Three-dimensional Evaluation Of Mandibular Stability During Intermaxillary Fixation After Bilateral Sagittal Split Ramus Osteotomy Surgery

Purpose:To establish a method for three-dimensional evaluation of mandibular stability,and confirm its reproducibility.And analyze the short-term relapse tendency of mandibular after bilateral sagittal split ramus osteotomy surgery in three-dimension measurement.Methods:CBCT images of forty-nine patients seeking for orthognathic surgery were collected in this study,which were taken 4 days preoperatively(T0),4 days postoperatively(T1),4～6 weeks postoperatively(T2),and 3 months postoperatively(T3).A three-dimensional analytic method for measuring mandibular was set up in Pro Plan CMF 2.1 software.Three-dimensional reconstructed images of all cases were selected,and measurements results on the three-dimensional model were collected every day for three consecutive days.The measurement results were recorded in CSV format,and the data was re-read in Microsoft Excel software,averaged,and recorded it as the first group.The measurement was repeated after an interval of one week,and the average of the measurement results was recorded as the second group.SPSS 20.0 software was used to perform Intraclass Correlation Coefficient(ICC)on both groups’ of measurement results to observe their test-re test repeatability.For two groups,each measurement item was repeated three times to get the average value.Statistical analysis was performed using SPSS 22.0.Repeated-measure analysis of variance was conducted to statistically analyze the angle and distance obtained at different time to determine the displacement of each phase after the operation.P<0.05 indicates that the difference is significant.Results:The were about 100%(10/10)items in mandibular measurements,whose ICC>0.9.Mandibular advancement group:There was a horizontal relapse(9.3%)at point B during IMF,and the relapse at T2 accounted for about 60.9%of the relapse at T3;there was a horizontal relapse at point Pg(9.8%),and the relapse at T2 accounted for about 78.3%of the recurrence at T3;at the same time,the mandibular plane rotated 1.27° clockwise after surgery.It was relatively stable in the other directions.Mandibular regression group:there was a horizontal relapse at point B during IMF(7.2%),and the relapse at T2 accounted for about 81.7%of the relapse at T3;there was a horizontal relapse at point Pg(8.1%)as well as a vertical relapse,and the amount of relapse at T2 accounted for about 73.4%of the amount of relapse at T3.It was relatively stable in the other directions.Conclusions:The three-dimensional CT head reconstruction,fixed-point and three-dimensional coordinate system of all patients under this experiment were successfully established.The measurement objects included the distance from the point to the surface,the angle between the line and the line,and the angle between the surface and the surface.The arbitrary movement of the mandible can be described and measured in terms of translation and rotation.The established method is easy to operate,and the reproducibility of the fixed point of the bony landmark is high,and it can be applied to the subsequent measurement research of larger sample size.There is a three-dimensional relapse tendency of mandibular in short-term after BSSRO,but the result is rather stable.