The aim of this clinical study was to evaluate bacterial colonization, marginal bone loss, and optical alveolar density in implants with Morse taper (MT) and external hexagon (EH) connections. Thirty-five implants were installed in 7 patients (mean age: 65.8 ± 6.7 years). Implants were divided into 2 groups, according to platform design: G1 - MT, installed 2mm infra-osseous and G2 - EH, positioned according to Branemark protocol. Patients were evaluated at baseline (T0), 21 days (T1), 3 months (T2), 6 months (T3), and 12 months (T4) after installations. Bone loss and alveolar density were evaluated by standardized periapical radiographs and bacterial profile with checkerboard DNA–DNA hybridization. Statistical analyses were performed using SPSS 23.0. To present the results, boxplots and a line graph of mean were used. P-values ≤ .05 were statistically significant. After 3 months, alveolar bone loss was significantly higher in the G2 (T2-T0: P = .006; T3-T0: P = .003; and T4-T0: P = .005). No significant differences between G1 and G2 groups were observed for optical alveolar density. Microbiological analysis showed similar profiles between studied groups; however, there were significantly higher counts of Tannerella forsythia (P = .048), Campylobacter showae (P = .038), and Actinomyces naeslundii (P = .027) in G1 after 12 months. Based on the results of this study, it can be concluded that there was less peri-implant bone loss in MT compared to EH connections, but microbiological profile did not seem to influence bone changes.

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