Degenerative and regenerative morphological aspects in peri-implantitis.

The purpose of this study was to describe the tissues surrounding two early failed dental implants morphologically and ultrastructurally. In the first case, the implant's surface was analyzed by scanning electron microscopy (SEM) using an environmental scanning electron microscope and the surrounding tissues were analyzed by light microscopy (LM) and transmission electron microscopy. In the second case we used only LM. By SEM analysis, very thin connective tissue was seen at the implant's apex; in the middle part, highly vascularized connective tissue and poorly mineralized areas were found, and there were fewer mineralized areas at the implant's base. Histologically and ultrastructurally, we identified a heterogeneous cellular population including fibroblast-like cells and osteoblasts with abundant amorphous extracellular matrix, as well as a number of inflammatory cells, predominantly neutrophils. In a small area around the implant, microorganisms classified as Actinomyces were identified. In this case, degenerative aspects were predominantly caused by infection. In the second case, our observations focused on recruitment of mesenchymal stem cells, their proliferation and differentiation into epithelial cells with keratinocyte phenotype, and formation of de novo capillaries from mesenchymal progenitors of endothelial cells. These regenerative events were accompanied by multiple areas of mineralization, culminating in bone formation around the implant. Correlative microscopic observations are necessary to conduct in future studies, in various clinical conditions and post-operative stages, to better define the cellular events involved in healing and osseointegration; our observations clearly depict significant regenerative aspects despite the degenerative ones.