The Three-dimensional Analysis Of Mandible And The Occlusion Plane Of Mandibular In Angle Class Ⅲ Malocclusion With Facial Asymmetry

Objective:The aim of this study was to analyze the characters in 3D direction of morphology,spatial position of the mandible and the anatomical occlusion plane in Angle class Ⅲmalocclusion with facial asymmetry.To further grasp the development situation of mandible and provide references for the orthodontic treatment in patients with facial asymmetry in clinical.Method:Twenty adult patients with facial asymmetry were selected as the experimental group,and twenty normal patients were randomly selected as the control group.The inclusion criteria of the experimental group were as follows :(1)When the centric relation position and mandibular postural position,a chin point deviation from the MSP was greater than2.0 mm and it was Angle class Ⅲ malocclusion;(2)No periodontal disease;(3)There was no orthodontic history and other genetic diseases;(4)Dentition were complete;(5)ANB <0°.The inclusion criteria of the control group were as follows:(1)When the centric relation position and mandibular postural position,a chin point deviation from the MSP was less than 2.0 mm;(2)No periodontal disease;(3)There was no orthodontic history and other genetic diseases;(4)Dentition were complete;(5)5° > ANB > 0°.The CBCT scans were taken before orthodontic treatment according to the same requirements,and the 3D models were reconstructed by the Mimics software 17.0.The measurement items were as follows: the height,width,thickness of mandibular ramus and the length,total length of mandible on both sides;the MSP was used as the mirror image plane of the mandible to obtain the coordinates of the mark points in the same coordinate system;the angles between the occlusion plane and the three reference planes were measured,that is the pitch angle \ the roll angle \ the yaw angle.The data was analyzed by SPSS 22.0statistical software,except for Mann-Whitney U test was used for the comparison of coordinate point between the two groups,and the Independent-Sample t test was used for the analysis of other data,Pearson correlation analysis was used to compare the correlation of data in the experimental group(α=0.05).Results:1.There was no statistical difference in gender and age between the experimental group and the control group.(P>0.05)2.Three-dimensional analysis of the symmetry of mandibular in patients with facial asymmetry.There was a statistical difference in the hard tissue of two sides of the mandible between the experimental group and the control group(P<0.05).The degree of chin deflection was negatively correlated with the height of mandibular ramus,the length of mandibular body and the total length of mandible in the deflection side(P<0.05),the correlation coefficients were-0.728,-0.907 and-0.881.The degree of chin deflection was negatively correlated with the height of mandibular ramus,the length of mandibular body and the total length of mandible in the opposite side(P<0.05),the correlation coefficients were-0.680,-0.845 and-0.953.3.Three-dimensional analysis of the spatial position symmetry of the mandible in patients with facial asymmetry.After mirroring the both sides of the mandible,the difference of the same coordinate site between two groups was different(P<0.05),and the control group was smaller than the experimental group.Spatial position correlation analysis on both sides of the mandible in the experimental group was showed:in the non-deflection side,the change of Co point on the Z-axis was positively correlated with the degree of chin deflection,the correlation coefficient was 0.417;in the deflection side,the changes of Go point in three directions were highly correlated with the degree of chin deflection,on the X and Y-axis,it presents negative correlation,the correlation coefficients were-0.499,-0.534,on the Z-axis,it presents the positive correlation,the correlation coefficient was 0.675.4.Three-dimensional analysis of anatomical occlusion plane in patients with facial asymmetry4.1 The change in the horizontal direction of anatomical occlusion plane in the experimental groupIn the horizontal direction,the anatomical occlusion plane is mainly represented by the clockwise rotation.The correlation between the degree of chin deflection and the roll angle showed that the two were positively correlated,the correlation coefficient was 0.702,P<0.05.4.2 The change in the coronal direction of anatomical occlusion plane in the experimental groupIn the coronal direction,the anatomical occlusion plane is mainly represented by top spin.The correlation between the degree of chin deflection and the pitch angle showed that the two were negatively correlated,the correlation coefficient was-0.415,P<0.05.4.3 The change in the sagittal direction of anatomical occlusion plane in the experimental groupIn the sagittal direction,the anatomical occlusion plane showed a tendency of swinging to the deflection side.The correlation between the degree of chin deflection and the yaw angle showed that the two were positively correlated,the correlation coefficient was 0.393,P<0.05.Conclusion:1.The morphology,spatial position of the mandible and the anatomical occlusion plane were highly correlated with the degree of deflection of the chin in Angle class Ⅲmalocclusion with facial asymmetry.As the degree of chin deflection increases,the upward rotation of the mandible and the counterclockwise upward rotation of the anatomical plane are increasing,it could also be one of the reasons that which facial asymmetry often accompany Class Ⅲ occlusion relation.2.The three-dimensional analysis of hard tissue and anatomical occlusion plane of the mandible can provide references for the occlusion adjustment of patients with mild facial asymmetry and the design of the operation scheme for the patients with severe facial asymmetry by clinical orthodontist.