Abstract: Objective: To measure the physiological alveolar bone thickness of the mandibular first molar with different facial types using cone beam CT (CBCT) and evaluate the transverse position of the mandibular first molar. Methods: Fifty patients who had taken CBCT before orthodontics at the Second Department of Orthodontics, Hefei Stomatological Hospital from January 2023 to October 2023 were selected. They were divided into high angle group, mean angle group, and low angle group. The data were imported into the supporting 3D software to measure and analyze the thickness of alveolar bone at different depths in four locations. Results: The bone thickness of the first mandibular molar in high angle patients was the smallest. The lingual bone thickness of the first mandibular molar was higher than that of the buccal side. The thickness of the mesial lingual alveolar bone at the 4mm root of the mandibular first molar enamel cementum junction (CEJ) was higher than that of the distal lingual side, and there was no significant difference in the thickness of the mesial buccal alveolar bone compared to the distal buccal side. The thickness of the alveolar bone on the distal buccal side of the first mandibular molar at 8mm of the CEJ was higher than that on the mesiobuccal side, and there was no significant difference in the thickness of the alveolar bone on the mesiolingual side compared to the distal lingual side. The thickness of the alveolar bone below the CEJ of the first mandibular molar at the same measurement site, which was 8mm in the root, was higher than that of the alveolar bone at 4mm in the root. Conclusion: Different vertical facial types, measurement sites, measurement depths, and tooth anatomical shapes all reflect the differences in the transverse position of the mandibular first molar in the alveolar bone.

Key words: mandibular first molar, alveolar bone thickness, vertical facial type, cone-beam CT