Impacts of Ultrasonic Activated Sodium Hypochlorite on Delayed Replantation of Avulsed Tooth: Cleaning Efficiency and Healing Effectiveness

AIMS: To evaluate the cleaning efficacy and biological effects of ultrasonic (US)-activated sodium hypochlorite (NaOCl) for root surface decontamination and decellularisation in delayed tooth replantation. METHODOLOGY: Cementum discs prepared from extracted healthy single-rooted teeth were treated with varying NaOCl concentrations (1%-5.25%), with or without US activation. Necrotic periodontal ligament (PDL) tissue clearance, cementum integrity and elemental composition were inspected by scanning electron microscopy and energy dispersive X-ray spectroscopy. Biocompatibility of the treated cementum discs with human periodontal ligament cells (PDLCs) and rat bone marrow mesenchymal stem cells was assessed, alongside osteogenic differentiation, inflammatory cytokine expression, collagen type I (COL-I) and receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) signalling. A Sprague-Dawley rat maxillary incisor delayed replantation model was established to assess in vivo healing outcomes of US-activated NaOCl, evaluated by micro-computed tomography, haematoxylin and eosin staining and Masson's trichrome staining and tartrate-resistant acid phosphatase (TRAP) histochemistry. RESULTS: Increasing NaOCl concentration accelerated removal of necrotic PDL. US activation significantly shortened NaOCl treatment time (p < 0.05) and allowed effective necrotic PDL removal at 1% NaOCl without damaging cementum. Treated cementum surfaces showed higher calcium/phosphorus and lower carbon/nitrogen contents (p < 0.01). US-assisted 1% NaOCl enhanced cell adhesion, osteogenic differentiation and COL-I expression while reducing interleukin-6, tumour necrosis factor-α and the RANKL/OPG ratio. In vivo, NaOCl combined with US activation significantly reduced root resorption volume (p < 0.05), preserved periodontal architecture, and decreased TRAP-positive osteoclast counts compared with saline or untreated controls. CONCLUSIONS: US-activated 1% NaOCl achieves rapid, selective removal of necrotic periodontal tissue while preserving cementum and producing a decellularised surface. This strategy attenuates inflammatory responses, suppresses osteoclastogenesis, mitigates inflammatory root resorption and may extend the therapeutic window for delayed tooth replantation.