![]() Genetic factors that affect human craniofacial structures were identified through an experiment that used monozygotic twins (MZ), dizygotic twins (DZ), and their siblings. The other two planes are the same.ĭespite studies that investigated the mechanisms and contributions of each rotation in the total mandibular rotation, there has been no study on heritability of the rotation within the mandible. Ricketts corpus axis (Xi-Pm) replaces Björk’s core of mandible. To prevent confusion among terms, the present study follows Björk’s definition of rotation. also explained that surface changes produce external rotation that is compensated for by internal rotation. described Björk’s total rotation as internal rotation, which is masked by surface changes and alterations in the rate of tooth eruption. They called this the “intramatrix rotation,” and it signifies the independent rotation of the mandibular core that appears inside the soft tissue matrix. After overlapping two cephalometric x-rays, Björk and Skieller found a difference in the implant inclination and mandible inclination relative to the SN plane. The measurements are a clinical interpretation that represents the mandible position and change of inclination. Björk and Skieller called the implant line inclination change as the “total rotation.” This refers to the angle between the mandibular core and the SN plane, which shows the rotation of the core of the mandible “matrix rotation” is the combined transversions of the condyle growth between the skull base and the core of the mandible and the modification of the mandible due to bone remodeling. ījörk and Skieller distinguished mandibular growth rotation into total rotation, matrix rotation, and intramatrix rotation using implant superimposition method. A metallic implant study has enabled the ability to distinguish condylar and bone remodeling growth, and the concept of rotational growth was introduced as the bony core. Furthermore, there have been attempts to visualize matrix rotation and intramatrix rotation within the jaw. So far, studies have been concentrated on locating bone growth centers or evaluating the range of rotation by location. This was because of the complex properties of the bone growth process in which condylar growth and remodeling of the mandible take place at the same time. However, it was not until the middle of the 1900s that research on these patterns was thoroughly performed despite their importance. Occlusal plane change, especially with regard to the functional occlusal plane, may not be stable due to strong genetic influences.Įvaluation of bone growth patterns is one of the most important factors in establishing treatment plans for growing patients. Conclusionīased on these findings that showed a strong genetic effect on total rotation and matrix rotation, maintaining these rotations should be carefully considered in the orthodontic treatment plan, while the lower border of the mandible may be responsive to various treatments. All of the three types of occlusal plane showed high heritability, and among the three types, the functional occlusal plane showed the highest heritability ( h 2 = 0.76). The heritability of the total rotation (0.48) and matrix rotation (0.5) between the MZ and DZ groups was higher than that of the intramatrix rotation (− 0.14). The ICC mean values for 13 cephalometric measurements were 0.85 (MZ), 0.62 (DZ), and 0.52 (siblings) respectively. With regard to mandibular rotation, the MZ twin group showed significantly higher ICC values compared to the DZ twin and sibling groups. Heritability ( h 2) was calculated by using the intraclass correlation coefficient (ICC) and Falconer’s method. Three types of occlusal planes (bisected occlusal plane, functional occlusal plane, and the MM bisector occlusal plane) were used to evaluate genetic influence on the occlusal plane. Lateral cephalograms were taken, and 13 variables related to internal and external mandible rotation were measured. The samples consisted of 75 pairs of Korean twins (39.7 + 9.26 years MZ group, 36 pairs DZ group, 13 pairs sibling group, 26 pairs). ![]() ![]() The purpose of this study is to investigate the heritability of total rotation, matrix rotation, and intramatrix rotation of the mandible in Korean monozygotic (MZ) twins, dizygotic (DZ) twins, and their siblings. ![]()
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