| Background and ObjectiveSkeletal Class Ⅲ malocclusion with translation-dominant type(T-type)of facial asymmetries,a common deformity,is characterized by facial asymmetry,transverse and sagittal abnormalities,and the deviation of chin.The purpose of the study was to analyze the craniofacial characteristics in skeletal Class Ⅲ adults with T-type of facial asymmetries based on the date obtained from cone-beam computerized tomography(CBCT).MethodsA total of 62 adult patients before treatment admitted in the orthodontic department of Shandong University Dental School from 2017 to 2020 were selected.Patients were divided into two groups-the skeletal class Ⅲ malocclusion group with T-type of facial asymmetry and the skeletal class Ⅲ malocclusion group with non-facial asymmetry based on sagittal facial type.Each group had 31 patients(10 males,21 females).The ages of patients in the two groups were 20.58±3.31 years,20.23±3.99 years,respectively.CBCT scanner was employed to obtain the DICOM data from all patients Linear and angular measurements were performed with MIMICS 21.0,and SPSS 22.0 was employed for statistical analysis.The paired t-test was used for the measurement results in skeletal class Ⅲ malocclusion group with T-type of facial asymmetry,and the difference between the two groups was determined by independent sample t-test(the data were normally distributed and showed homogeneous variance)or Wilcoxon rank-sum test(The data did not conform to normal distribution or exhibited heterogeneity of variance)Results1.In the group of skeletal class Ⅱ malocclusion group with T-type of facial asymmetry,the torque of maxillary first molar,the distances from mesiopalatal tip of maxillary first molar(UP),root furcation of maxillary first molar(UF),and Jugal point(J)to the craniomaxillary median sagittal plane(CMSP)and the distance from UP to Frankfort horizontal plane(FHP)on the deviated side were greater than those of the non-deviated side(P<0.05),while the distances from UF and J to the FHP and coronal plane(CP)showed no statistical difference(P>0.05).It indicated that the first molar on the deviated side was more buccal inclined and the palate tip was drooping.The arch and basal bone of the first molar were transverse asymmetry,and the deviated side was wider.No significant difference was found in the vertical direction and sagittal direction.2.In the group of skeletal class Ⅲ malocclusion group with T-type of facial asymmetry,the torque of mandibular first molar,the distances from central fossa of mandibular first molar(LC),root furcation of mandibular first molar(LF),the buccal cortex of the root bifurcation of the mandibular first molar(LW),gonion(Go)and antegonial notch(Ag)to CMSP on the deviated side were greater than those of the non-deviated side(P<0.05),while the distances from LF,LW,Go and Ag to the FHP and CP were smaller than those of the non-deviated side(P<0.05).It indicated that the lingual inclination of the mandibular first molar on the deviated side was more obvious.And the position of the mandibular body is more outward,upward and backward on the deviated side.No difference was observed in the distance between the condylar apex and the medial and lateral points to the three reference planes,suggesting that the condylar position have no difference in the three-dimensional direction.3.The lengths of condyle unite,mental unit,condyle,mandibular body and the height of mandibular ramus on the deviated side were all smaller than those on the opposite side(P<0.05).ConclusionsThere were horizontal compensations of teeth and basal bones in the upper jaw of these patients.The mandibular ramus deviates horizontally to the deviated side,accompanied by vertical and sagittal rotation.The position of the mandible is more upward,outward and backward on the deviated side when the reference planes were based on cranial-maxillary complex.The asymmetry of mandibular exists in condyle and mental units,and the change of condyle may play a major role in facial asymmetry dominated by T-type. |
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