X-ray Measurement And Analysis Before Orthodontic Intrusion At Maxillary Central Incisors In Skeletal Class Ⅱ High-angle Patients With Deep Overbite

Objective:To assess alveolar and positional features of maxillary central incisors before orthodontic intrusion and find an optimal angle range of incisor inclinations for intrusion in skeletal class Ⅱ high-angle patients with deep overbite.Methods:111 adult patients with deep overbite were divided into three groups according to sagittal and vertical skeletal patterns as skeletal Class Ⅱ high-angle(Study Group,SG),skeletal Class Ⅱ normal-angle(Control Group Ⅱ,CGⅡ)and skeletal Class Ⅰ normal-angle(Control Group Ⅰ,CGI)group with 37 patients in each group in this retrospective study.Alveolar bone thickness at the sites of 3 mm,6 mm,9 mm from the cementoenamel junction and root apex which were measured as labial,palatal and total alveolar bone thickness(L1-L4,P1-P4,T1-T4,respectively),and vertical distance from incisor apex to palatal plane as bone height(BH)were used to assess the amount of alveolar bone from CBCT images.U1-SN represented the inclination angle of maxillary central incisor from cephalogram.1.5 mm(I1.5)and 2.4 mm(I2.4)were set as two levels of intrusion amount.If the intrusion amount of maxillary central incisor along the tooth axis was no less than the set value,it was recorded as 1;otherwise,it was recorded as 0.The percentages of two levels of intrusion amount(I1.5 and 12.4)recorded as 1 were compared in the three groups.SPSS 20.0 was used for statistical comparisons.In addition,arranging the studied maxillary central incisors according to values of U1-SN on an ascending order,a heatmap was made in each group to show the distributions of the two levels of intrusion amount(I1.5 and I2.4)and alveolar bone thickness.Results:Significant differences in L4,BH and U1-SN were found among the groups(P<0.05).The percentages of maxillary central incisors which achieved two intrusion levels in SG were the smallest(P<0.05)(I1.5=1,14.86%and 12.4=1,13.51%).The heatmaps showed that the bands represented 1 were gathered in a narrow range of values of U1-SN(99.0°～108.3° for I1.5=1 or 101.3°～108.3° for I2.4=1)in SG.Conclusion:Maxillary central incisors were more lingual-inclined and surrounding alveolar bone was thinner and longer in skeletal Class Ⅱ high-angle patients with deep overbite compared with skeletal Class Ⅰ and Class Ⅱ normal-angle patients Inclinations of most maxillary central incisors at natural dentition were not optimal for intrusion no less than 1.5 mm along the initial tooth long axes,especially in skeletal Class Ⅱ high-angle patients.The recommended optimal ranges for inclinations of maxillary central incisors which were assessed by U1-SN on lateral cephalogram might be helpful for intrusion designs in the treatment of skeletal Class Ⅱ high-angle patients with deep overbite.