Alveolar bone remodeling following orthodontic closure of missing mandibular first molar spaces: a CBCT-based...

Loss of the mandibular first molar is a common and detrimental clinical issue that often leads to alveolar bone resorption in the edentulous area, complicating future prosthetic or orthodontic interventions. This study aimed to evaluate the efficacy of orthodontic closure of missing mandibular first molar spaces and its impact on alveolar bone remodeling.

Fifteen patients (17 sites) who underwent orthodontic closure of mandibular first molar spaces were retrospectively analyzed using cone-beam computed tomography (CBCT). The mesiodistal and buccolingual angulations of the mandibular second molars were measured in sagittal and coronal planes, respectively. The alveolar bone height was reflected by the distance from the cemento-enamel junction to the alveolar bone margin (CEJ-BM) at six sites on both the second premolars and second molars. Moreover, CBCT before and after orthodontic treatment were superimposed, and changes of alveolar bone width were obtained at three levels (3 mm, 6 mm and 9 mm below the cemento-enamel junction plane) and at three sections (mesial, middle and distal) within the edentulous region. Changes in alveolar bone volume within the extraction site were also calculated. Statistical analysis was performed by paired t-test.

Orthodontic space closure significantly improved second molar angulations in both the mesiodistal (p < 0.001) and buccolingual (p < 0.01) angulations. In 57.35% of measured sites, alveolar bone height increased, with significant elevations at the distobuccal, distolingual, and mesiobuccal sites of the second molar (p < 0.05). Alveolar bone width significantly increased at 3 mm and 6 mm below the CEJ plane after orthodontic closure (p < 0.05), accompanied by a notable increase in bone volume (before treatment: 2922.0 ± 479.0 mm³, after treatment: 3003.8 ± 489.6 mm³, p < 0.05).

Orthodontic closure of mandibular first molar spaces promotes alveolar bone remodeling, including improvements in angulation, bone height, width, and volume. This approach offers a biologically advantageous alternative for managing molar loss, enhancing both function and long-term periodontal support.