The present study aimed to histologically and immunohistochemically evaluate radiotherapy-induced changes in periodontal tissues in a rat model of experimental periodontitis, with particular focus on periodontal ligament width (PerioW) and the RANK/RANKL/OPG axis at different healing stages.<h4>Methods</h4>Seventy-two male Sprague-Dawley rats were allocated to three groups: irradiation only (Rt), ligature-induced periodontitis only (Pt), and ligature-induced periodontitis followed by irradiation (PtRt). This evidence concerns the gene TNFSF11 and periodontitis.