Changes in the Periodontal Gap After Long-Term Tooth Movement into Augmented Critical-Sized Defects in the Jaws of Beagle Dogs

Background/Objectives: Extensive and closely coordinated remodeling processes take place in the periodontal ligament (PDL) and the adjacent bone during orthodontic tooth movement. In complex orthodontic cases, it is necessary to move teeth into an augmented bony defect, for example, in patients with cleft lip, alveolus, and palate. The important role of the PDL during tooth movement is well accepted but not fully understood. Therefore, the present study investigated the PDL after 23 weeks of tooth movement into an augmented critical-sized defect. Methods: The second molars of four beagle dogs were moved into a critical-sized defect, which was filled with bovine xenograft or nanocrystalline hydroxyapatite. Autogenous bone served as control. After 23 weeks, histological samples were microscopically analyzed, and the dimension of the PDL was measured. For statistical calculations, a Wilcoxon–Mann–Whitney test was used. Results: The PDL was significantly wider on the tension side compared with the compression side for all replacement materials analyzed (p ≤ 0.05). These results apply to both the mesial and distal roots. Conclusions: The remodeling processes reached equilibrium within 23 weeks, resulting in a wider gap on the tension side, which contrasts with the situation a few days after the initial force application.