Inclusion Criteria:  root canal-treated teeth exhibiting clinical and radiographic evidence of chronic apical periodontitis lesions Teeth with post-treatment apical periodontitis had endodontic therapy completed more than 2 years earlier and required retreatment. Radiographically, the diameter of the periapical radiolucency ranged from 2 to 7 mm. Termini of the root canal fillings ranged from 0-4 mm short of the radiographic apex, with no overfilling. The teeth had intact coronal restorations, with no obvious exposure of the root-filling material to the oral cavity. Selected teeth had enough crown structure for adequate isolation with a rubber dam and showed an absence of periodontal pockets or attachment level deeper than 4 mm.  Exclusion Criteria:  teeth from patients who had received antibiotics within the previous 3 months or who had any general disease, teeth that could not be properly isolated with rubber dam, teeth with absence of coronary sealing, teeth with periodontal pocket depth >4 mm; and teeth with crown/root fracture. Only one tooth was included from each patient.