This study will evaluate the synergistic effect of CHX + H2O2 when used as an irrigant during biomechanical preparation.in root canal treatment on periapical healing and compared with Chlorhexidine( CHX) and Sodium Hypochlorite (NaOCl).

After a thorough history, clinical and radiographic examination with all eligibility confirmation, written informed consent will be taken from the patient after explaining the procedure and its associated risks and benefits. Patients randomly allocated to one of the three study groups Sodium hypochlorite (NaOCl), Chlorhexidine (CHX) and combination of (CHX+H2O2). All three irrigants will be used according to standard protocol during biomechanical preparation. Pain analysis will be carried out preoperatively and postoperatively at every 6 hours for 1 day and then every 24 hours till 7 days after the intervention. All the subjects will be followed up for evaluation of clinical and radiographic success at 3, 6 months and 1year.

Inclusion Criteria:

• All patients over 18 years of age.
• Mature permanent mandibular molars.
• A radiographic evidence of periapical radiolucency (minimum size > 2mm×2mm) and a diagnosis of pulpal necrosis, as confirmed by the negative response to cold and electrical tests; and absence of bleeding on entering the pulp chamber.

Exclusion Criteria

• Diabetics, immunocompromised patients, pregnant females, any systemic disease.
• Patients with a history of analgesic intake within the past 3 days and antibiotics in the last month.
• Patients with pockets ≥ 4mm or having marginal or furcal bone loss due to periodontitis.
• Non-restorable tooth, fractured, perforated roots and inflammatory root resorption.
• Teeth those are not suitable for rubber dam isolation.
• Primary teeth.