Molar morphology and the expression of Carabelli's trait in 45,X females

The purpose of this study was to observe the expression of Carabelli's trait in maxillary first (M1) and second (M2) permanent molars in relation to tooth crown size and cusp number and to consider the role of the shortage of sex chromosome material in these features during tooth crown development.

The data were derived from dental casts belonging to the KVANTTI Research Project on sex chromosome abnormalities headed by Professor Lassi Alvesalo in Finland. The subjects comprised 86 45,X females, 51 first-degree female relatives, and 150 population control females. Carabelli's trait was divided into three grades and cusp number was classified into two classes in Dahlberg's P12 and P9. The tooth crown diameters were measured with a sliding digital caliper.

M1 in the 45,X females expressed a lower frequency of Carabelli's trait (19.8%) than in the female relatives (37.2%, P < 0.05). There was also a higher frequency of the three-cusp pattern (11.1%) than in the female relatives (2.4%, P = 0.055) or the control females (1.3%, P < 0.001). The expression of Carabelli's trait in M2 was of the same magnitude in the 45,X females and normal controls and was related to tooth crown size, whereas its expression in M1 of the 45,X females was associated with the cusp number rather than the tooth crown size.

The shortage of one X chromosome in females has an influence on the morphology of the lingual cingulum region of the maxillary first permanent molar during tooth crown development.