Root morphology of mandibular premolars in human 45,X females

The teeth of 87 Finnish 45,X females, 60 of their first-degree relatives and 87 normal females were examined. The presence of separate mesial and distal root canals and separate root apices was noted from orthopantomograms. Of the 45,X females, 40 (or 46%) had lower premolars with separate root canals; 30 individuals in first and 28 in second premolars. The number of first and second premolars with separate mesial and distal root canals was 40 and 43, and of those also showing separate apices, 28 and 21 respectively. Three of the female relatives and two of the normal females had premolars with separate mesial and distal root canals. The differences between the 45,X females and the two control samples were highly significant (p less than 0.001; Fisher exact test). The findings indicate increased molarization of the premolars in 45,X females; this contrasts with the earlier observation of a tendency to reduced crown morphology. The present outcome supports the hypothesis that the X chromosome has gene(s) involved in the regulation of root morphology.