3D Analysis Of Changes In The Soft And Hard Tissues Of The Lip And Chin After Orthognathic Surgery In Patients With Skeletal Class Ⅲ

Objective:The soft and hard tissue change pattern in conventional 2D cephalogram measurement cannot meet the current stage of 3D digital design,this study uses high-precision CT combined with 3D measurement software to measure and explore the soft and hard tissue change in the lip and chin after orthognathic surgery in patients with bony class III malocclusion,and investigate its correlation and pattern,and finally verify the reliability of this 3D measurement method,for orthognathic surgery clinical treatment digital design.Methods:Thirty-nine adult patients aged 18-28 years who underwent bimaxillary orthognathic surgery at the Department of Plastic and Reconstructive Surgery,Jilin University Dental Hospital between October 2020 and May 2022 were collected,of whom 9 were male and 10 were female.All patients were grouped according to whether they underwent chinoplasty or not,in which Group A(Group A)was the group of patients who underwent chinoplasty,19 patients,see Table 1,and Group B(Group B)was the group of patients who did not undergo chinoplasty,20 patients.All patients underwent whole-head computed tomography scans to obtain facial data 1 week before(T0)and 12 months after(T1)surgery,and 3D reconstruction and alignment of preoperative and postoperative facial soft and hard tissues were performed by ProPlan CMF 3.0 software.First,the changes in the thickness of the soft tissue of the lip and chin after orthognathic surgery in patients with bony Class III malocclusion were measured and Holdaway analysis was performed to assess the effects of orthognathic surgery on the characteristics and position of the soft tissue of the lip and chin;second,the correlation and change patterns of the anatomical markers of the soft and hard tissue of the lip and chin were measured and compared between the two groups of patients after orthognathic surgery;finally,the data measured at two different time points in 39 samples were analyzed by intra-group The statistical analysis of correlation coefficient(ICC)was performed to compare the consistency of the two measurements.P<0.05 was considered to be statistically significant.Results:1.The postoperative soft tissue thickness of Sn and LL increased significantly(P<0.05)in group A compared to preoperative.The postoperative soft tissue thickness of LL increased significantly(P<0.05)in group B compared to preoperative.The postoperative changes of Sn-H,LL-H,Si-H,Mes-H,and H angle tended to normal values in both groups,in which the preoperative and postoperative changes of Sn-H,LL-H,Si-H,and H angle in group A were statistically different(P<0.05);the changes of Sn-H,LL-H,Si-H,Mes-H,and H angle in group B were statistically different(P<0.05).2.The preoperative and postoperative matching color scale comparison revealed that the amount of anterior emergence in the subnasal area and upper lip was the largest in group A,and the amount of anterior emergence gradually became smaller along the sub-region to the periphery to the cheek;the amount of mandibular recession was the largest in the red lip and chin-labial sulcus area of the lower lip,and the amount of soft tissue recession gradually decreased along this area to the periphery.In group B,the amount of anterior outflow was the largest around the nasal flanks bilaterally,and the amount of soft tissue anterior outflow gradually decreased along the sub-region to the red lips;the amount of mandibular backwardness was the largest from the lower lip edge to the sub-chin area and from both sides to the area within the chin hole,and the amount of soft tissue backwardness gradually decreased along this area to the periphery.3.The amount of soft tissue change(ΔSM)and hard tissue change(ΔBM)before and after operation in group A was analyzed by linear regression.Where,LL(R 2=0.832,Δ SM/Δ BM=1:0.74),Si(R=0.987,squared Δ SM/Δ BM=1-0.74),Pos(R squared=0.971,Δ SM/Δ BM=1:0.81),Mes(R squared=0.978,Δ SM/Δ BM=1:0.78)Soft tissue changes and hard tissue changes were significantly correlated(P<0.05);In sagittal direction,LL(R2=0.934,Δ SM/Δ BM=1:0.92),Si(R2=0.847,Δ SM/Δ BM=1:1.07),Pos(R2=0.909,Δ SM/Δ BM=1:0.89),soft tissue changes and hard tissue changes were strongly correlated.Mes(R2=0.455,Δ SM/ΔBM=1:0.99)was weakly correlated with hard tissue(P<0.05).In the vertical direction,LL(R2=0.686,Δ SM/Δ BM=1:1.08)and Mes(R2=0.709,Δ SM/ΔBM=1:1.04)showed strong correlation between soft tissue changes and hard tissue changes.However,Si(R2=0.469,Δ SM/Δ BM=1:0.97)and Pos(R2=0.444,Δ SM/Δ BM=1:0.83)were weakly correlated with hard tissue changes and had statistical significance(P<0.05).The ratio between soft tissue movement and corresponding bone tissue movement after orthognathic surgery(ΔSM/ΔBM)was calculated.The correlation between the amount of soft and hard tissue changes in the three directions was statistically significant(P<0.05).The correlation between the amount of soft and hard tissue changes in the three directions was statistically significant(P<0.05).4.The amount of soft tissue change(Δ SM)and hard tissue change(Δ BM)in group B before and after surgery was analyzed by linear regression.Where,LL(R2=0.355,Δ SM/Δ BM=1:0.74)Soft tissue changes were weakly correlated with hard tissue changes,Si(R2=0.618,Δ SM/Δ BM=1:0.74),Pos(R2=0.854,Δ SM/ΔBM=1:0.81),Mes(R2=0.886,Δ SM/Δ BM=1:0.78)Soft tissue changes and hard tissue changes were significantly correlated(P<0.05);Sagittal upward Sn(R2=0.620,Δ SM/Δ BM=1:0.92),UL(R2=0.787,Δ SM/Δ BM=1-0.86),LL(R squared=0.717,Δ SM/Δ BM=1:0.71),Si(R squared=0.841,Δ SM/Δ BM=1:0.99),Pos(R squared=0.963,Δ SM/Δ BM=1:0.88)soft tissue changes and hard tissue changes were strongly correlated,but Mes(R2=0.446,Δ SM/Δ BM=1:0.78)soft tissue changes and hard tissue changes were weakly correlated and had statistical significance(P<0.05).Vertical upward UL(R2=0.574,Δ SM/Δ BM=1:1),Mes(R2=0.936,Δ SM/Δ BM=1:0.88)soft tissue changes and hard tissue changes were strongly correlated.However,Si(R2=0.399,Δ SM/Δ BM=1:1.13)and Pos(R2=0.599,Δ SM/Δ BM=1:1.12)were weakly correlated with hard tissue changes and had statistical significance(P<0.05).5.The intra-group correlation coefficients(ICC)of the data after fixed-point measurements of the soft and hard tissues of the faces of the 39 samples by different measures were greater than 0.75.Conclusion:The three-dimensional measurement method used in this study was reliable.Soft tissue thickness changes in the lip and chin after orthognathic surgery in patients with bony Class III malocclusion deformity were negatively correlated with bone tissue changes,and the ratio of soft tissue movement relative to bone tissue in different parts of the lip and chin was different in the 3-dimensional direction.The soft and hard tissues of the lower lip and chin were more correlated in 3 directions of movement,while the soft and hard tissues of the upper lip were only correlated in the sagittal direction.Therefore,a comprehensive consideration is needed when performing orthognathic preoperative design in patients with bony Class Ⅲ malocclusion.