Radiographic Outcome of Endodontic Treatment of Teeth with Primary Apical Periodontitis: Results from a Postgraduate Clinic

<b>Objective:</b> The aim of the study was to analyze factors influencing the radiographic outcome of first-time endodontic treatment of teeth with periapical lesions. <b>Methods:</b> From March 2008 to October 2022, 804 cases of primary apical periodontitis with radiographically detectable lesions were treated conservatively by postgraduate students at the Department of Endodontics. A total of 437 patients had recall 11-48 months after completion. Post-operative and control radiographs of the teeth were scored by the periapical index (PAI) adjusted to define strict and lenient criteria for success. Patients' sex and age, the tooth treated, the number of visits, and several tooth- and treatment-related factors were registered and related to radiographic outcomes in bivariate and regression, with actual <i>p</i> levels recorded. <b>Results:</b> Overall success rate was 68% by strict and 83% by lenient criteria. In binary analyses, a high preoperative PAI score, older age, poorer periodontal status, tooth type (anterior teeth and premolars), and higher number of visits were negatively related to the outcome. Logistic regression analysis of the whole material confirmed an adverse effect on outcome by these factors. In particular, the number of visits (OR = 1.3, <i>p</i> = 0.003) and the initial PAI (OR = 1.9, <i>p</i> < 0.001) were the strongest predictors of reduced success. <b>Conclusions:</b> Outcome of treatment of primary apical periodontitis by postgraduate students was negatively affected by higher preoperative PAI score, higher patients' age, poorer periodontal status, and higher number of visits for completion. <b>Clinical Relevance:</b> This study provides clinically relevant insight into multiple prognostic factors that influence the outcome of primary root canal treatment in teeth with periapical lesions, including patient-related, tooth-related, and procedural variables. The results reflect real-world outcomes in a postgraduate clinical setting and confirm the favorable outcome of single-visit treatments found in randomized studies.