Mandibular morphology in monozygotic twins: a cephalometric study.

BACKGROUND The understanding of relative effects of genetics and environmental factors on mandible growth would increase effectiveness of orthodontic therapy and treatment planning. The purpose of this study was to clarify whether the skeletal morphology of mandible is phenotypically alike in two individuals in a pair of young adult monozygotic (MZ) twins. METHODS The 90 twin pairs were classified as MZ by 15 specific DNA markers and Amel fragment. Cephalometric analysis of mandible morphology using 27 parameters was done and Pearson's intra-pair correlation coefficient for each variable was calculated. RESULTS The highest correlations of cephalometric variables between two individuals in the same MZ twins pair was in the total mandibular and corpus length (r=0.94). The lowest correlations was established for depth of antigonial notch (r=0.65) and articular angle (r=0.68) in female pairs. Statistically significant differences (p ≤ 0.05) of intra-pair correlation coefficients between genders was found only for total mandibular length (distances Co-Gn and Ar-Gn). CONCLUSIONS Mandibular length has highest intra-pair correlation coefficient among similar linear cephalometric variables in MZ twins. The females demonstrated greater variability of mandible skeletal cephalometric measurements within the MZ twin pair than the men.