Biological and microbiological properties of dental implants and their relation to peri-implant diseases

With the increasing use of dental implants in the population, the past three decades have seen a dramatic growth in the prevalence of two new oral diseases: peri-implantitis which affects both soft and hard tissues surrounding the implant, and mucositis which precedes peri-implantitis and involves instead only soft tissues. Mucositis affects 50% to 90% of implants, while almost 20% of implants develop peri-implantitis that can lead over time to implant loss. The underlying hypothesis of this research project is that dental implant properties and their interaction with surrounding soft and hard tissues and oral microbiome play an important role in the maintenance of peri-implant health. Regarding specific characteristics of dental implants, experimental data are in part still lacking on biochemical behavior of implant surfaces and of possible new coatings able to reduce bacterial colonization. From the microbiological viewpoint, based on the lessons learned from the study of periodontal diseases, there are reasons to believe that specific members of the oral microbial communities represent a prerequisite for the development of peri-implant diseases. A thorough profiling of the microbial organisms associated with disease is thus the first step to undertake in order to develop novel prevention and therapeutic strategies. Currently available studies, however, adopted a study design which is not accounting for inter-subject variability, focused on few cultivable microbes only, or used low-resolution microbial profiling. Overall, there are thus several open questions on implant characteristics and microbiologic aspects that need to be addressed for the next generation of implant care. Because these aspects are tightly interconnected, in this thesis I employed an integrated approach to study multiple aspects of biological and microbiological properties of dental implants and their relation to peri-implant diseases. Starting from implant surfaces, we evaluated the biochemical behavior of a specific type of moderately rough surface. We found that, in-vitro, this surface called OGI (Osteo Growth Induction) positively acts on osteogenic and angiogenic commitment of mesenchymal stem cells (MSC). Still in the field of implant surfaces, we developed and tested in-vitro a potential anti-biofilm sericin-based coating obtaining very promising bacterial inhibition values. Finally, we investigated in-vivo through shotgun metagenomics the plaque microbiome associated with peri-implant health and disease unraveling specific microbial and functional signatures associated with these conditions and identifying specific disease-associated microbiome features. In this work we showed that peri-implant diseases are connected with the specific composition of the plaque microbiome and that implant surfaces, in addition to a potential strong bioactive role, if properly treated can significantly reduce microbial adhesion on them. Stressing that maintenance therapy always remains something essential, new scenarios for the future are possible. Besides the need of employing implants with adequate micro- and macro-characteristics, the ever more in-depth knowledge of the peri-implant microbiome will allow to implement increasingly effective anti-biofilm implant surfaces and to introduce microbiome-based protocols of diagnosis, prevention and personalized therapy.