Journal of Periodontology; Copyright 2016 DOI: 10.1902/jop.2016.160017 1 Microbial Colonization of the Peri-implant Sulcus and Implant Connection of Implants Restored With Cemented Versus Screw-Retained Suprastructures: A Cross-sectional Study David Penarrocha-Oltra*, Alba Monreal-Bello*, Maria Penarrocha-Diago*, Jorge Alonso † , Daniele Botticelli ‡ , Luigi Canullo § *Section of Oral Surgery, Stomatology Department, Faculty of Medicine and Dentistry, University of Valencia, Spain. † Section of Prosthodontics and Occlusion, Stomatology Department, Faculty of Medicine and Dentistry, University of Valencia, Spain. ‡ ARDEC Ariminum Odontologica Rimini, Italy. Programa Odontológico Internacional Cartagena de Indias, Colombia. § Private Practice in Rome, Italy. Background: To study peri-implant and intra-connection microflora of healthy implants restored with cemented and screwed suprastructures. Materials and Methods: Patients with 2-3 implants restored with cemented or screwed restorations and 5 years of follow-up were recruited. Samples were taken from peri-implant sulci, adjacent teeth and connections inner portion. Prevalence of positive sites and bacterial loads for 10 microorganisms were obtained with quantitative real-time PCR. Implant connection permeability to the studied microorganisms was estimated using a standardized bacterial contamination index. Statistical analysis was performed using a generalized estimating equations model, Wald’s Chi 2 and the Least Significant Difference test. Results: The final sample consisted of 18 patients (55 implants) in the cemented group and 22 patients (46 implants) in the screwed group. Regarding prevalence of positive sites significant differences between groups were only found for Tannerella forsythia, which was 8.7 times more frequent at peri- implant sulci of cemented than of screw-retained prostheses. Bacterial loads of Porphyromonas gingivalis, Tannerella forsythia, Parvimonas micra and Total Bacterial Count were significantly higher at peri-implant sulci for the cemented group; at connections inner portion, values were significantly higher for Parvimonas micra and Fusobacterium nucleatum for the screwed group. Contamination index values demonstrated higher permeability to most microbes in the cemented group. Conclusions: Internal implant surfaces resulted microbiologically contaminated for both cemented and screwed suprastructures. Differences were found between the two methods of prosthetic retention: the cemented group presented significantly higher bacterial loads in the peri-implant sulcus, but significantly lower bacterial loads at the implant connection inner portion. KEY WORDS: cemented prosthesis, screw-retained prosthesis, dental implant microbiology. The noxious effect of Gram-negative anaerobic bacteria on peri-implant tissue health was pointed out in different studies. 1 In vitro and in vivo studies proved that bacteria could penetrate through implant- abutment microgaps and reach the inner spaces of two-stage implants. 2,3 From the connection inner portion, microorganisms may reach the peri-implant area close to the bone by leaking through the implant-abutment interface and interfere with peri-implant tissues health. 4-6 In fact, Broggini et al. 7,8 found the highest inflammatory cell concentration 0.5 mm apical to the implant-abutment interface.