Retrograde peri-implantitis: diagnostic, clinical and histopathological features

Dental implants are a predictable and successful option to replace missing teeth, however they are not free from biological complications. Peri-implantitis prevalence is consistently rising and is currently one of the most investigated conditions in dentistry. However, another pathological condition called retrograde/periapical peri-implantitis (RPI) might affect dental implants. The RPI involves only the peri-apical portion of the implant and is detected radiographically as a radiolucent area, without pathological probing and signs of marginal bone loss. A very low prevalence (0.26-1.86%) has been reported for RPI, therefore, also considering the few articles available in scientific literature on the topic, the pathology is still relatively unknown among clinicians. There is no consensus about RPI aetiology: the main possible causes hypothesized are implant insertion in a site with a pre-existing unhealed infection or inflammation, implant placement in a site that previously housed an endodontic treated tooth with further bacteria reactivation, pulpal/periapical endodontic lesions at adjacent teeth or bone overheating during implant drilling. Several treatment strategies have been reported: antibiotic therapy with/without endodontic treatment of the adjacent tooth or surgical/chemical debridement of the apical implant site with/without guided bone regeneration (GBR) procedures and with/without the resection of the implant apex. In a systematic review, our study group highlighted how surgical and mechanical debridement of the apical part of the implant associated with GBR was the most used surgical treatment option. After the publication of one crosssectional and one retrospective study with the maximum follow-up available in literature, on the topic, our department was considered as a referral center for diagnosis and treatment of RPI by private practitioners based in Rome. The aims of this case series are to report prospective data and histopathological findings of RPI in a single center and to evaluate implant survival after a standardized surgical approach. During the observational period, a total of 4 patients were referred to our department for retrograde peri-implantitis treatment. Three male patients and one female, with a 4 mean age of 61.75±13.81 years, in all cases, prior to implant placement, teeth extracted had previous endodontic treatment. Patients reported symptoms of RPI after a mean period of 134.5±69.69 days (range: 34-192 days). All patients were treated with the same surgical approach: antibiotic therapy, mechanical curettage, chemical decontamination and guided bone regeneration. Furthermore, the periapical lesion was carefully enucleated and collected for histopathological examination. No implant was lost after treatment: a 100% survival rate was detected after a mean follow-up of 1.5±0.57 years (range: 1-2 years). The histopathological examination revealed, in all cases, the presence of a chronic inflammatory infiltrate with occasional multinucleated giant cells inglobating unidentified foreign particles and signs of bone remodeling. Based on the analysis of patients’ characteristics and histopathological samples, it can be speculated that bacteria from teeth with failed endodontic treatment or residual lesions were reactivated by drilling for implant osteotomy, with subsequent colonization of the implant apex. Since in all cases previous teeth in implant sites were endodontically treated, foreign body particles incorporated in the inflammatory tissues might be derived from remains of previous root canal therapy. Therefore, within the limitations of the study, it could be cautiously concluded that RPI can be predictably and successfully treated with surgical curettage and GBR. Further studies, with larger sample, are needed to confirm these clinical findings.