Three-dimensional Analysis On Dental Compensation In Patients With Skeletal Class Ⅲ Malocclusion And Mandibular Asymmetry

Objective: The purpose of this study was to analyze three-dimensional dental compensation in reference to the maxillary and mandibular basal bones using cone-beam computed tomography(CBCT)and three-dimensional reconstruction measurement technology and to evaluate the correlations between dental compensation and skeletal asymmetry variables in patients with skeletal Class III malocclusion and mandibular asymmetry,in order to provide clinical guidance and reference for the preoperative orthodontics of orthognathic surgery.Methods:1.Twenty-nine patients with skeletal Class III malocclusion and mandibular asymmetry(asymmetry group)and twenty-eight subjects with individual normal occlusion(control group)were included.Skeletal and dental measurements were acquired from reconstructed CBCT images using INVIVO 5 software.2.All measurements were compared between groups and between the deviated and non-deviated sides of the asymmetry group using SPSS 21.0statistical analysis software.Correlation analyses for the association between skeletal and dental variables were performed.Results:1.There were statistically significant differences between the two sides in the ramus length,the mandibular body length,and the gonial angle in asymmetry group(P<0.05),and the differences between the two sides of the control group were not statistically significant;2.In the vertical dental measurement variables,there were statistically significant differences between the two sides in AOP,OP,U5 Mx P,U6 Mx P,U7 Mx P,and L3 Mn P in asymmetry group(P<0.05).In the asymmetry group,U5 Mx P,U6 Mx P,U7 Mx P on the deviated side were smaller than those on the non-deviated side and the AOP and OP on the deviated side were greater.3.In the transverse dental measurement variables,there were statistical differences between the two sides in Width U3,Width U4,Width U6,Width L3,Width L4,Width L6,Torque U3,Torque U5,Torque U6,Torque U7,Torque L3,Torque L5,Torque L6,Torque L7 in asymmetry group(P<0.05).In the asymmetry group,Width U3,Width U4,Width U6 on the deviated side were larger than those on the non-deviated side.Width L3,Width L4,Width L6 on the deviated side were smaller;Torque U3,Torque U5,Torque U6,Torque U7 on the deviated side were larger;Torque L3,Torque L5,Torque L6,Torque L7 on the deviated side were smaller.4.In the sagittal dental measurement variables,there were statistically significant differences between the two sides in U6 dev,U7dev,L3 dev,Inclination U6,Inclination L7 in asymmetry group(P<0.05).5.The L3 Mn P,Width U4 and Width U6 on deviated side were positively correlated with the Me-dev;the Width U4,Width U6 on the non-deviated side were negatively correlated with the Me-dev;Width L3,Width L4,Width L6 on the deviated side were negatively correlated with the Me-dev,and Width L3,Width L4,Width L6 on the non-deviated side were positively correlated with the Me-dev;Torque U5 and Torque U6 on the deviated side were positively correlated with the Me-dev;while Torque U3,Torque U6 on the non-deviated side were negatively correlated with Me-dev.Conclusions:1.Compared with subjects with individual normal occlusion,there were significant differences between two sides of patients with skeletal Class III malocclusion and mandibular asymmetry in the ramus length,the mandibular body length,and the gonial angle.The ramus length,the mandibular body length and the gonial angle on the deviated side were smaller in patients with skeletal Class III malocclusion and mandibular asymmetry.2.Compared with subjects with individual normal occlusion,there were significant differences between two sides of patients with skeletal Class III malocclusion and mandibular asymmetry in the vertical height of the maxillary second premolar,maxillary first molar,maxillary second molar,and anterior occlusal plane and maxillary occlusal plane.The vertical height of the maxillary second premolar,maxillary first molar,and maxillary second molar were smaller on the deviated side.And the anterior occlusal plane and maxillary occlusal plane of the deviated side were steeper.3.There were significant differences between two sides in the distance from the teeth to the midline and the torque in patients with skeletal Class III malocclusion and mandibular asymmetry.Among them,the maxillary teeth on the deviated side were more baccal and further from the midline.The mandibular teeth on the deviated side were more more lingual and closer to the midline.4.In the sagittal direction,there may be differences in the positions of the teeth on both sides of the patients with skeletal Class III malocclusion and mandibular asymmetry.The maxillary first molar and the mandibular second molar on the deviated side were more mesially inclined,and the positions of the crown of the maxillary first and second molar were more mesial;5.In patients with skeletal Class III malocclusion and mandibular asymmetry,on the deviated side,the greater the degree of menton deviation,the greater the distance from the maxillary premolars and molars to the midline,the smaller the distance from the mandibular canines,premolars and molars to the midline,and the more buccal inclined of the maxillary first molar.