Differences in heritability of craniofacial skeletal and dental characteristics between hypo- and hyper-divergent patterns using Falconer's method and principal component analysis

Objectives: To investigate the difference in heritability of craniofacial skeletal and dental characteristics between hypodivergent and hyperdivergent patterns. Materials and Methods: 53 Korean adult monozygotic (MZ) and dizygotic (DZ) twins and their siblings were divided into a hypodivergent group (Group 1, SN-MP < 35 degrees, 17 MZ pairs; 11 DZ and sibling [DS] pairs of the same gender) and hyper-divergent group (Group 2, SN-MP > 35 degrees, 16 MZ pairs; 9 DS pairs of the same gender). A total of 56 cephalometric variables were measured using lateral cephalographs. Craniofacial structures were divided into anteroposterior, vertical, dental, mandible, and cranial base characteristics. Falconer's method was used to calculate heritability (h(2) > 0.8, high). After principal component analysis (PCA), the mean h(2) value of each component was calculated. Results: Group 1 exhibited high heritability values in shape and position of the mandible, vertical angular/ratio variables, cranial base shape, and maxillary incisor inclination. Group 2 showed high heritability values in anteroposterior position of the maxilla, intermaxillary relationship, vertical angular variables, cranial base length, and mandibular incisor inclination. Occlusal plane inclination showed high heritability in both groups. Although vertical structure presented a high overall mean h(2) value in Group 1, there were no structures that exhibited a high overall mean h(2) value in Group 2. PCA derived 10 components with 91.2% and 92.7% of cumulative explanation in Groups 1 and 2, respectively. Conclusions: It is necessary to estimate or predict growth according to vertical pattern for providing differential diagnosis and orthodontic/orthopedic treatment planning.