Single And Multiple-visit Endodontic Retreatment Outcome.

Inclusion Criteria: * Patient willingness to participate in the study. * Previously root filled Permanent teeth with post-treatment apical periodontitis requiring nonsurgical root canal retreatment. * Failure of previous root canal treatment will be determined based on clinical and radiographic findings. Clinical indicators of failure will include pain, tenderness to palpation/percussion, swelling, sinus tract.Radiographic criteria will include persistent periapical radiolucent lesions in teeth in which initial treatments were performed at least 4 years previously. * Root canal fillings no more than 4mm short of the apex. * Patients showing no significant systemic disease Exclusion Criteria: * Patients who are pregnant, diabetic, immunocompromised, serious medical illness or requiring antibiotic premedication. * Patient under 18 years of age. * Patient under corticosteroid use. * Patients with history of antibiotic use in last 3 months or analgesic use in last one week will also be excluded. * Multiple teeth that require treatment to eliminate the possibility of pain referral.Patients with unrestorable carious lesions, fractures involving the periodontium, and/or periodontal pockets ≥ 4mm deep or having marginal or furcal bone loss due to periodontitis . * Teeth with the procedural errors preventing access to apical third and missed canals will be excluded. * Teeth that are not suitable for rubber dam isolation. * Teeth with intraradicular post.