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 = 13 pairs/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 (h2; close to or below 0, low heritability; close to or above 1, high heritability). In the facial horizontal and vertical aspects, the highest h2 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 h2 values, most of the dental variables showed low h2 values. In the mandible and cranial base, lower gonial angle, mandibular body length, and cranial base angle showed high h2 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 h2 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. Address correspondence and reprint requests to Dr Seung-Hak Baek, DDS, PhD, Department of Orthodontics, School of Dentistry, Dental Research Institute, Seoul National University, Daehak-no #101, Jongro-gu, Seoul, Republic of Korea; E-mail: drwhite@unitel.co.kr; Dr Young Ho Kim, DDS, PhD, Department of Orthodontics, Institute of Oral Health Science, Ajou University School of Medicine, 164, Worldcup-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16499, Republic of Korea; E-mail: ajouorthod@naver.com Received 19 May, 2017 Accepted 11 November, 2017 EK and JS contributed equally to this work as co-first authors. The authors report no conflicts of interest. © 2018 by Mutaz B. Habal, MD.

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