Determining The Relationship Between Hard and Soft Tissue Movements in Orthognathic Surgery Patients Using Multiple Imaging Modalities

Abstract

Orthognathic surgery encompasses various surgical procedures used for the correction of dentofacial deformities from malocclusions, prognathism, retrognathism, obstructive sleep apnea, to TMJ disorders and others. While the primary objective of orthognathic surgery is to optimize the occlusion and improve overall masticatory function, enhancement of the facial aesthetics is also an outcome of concern. However, tissue manipulation can result in unpredictable and sometimes, unfavorable outcomes. Thus, it is important to understand the impact hard tissue movement has on the soft tissue. Purpose: The primary outcome of this study was to determine the hard to soft tissue ratio following orthognathic surgery. Secondary outcomes focused on evaluating changes in soft tissue. Methods: Pre and post-operative cone beam computed tomography (CBCT) scans were taken prior to surgery and between 2 and 4 weeks post-operatively. 3D Photos were captured pre-operatively and at 3-months, 6-months and 12-months post-operatively. Image analysis was done using Dolphin® software. Three separate analysis were done: the magnitude of bony movement (HT), comparing hard to soft tissue movement (HT: ST), and changes in soft tissues (ST). The primary and secondary outcomes were then evaluated using these analyses stratified by time, sex, procedure type, age and BMI. Both a Wilcoxon signed-rank test and a regression model fit were used to evaluate the data. All patients planned for orthognathic surgery at Dalhousie University were screened and enrolled if they met the inclusion criteria. Results: 12 total patients completed the 12-month follow up, 19 patients completed the 6-month follow up and 44 patients completed the 3-month follow up. There were 3 treatment groups: LF, BSSO and LF BSSO. There was no statistically significant change in the HT: ST ratio at 12-months post-operatively. There was a trend in the data that showed maximal increase in the HT: ST ratio at 6 months (1: 1.53, n=19, p=0.38), however it was not statistically significant. The nasolabial angle showed the greatest change with maxillary surgery (2.56mm, n=7, p=0.03) and in males (1.45mm, n=17, p=0.04). The mentolabial angle changed more in patients in the BSSO treatment group (5.08mm, n=11, p=0.03). The alar width increased after surgery (2.58mm, n=14, p=0.001), with the greatest changes in the LF treatment group (1.77mm, n=14, p=0.06). There were no significant differences seen in the mouth width, height of philtrum, and upper and lower lip thicknesses. Conclusion: The hard to soft tissue ratio does not change significantly 12-months post-surgery. Minor soft tissue changes were seen at the level of the nasolabial angle, mentolabial angle and the alar width. The patient attrition rate was significant in this study, and the study findings should be interpreted accordingly.