Stratified Randomized Controlled Trial of ∅3.3 mm Versus ∅4.1 mm Hydrophilic Titanium-Zirconium Implants Supporting Posterior Mandibular Fixed Prostheses in Hyperglycaemic Subjects.

OBJECTIVE: To compare ⌀3.3 mm and ⌀4.1 mm hydrophilic titanium-zirconium implants supporting fixed dental prostheses (FDPs) in mandibular distal-extension situations among participants with varying degrees of hyperglycaemia. MATERIALS AND METHODS: Participants were stratified according to HbA1c (5.8%-< 7.0% vs. ≥ 7.0%) and subsequently randomized within each stratum to receive either ⌀3.3 mm or ⌀4.1 mm titanium-zirconium implants. Each participant received a two-implant-supported multi-unit FDP. The primary outcome was marginal bone level (MBL) change at 12 months after prosthesis delivery. Secondary outcomes included implant stability quotient (ISQ), peri-implant indices, Healing Index and patient-reported outcomes. RESULTS: Of 88 enrolled participants, 83 (166 implants) were evaluated. Implant survival was 100%, with no peri-implantitis. At 12 months, MBL did not differ significantly between the ⌀3.3 mm [0.27 mm (IQR, 0.07-0.68)] and ⌀4.1 mm groups [0.27 mm (IQR, -0.04 to 0.54); p = 0.078]. Participants with HbA1c ≥ 7% had approximately sevenfold higher odds of MBL ≥ 0.5 mm than those with HbA1c < 7%. Secondary ISQ was significantly higher with ⌀4.1 mm implants (79.6 vs. 76.1; p < 0.001), whereas early healing was better with ⌀3.3 mm implants (p = 0.005). Chewing ability improved significantly from baseline to 12 months irrespective of implant diameter or HbA1c category (p < 0.0001). CONCLUSION: At 1 year, ⌀3.3 mm and ⌀4.1 mm hydrophilic Ti-Zr implants demonstrated no statistically significant difference in MBL although ⌀4.1 mm implants demonstrated higher stability. Patient-reported chewing ability improved substantially following rehabilitation for both implant diameters. Higher HbA1c was associated with greater odds of clinically relevant MBL. TRIAL REGISTRATION: The trial was registered prospectively with the Clinical Trials Registry-India (CTRI/2017/08/009315).