Aim <p>This prospective controlled clinical study aimed at evaluating the performance of 5.5 mm-long implants to support two-unit fixed prosthesis in the posterior regions of the mandible and the maxilla.</p> Materials and methods <p>A total of 44 patients (30 females and 14 males) were included and received 51 test implants (5.5 mm in length) and 51 control implants (≥6.5 mm in length) to support two-unit fixed partial prosthesis in the mandible and the maxilla. Intermediate abutment was used in all cases. The patients were followed for 12 months. Changes in the marginal bone loss, implant survival, and prosthetic complications were compared between the two groups.</p> Results <p>The patient’s mean age was 64 years (range: 42–48 years). All the implants in the test group were placed at the molars site compared to 26 implants in the control group (<i>p</i> &lt; 0.001). Bone type (<i>p</i> = 0.224) and insertion torque (<i>p</i> = 0.671) were similar between the groups. None of the implants failed. The changes in marginal bone level at mesial (median: 0.3 mm; range: −1.3 to 2.9 mm for control, and 0.2 mm; −0.7 to 1.6 mm for test; <i>p</i> = 0.138) and at distal (median: 0.3 mm; range: −1.3 to 1.5 mm for control, and 0.2 mm; −1.2 to 1.4 mm for test; <i>p</i> = 0.0633) were similar between the study groups. The prostheses were free of technical complications.</p> Conclusions <p>This prospective controlled clinical study supports the use of 5.5-mm long implants in the context of fixed partial prosthesis and posterior regions. No statistically significant differences have been observed in marginal bone stability, implant survival and prosthetic complications compared to longer implants. Within the limits of this study, 5.5 mm implants appear to be a predictable option for fixed posterior partial dentures.</p>