Modulation of Osteoclast Differentiation using Statin–Loaded Carbonate Hydroxyapatite Nanoemulsion during Orthodontic Relapse in Rats

Background: Orthodontic relapse remains a persistent biological concern, predominantly attributed to early posttreatment activation of osteoclasts. This study aimed to assess the potential of a simvastatin-loaded carbonate hydroxyapatite (CHA) nanoemulsion in attenuating osteoclastogenesis and improving alveolar bone stability following orthodontic treatment. Materials and Methods: An in vivo randomized controlled experimental design was conducted using 32 male Wistar rats ( Rattus norvegicus , 200–250 g). Orthodontic tooth movement was initiated with a 30 cN nickel–titanium closed-coil spring for 7 days, followed by 7 days of stabilization. After appliance removal, rats were divided into control and experimental groups. The treatment group received local intrasulcular application of statin–CHA nanoemulsion (0.05 mg simvastatin +0.1 mg CHA/15 μL) on days 0, 4, and 7. Alveolar bone specimens were harvested on days 0, 1, 7, and 14 for histological examination (H and E staining). Data were analyzed using two-way analysis of variance followed by Tukey’s post hoc test ( P < 0.05). Results: Osteoclast numbers peaked on day 1 in both groups but were significantly lower in the treatment group (17.25 ± 0.95) than in controls (30.00 ± 1.15; P < 0.001). Suppression of osteoclast activity persisted up to day 14 ( P < 0.05). Conclusion: Simvastatin–loaded CHA nanoemulsion effectively inhibits osteoclast differentiation during orthodontic relapse, representing a biologic strategy for improving postorthodontic stability.