A Three-dimensional Analysis Of Skeletal And Dental Characteristics In Adult With Skeletal Class Ⅲ Malocclusions And Facial Asymmetry

Objective: To evaluate the skeletal and dental characteristics in adult with skeletal class Ⅲ malocclusions and facial asymmetry and to analyse the relationships among various parts of the stomatognathic system by using CBCT(cone-beam computed tomography)and three-dimensional reconstruction measurement technology.Methods: Fifty-six asymmetric CBCT data were evaluated by Mimics 10.0 and 3-Matic software.Skeletal and dental measurements were performed and t-test was used to assess the differences between the deviated and nondeviated sides.Pearson correlation analysis was used to determine the correlations among measurements.Results:(1)Skeletal indices:Ramal height,mandible body length,RHASN,maxillary height,condylar height,condylar volume and condylar surface were significantly smaller on the deviated side than on the nondeviated side(P < 0.01).There was no significant difference in RHBSN,glenoid fossa width,glenoid fossa height,tuberculum articulare angle,condylar anteroposterior position and axial condylar angle(P >0.05).The mean value of the mandibular inclination,maxillary inclination and occlusal plane inclination were 1.01o,0.98o and 1.88o.Among subjects of this experiment,the proportion of mandibular canting,maxillary canting and occlusal canting were 45.45%,54.54% and 63.63%.(2)Dental indices: The buccolingual angle and crown root ratio of mandibular first molar were significantly larger on the deviated side than on the nondeviated side(P <0.05).The buccal and total cancellous bone thickness of mandibular first molar were found to be significantly smaller on the deviated side when compared with the nondeviated side(P <0.05).There was no significant difference in the ratio of buccal and total cancellous bone thickness on mandibular first molar(P >0.05).The measurements of maxillary first molar and maxillary alveolar bone morphology were not significantly different between the two sides(P >0.05).(3)Pearson correlation analysis: Menton deviation was significantly correlated with differences in ramal height(P <0.01),mandible body length(P <0.05),RHASN(P <0.01)and condylar volume(P <0.05)between the two sides.A negative correlation was discovered between buccolingual angle of mandibular first molar and ramal height(P <0.01).Conclusions:(1)The adult with skeletal class Ⅲ malocclusions and facial asymmetry may be caused by length differences in mandibular basic units as well as the spatial rotation of mandible and these will probably cause maxillary asymmetry.(2)An asymmetry in condylar morphology served as the major component of TMJ asymmetry in adult with skeletal class Ⅲ malocclusions and facial asymmetry.(3)In skeletal class Ⅲ patients with facial asymmetry,although the buccolingual compensation of first molar was found,especially in mandibular first molar,the position of first molar in the alveolar bone was symmetrical due to the remodeling of alveolar bone.(4)The asymmetry of alveolar bone morphology were mainly manifested in the reduction of the buccal and total cancellous bone thickness on the mandibular deviated side.(5)A vertical skeletal discrepancy was proved to have a significant correlation with transverse dental compensation.