Staging and Grading Advanced Periodontitis with Large Language Models from Standardized Case Summaries: A Multicenter...

Background/Objectives: To evaluate the concordance of three general-purpose large language models (LLMs), ChatGPT, Claude, and Gemini, with an adjudicated expert consensus classification of Stage, Grade, and Extent in Stage III-IV periodontitis when applying the 2018 American Academy of Periodontology/European Federation of Periodontology (AAP/EFP) rules to clinician-prepared, standardized case summaries. Methods: In this multicenter retrospective concordance study (two centers, 105 patients), two periodontologists independently classified each case from complete charts and radiographs; discordant cases were adjudicated. De-identified summaries containing pre-extracted clinical, radiographic, and modifier variables were presented to each LLM in three independent sessions per case; the modal decision was the primary index result, and single-session performance was also reported. Stage and Grade concordance (Cohen's/weighted kappa) were co-primary endpoints; Extent and full concordance were secondary. Results: Modal Stage concordance was almost perfect for ChatGPT (κ = 0.98) and Gemini (κ = 0.92) and substantial for Claude (κ = 0.73); single-session Stage κ ranged from 0.73 to 0.98. Grade (weighted κ = 0.97-1.00) and Extent (κ = 0.93-1.00) concordance were almost perfect. Full concordance ranged from 85.7% (Claude) to 99.0% (ChatGPT). Every classifiable modal Stage discordance understated severity: Claude and Gemini assigned Stage II or I to 14 Stage III cases in which attachment loss met the Stage III threshold but radiographic bone loss was below 33%. Conclusions: Given pre-extracted variables and explicit instructions, the LLMs applied the classification rules with substantial to almost perfect concordance; this reflects rule application, not independent diagnosis. Performance was model-specific, Gemini showed greater session-to-session variability, and two models systematically understaged borderline Stage III cases. The findings support only clinician-supervised, educational use with local validation.