Root lengths in the permanent teeth of Klinefelter (47,XXY) men

Earlier studies on human teeth have provided proof of an expression of the X and Y chromosome genes in tooth crown growth. The Y chromosome promotes the growth of permanent tooth crown enamel and dentin, whereas the effect of the X chromosome seems to be restricted mainly on enamel formation. Also, there are evidences that both of the sex chromosomes are expressed in tooth root growth. The permanent tooth crowns in 47,XXY males or individuals with an extra X or Y chromosome show increased size compared to normal men, which is mainly due to increased enamel thickness, the dentin thickness is somewhat reduced. There is some evidence of increased mesio-distal tooth crown size also in their primary dentition. The aim of the present study was to determine their complete permanent tooth root lengths. The study groups consisted of 49 47,XXY males, 22 relative males, 8 relative females, 35 population control males and 46 population control females from the Kvantti research project. Root length measurements were made from panoramic radiographs on both sides of the jaw using a digital sliding calliper. The results showed growth increase in the final tooth root sizes in 47,XXY males which conceivably become evident beginning 8 years after birth up to the age of 14 years, at least. The present results and earlier ones on 45,X and 45,X/46,XX females, normal females and males indicate that the promoting effect of the Y chromosome on tooth root growth is greater than that of the X chromosome. These differential effects are conceivably causative factors in the development of the sexual dimorphism in tooth root size.