Development of a rat model for prophylactic free gingival graft to mitigate orthodontic-related alveolar bone fenestration/dehiscence.

BACKGROUND: Alveolar bone dehiscence/fenestration is common during orthodontic excessive tooth movement, especially in patients with thin gingiva and alveolar bone, compromising treatment outcomes. Free gingival grafting (FGG) shows preventive potential, but its mechanism remains unclear due to limited animal models. METHODS: Forty 6-week-old male Sprague-Dawley (SD) rats were randomized into 3 groups: FGG + force (FGG + orthodontic force), Sham + force (incision/suture without graft + force) and Blank (no surgical procedure + no force). Right incisors served as internal controls. Orthodontic force (80 ± 1 g) was applied 1 week post-FGG. Rats were euthanized at 4, 8, and 12 weeks post-force application. Micro-CT quantified alveolar bone parameters; histological staining (H&E) and immunohistochemistry (OPN, RUNX2) evaluated bone remodeling. RESULTS: Micro-CT analysis of the overall data (all time points combined) revealed that in the FGG + force group, the left experimental side had significantly greater alveolar bone height, thickness, bone volume, and bone mineral density compared with the contralateral control side (p < 0.05). No significant left-right differences were observed in the Sham + force or Blank groups. Histologically, newly formed epithelial pegs confirmed successful graft integration. Immunohistochemistry showed upregulation of osteogenesis-related proteins RUNX2 and OPN in the FGG + force group, consistent with improved bone morphological parameters. CONCLUSION: In this study, we established an excessive orthodontic tooth movement model of maxillary anterior teeth in Sprague-Dawley rats to simulate the changes of alveolar bone resorption and bone defects that frequently occur during orthodontic treatment in patients with thin gingiva and thin alveolar bone. Using micro-CT and histopathological examination, we found that performing FGG prior to orthodontic intervention alleviated orthodontic force-induced alveolar bone resorption during excessive tooth movement. This study provides a referable rat model for exploring the regulatory effect of keratinized gingival grafting on alveolar bone remodeling, and lays a preliminary experimental foundation for the prophylactic application of FGG in orthodontic patients with a thin gingiva-thin bone phenotype.