Comparison of Narrow (<3.75 mm) and Standard (≥3.75 mm) Diameter Implants Supporting the Same Multiple Fixed Prostheses and Mirroring Real-World Clinical Scenarios: Non-Randomized Clinical Trial

<b>Objective:</b> To compare the survival of narrow (<3.75 mm) implants and standard diameter (≥3.75 mm) implants supporting the same multiple fixed prostheses and mirroring real-world clinical scenarios. <b>Methods:</b> This is a controlled clinical trial where both test (diameter < 3.75 mm) and control (diameter ≥ 3.75 mm) implants supported the same prosthesis. The principal variable was implant survival and the secondary variables included demographic, surgical and prosthetic variables. Statistical analyses were conducted to compare these variables between the study groups. <b>Results:</b> A total of 42 patients participated in this study, with an age range of 39 to 92 years. The follow-up period was 36 months. Narrow diameter implants (NDIs) were predominantly placed in the premolar region and more frequently in bone types I and II compared to wider diameter implants. No implant failures were recorded during the study period. Marginal bone level remodeling showed statistically significant differences between the study groups at 12-month follow-up. However, these differences were no longer significant after 3 years of follow-up (Test: median -0.2 mm, range -1.5 to 0.8 mm; Control: median 0.0 mm, range -1.3 to 0.8 mm; <i>p</i> = 0.119). None of the prostheses failed, and all remained free of technical complications throughout the study. <b>Conclusions:</b> Within the limitations of this study, narrow-diameter implants demonstrated comparable clinical outcomes to standard-diameter implants when supporting the same prostheses.