Clinical Performance of Extra-Short (≤5.5 mm) Compared to Longer Implants Splinted under the Same Prosthesis: A Randomized Clinical Trial

<b>Objective:</b> This randomized controlled split-mouth trial compared the performance of 5.5 mm length implants (test group; TG) splinted within the same fixed prosthesis as longer implants (≥6.5 mm; control group; CG) in posterior regions. <b>Methods:</b> The primary hypothesis was that implant length does not affect marginal bone loss (MBL) one year post-implantation, while the secondary hypotheses included implant survival, peri-implant clinical variables, and prosthetic complications. Fifteen patients (eight males, seven females) with a mean age of 67 ± 9 years were included. <b>Results:</b> No significant difference in the implant position between groups (<i>p</i> = 0.808) was observed. Implant diameters ranged from 3.00 to 4.25 mm, and the most common bone type was type I (67%). Bone density (<i>p</i> = 0.574) and implant insertion torque (<i>p</i> = 0.888) were similar between groups. Mesial MBL (mean: -0.1; range: -1.19 to 0.24 for TG, and -0.03; -1.75 to 0.45 for CG; <i>p</i> = 0.955) and distal MBL (mean: -0.05; range: -1.41 to 0.27 for TG, and 0.08; -1.45 to 0.72 for CG; <i>p</i> = 0.118) did not show statistical differences. There were no implant failures or technical complications. <b>Conclusions:</b> These findings suggest that 5.5 mm length implants could be a viable option for use in posterior regions, providing similar clinical outcomes to longer implants one year post-implantation.