The Characteristics Of Teeth And Alveolar Bone In Maxillary Posterior Region Of Adult Patients With Different Vertical Patterns In Skeletal Class Ⅲ Malocclusion:CBCT Analysis

Objective:Cone-beam computed tomography(CBCT)was used to analysis the characteristics of teeth and alveolar bone in the maxillary posterior region of untreated skeletal class Ⅲmalocclusion adult patients with different vertical skeletal patterns and to explore the differences of compensation characteristics in diverse vertical facial patterns,aiming to provide reference for the formulation of clinical treatment plans to skeletal class Ⅲ adult patients.Methods:77 adult skeletal class Ⅲ malocclusion patients(ANB<0.7° with an average age of 20.79±3.38 years old)were selected from the Department of Orthodontics,Stomatological Hospital of Shandong University from January 2018 to June 2021.Lateral cephalogram and CBCT were taken for each patient at their first visit.The patients were divided into three groups according to the vertical skeletal pattern:hyperdivergent group(SN-MP>37°and FHI<62%),normodivergent group(26°≤SN-MP≤37° and 62%≤FHI≤65%)and hypodivergent group(SN-MP<26° and FHI>65%).CBCT data were imported into Mimics 21.0 software to measure the related items of teeth and alveolar bone in the maxillary posterior region,including the mesiodistal and buccolingual inclination of maxillary premolars and molars,tooth height,posterior occlusal plane inclination,curve of Wilson,height and thickness of the alveolar bone in maxillary posterior region,dental arch width of maxillary middle and posterior segments,maxillary and mandibular basal arch width and the height of hard palate.One-way ANOVA and LSD-t test were used to analyze the differences of each item between three groups.The level of significant difference was set to α=0.05.Results:1.Sagittally,the maxillary posterior teeth inclined distally in hyperdivergent group(P<0.05);2.Vertically,compared with hypodivergent group,the posterior occlusal plane inclination and palatal height in hyperdivergent group was greater(P<0.05),the tooth height was only statistically different between hyper-and hypodivergent groups in maxillary second premolar(P<0.05);the alveolar bone height was only statistically different between hyperand hypodivergent groups in buccal side of maxillary first molar and between normo-and hypodivergent groups in palatal side of maxillary second molar(P<0.05);3.Transversely,compared with the hypodivergent group,the maxillary and mandibular basal arch width decreased while their difference increased in the hyperdivergent group(P<0.05).the maxillary molars in the hyperdivergent group were more buccally inclined(P<0.05);the dental arch width of the maxillary middle segment was significantly smaller in the hyperdivergent group than that in the hypodivergent group(P<0.05)while the dental arch width of the maxillary posterior segment has no statistically significant difference among three groups(P>0.05);the thickness of alveolar bone on the buccal and palatal sides of maxillary posterior region was almost thicker in the hypodivergent group than normo-and hyperdivergent groups,and the difference at some sites was statistically significant(P<0.05).Conclusion:1.There are differences in three-dimensional compensation characteristics of teeth and alveolar bone in the maxillary posterior region of skeletal class Ⅲ adult patients with different vertical skeletal patterns.2.The hyperdivergent skeletal class Ⅲ patients have larger degree of compensation of maxillary posterior teeth and smaller amount of alveolar bone,which lead to the reduction of teeth movable region.Orthodontists should pay attention to the movement direction and boundary restriction during treatment process.3.CBCT can accurately evaluate the tooth position and surrounding bone characteristics.CBCT should be used to analyze the compensation characteristics of skeletal class Ⅲ patients with different vertical skeletal patterns to judge the boundary of orthodontics tooth movement before orthodontic treatment.