Vertical Microgap and Passivity of Fit of Three-Unit Implant-Supported Frameworks Fabricated Using Different Techniques

Purpose: This study compared the vertical microgaps of milled zirconia and cobalt-chromium (Co-Cr) implantsupported fixed dental prosthesis frameworks to those seen in one-piece frameworks cast with different techniques. Materials and Methods: Two threaded implants were used to simulate the rehabilitation of a maxillary partially edentulous space from the second premolar to the second molar. Three-unit screwretained prosthetic frameworks were fabricated and divided into the following groups (n = 10 in each group): 1 = cast in Co-Cr using burnout cylinders; 2 = cast in Co-Cr using cast-on Co-Cr cylinders; 3 = onepiece cast in Co-Cr using a passive fitting technique; 4 = milled Co-Cr framework; 5 = milled zirconia framework. The microgap was measured under an optical microscope at ×25. Readings were made with one screw tightened and with both screws tightened. Data were submitted to statistical analysis to enable comparison between groups (α = .05). Results: All frameworks presented microgaps less than 70 μm under all reading conditions, except for group 1 with the readings made on the side opposite the tightened side (124.22 μm). With one screw tightened, the microgap on the tightened side was significantly smaller in groups 2, 3, and 4. On the opposite side, groups 3, 4, and 5 presented significantly smaller microgaps compared to the other groups. When both screws were tightened, the microgap was significantly smaller in groups 2, 3, and 4. Conclusion: One-piece cast frameworks associated with a passive fitting technique and milled Co-Cr frameworks presented smaller microgaps than the other fabrication methods and materials that were tested. Keywords: computer-aided design, computer-assisted manufacture, dental implants, implant-supported dental prosthesis, prosthetic fit, prosthodontics, screw retention