Comparison of Lip Line Cant Change After 1-Jaw and 2-Jaw Surgery

Objectives: The purpose of this study was to compare the lip line cant (LLC) changes after 1 and 2-jaw surgery, and to evaluate the correlations of the craniofacial factors affecting LLC. Methods: The study subjects were selected (LLC amount within 1.5-6.08) from among the patients diagnosed with Class III malocclusion who underwent one (n = 20) or 2-jaw surgery (n = 20). Cone beam computed tomography images were obtained immediately before the operation (T1) and 6 months after the operation (T2). Preoperative and postoperative craniofacial measurements were obtained. Results: The study subjects showed 3.128 LLC on average before undergoing 1-jawsurgery, and theirLLCchanged to 1.278 after the surgery. As for 2-jaw surgery, the subjects showed 3.388 LLC on average before the surgery and 0.988 after the surgery. LLC at pre-treatment may be more affected by a cant of the occlusal plane in the mandible than maxilla. In the comparison of the value of changes of LLC, the value of 2-jaw surgery was bigger than the value of 1-jaw surgery but the difference was statistically insignificant. Limitations: This study had a limitation in that the muscles were not considered. And the metal bracket or metal crown and bridge, however, can cause noise and blurring artifacts in CT, which can lead to a low resolution. And the limited number of the patients should be considered. Conclusions: In correlation analysis, both pre-surgery LLC and change of LLC have correlation with almost all the craniofacial measurement. Lip-line cant of patients with facial asymmetry has higher correlation with mandibular cant than with other cants. To improve the LLC, a surgical plan should be established to minimize the mandibular cant using the computer simulation as well as the maxillary cant.