Study On The Transverse Relationship Of Mandibular First Molars With Different Vertical Bone Types Of Angle Class Ⅲ In Adults

Objective Using CBCT three-dimensional imaging technology to study the lateral relationship of mandibular first molars in adult patients with Class III,aiming to analyze the lateral compensation differences of mandibular first molars in adult patients with different vertical skeletal facial types,and to evaluate the quantitative compensation of mandibular first molars.Whether there is an adequate safety margin between the molar root and the alveolar bone.It not only provides a theoretical basis for the rational plan design of the first stage,but also provides a certain clinical reference for the prevention of periodontal diseases such as bone fenestration and bone dehiscence during the treatment process,as well as safe and effective movement.Methods The patients with Class III who visited the department of orthodontics in our hospital from September 2019 to December 2021 were selected as the research subjects,and were divided into three groups according to the size of FMA values: high angle group,average angle group and low angle group,respectively,each group was randomly sampled and 20 people were selected for inclusion in this study,a total of 60 people were selected for the study with age limit of 18 to 32 years old and mean age23.3 years.The CBCT taken before orthodontic treatment was studied,and the data was transmitted to the Invivo Dental 5.0 system for measurement.Measurement items include(1)L6W1(mm);(2)L6W2(mm);(3)L6W3(mm);(4)L6/MP(°);(5)MBb-3(mm);(6)MBb-6(mm);(7)MBb-9(mm);(8)DBb-3(mm);(9)DBb-6(mm);(10)DBb-9(mm);(11)MLp-3(mm);(12)MLp-6(mm);(13)MLp-9(mm);(14)DLp-3(mm);(15)DLp-6(mm);(16)DLp-9(mm).Statistical analysis of all the above measured values was performed with SPSS 20.0 software.Results(1)There was no significant difference between the three groups in the measurement of the width of the mandibular first molar alveolar arch and the width of the basal arch(P>0.05);The measured value of the dental width of the mandibular first molar in the high-angle group was smaller than that in the low-angle group,and the difference was significant(P<0.05);(2)Measurement of buccal-lingual inclination of mandibular first molars: the inclination of the high-angle group was smaller than that of the average-angle group and the low-angle group,and the difference was significant(P<0.05);(3)Comparison of buccal and lingual alveolar bone thickness of mandibular first molars at different sites: MBb measured at 3 mm in pairwise comparison showed that the value of the high-angle group was smaller than that of the low-angle group and the average-angle group,and the difference was statistically significant(P<0.05);The measurement results of MBb at 6mm and 9mm,MLp at 3mm and 9mm,and DBb at3 mm were found to be significantly smaller in the high-angle group than in the low-angle group(P<0.05).The measurement result of DLp at 9mm was that the value of the low-angle group was greater than that of the high-angle group and the average-angle group,and the difference was statistically significant(P<0.05);MLp at 6mm,DBb at6 mm,9mm,and DLp at 3mm,6mm were not significantly different in pairwise comparisons(P>0.05).Conclusion(1)The dental width of the mandibular first molars in adult Class III patients in the low-angle group is greater than that in the high-angle group;(2)The buccal-palatal inclination of the mandibular first molar in the adult Class III high-angle group was more lingually inclined than that in the low-angle group and the average-angle group;(3)In the comparison of the alveolar bone thickness of the mandibular first molar between the adult Class III high angle patients and the other two groups,the thickness of the mandibular first molars was relatively thin at multiple sites;(4)The above suggests that we should consider the influence of different vertical bone profiles on the posterior teeth before clinical correction,especially for the plan design and correction process of patients with Class III malocclusion and high angle,and should cooperate with CBCT software.The specific situation of the orthodontic treatment process is specifically analyzed,and the tooth compensation situation is carefully evaluated to determine the orthodontic plan to achieve a good orthodontic effect.