A Radiographic Classification for Retrograde Peri-implantitis

Retrograde peri-implantitis (RPI) is an inflammatory disease that affects the apical part of an osseointegrated implant, while the coronal portion of the implant sustains a normal bone-to-implant interface. It is a diagnostic and therapeutic dilemma for implantologists. There is lack of a standard classification system and a definite treatment algorithm for the same. This article aims to introduce a classification system for RPI based on the radiographic amount of bone loss around an implant apex. A search of PubMed database was conducted with the keywords "retrograde peri-implantitis" and "implant periapical lesion." Preoperative intraoral periapical (IOPA) radiographs of implants with RPI in case reports/case series were compiled. A total of 54 lOPAs from 36 articles were compiled and were assessed. Three different classes were proposed. The amount of bone loss from the apex of the implant to the most coronal part of radiolucency was calculated as a percentage of the total implant length and classified into one of the three classes: Mild, moderate, and advanced. Treatment options and prognosis have been suggested for each class. The proposed classification may allow for an easy and reproducible radiographic assessment of the RPI lesion and may serve as a guideline to prognosis and treatment planning.