Levels of evidence for the outcome of endodontic surgery

The purpose of this investigation was twofold: (1) to search for clinical articles pertaining to success and failure of periapical surgery and (2) to assign levels of evidence to these studies except case reports. Electronic and manual searches were conducted to identify all the literature regarding success and failure of periapical surgery since 1970. Articles were reviewed, and each article was assigned to a level of evidence from I (highest level) to 5 (lowest level). This search located 79 clinical studies. Among these studies, there were no level of evidence-1 randomized clinical trial studies. Five of the seven level of evidence-2 randomized clinical trials compared postoperative pain between surgical and nonsurgical retreatment. Only two level of evidence-2 randomized clinical trials compared the outcomes of surgical treatment with that of nonsurgical treatment. The majority of frequently quoted "success and failure" studies were case series (level of evidence 4).