A Comparative Evaluation of the Degree of Pain and MMP-9 Expression Following Instrumentation of Necrotic Pulps With Apical Periodontitis in One or Two Visits

Inclusion Criteria: * Age between 18-40 years. * Males/Females. * Straight single canaled permanent teeth: * Non-Vital pulps. * Negative response to cold pulp tester (ethyl chloride spray\*). * Absence of spontaneous pain. * Chronic apical periodontitis with negative response to percussion * Slight widening in the periodontal membrane space or with periapical radiolucency not exceeding 2\*2 mm radiographically. The Periapical Index (PAI) score by Ørstavik is 2 or 3 (Ørstavik et al., 1986 43) * Systemically healthy patients (ASA I or II) * No anti-inflammatory or antibiotic medications taken in the past month * Patients' acceptance to participate in the trial. * Patients who can understand pain scale and can sign the informed consent (Appendix I). * Patients' acceptance to participate in the trial. Exclusion Criteria: * Medically compromised patients having significant systemic disorders. (ASA III or IV). * Teeth with swelling or fistulous tract. * Teeth with acute or chronic periapical abscess. * Mobility Grade II or III. * Previous root canal therapy. * Non-restorable teeth. * Immature teeth. * Pregnant females.