The purpose of this study is to determine the part played by the quality parameters of root canal filling on the prevalence and distribution of periapical lesions in endodontically treated teeth. The studied group comprised a number of 167 patients, with ages from 20 to 59, having a number of 596 root treated teeth. The quality of root canal filling (length, density) and the diagnosis of various forms of chronic apical periodontites were evaluated by radiography. The data were registered in tables and presented as made under Microsoft Excel. According to the quality standards determined for the length and density parameters, a percent of 38.9% of the studied teeth present correct root filling, 39.5% present root underfilling, 5.3% presents root overfilling, and a percent of 15.9% are teeth with root filling with a correct length and inadequate density. In case of tooth root filling where we diagnosed the presence of periapical lesions, the
distribution of the types of chronic apical periodontitis was as follows: 33.7% fibrous PAC, 41% periapical granuloma, 9% root cyst, 26.3% periapical diffuse osteitis. Adequate root fillings are characterized by the lowest frequency of periapical lesions (17.6%), while underfillings were associated with the highest values(80.9%). The quality parameters of the root fillings influence significantly the success rate of the longterm endodontic treatments.