Furthermore, the host‐response and interaction between lymphocyte‐ and monocyte‐macrophage lineage as well as the influence of nano‐ and microparticles on the microbial biofilm and cytokine release in peri‐implant inflammation is not elucidated and future studies could shed more light on the etiological discussion.

Within this study, the first histological comparison of human peri‐implantitis lesions around ceramic and titanium implants was performed. However, we have to acknowledge several limitations. First, this pilot study has only a small number of samples. Due to the limited sample size conclusions have to be drawn carefully but could help optimize the study protocol in future studies with a larger sample size. In the current study Y‐TZP implants of a single manufacturer and type (one‐piece implants) were examined. To validate the present findings, peri‐implantitis around different ceramic implant systems with different surface treatment like sandblasting, etching, and special coatings of the implant as well as different modification of the implant material like ATZ should be considered in future clinical studies. All implant samples for this investigation were obtained from patients with severe peri‐implantitis (late phase of peri‐implantitis) with the indication for removal of the implant. A comparison between clinical conditions at explantation and histological appearance cannot be performed, since the definition of Lang et al. was used as general end point in the present study. In future studies the clinical conditions (e.g., attached gingiva, prosthetic restoration, grafting procedures) and histological appearance could be considered as well as the clinical conditions at implant placement and at the time of implant removal compared. The complete clinical history of implants from placement to removal would be preferential but can only be acquired if the patients have not been referred solely for the surgical removal of the implant.

A conclusion concerning the etiology of peri‐implantitis, conversion of mucositis into peri‐implantitis, early peri‐implantitis, and histological progression pattern of peri‐implantitis cannot be derived from the available samples, mainly due to ethical concerns of sample harvesting.

Within this investigation, it could be demonstrated that the immunohistological cellular composition seems to exhibit interindividual differences and is not only associated with the implant material. Profound research with a higher patient sample size is, therefore, needed for thorough understanding of the pathogenesis of peri‐implantitis in general and of peri‐implantitis around ceramic implants in particular. With such knowledge, the clinicians might find an optimal treatment modality to manage this difficult‐to‐treat disease.