Three-dimensional changes in the mandible and articular fossae following Herbst appliance therapy: a preliminary CBCT study

Objective: The purpose of this study was to compare three-dimensional (3D) skeletal changes in the mandible and the articular fossae of a group of Class II malocclusion subjects treated with the Herbst appliance (HAG) and a Class II comparison group (CG) treated using conventional fixed orthodontic appliances. Patients and methods: The preliminary findings of the study were evaluated using 3D virtual models generated from cone-beam computed tomographies (CBCTs) taken at two time points (T0 = baseline and T1 = eight months following treatment) of sixteen HAG and five CG subjects. Voxel-based registration on the anterior cranial fossa was used to assess mandibular displacement/articular fossa remodeling, while regional registration on the mandibular symphysis was performed to evaluate mandibular growth. Results: At the end of Herbst therapy (T1), the condyles of HAG subjects were in similar orientation within the temporomandibular joint (TMJ) region as at T0. Downward displacement of the mandible was observed in both HAG and CG, but forward displacement of the mandible was measured only in the Herbst group. An increase in mandibular length (approximately 2 mm), associated with additional growth of the posterior surface of the condyles and rami, was observed in the HAG patients at T1; however, no change in mandibular length was found in CG. Vertical growth of the mandible was greater slightly in HAG than in CG. No bone remodeling was found in the articular fossae in both groups after eight months of treatment or observation. Conclusions: After Herbst appliance therapy, mandibular forward displacement was achieved due to increased bone deposition and remodeling in the mandibular posterior rami and condylar surfaces of HAG patients. No changes in the articular fossae were found.