| Objective:Based on the analysis of 3D CT data,we compare the surgical simulation design before digital surgery for patients with osteo mandibular protrusion and the measurement of the change of condyle position in the articular fossa after orthognathic surgery,in order to evaluate the effect of orthognathic surgery as well as the accuracy of condyle position design during surgery and the short-term stability after surgery.Methods:According to the inclusion criteria,44 patients with osseous mandibular protrusion who underwent surgery in the Stomatological Hospital of Nanchang University from September 2015 to September 2020 were selected.Among them,the maxillary Le Fort I type osteotomy + bilateral sagittal split ramus osteotomy(BSSRO)was performed in 25 cases,which were defined as the bimaxillary group.Nineteen patients who underwent BSSRO alone were defined as monocillary group.The whole head CT data were collected preoperatively,within 1 week and 6 months after surgery.CT data designed by surgical simulation before digital surgery,CT data 1 week after orthognathic surgery and 6 months after orthognathic surgery were defined as T0,T1 and T2 groups,respectively.Mimics20.0 software was used for 3D reconstruction and surgical model analysis,and indexes that could reflect condyle characteristics were measured respectively: The Lateral pole of condyle head(CL),Medial pole of condyle head(CM),Sigmoid(Sig),and Condylar apex of condyle head(C0)position coordinates.The movement of condyle in X,Y and Z axes was calculated according to the change of the coordinate value of C0.The condylar rotation angles Pitch,Yaw and Roll were calculated by the coordinate values of Cl,CM and Sig to evaluate the changes of the spatial attitude Angle of the condyle.The size of the space between the distal middle bone segment and the proximal middle bone segment at the bilateral mandibular osteotomy line was measured.The space Angle less than 4° or the distance less than 5mm was defined as the small space group,otherwise,it was defined as the large space group.The condylar data of the T0 and T1 groups were analyzed to evaluate the accuracy of the actual condyle position after orthognathic surgery and the repeatability of the three-dimensional measurement method compared with the preoperative surgical design of digital surgery.The condylar data of the T1 and T2 groups were analyzed for the short-term stability of the condyle position after orthognathic surgery.Paired t test and independent t test were conducted with SPSS19.0 software for related data.Results:1.(1)There was no significant difference in ANB Angle and condylar movement along XYZ axis between T0 group and T1 group.There were no significant differences in the translational changes of condyle in the three directions of XYZ axis and the spatial attitude Angle of condyle between the large space group and the small space group in all patients.(2)The translational quantity of ANB Angle and condyle in XYZ axis was not significantly different in the bimaxillary group(comparison between T0 group and T1 group),while there was no significant difference in the translational quantity of ANB Angle and condyle in XYZ axis in monocillary groups(comparison between T0 group and T1 group).(3)There were no significant differences in the variation of ANB Angle,the variation of condylar movement along the XYZ axis and the spatial attitude Angle of condyle between the bimaxillary group and the monocillary group.2.(1)In all patients,there was no significant difference in ANB Angle between T1 group and T2 group,no significant difference in the translation of condyle along the X-axis direction,but significant difference in the backward movement along the Y-axis direction,and significant difference in the downward movement along the z-axis direction;In all patients,there were no significant differences in the translational changes of condyle in the three directions of XYZ axis and the spatial attitude Angle of condyle between large and small space groups.(2)There was no significant difference in the ANB Angle of patients in the bimaxillary group(compared with T1 and T2 groups).There was no significant difference in the translation of condyle in the X and Y axes,but there was significant difference in the downward movement of condyle in the Z axis.There was no significant difference in the ANB Angle in monocillary group(comparison between T1 and T2 groups).In monocillary group,there was no significant difference in the translation of condyle in the X-axis direction,but there was significant difference in the backward movement in the Y-axis direction and significant difference in the downward movement in the z-axis direction.(3)There was no significant difference in the change of ANB Angle between the two groups(T1 and T2),and there was no significant difference in the change of condylar movement along the X-axis direction.The condylar movement along the Y-axis direction showed significant difference,while the condylar movement along the z-axis direction showed significant difference.(4)The comparison between the two groups(T1 group and T2 group)showed a significant difference in the attitude Angle of condyle Pitch,which is rotation about the X axis;the attitude Angle Yaw,which is rotation about the Y axis,showed no significant difference;and the attitude Angle Roll,which is rotation around the Z axis,showed a significant difference.Conclusion:1.Digital surgery has a high application accuracy in orthognathic surgery.The mean value of ANB Angle difference is 0.92°,and the mean value of condyle rotation Angle Pitch,Yaw and Roll is about 1.27°,1.05° and 2.00°.The mean linear difference of displacement change on the XYZ axis is about 1.07 mm,and the 3D accuracy is expected to reach the difference level of 1mm.Preoperative simulation can improve the operation effect and the operation precision is high.2.The three-dimensional measurement method used in this study has strong pertinence,clear and simple fixed points,and the measurement items can fully and intuitively reflect the translation of condyle in three-dimensional space with high repeatability.Therefore,this measurement method can provide a strong support for quantifying the accuracy and stability of the condyle after orthognathic surgery,and is intended to provide an effective basis for clinical work with a large sample size.3.Both bimaxillary surgery and monocillary surgery can effectively correct bony mandibular protrusion deformity and achieve good surgical results.Moreover,according to the study results,we can see that the position of condyle after bimaxillary surgery is better than that after monocillary surgery for short-term stability.4.Our study found that in patients with bony mandibular protrusion 6 months after orthognathic surgery,the condyle would shift backward and downward,and the condyle would rotate outward after axial position,and the condyle would tend to return to the original position,indicating that orthognathic surgery would not significantly affect the position of the condyle in patients.Therefore,our study can predict the short-term changes of condyle position after orthognathic surgery,and provide reference for clinicians to improve the accuracy of orthognathic surgery. |
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