Aim to compare acute pain rate after single-visit ortwo-visits treatment of teeth with necrotic pulp and apical periodontitis .90 teeth with a diagnosis of pulp necrosis and apical radiolucency at the apex.Working length was established with EAL and confirmed radiographically. Flex-R files were used to complete canal preparation. Level ofdiscomfort were recorded and cases with acute postoperative pain.

90 teeth with a diagnosis of pulp necrosis and apical radiolucency at the apex.Working length was established with EAL and confirmed radiographically. M4system with Flex-R files were used to complete canal preparation. Level ofdiscomfort were recorded and cases with severe postoperative pain and/orswelling were classified as acute pain.

Inclusion Criteria: a) Radiographic evidence of apical periodontitis (minimum size ≥2.0mm x 2.0 mm) and a diagnosis of pulpal necrosis confirmed by negativeresponse to hot and cold tests and b) Need for retreatment. Thermal pulptesting was performed by the author, and radiographic interpretation wasverified by one certified oral surgeon

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Exclusion Criteria:

• patients without inclusion requirements or failure to obtain patient ́sauthorization. Patients, were excluded if they were younger than 18 yearsold, pregnant, had a positive history of antibiotic use within the past month,suffered from diabetes, or other systemic diseases. Teeth with periodontalpockets deeper than 4 mm also were excluded of the study

Patients from 18-65 years, both: male , fenale

Each participant will be evaluated a week after the treatment

Acute pain rate

Evaluate the acute pain rate

compare Incidence of acute painafter single-visit ortwo-visits treatment of teeth with necrotic pulp