Correlation Between Height and Impacted Third Molars and Genetics Role in Third Molar Impaction

This study sought to evaluate the relationship between height of an individual and the presence of impaction of maxillary and mandibular third molars, and to determine the role of genetics in third molar impaction.

This was a case-control study, with cases consisted of 200 subjects with third molar impactions; and 200 controls without third molar impactions. Height of subjects was measured, and saliva samples were collected from all the subjects. DNA was extracted from saliva samples. To investigate the role of selected genes in the etiology of third molar impactions, Taqman Genotyping using SNPs identified for jaw growth, height and tooth agenesis was employed. Five candidate genes were investigated using 11 markers (SNPs).

The mean height of cases was significantly lower than that of the control subjects (p = 0.04). No difference was found in allele frequency between cases and controls for 10 of the 11 SNPs. However, for rs6504591 the p value was near significance (p = 0.07) with odd ratio of 2.131. Subjects with lower third molar impactions were significantly shorter than those who have fully erupted third molars.

Subjects with lower third molar impactions were significantly shorter than those who have fully erupted third molars. We observed that individuals with third molar impaction tend to have T allele at the locus, suggesting that the T allele at the locus may increase the risk for having an impacted third molar. The rs6504591 G/T variation on human chromosome 17 (WNT9B gene) appears to increase risk by twofolds for impaction albeit with inability to detect significance due to small sample size.