Prognostic performance of the 2017 World Workshop classification on staging and grading of periodontitis compared with the British Society of Periodontology's implementation

Background: The British Society of Periodontology (BSP) implemented a simplified version of the 2017 World Workshop Classification (WWC) on staging and grading of periodontitis, for use in UK clinical practice. The aim of this study was to assess the long-term (>10 years) prognostic capability of BSP's implementation (BSP-i) compared with the 2017 WWC, using periodontal-related tooth loss (TLP) as a disease outcome.

Methods: Data on medical history, smoking status, and clinical periodontal parameters were retrieved from 270 patients who received non-surgical and surgical periodontal therapy from 1966 to 2007. Each patient received a baseline diagnosis according to the 2017 WWC and the BSP-i guidelines for implementation. Univariate multilevel Cox regression frailty models were performed to analyze the association between variables with TLP. A post-hoc comparison with Bonferroni correction was performed to analyze interclass comparisons. The prognostic performance of both systems was analyzed using Harrell C index.

Results: The prognostic performance of both systems was very similar (0.922 for the 2017 WWC and 0.925 for the BSP-i). The singular prognostic performance of BSP stage was slightly higher than that of 2017 WWC stage (0.9212 versus 0.9188), while the 2017 WWC grade showed a slightly better performance than BSP grade (0.9175 versus 0.9155). BSP-i's extent performed better than the 2017 WWC extent (0.9203 versus 0.9098); however, in the 2017 WWC extent, the class "localized" was associated with a better prognosis than "generalized."

Conclusion: The overall prognostic performance of the two systems was excellent, with both systems having a Harrell C index score of >0.92.