Effect of Hypertonic Saline (3%) as a Final Flush Irrigant on Post-Operative Pain and Substance P Expression Following Single-Visit Root Canal Treatment in Patients With Symptomatic Irreversible Pulpitis Related to Mandibular Premolars: A Randomized Controlled Trial

Post-operative endodontic pain is linked to periapical release of Substance P (SP), a neuropeptide that sustains neurogenic inflammation via NK-1 receptor binding. 3% hypertonic saline has documented osmotic decongestant and NF-κB-mediated anti-inflammatory/cytokine-suppressive effects in non-dental models, providing biological rationale for its use as a final irrigant. This is a two-arm, parallel-group, participant- and assessor-blinded RCT conducted at the outpatient endodontic clinic, Faculty of Dentistry, Cairo University. After standardized access, working length determination, and a baseline periapical fluid sample (S1), canals will be shaped with continuous rotary NiTi instrumentation and irrigated with 2.5% NaOCl. After smear layer removal (2.5% NaOCl then 17% EDTA), participants receive a final flush of either 5 mL 0.9% normal saline (control) or 5 mL 3% hypertonic saline (intervention), delivered via a 30-gauge side-vented needle 2 mm short of working length. A second periapical fluid sample (S2) is then collected. Canals are obturated by lateral compaction in the same visit. Participants record VAS pain scores pre-operatively and at 6, 12, 24, and 48 hours, and log ibuprofen 400 mg tablet consumption at 24 and 48 hours. SP will be quantified from S1/S2 samples by ELISA, blinded to group allocation.