Clinical Outcomes of Plasma-Assisted Saline Irrigation in Nonsurgical Root Canal Treatment: A Preliminary Retrospective Cohort Study

Background: Effective root canal disinfection is essential for successful nonsurgical root canal treatment (RCT). Although sodium hypochlorite (NaOCl) remains the standard irrigant, it carries a risk of chemical tissue injury if extruded beyond the root canal system and may have limited penetration into anatomically complex regions. Underwater discharge plasma (UDP) generates reactive oxygen and nitrogen species (RONS) through high-frequency, high-voltage electrical discharge in aqueous media, and preclinical and in vitro studies have reported broad-spectrum antimicrobial activity. This study evaluated the clinical and radiographic outcomes of nonsurgical RCT performed using physiological saline-based UDP irrigation without NaOCl in a heterogeneous real-world clinical cohort. Methods: This single-center retrospective cohort study included 186 teeth from 134 patients treated with the PLAZEN RCT® UDP device and physiological saline irrigation, without NaOCl. The median follow-up period was 16 months. Radiographic outcomes were assessed using the Periapical Index (PAI) system, and treatment success was evaluated according to prespecified Strict and Loose criteria incorporating both radiographic and clinical findings. Stratified analysis was performed according to preoperative PAI score: Group A (PAI 1–2) and Group B (PAI 3–5). UDP-related adverse events, defined as thermal tissue injury caused by discharge heat, were ascertained through retrospective review of clinical records, operative notes, and serial periapical radiographs. Results: Among the 186 treated teeth, radiographic outcomes were classified as Healed (85.5%), Healing (3.8%), and Unhealed (10.8%). Overall Strict and Loose success rates were 79.6% and 82.3%, respectively. Initial treatment showed numerically higher success rates than retreatment. In the stratified analysis, Group A showed an 84.1% success rate with 100% tooth survival, whereas Group B demonstrated Strict and Loose success rates of 68.5% and 83.3%, respectively. Exploratory multivariable analysis showed that periodontal pocket depth > 3 mm was the most consistent factor associated with lower odds of treatment success, whereas associations involving canal obliteration and higher preoperative PAI score were less stable across sensitivity analyses and should be interpreted with caution. No UDP-related adverse events were recorded during follow-up. Attrition sensitivity analyses were performed, and the outcome estimates should be interpreted with caution, given the retrospective design and substantial loss to follow-up. Conclusions: In this preliminary observational cohort, physiological saline-based UDP irrigation without NaOCl was associated with favorable observed periapical healing outcomes and no recorded UDP-related adverse events over a median follow-up of 16 months. However, loss to follow-up was substantial; when all 116 teeth lost to follow-up were classified as treatment failures, the worst-case Strict success rate decreased to 49.0%. Therefore, these findings should be interpreted as preliminary descriptive evidence of clinical feasibility rather than as evidence of comparative efficacy or definitive clinical safety. Adequately powered randomized controlled trials with concurrent NaOCl control arms and long-term follow-up are warranted to evaluate the comparative effectiveness, safety, and reproducibility of physiological saline-based UDP irrigation protocols.