Abstract: Objective: To evaluate the effects of different root canal irrigants and obturation sealers on the fracture resistance of tooth roots. Methods: A total of 170 mandibular single-rooted premolars meeting the criteria were selected and randomly divided into five experimental groups (Groups A-E, irrigated with normal saline, 1% NaClO, 3%NaClO, 5.25%NaClO, and Ultra Clean) and two control groups (Group F: no instrumentation or obturation; Group G: instrumentation only). All experimental groups were instrumented using the M3 Pro 2016 rotary nickel-titanium file system and further subdivided into three subgroups based on the obturation sealer used: AH-Plus, C-root SP, and Vitapex. After standardized irrigation and single-cone obturation, the samples were screened via X-ray, embedded to simulate the periodontal ligament, and subjected to fracture resistance testing using a universal testing machine. Results: Root canal instrumentation significantly reduced fracture resistance [Group G: (254.30±26.74) N vs. Group F: (673.16±29.06) N, P<0.05]. Sodium hypochlorite irrigants significantly weakened root fracture resistance in a concentration-dependent manner, with the 5.25% NaClO group showing the most pronounced effect. Among the obturation materials, the bioceramic sealer (C-root SP) resulted in higher fracture resistance compared to resin-based (AH-Plus) and calcium hydroxide-based (Vitapex) sealers. Conclusion: Both mechanical instrumentation and chemical irrigation reduce root fracture resistance, while the use of bioceramic sealers can enhance the structural integrity of teeth after root canal treatment. Clinical material selection should comprehensively consider material properties to optimize treatment outcomes.

Key words: C-root SP, Ultre Clean, fracture resistance