Comparison of the Mandibular Alveolar Bone Width in Skeletal Class Ⅲ Malocclusion with Open Bite and Non-open Bite Using Cone-beam Computed Tomography

Introduction: For skeletal Class III malocclusions requiring surgical orthodontic treatment, labial inclination of the mandibular incisors is often necessary to improve dental compensation. However, the alveolar bone width of the mandibular symphysis in these patients is prone to be narrower than in patients with individual normal occlusion so that movement of the lower incisors is limited. Therefore, we investigated the alveolar bone width of the mandibular symphysis and molar areas in skeletal Class III malocclusion cases with either non-open bite or open bite without incisor attrition using cone-beam computed tomography (CBCT). Materials and Methods: Among patients 16 years old or older with skeletal Class III malocclusion who underwent CBCT, we enrolled 30 patients with open bite without incisor attrition and 30 patients with non-open bite. Using CBCT, we measured the width of the lingual side cortical bone at 2.0, 4.0, 6.0, and 8.0 mm below the cementoenamel junction (CEJ) and the width of the alveolar bone of the symphysis at 10 mm below the CEJ of the lower central incisor. Results : The mandibular anterior alveolar bone width, measured at 2.0, 4.0, 6.0, and 8.0 mm from the CEJ, was significantly narrower in the open-bite group than in the non-open-bite group. Between the distal root of the lower first molars and the second molars, the right buccal cortical bone of the open-bite group was significantly narrower at 6.0 mm and 8.0 mm from the CEJ than that of the non-open-bite group, but no significant difference was found in the left buccal cortical bone. Additionally, the right lingual cortical bone at 6.0 mm and the left lingual cortical bone at 2.0 mm and 4.0 mm from the CEJ were significantly narrower in the open-bite group than in the non-open-bite group. Furthermore, the width of the right alveolar bone was significantly narrower in the open-bite group than in the non-open-bite group at 8.0 mm from the CEJ. Discussion: In the case of patients with skeletal Class III malocclusion, there was less mechanical stimulation in the open-bite group than in the non-open-bite group. This suggests that the occlusal forces were smaller and the width of the mandibular molar alveolar and buccal cortical bone narrower in the open-bite group than in the non-open-bite group.