Assessment Of Bone Quantity In The Infrazygomatic Crest Region In Adult Patients With Different Vertical Skeletal Patterns

Objectives:In order to provide the orthodontist with an optional safe area for clinical treatment,cone-beam computed tomography（CBCT）was used to evaluate the difference in bone thickness in the infrazygomatic crest region of adult patients with different vertical skeletal patterns of skeletal classⅠmalocclusion.Methods:From the CBCT image database,a total of 120 skeletal classⅠadult patients were selected,and divided into hyperdivergent group,normodivergent group,and hypodivergent group based on the MP-FH angle,with 40 cases in each group.The DICOM data were imported into Smart V2 analysis software for 3D image reconstruction.The horizontal observation line and vertical observation line were adjusted in the sagittal plane,coronal plane,and cross-sectional plane so that the two lines passed the alveolar crest of the right maxillary first molar,and the inter-root area was equally divided.Six levels were selected in the cross section from proximal to mid-distal:between the maxillary second premolar and first molar(U5_b-U6_mb),the mesiobuccal root of the first molar(U6_mb),between the mesiodistal roots of the first molar(U6_mb-U6_db),the distobuccal root of the first molar(U6_db),between the first molar and second molar(U6_db-U7_mb),the mesiobuccal root of the second molar(U7_mb).The buccal alveolar bone thickness and bone cortical thickness were measured in cross-section at 5 mm,7 mm,9 mm,and 11 mm from the top of the alveolar ridge.The effective bone thickness from the implantation site to the maxillary sinus was measured at 50°,60°,and 70°implantation at buccal alveolar bone thickness≥3 mm and bone cortical thickness≥1 mm.The results were statistically analyzed using SPSS 25.0 software.The buccal alveolar bone thickness,bone cortical thickness,and effective bone thickness were tested for normal distribution,and the data that met the normal distribution were expressed as±.Multiple groups were compared using one-way ANOVA,and a post-hoc test was performed between the groups,with P<0.05 representing a statistically significant difference.Results:1.Between the three groups of vertical skeletal types,age and ANB did not statistically differ（P>0.05）.MP-FH was statistically different（P<0.05）.2.Comparison of different vertical sections and mesiodistal levels in the zygomatic alveolar crest area showed that the thickness of the buccal alveolar bone gradually increased from the top of the alveolar crest to the root side and from mesial to distal,except for the mesiobuccal root of the first molar（P<0.05）.3.Comparison of different vertical sections and mesiodistal levels in the zygomatic alveolar crest area showed that the thickness of the buccal cortical bone gradually increased from the top of the alveolar crest to the root side and from mesial to distal（P<0.05）.4.There was a significant difference in buccal alveolar bone thickness between different vertical skeletal types（P<0.05）.Post-hoc test showed that the hypodivergent group>hyperdivergent group at all levels（P<0.05）.5.There was a significant difference in the thickness of buccal cortical bone between different vertical skeletal types（P<0.05）.Post-hoc test showed that the hypodivergent group>hyperdivergent group at all levels（P<0.05）.6.In the hypodivergent group,there was a significant difference in the effective bone thickness at U6_mb-U6_dblevel of 11 mm,U6_db-U7_mblevel of 7 mm and 9 mm,U7_mblevel of 7 mm and 9 mm at three angles（P<0.05）.In the normodivergent group,there was a significant difference in the effective bone thickness at U6_db-U7_mblevel of9 mm and 11 mm,U7_mblevel of 9 mm at three angles（P<0.05）.In the hyperdivergent group,there was a significant difference in the effective bone thickness at U6_db-U7_mblevel of 11 mm,U7_mblevel of 9 mm and 11 mm at three angles（P<0.05）.Post-hoc test comparison of effective bone thickness at all levels showed that 70°>60°（P<0.05）.Conclusion:1.There are differences in the thickness of the buccal alveolar bone and the cortical bone in the zygomatic alveolar crest area in adult patients with different vertical skeletal types of classⅠmalocclusion.Compared to patients with other vertical skeletal types,patients in hypodivergent group have a wider range of implant sites to choose from.2.It is recommended to insert the miniscrews at 50°to 70°between the maxillary first and second molars at 7 mm from the top of the alveolar crest in hypodivergent group.It is recommended to insert the miniscrews at 70°between the maxillary first and second molars at 9 mm from the top of the alveolar crest,or at 50°to 70°at the mesiobuccal root of the second molar of 7 mm from the top of the alveolar crest in normodivergent group.Hyperdivergent group is prone to perforation of the maxillary sinus and need to be carefully evaluated and informed the advantages and disadvantages before implanting miniscrews.3.The vertical skeletal patterns should be taken into consideration when placing miniscrews in the infrazygomatic crest region and designing the orthodontic plans in clinical practice.