# Chin Morphology in Relation to the Skeletal Pattern, Age, Gender, and Ethnicity
## 4 Discussion  
In this study, we investigated the relationship between chin size and vertical and anteroposterior skeletal patterns, gender, ethnicity, and age. Furthermore, the relationship between the three-dimensional volume of chin and the parameters of maxillofacial morphology have never been investigated before. More anterior growth of the mandible corresponds to a thicker symphysis, which has been reported in many studies [27]. [PERSON] et al. found that the chin surface area in Class III patients was the greatest and could be used as a parameter for differential diagnosis of Class III malocclusion [28]. The current study showed similar results, with chin volume and chin depth showing the greatest values in Class III patients. On the other hand, in the multivariate analysis, the only parameter related to anteroposterior skeletal pattern was chin depth. The greater the chin depth, the greater the likelihood that the mandible was anterior to the maxilla, as in all Classes (Table 3). It has been reported that the chin depth is greater in Class III patients [29], which is consistent with the present results. Based on the hypothesis that the origin of the chin is due to the spatial compensation of the laryngeal area, the need for spatial compensation is rather reduced in Class III, where the mandible is located anteriorly, and the laryngeal volume is large. The results of this study are consistent with this hypothesis. In the univariate analysis, vertical skeletal pattern was significantly associated with chin volume with the chin volume being larger in the hyperdivergent pattern. Multivariate analysis showed a positive correlation with chin volume, but negative correlations with chin width and chin depth and no association with chin height. In other words, as chin volume increased, it was more likely to be hypodivergent, normodivergent, and hyperdivergent; similarly, as chin width increased, it was more likely to be hyperdivergent, normodivergent, and hypodivergent (Table 4). Regarding the relationship between vertical skeletal pattern and symphysis, an increase in height and decrease in width has been reported with increasing hypertrophy, and chin size decreases with increasing hypertrophy in vertical skeletal pattern [17; 18; 29]. Contrastingly, [PERSON] et al. reported that the width becomes smaller with hypertrophy, but chin height is not affected in the chin evaluation based on point B [19]. The results of this study based on point B were the same. The results of the present study are consistent with the finding that the vertical skeletal pattern has more influence on the shape of the symphysis than the anteroposterior skeletal pattern [30]. The vertical skeletal pattern is associated with mandibular rotation relative to the base of the cranium, with an anterior rotation in patients with hypodivergent pattern and a posterior rotation in hyperdivergent pattern [31; 32]. Patients with hyperdivergent pattern with a posterior mandible are known to have a smaller laryngeal volume [6] and based on the hypothesis that the origin of the chin is due to the spatial compensation for the laryngeal volume; the results of this study are consistent with this hypothesis. The addition of genioplasty, a surgical vertical or horizontal shift of the chin, to orthognathic surgery of the mandible leads to a more harmonious facial soft tissue morphology and a higher degree of satisfaction with the result than mandibular advancement alone [33]. However, changes in the position of the chin may result in bad joints and unexpected soft tissue changes [34]. This study demonstrates the connection between chin shape and skeletal pattern. When altering the position and morphology of the chin in orthognathic surgery, three-dimensional evaluations of the chin, such as the direction of the slide, the osteotomy line, and the degree of bone grinding, may be helpful in treatment planning.