Three-Dimensional Heat Map Analysis Of Mandibular Average Cortical Bone Thickness In Skeletal Class Ⅲ Patients With Different Vertical Skeletal Patterns

Objective:In clinical practice,skeletal Class Ⅲ malocclusion is a prevalent and complicated scenario.The thickness of cortical bone has important guiding significance for the implementation and evaluation of orthodontic treatment.The aim of this study is to generate a heat map of the average mandibular cortical bone thickness distribution in skeletal Class Ⅲ patients with different vertical skeletal facial types,and to provide some reference for clinical orthodontic treatment of such patients.Methods:A total of 71 skeletal class Ⅲ patients who were admitted to the Stomatological Hospital of China Medical University from April 2022 to February 2023 and underwent spiral CT and lateral cephalograms were selected as the research objects.Spiral Computed Tomograph(SCT)images of all subjects were taken by the same radiologist and saved as Digital Imaging and Communications in Medicine format.Lateral cephalograms were analyzed using Winceph9.0 software.Obtain the SN planemandibular plane Angle(MP-SN)and the Frankfurt horizontal plane-mandibular plane Angle(FMA)angular values,and group by them.According to the vertical facial type,they were divided into three groups:high Angle group(MP-SN≥37.7° or FMA≥32°)20 cases,average Angle group(27.3°<MP-SN<37.7° or 22°<FMA<32°)34 cases,and low Angle group(MP-SN≤27.3° or FMA≤22°)17 cases.The Dicom data were imported into Proplan software for modeling and tooth mask color marking.The 3D mandibular model with clear alveolar socket after 3D reconstruction was named "mandibular reduced teeth",and the Dicom data with black tooth mask color marked was named "Dicom 1".The "Dicom 1" data were imported into ITK-SNAP 3.8.0 and 3D Slicer 5.0.3 software for binary conversion and named "Dicom 2".The "Dicom 2" and "mandibular reduction teeth" models were imported into Stradview 7.1 to generate the mapping of mandibular cortical bone thickness.Then,the individual model,standard model and individual thickness data were input into wxRegSurf v22 for model registration,and the individual model parameters were mapped to the standard model.Statistical parameter mapping was performed in Matlab R2021a SurfStat plug-in to generate the average mandibular cortical bone thickness heat map and statistical difference significance distribution map of different facial types.Matlab R2021a software was used to analyze the measurement results.Results:1.There were significant differences in mandibular cortical bone thickness between genders in skeletal class Ⅲ patients(P<0.05).(2)In skeletal class Ⅲ,significant differences were found in the mean thickness of mandibular cortical bone among different vertical skeletal facial types(P<0.001),low Angle group>average Angle group>high Angle group.(3)In skeletal class Ⅲ,there were significant differences in mean mandibular cortical bone thickness between different vertical facial types and genders(P<0.001),low-angle male>low-angle female>Average-angle male>High-angle male>Average-angle female>high-angle female(4)The distribution map of statistical differences in cortical bone thickness between groups showed that the female low-angle group had greater statistical differences in the medial condylar neck and sigmoid notch area than the female average-angle group.Compared with the average Angle group,the high Angle group had a greater statistical difference in the lateral oblique area.There were significant differences in the lateral oblique line,lingual alveolar bone area and medial condylar neck area between the female low-angle group and the high-angle group.There were significant differences in the condylar neck,sigmoid notch,and oblique line of mandibular body between the male low-angle group and the average Angle group.There was a significant difference in sigmoid notch area between the average Angle group and the high Angle group in males.There were significant differences in condylar neck,sigmoid notch,lateral oblique line and genioglossus attachment area between the male low-angle group and the high-angle group.(5)The significant distribution map of mean cortical bone thickness among the three groups showed that there were significant differences in sigmoid notch,condylar neck,and oblique line of mandibular body among the three groups in males.There were significant differences in the medial condylar neck,lateral oblique line and sigmoid notch among the three groups in females.Conclusion:1.There are differences in the thickness of mandibular cortical bone between males and females in skeletal class Ⅲ patients.2.In skeletal class Ⅲ,there were significant differences in the average mandibular cortical bone thickness among different vertical facial types,and the low-angle group>average-angle group>high-angle group.3.In skeletal Class Ⅲ,significant differences in cortical bone thickness were observed in some regions among different vertical facial types.