Influence of CAD/CAM on the fit accuracy of implant-supported zirconia and cobalt-chromium fixed dental prostheses.

STATEMENT OF PROBLEM: Relatively little information is available on the accuracy of the abutment-implant interface in computer-aided design and computer-aided manufacturing (CAD/CAM)-fabricated zirconia and cobalt-chromium frameworks. PURPOSE: The purpose of this study was to compare the fit accuracy of CAD/CAM-fabricated zirconia and cobalt-chromium frameworks and conventionally fabricated cobalt-chromium frameworks. MATERIAL AND METHODS: Four groups of 3-unit, implant-supported, screw-retained frameworks were fabricated to fit an in vitro model with 3 implants. Eight frameworks were fabricated with the CAD/CAM system: 4 in zirconia and 4 in cobalt-chromium. Another 8 were cast in cobalt-chromium with conventional casting, including 4 with premachined abutments and 4 with castable abutments. The vertical misfit at the implant-framework interface was measured with scanning electron microscopy when only 1 screw was tightened and when all screws were tightened. Data were analyzed with the Kruskal-Wallis and Mann-Whitney tests (alpha=.05). RESULTS: The mean vertical misfit values when all screws were tightened was 5.9 +/-3.6 mum for CAD/CAM-fabricated zirconia, 1.2 +/-2.2 mum for CAD/CAM-fabricated cobalt-chromium frameworks, 11.8 +/-9.8 mum for conventionally fabricated cobalt-chromium frameworks with premachined abutments, and 12.9 +/-11.0 mum for the conventionally fabricated frameworks with castable abutments; the Mann-Whitney test found significant differences (P<.05) among all frameworks, except between the conventionally fabricated frameworks (P=.619). No significant differences were found among the groups for passive fit gap measurements (P>.05). CONCLUSIONS: When all of the screws were tightened, the CAD/CAM frameworks exhibited better fit accuracy compared with the conventionally fabricated frameworks. High levels of passive fit were achieved for the evaluated techniques.