Levels of evidence for the outcome of endodontic retreatment.

The purpose of this investigation was 2-fold: (a) to complete a thorough search of published literature related to clinical studies on the success and failure of nonsurgical retreatment, and (b) to assign levels of evidence to these publications. Clinical studies related to success and failure of retreatment since 1970 were identified using both electronic and manual literature searches. After identification of pertinent literature, each article received a level of evidence (LOE) from one (high) to five (low). Thirty-one clinical studies and six review articles related to this subject were identified. There was no LOE 1 Randomized Control Trials (RCT). There were three LOE 2 RCTs, one LOE 2 Cohort, and two LOE 3 Case Control Studies. Thirteen Case Series (LOE 4), which comprise the most highly quoted success and failure data, were found. Twelve Case Reports (LOE 5) and six review articles (LOE 5) were found. Based on these findings, it appears that few high level studies have been published in the past 34 yr related to the success and failure of endodontic retreatment.