROM AUTHOR]