Purpose: The purpose of this trial was to evaluate crestal bone level changes radiographically in a standardized fashion over a period of 12 months in humans for implants with a 0.7-mm machined collar (implant type A) versus type B implants with a 1.5-mm machined collar. Materials and Methods: Twenty-five patients with multiple missing teeth in posterior sectors were randomly assigned to one of the two groups: A (0.7-mm machined-collar implants) or B (1.5-mm machined-collar implants). Changes at crestal bone level were assessed by measuring the shoulder-crest distance (SCD) on the mesial and distal aspects of each implant on customized periapical radiographs, which were taken on the day of surgery and 3, 6, and 12 months after surgery. Results: Eighty-one implants were included in the study. Mean SCD was 0.54 ± 0.53 mm at baseline and 1.49 ± 0.40 mm after 12 months. For 0.7-mm-collar implants, mean SCD was 1.40 ± 0.39 mm, while it was 1.56 ± 0.40 mm for 1.5-mm-collar implants. Statistically significant differences were found only between the two types of implants for distal measurements at 3 and 12 months after placement. Conclusion: Both 0.7- and 1.5-mm machined-collar implants can be used with predictable results, as changes in peri-implant crestal bone levels are similar for both implant types and do not seem to be significant from a clinical point of view. The SCD may well depend more on the location of the abutment-implant interface than on machined-collar height. Keywords: bone resorption, dental implants, implant stability, marginal bone levels, surface properties