Reverse, hormone-dependent sex difference in molar tooth mass in pubertal mice

The weighed mass of molar teeth of male pubertal (35-day-old) mice was significantly smaller than that of females. X0 females, and chromosomal males (XY) rendered phenotypically female by the testicular feminization gene (Tfm), had high (female-type) molar mass. Chromosomal females (XX or X0) rendered hormonally phenotypically male by the sex reversal gene Sxr, had low (male-type) molar mass. It is concluded that the sex difference was due to hormonal rather than chromosomal factors. Reported sex differences in mammalian tooth size have mainly been in the opposite direction, a discrepancy which may be due to co-existence of opposite dimorphisms of mass and diameter, or to age-specific changes in ontogeny. However, the most likely explanation is that developmental species differences exist.