Timing of force application affects the rate of tooth movement into surgical alveolar defects with grafts in beagles

Introduction: The purpose of this study was to investigate the influence of the timing of orthodontic force application on the rates of orthodontic tooth movement into surgical alveolar defects with bone grafts in beagle dogs. Methods: Twelve beagles were randomly divided into 2 groups according to the surgical procedure: alveolar osteotomy alone (control) or osteotomy with bone graft (experimental group). The maxillary second premolars were protracted for 6 weeks into the surgical sites: immediately, at 2 weeks, and at 12 weeks after surgery. The orthodontic tooth movement rates and alveolar remodeling concomitant with surgical defect healing were evaluated by model measurements and histomorphometry as well as microcomputed tomography and histology. One-way analysis of variance and the Scheffe post hoc comparison were performed for investigating the rates of orthodontic tooth movement and mineralized bone formation. Results: Both the orthodontic tooth movement rate and the mean appositional length of mineralized bone in the tension side of teeth were significantly accelerated when force was applied at 2 weeks in the control group and immediately in the experimental group (P < 0.001). The 2-week control group showed a dramatic increase in apposition rate during 4 to 6 weeks after force application, whereas the immediate protraction experimental group did within the first 3 weeks (P < 0.001). Decreased orthodontic tooth movement rates and reduced bone remodeling activities were apparent in the 12-weeks groups, especially in nongrafted defects. Conclusions: A bone graft into the surgical defect can not only allow immediate force application for accelerating orthodontic tooth movement with favorable periodontal regeneration, but also decrease the risk of inhibited orthodontic tooth movement in case of delayed force application after surgery.