Aim to compare Incidence of flare-ups and apical healing after single-visit or two-visits treatment of teeth with necrotic pulp and apical periodontitis after a two-year control period.

110 teeth with a diagnosis of pulp necrosis and apical radiolucency at the apex. Working length was established with EAL and confirmed radiographically. M4 system with Flex-R files were used to complete canal preparation. Level of discomfort were recorded and cases with severe postoperative pain and/or swelling were classified as flare-ups.

110 teeth with a diagnosis of pulp necrosis and apical radiolucency at the apex. Working length was established with EAL and confirmed radiographically. M4 system with Flex-R files were used to complete canal preparation. Level of discomfort were recorded and cases with severe postoperative pain and/or swelling were classified as flare-ups.

Inclusion Criteria:

• a) Radiographic evidence of apical periodontitis (minimum size ≥2.0 mm x 2.0 mm) and a diagnosis of pulpal necrosis confirmed by negative response to hot and cold tests and b) Need for retreatment. Thermal pulp testing was performed by the author, and radiographic interpretation was verified by one certified oral surgeon.

Exclusion Criteria:

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

Each participant will be evaluated a week after the treatment.