A critical review of existing peri-implantitis classification systems and a novel three-dimensional framework.

Background: Peri-implantitis remains a clinically relevant complication characterized by soft tissue inflammation and progressive bone loss. Existing classification systems vary in their emphasis on clinical severity or defect morphology and seldom provide operational, treatment-linked guidance-particularly for apical disease. Methods: We conducted a structured critical review of PubMed, Scopus, and Web of Science for studies published in English from January 1990 to December 2023 (last search: December 31, 2023). Full search strategies are reported in Supplementary file 1. Grey literature and conference abstracts were excluded a priori. Two reviewers independently screened records in consensus; a PRISMA-style flow diagram summarizes the selection process. Using a predefined rubric (domains covered, anchors, required inputs, treatment linkage, validation/reliability), we synthesized ten published classification systems (2004-2019) and complemented them with one proposed framework. Results: Across systems, recurrent gaps included limited integration of clinical parameters with radiographic morphology, inconsistent coverage of implant apical lesions (IALs), and sparse, non-graded treatment guidance. We therefore introduce a three-dimensional framework that classifies lesions as crestal, apical (IAL), or lateral, each with severity strata and operational thresholds (radiographic bone loss relative to functional implant length:<25%, 25-50%,>50%). A standardized measurement protocol is specified (paralleling periapical radiographs as default; selective cone beam computed tomography (CBCT) for suspected buccal/facial dehiscence or equivocal lateral defects), with rules for cases lacking baseline radiographs. A one-page decision algorithm links categories to management options whose strength of recommendation follows the EFP 2023 S3 guideline; laser use is presented as an adjunct where evidence is mixed. Three clinical vignettes illustrate how the framework informs treatment planning. Plans for inter-rater reliability testing are outlined. Conclusion: This review consolidates and contrasts existing systems and offers an implementable, consensus-aligned framework that unifies morphology, severity, and apical disease with transparent, evidence-graded treatment pathways. Prospective validation and reliability studies are warranted.