Agreement among international periodontal experts using the 2017 World Workshop classification of periodontitis

Background: A new periodontitis classification was recently introduced involving multidimensional staging and grading. The aim of the study was to assess if individuals well-trained in periodontics consistently used the new classification for patients with severe periodontitis. The secondary goal was to identify “gray zones” related to classifications. Methods: Participants (raters) individually classified 10 pre-selected severe periodontitis cases using the 2017 World Workshop classification. An internet case-based study was conducted after inviting members from American Academy of Periodontology and European Federation of Periodontology. Gold-standard diagnoses were determined by five experts who developed the new periodontitis classification. Inter-reliability agreement among raters was assessed using Fleiss Kappa index with the jackknife method for linearly weighted kappa calculations. McNemar test was used to determine symmetry between raters and gold-standard panel. Results: A total of 103 raters participated and classified nine clinical cases. Fleiss Kappa values showed moderate inter-examiner consistency among raters for stage (K value: 0.49; 95% CI, 0.19 to 0.79), grade (K value: 0.50; 95% CI, 0.30 to 0.70) and extent (K value: 0.51; 95% CI, 0.23 to 0.77). When analyzed as composite (stage, grade, extent) a moderate inter-reliability was present among raters, k = 0.479 (K value: 0.47; 95% CI, 0.442 to 0.515). Agreement between raters and gold-standard panel was staging 76.6%; grading 82%; and extent 84.8%. In six of nine cases 77% to 99% of raters consistently agreed with gold-standard panel, and the other three cases had gray zone factors that reduced rater consistency. Conclusions: Clinicians trained in the 2017 World Workshop periodontitis classification demonstrated moderate concordance in classifying nine severe periodontitis cases, and in six of nine cases raters consistently agreed with the gold-standard panel.