Subgingival microbiome in patients with healthy and ailing dental implants.

Implants have revolutionized dental rehabilitation, prosthetic dentistry, and maxillary reconstruction1,2. Marketing estimates show that over 2 million dental implants were inserted annually in the United States at the turn of the millennium3. Although dental implants survive well, infections at peri-implant sites have been widely reported4,5,6. Peri-implant diseases present in two forms: peri-implant mucositis (PM) and peri-implantitis (PI). In PM, inflammation is confined to the soft tissues surrounding a dental implant, with no sign of any loss of supporting bone after the initial bone remodeling that takes place during healing5. PI is characterized by inflammation around the implant, involving both soft tissues and a progressive loss of supporting bone to an extent greater than occurs upon biological remodeling, and may eventually lead to loss of the implant (implant failure)7. Peri-implant diseases have become emerging problems as the number of implants placed increases. The prevalence of mucositis is ~80% in implant patients and ~50% in the implants per se, whereas peri-implantitis has been diagnosed in 28–56% of implant patients and 12–43% of implants8,9. Bacteria colonize the peri-implant crevice soon after implant placement to establish polymicrobial communities9,10, and the failure of dental implants is commonly ascribed to inflammation of the supporting bone and related soft tissues caused by microbiota in peri-implant biofilms11,12. PM and PI correspond in basic terms to gingivitis and periodontitis. Persistent gingivitis may lead to chronic periodontitis in susceptible individuals13. From the viewpoint of microbial ecology, red and orange complexes are more prevalent and more numerous in the lesions of established gingivitis, and this is even more apparent in periodontitis14. The microbial compositions of gingivitis have been compared with those of PM15, and those of periodontitis with PI16,17,18. However, PM, regarded as the precursor of PI, has seldom been investigated separately, and the relationships between the microbial communities of PM and PI remain unclear. Traditionally, studies on the pathogenesis of peri-implant microbiota have analyzed individual bacterial species in complex microbial communities. More recent work has shown that peri-implant diseases may be polymicrobial in etiology, caused by a shift in the microbial community, rather than a single pathogen16. Previous studies, using culture-based methods, 16S rRNA gene PCR, or DNA-DNA hybridization techniques, commonly addressed roles played by individual bacterial species and afforded limited information on the overall diversity of the peri-implant environment. Sequencing of 16S ribosomal genes has yielded deeper insights into the composition of the oral microbiome in health and disease, creating a paradigm shift in our understanding of such microbial communities19. Pyrosequencing of PCR-amplified 16S rRNA is a next-generation sequencing method that simultaneously generates thousands of sequences from individual samples. Such an unprecedented amount of information allows comprehensive examination of a taxonomically heterogeneous community and has revealed ever-greater levels of microbial diversity20,21. A recent study on peri-implant bacterial communities using 16S pyrosequencing revealed that the microbial profile of healthy implants was significantly more diverse than that of PI sites16. However, when the prevalence of individual species was evaluated using DNA-DNA hybridization methods, Renvert S. et al.6 found no difference in microbial diversity between PI and healthy sites, whereas others detected fewer species in healthy sites compared to PI sites22,23. In the present study, we analyzed subgingival plaque samples from healthy implants, PM and PI, using the 16S rRNA pyrosequencing method. This study was performed to compare the differences of the microbial communities of healthy implants, PM and PI, aiming to reveal the potential pathogens associated with peri-implant diseases.