Objectives: To evaluate the behaviour of peri-implant tissues around implants with different surface treatment. Materials and methods: Eight patients were identified according to these criteria: systemically good health, no history of periodontal disease, no contraindications for the surgical and prosthodontic protocol applied. Each patient received at least 2 implants (1 control, 1 test) into an edentulous quadrant. The control implants had dual acid-etched (DAE) surface in the apical portion and a machined coronal part, test implants had a completely DAE surface. Machined healing abutments were placed on control implants and DAE abutments on test ones. Standardized periapical radiographs were taken at baseline, 3 and 6 months, 1 year after surgery and then annually up to the 6 year follow-up. Histologic and microbiologic analyses of peri-implant tissues were conducted in the first year. Bleedeing on probing (BOP) and Plaque Index (PI) were recorded annually. The research project was approved by the Scientific Ethical Committee of Genoa University and all patients provided informed consent to the study. Statistical analysis: Differences in bone resorption over time were evaluated by Friedman test. For statistically significant differences post-hoc analysis with Wilcoxon signed-rank test was conducted with a Bonferroni correction. Any difference in bone resorption between the two types of implants or the maxilla operated, cortical or midullary bone quality were assessed by a repeated measure ANOVA for ranked data. The same analysis evaluated differences in PI and BOP. A p ≤0.05 was statistically significant. Results: A statistically significant difference in bone level was noted over time, in particular between baseline and the 1-year follow-up appointment (p=0.001), whereas no significant changes were observed after 1-year follow-up. At 1-year follow-up the difference in bone resorption between test and control was significant (p=0.030) with lower bone loss next to test implants. A statistically significant difference (p0.001) was found in bone resorption for the quality of cortical bone, with lower bone resorption in class 1 (dense) bone compared to class 2 (medium) and 3 (soft) during the first 3 years and a greater bone resorption in class 1 bone at subsequent follow-up appointments. In contrast, no statistically significant differences in the bone resorption were found for cancellous bone quality. No statistically significant differences were detected between test and control implants for BOP (p=0.82) and PI (p=0.38). Mean Probing Depth (PD) was 2,92 mm for test implants and 2,74 mm for control implants. No statistically significant difference was found in PD (p=0.235). Conclusions: Moderate bone loss was found 1 year after surgery, then a steady state condition was observed with less bone resorption next to test implants. Implant surface might affect the bone remodelling phase subsequent to the surgical trauma, but once osseointegration was established, implant surfaces did not affect bone maintenance over time. Implant surfaces did not affect soft tissue behavior in the present study. Keywords: implant surface, peri-implant tissue, bone loss