Heritability of Facial Skeletal and Dental Characteristics of Monozygotic and Dizygotic Twins Using Cephalometric Analysis and Falconer's Method

The purpose of this study was to investigate the heritability of facial skeletal and dental characteristics of the monozygotic (MZ) and dizygotic (DZ) twins. The samples consisted of Korean MZ and DZ twins (n=13pairs/each twin; 7 pairs of males and 6 pairs of females; mean age, 39 years, respectively). The linear, angular, and ratio variables, which could describe the size and shape of the facial horizontal and vertical, dental, mandible and cranial base structure, were measured. The Falconer's method was used to calculate the heritability (h(2); close to or below 0, low heritability; close to or above 1, high heritability). In the facial horizontal and vertical aspects, the highest h(2) values were shown at SNA (degree, 1.53), SNB (degree, 2.12), SN-Pog (degree, 2.19), SN-palatal plane angle (degree, 1.29), SN-mandibular plane angle (degree, 1.59), N-ANS/ANS-Me (1.66), and ANS-Me/N-Me (1.62). In the dental aspects, although L1-occlusal plane angle (degree, 1.38) and SN-occlusal plane angle (degree, 2.09) showed high h(2) values, most of the dental variables showed low h(2) values. In the mandible and cranial base, lower gonial angle, mandibular body length, and cranial base angle showed high h(2) values (N-Go-Gn [degree], 1.07; Go-Pog [mm], 0.92; N-S-Ba [degree], 1.51). The descending order of the overall mean h(2) values was the facial horizontal (1.10), facial vertical (0.71), mandible (0.59), cranial base (0.37), and dental characteristics (-0.11). The shape of facial skeletal structure and location of the occlusal plane within skeletal framework was more influenced by genetic factors than environmental factors.