Effects of chronic restraint stress on orthodontic tooth movement and bone remodeling in rats

Adult orthodontic patients are often exposed to various stressors, which can affect orthodontic treatment. Therefore, this study investigated the effects of chronic restraint stress on orthodontic tooth movement and alveolar bone remodeling in vivo.

Ten 8-week-old male Wistar rats were randomly divided into sham-stress orthodontic (CO) and stress orthodontic (SO) groups. Restraint stress was applied for 21 days. The orthodontic intervention involved mesial traction of the maxillary first molar from days 8 to 21. Serum inflammatory cytokine levels were measured, and micro-computed tomography scanning was performed to analyze tooth movement and alveolar bone parameters of the first molar. Osteogenic and osteoclastic activities and macrophage polarization in periodontal tissues were assessed by histological and immunohistochemical staining.

Tooth movement was significantly greater in the SO group than in the CO group, as were the serum interleukin-1β and -10 levels. The SO group had increased trabecular spacing, reduced bone density, and wider periodontal ligament spaces on the force-applied side of the alveolar bone. Enhanced osteogenic and osteoclastic activities were observed in both groups under orthodontic force, but significantly more osteoclasts were observed in the SO group than in the CO group. The inducible nitric oxide synthase to arginase 1 expression ratio was also significantly higher in the SO group than in the CO group.

Restraint stress may exacerbate orthodontic tooth movement and alveolar bone resorption, potentially mediated by systemic inflammatory responses, as well as enhance classically activated macrophage polarization in the alveolar bone.