A Comparative Study Of The Relationship Between The Width Of The Dental Arch And Basal Bone And The Oblique Degree Of The Occlusal Plane Of The Skeletal Class Ⅲ Malocclusions In Adolescents With Different Vertical Facial Types

Objective:The x-ray cephalometric films,CBCT images and three-dimensional reconstruction techniques were used to measure and analyze the differences of dental arch width and basal bone width and occlusal plane inclination between different vertical bone types in adolescent skeletal Class Ⅲ patients,so as to provide some reference for clinical treatment of class Ⅲ patients.Methods:According to the inclusion criteria,52 cases of adolescent skeletal class Ⅲ patients treated in the Orthodontics Department of Nanchang University Affiliated Stomatological Hospital from 2015 to 2020 were selected for x-ray lateral cephalometric radiographs and CBCT,aged 13-17 years,according to SN-MP and FH-MP angle measurement values were divided into 17 cases in high angle group, 16 cases in average angle group,and 19 cases in lower angle group.Use the Uceph cephalometric software to trace the relevant measurement points of the x-ray lateral cephalometric radiographs,and perform the measurement of the SN-MP and FM-MP angles and occlusal plane inclination related items,respectively with OP-A,OP-P, OP-C represents the occlusal plane of the anterior teeth,the occlusal plane of the posterior teeth,and the maxillary occlusal plane,and the angle formed by the occlusal plane and the FH plane is recorded as the occlusal plane angle.Import the CBCT file into the Invivo 6.0 software for three-dimensional reconstruction.The arch and basal bone width are measured by tracing and measuring the marked points. UCC,UPP,and UMM are used to represent the width of maxillary canines and maxillary canines and the maxillary first molars.LCC,LPP,and LMM represent the width between the mandibular canines,the width between the mandibular first premolars,and the width between the first mandibular first molars;and UBCC,UBPP, and UBMM represent the width of the base bone arch between the maxillary canines, the width of the base bone arch between the maxillary first premolars,the width of the base bone arch between the maxillary first molars,LBCC,LBPP,LBMM represent the width of the base bone between the the mandibular canines,the width of the base bone between the the mandibular first premolars,the width of the base bone between the the mandibular first molars.Enter the measured data into the spss23.0 software for statistical analysis.Results :Comparison of measurement results between different vertical bone face types:(1)Comparison of dental arch width measurement results: lower angle group>average angle group> high angle group.The difference between the lower angle group and the high angle group(except for LMM)in the upper and mandibular arch width measurement items was statistically significant(P<0.05);There was no statistically significant difference between the high angle group and the average angle group(P>0.05);there were no statistically significant differences between the average angle group and the lower angle group(except UPP)and other measurement items(P>0.05).(2)Comparison of the measurement results of the basal bone width: The measured values of the basal bone width of the anterior and middle maxillary basal bone are the highest in the lower angle group;the width of the anterior mandibular basal bone is the smallest in the high-angle group;the measurement item of the middle mandibular basal bone width is the lower angle group> In the high angle group,the difference was statistically significant(P<0.05);the measurement items of the basal bone width of the mandibular posterior segment were lower angle group>average angle group>high angle group,but the difference was not statistically significant(P>0.05);other measurement items there was no statistically significant difference between the groups(P>0.05).(3)Comparison of the difference between the width of the upper and lower dental arches and the difference between the width of the upper and lower basal bones: There was no significant difference in the difference between the upper and lower dental arch widths among the three groups(P>0.05);the anterior segment of the upper and lower basal bone width.There was no statistically significant difference between the three groups of the difference between and the posterior segment(P>0.05);only the midmandibular basal bone width difference was statistically significant between the highangle group and the lower angle group(P<0.05),the lower angle group>high-angle Group.(4)Comparison of measurement results of occlusal plane inclination: The results of the three groups are presented: high-angle group>average-angle group>lower angle group.The differences between high-angle group and lower angle group,high-angle group and average-angle group are statistically significant(except for the ∠OP-A of high-angle group and average-angle group)(P<0.05),the difference between the lower angle group and the average angle group was not statistically significant(P>0.05).Conclusion:1.The widths of the maxillary and mandibular dental arches and base bones of adolescent skeletal class Ⅲ patients tend to decrease gradually with the increase of the Mandibular plane angle,especially in the anterior and middle segments of the dental arch and base bones.2.In adolescents with skeletal class Ⅲ,the width of the posterior maxillary base bone tends to be smaller than that of the mandible,but the width of the maxillary dental arch is still larger than that of the mandible.3.The occlusal plane of the anterior teeth,the occlusal plane of the posterior teeth and the maxillary occlusal plane of the adolescents skeletal Ⅲ high angle group were steeper than those of the average angle group and the lower angle group.