Analyze The Crown-root Morphology Of Incisor Teeth With Different Vertical Facial Patterns In Adult Skeletal Angle Class Ⅲ Malocclusion With CBCT

Objective To describe the crown-root morphology of upper and lower incisors in adult skeletal class Ⅲ malocclusion patients with different vertical skeletal patterns using CBCT and computer-assisted measurement methods,and to analyze the correlation between the crown root morphology and the apical alveolar bone thickness,so as to provide guidance for the safe and effective movement of incisors in adult skeletal class Ⅲ malocclusion patients.Methods According to the inclusion criteria,80 adult patients were selected as the research objects.Wits value and Angle’s malocclusion classification were used as the sagittal grouping basis,PP-MP value and FHI value were used as the vertical grouping basis.The subjects were divided into four groups: Skeletal Class Ⅰ average Angle group,Skeletal Class Ⅲ high Angle group、average Angle group and low Angle group,with 20 cases in each group.The CBCT image data of all subjects were imported into the three-dimensional image processing software Invivo 5.0.The Midsagittal section of the right upper and lower incisors was selected as the measurement plane.Collum Angle(CA),labial surface Angle(LSA),labial alveolar bone thickness(BW),lingual alveolar bone thickness(LW),total alveolar bone thickness(TW)and the ratio of lingual to labial alveolar bone thickness(LW/BW)in the apical area.SPSS 22.0 statistical software was used to analyze the measured data.Results(1)Compared with the skeletal Angle Class Ⅰ average Angle group,the CA of maxillary lateral incisors decreased and the CA of mandibular incisors increased in the skeletal Angle Class Ⅲ average Angle group,the differences were statistically significant(P< 0.05).The LSA of the upper and lower incisors increased,and the differences were statistically significant(P < 0.05).(2)In skeletal Angle Class Ⅲ malocclusion,the CA of maxillary lateral incisors in the high Angle group was significantly higher than that in the average Angle group and the low Angle group,and the CA of mandibular incisors in the low Angle group was significantly higher than that in the high Angle group and the average Angle group(P < 0.05).The LSA of maxillary incisors in the high-angle group was greater than that in the low-angle group,and the LSA of mandibular incisors in the low-angle group was greater than that in the high-angle group,and the differences were statistically significant(P <0.05).(3)There was no significant difference in CA and LSA between mandibular central and lateral incisors in skeletal Class Ⅲ malocclusion(P > 0.05).(4)In skeletal Angle Class Ⅲmalocclusion,the BW of maxillary incisors was the widest in the low-angle group,and the BW of mandibular incisors was the narrowest in the high-angle group,and the differences were statistically significant(P < 0.05).TW of mandibular incisors was widened successively among the high Angle group,average Angle group and low Angle group,and the difference was statistically significant(P < 0.05).(5)The LW/BW of upper and lower incisors in the high-angle group was significantly higher than that in the low-angle group among skeletal class Ⅲ malocclusion groups(P < 0.05).(6)There was a positive correlation between CA and LSA in maxillary lateral and mandibular central incisors(P < 0.05).The CA of mandibular central incisor was positively correlated with BW and TW(P < 0.05).Conclusions(1)Compared with adults with normal skeletal facial type,the mandibular incisors in skeletal Class Ⅲ average-angle malocclusion had more obvious crown-root lingual inclination Angle and labial surface curvature.Some maxillary lateral incisors had crown-root labial inclination Angle.(2)In adults skeletal Class Ⅲ malocclusion,the mandibular incisors in low-angle group and the maxillary lateral incisors in high-angle group showed larger crown-root lingual inclination Angle and more significant crown labial surface curvature.(3)In adults skeletal Class Ⅲ malocclusion,the thickness of the labial alveolar bone of the mandibular incisors in the high-angle group was the thintiest.(4)Correlation analysis showed that the Collum angles of maxillary lateral and mandibular central incisors were positively correlated with labial surface angles.The Collum angles of mandibular central incisors was positively correlated with the labial and the total alveolar bone thickness in the apical area.