Purpose: The aim of this prospective clinical trial was to compare the three-dimensional marginal bone level, implant stability, and peri-implant health of two types of submerged dental implants that were restored with matching or platform-switched abutments. Materials and Methods: Twenty-five subjects were recruited (test group: 43 implants with internal conical connection and back-tapered collar carrying a platform-switched abutment; control group: 50 implants carrying a matched-platform abutment). Implant uncovering and conventional loading were performed after 3 months of healing, and the total observation time was 15 months. Marginal bone levels, resonance frequency analysis, insertion torque, and peri-implant health indices were recorded and analyzed statistically. Results: The cumulative implant survival rate was 100%. At the second-stage surgery, bone levels were similar between groups. One year after loading, mean crestal bone loss was 0.35 +/- 0.13 mm for test implants and 0.83 +/- 0.16 mm for control implants, a significant difference. Primary stability was significantly higher in the test group than in the control group, but this difference disappeared after 3 months of healing prior to loading. Between-group differences for peri-implant health indices were negligible. Conclusions: Both implant systems had the same survival rates. Implants with a built-in platform switch and conical connection with back-tapered collar design achieved higher primary stability at insertion and less bone resorption after 15 months.