ABSTRACT
<p><b>OBJECTIVE</b>This study aims to evaluate the time lapse between the endodontic and periodontal treatments of the combined periodontal-endodontic lesion to guide the clinical treatment.</p><p><b>METHODS</b>A systemic literature search was performed in articles published from 1980 to March 2017 using the electronic databases, including PubMed, EMbase, Cochrane, Web of Science, CNKI, CBM, and Wanfang Databases.</p><p><b>RESULTS</b>After screening, two randomized controlled trials, two prospective case series studies, and eight case reports were ultimately included. All clinical studies and case reports were treated with root canal therapy and periodontal nonsurgical or periodontal surgical treatment, with root canal therapy as the initial treatment step. Changes in the periodontal probing depth and attachment loss were reported in all clinical studies and case reports.</p><p><b>CONCLUSIONS</b>An observational period between the endodontic and periodontal nonsurgical treatments may not be required. However, given that the quality of several included studies was limited, and the number of randomized controlled trials was small, a large number of randomized controlled trials are needed to verify this result.</p>