Heritability of mandibular asymmetries in sagittal direction: A cephalometric study.

Abstract

Aim of the work: If we figure out mandible asymmetry etiology, we can inspire further scientific research, create more effective treatment schemas and recommend means of prophylaxis that could stop mandible asymmetry development. The aim of this work was to analyze monozygotic and dizygotic twins' mandibular asymmetry in sagittal direction using cephalometric data and to analyze its dependence of genetic and environmental factors.

Material and methods: Study sample consisted of 80 dizygotic (DZ) and 80 monozygotic (MZ) twins of same sex. 3 cephalometric measurements were made to determine mandible asymmetry in sagittal direction. Indexes of mandibular asymmetry (IMA1, IMA2) were calculated. Data analysis was done using Microsoft Excel (2013). Genetic and environmental factors influencing mandible asymmetry was determined.

Results: Mandibular dental asymmetry was bigger in monozygotic twins' group but the results were not statistically significant. Mandibular skeletal asymmetry was significantly bigger in dizygotic twins' group: IMA1(DZ)=3.05±1.94, IMA1(MZ)=1.92±1.05, p=0.005. IMA2(DZ)=3.12±2.04, IMA2(MZ)=1.88±1.04, p=0.004. Distance between distal borders of the ramus is mostly determined by genetic factors.

Conclusions: 1. Mandibular skeletal asymmetry was significantly bigger in dizygotic twins' group. Mandibular dental asymmetry and symmetry did not differ in groups significantly. 2. Skeletal mandible's asymmetry is more determined by genetics than environmental factors, but lower molars' sagittal position is determined more by environment.