The present study was inspired by the concept that upon advanced loss of cortical peri-implant bone, the remaining peri-implant trabecular bone is subjected to masticatory forces and reinforced as a consequence of functional adaptation [15]. This adaptation depends on vital osteocytes [16]. Therefore, the present human case series aimed at investigate the peri-implant bone in advanced peri-implantitis with a focus on the morphology and the vitality of osteocytes. The histomorphometric analysis suggests that bone remaining at advanced peri-implantitis is vital and mainly cortical, presumably originating by reinforcement of the original trabecular bone.

Previous studies also used human biopsy material, but focused on the histopathological features of soft-tissue samples taken at peri-implantitis sites [5, 19, 20]. So far, disease progression and related extension of the bony defects have been assessed histologically in preclinical ligature models resulting in 5 to 7 mm peri-implant defects within 1 year [21,22,23]. None of the aforementioned preclinical studies reported a histomorphometric analysis of the residual bone, and the implants were not subjected to masticatory loading. Thus, we cannot relate our findings to those observed with previous preclinical studies except with respect to the extent of advanced peri-implant defects.

Among the limitations of the present study is the lack of soft tissue in the biopsy due to ethical considerations. Accordingly, the histological outcomes could not be correlated with inflammatory infiltrates residing in the subepithelial connective tissue compartment [6, 7, 20]. It also remains unclear to what extent the progression of bone loss may even support osseointegration of the implants. Previous studies evaluating human biopsy material have reported a wide range of bone-to-implant contacts ranging from 19 to 93% at machined implants [24,25,26]. The high bony coverage of these and our cases can be explained by the functional corticalization of the originally trabecular bone. Strong support for this hypothesis comes from our histological observations where marginal bone showed characteristic signs of heterogeneous bone remodeling with significant areas of lamellar bone in-between and parallel to the surface of older trabeculae, representing signs of compaction of former trabecular bone, an observation also made, e.g., during the growth of the metaphysis [27].