Grade C Periodontitis in Young Adults: A Subcategory or a Distinct Disease Entity?

Objective To assess the correspondence between periodontitis categories defined by 1999 AAP and 2018 AAP/EFP classification systems, and to characterize clinical features within Grade C periodontitis. Methods A cross‐sectional study was conducted on patients with periodontitis. Participants were examined and classified according to both classifications. Comparative analyses between aggressive (AgP) and chronic (CP) periodontitis within Grade C included age, bone loss patterns, clinical attachment loss, furcation involvement, and tooth mobility. The association between classifications was illustrated using alluvial diagrams and analyzed using V Cramer's coefficient. Results Among 427 patients, Grade A and B periodontitis corresponded to CP. Grade C included cases previously classified as AgP as well as severe CP. Correspondence between periodontitis types and grades showed a significant association p < 0.001. The strength of this association was large V = 0.63 95% CI [0.55, 0.76]. Although grouped under the same grade, significant differences were observed between AgP and CP. AgP cases were younger and had more frequent, preferential involvement of incisors and first molars, vertical or combined bone loss, advanced furcation defect, and hypermobility. Conclusion While the 2018 classification has advanced diagnostic criteria for periodontal diseases, future revision of the Grade C category could enhance diagnostic specificity by integrating phenotypic variations.