Purpose: A single-blind randomized controlled split-mouth trial was performed to compare the 36-month outcomes of machined and titanium oxide-anodized (ADZ) dental implant surfaces immediately loaded with fixed partial dentures in the posterior mandible. Materials and Methods: Ten patients with bilateral partial edentulism in the posterior mandible received 42 implants; 20 were placed on the test side (ADZ) and 22 were placed on the control (machined) side. The implants were loaded within 24 hours after placement. Changes in the radiographic bone level (RBL) were measured on standardized periapical films at baseline, 12 months, and 36 months. The mean changes in RBL were compared using a paired t test, and the mean changes in RBL with regard to implant position and implant surface type were compared via two-way analysis of variance. Results: After 36 months of functional loading, the overall cumulative success rate for all implants was 95%. The mean change in RBL at 36 months was 0.35 mm and 0.32 mm for ADZ and machined implants, respectively (not statistically significantly different between groups; P = .88). A reduction in RBL was observed for both machined and ADZ implants between 12 and 36 months, but only the machined implants demonstrated a statistically significant decrease in RBL during the observation period. Conclusions: No statistically significant differences in RBL change were found between machined and ADZ implant surfaces after 36 months in function, and both surfaces demonstrated minimal marginal bone remodeling. As such, immediate loading of ADZ and machined dental implants supporting fixed partial dentures may be a suitable long-term treatment option in the posterior mandible. Keywords: dental implant, immediate loading, machined surface, partially edentulous mandible, randomized controlled trial, titanium oxide surface