Abstract:

Objective To assess the bone thicknesses of the infrazygomatic crest in the adult patients with different vertical skeletal patterns of skeletal classⅠmalocclusion based on cone-beam computed tomography（CBCT），and to provide the basis for the choice of clinical treatment methods for the orthodontists. Methods A total of 90 adult patients with skeletal class I malocclusion were selected and divided into low angle group， average angle group，and high angle group， and there were 30 patients in each group. The buccal bone thickness of the patients at different vertical levels and proximal，distal and mesial levels were detected on the CBCT images and the effective bone volume was measured at buccal alveolar bone thickness ≥ 3 mm with the 50°，60°and 70° implantation angles. Results In different vertical sections， except for the proximal mesiobuccal root level of the maxillary first molar（U6_mb）， the buccal alveolar bone thickness was increased gradually from the top of the alveolar ridge to the root side（P<0.05）. At different proximal，distal and mesial levels， the buccal bone thickness of the patients was gradually increased from the proximal to the distal mesial direction in all levels except U6_mb（P<0.05）. The maximum buccal bone thickness of the patients was 11 mm from the top of the alveolar ridge at the proximal mesiobuccal root of the maxillary second molar（U7_mb）； the minimum buccal bone thickness was 7 mm from the top of the alveolar ridge at U6_mb.There was significant difference in the buccal bone thickness of the patients with different vertical bone facial types （P<0.05）， the buccal bone thickness of the patients in low angle group was higher than those in average angle group and high angle group （P<0.05），and the buccal bone thickness of the patients in average angle group was higher than that in high angle group （P<0.05）.Among the patients in low angle group， there were significant differences in bone thicknesses between the distal mesiobuccal root of the maxillary first molar and the proximal mesiobuccal root of the maxillary second molar （U6_db-U7_mb） at from the top of the alveolar crest was 7 mm，at U7_mb when the distance from the top of the alveolar crest was 7 mm and 9 mm， at U6_mb-U6_db when the distance from the top of the alveolar crest was 11 mm at three angles（P<0.05）.The bone thickness was ≥6 mm at U6_db-U7_mb， when the distance from the top of the alveolar crest was 7 mm at three angles， and when the distance from the top of the alveolar crest was 9 mm at 70° at U7_mb.Among the patients in average angle group， there were significant differences in the bone thicknesses between U6_db-U7_mb at 9 mm from the top of the alveolar crest， U7_mb at 9 mm and 11 mm from the top of the alveolar crest at three implantation angles，and the bone thickness ≥6 mm at U7_mb when the distance from the top of the alveolar crest at three angles was 7 mm and at U7_mb when the distance from the top of the alveolar crest was 9 mm at 70°（P<0.05）. Among the patients in high angle group， there were significant differences in bone thickness between U6_db-U7_mb 11 mm from the top of the alveolar ridge and U7_mb 11 mm from the top of the alveolar ridge at three implantation angles（P<0.05）. The thicknesses of bone implantation at different angles could be ranked as follows， 70°>50°>60° in all dimensions. Conclusion There are differences in the buccal bone thickness in the zygomatic crest area among the adult patients with different vertical facial bone patterns. The patients in low angle group have more options for the implantation sites， while the patients in high angle group are more prone to maxillary sinus perforation.Therefore，when placing dental implants and designing orthodontic treatment plans in this area，the vertical facial bone pattern should be taken into consideration.

Key words: Miniscrew, Infrazygomatic crest, Vertical skeletal pattern, Insertion angle, Bone thickness