| ObjectivesLaterognathism of the mandible is a common jaw malformation in clinic.Patients typically manifest as skeletal Class ? malocclusion,deviation of the midline and tilt of the occlusal plane.Orthodontic-orthognathic combination therapy is usually required to initiate only after the growth and development of jaw finish.The conventional treatment includes preoperative orthodontics,orthognathic surgery and postoperative orthodontics.Although the overall satisfaction of patients with laterognathism of the mandible is high after orthognathic surgery,some patients are still not satisfied for the frequent presence of postoperative asymmetry,which requires that postoperative effects should be estimated accurately in advance.In recent years,researchers around the world have focused on the anterior head rather than the posterior.Our experiment was designed to improve patient satisfaction and optimize the current method of orthognathic surgery.In this experiment,three-dimensional reconstruction was used to stimulate the Computed Tomography(CT)image of patients with laterognathsim of the mandible before the operation and six months later.The changes in the mandibular ramus were evaluated through observing a total of 15 marked points on the maxilla and mandible.The average thickness of the soft tissue in the mandibular angle region was also measured to reflect the changes.MethodsExperiment 1:The CT data of 18 patients before and six months after orthognathic surgery were collected and imported into mimics 20.0 software.Three-dimensional models of left ear,right ear,orbit,pyriform,mental region,left and right mandibular ramus were established respectively.Six mark points of the base of skull were decided to locate the reference plane.The statistical difference between preoperative and postoperative coordinates of the mark points in the base of skull were analyzed to prove that this experiment was performed in the same reference frame.Experiment 2:Using SPSS16.0 software,paired t-tests were performed to compare the difference of the distances between the mark points and the reference plane preoperatively and postoperatively to infer the changes in various locations of the maxilla and mandible.Experiment 3:The soft tissues in the mandibular angle was segmented from the whole model by setting up four planes and one curved surface,where the volume and area of outer surface were read by 3-matic software and then the mean thickness of the region could be calculated.The differences in soft tissue volume,surface area,and average thickness before and after surgery were analyzed using SPSS software.Experiment 4:The change rate of soft tissue thickness in both sides and the displacement of points B and R2 for each patient were calculated.Pearson correlation analysis was performed to analyze the statistical difference using SPSS software.ResultsExperiment 1:There was no significant difference in the locations of mark points in base of skull,which proved that all the patients were analyzed their preoperative and postoperative CT images in the same reference plane.Experiment 2:According to the rotation direction of the maxilla and mandible,patients were divided into right-handed and left-handed jawbone group.The distance and direction of the each point showed that:the maxilla moved forward,downward and rotated to the affected side;the mandible underwent an overall counterclockwise rotation and retreat,and then rotated to affected side;internal rotation of the mandibular ramus occurs for the axis of the line between the condylar process and mandibular angle,the degree of rotation in the healthy side was greater than that in affected side.The leading edge of mandibular ramus rotated upward to fix the lower part on the mandibular body,which resulted in the change of curvature in the leading edge of mandibular ramus.Experiment 3:A significant decrease in the surface areas of soft tissue and an rise in average thickness in both sides were observed in both groups,The latter change could be credited to the rotational movement of the mandible,which had a pulling and squeezing effect on the soft tissue in this side,and changed the soft tissue thickness.The thickness of soft tissue in the affected side changed more significantly than the healthy side because the mandibular body rotated to affected side to squeeze the soft tissues on that side,while the receding and lifting movement of the mandible also squeezed soft tissues on the other side.So,the thickness increase was milder in the healthy side.Experiment 4:In the right-handed jaw group,there was no significant statistical correlation between the displacement of R2 points in both sides and the change rate of the thickness of soft tissues on the same side;a significant statistical correlation was also lacked between the displacement level of the B point and change rate of the thickness of left soft tissues,while there was a statistical correlation between the change degree of B point location and the thickness of right soft tissues.The change rate of the thickness of right soft tissue was positively correlated with the level of point B displacement.In the left-handed jaw group,there was no significant statistical correlation between the displacement of the R2 points on both sides and the change rate of the thickness of soft tissues on the ipsilateral side;it was the same with the B point in the right side while the results in the left side;showed a significantly positive correlation.The change rates of the thickness of soft tissues in both sides in the left-handed group were exchanged into the right-handed group and formed a cross-group,of which the results were consistent with those in the right-handed group.Conclusions1.Patients with laterognathism of the mandible after undergoing orthognathic surgery,the maxilla will undergo a clockwise and affected-side rotation after orthognathic surgery;2.The mandible rotates counterclockwise and affected-side;3.The leading edge of the ascending ramus of the mandible rotates inward around the axis which connects the condyle and the corner of the mandible;4.The average thickness of the soft tissues in the mandibular angles increases on both sides,and the healthy side changes more affected side;5.The rate of change in the average thickness of affected-side soft tissues is positively related to the rotating distance of the anterior region of the mandible. |
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