title: Influence of CAD/CAM on the fit accuracy of implant-supported zirconia and cobalt-chromium fixed dental prostheses.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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 (α=.05).
  
  
  RESULTS
  The mean vertical misfit values when all screws were tightened was 5.9 ±3.6 μm for CAD/CAM-fabricated zirconia, 1.2 ±2.2 μm for CAD/CAM-fabricated cobalt-chromium frameworks, 11.8 ±9.8 μm for conventionally fabricated cobalt-chromium frameworks with premachined abutments, and 12.9 ±11.0 μm 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.
authors.affiliation: Assistant Professor, Department of Dentistry, School of Dentistry, State University of Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil. Electronic address: danillogonzaga@yahoo.com.br.
authors.forename: Danilo Gonzaga B
authors.initials: DG
authors.lastname: de França
authors.affiliation: Graduate student, Department of Dentistry, School of Dentistry, Federal University of Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil.
authors.forename: Maria Helena S T
authors.initials: MH
authors.lastname: Morais
authors.affiliation: Associate Professor, Department of Fixed Prosthodontics, Occlusion and Dental Materials, School of Dentistry, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil.
authors.forename: Flávio D
authors.initials: FD
authors.lastname: das Neves
authors.affiliation: Associate Professor, Department of Dentistry, School of Dentistry, Federal University of Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil.
authors.forename: Gustavo A S
authors.initials: GA
authors.lastname: Barbosa
mesh_terms: D002516:Ceramics / Q000737:chemistry; D002858:Chromium Alloys / Q000737:chemistry*; D017076:Computer-Aided Design; D000044:Dental Abutments; D003735:Dental Casting Technique; D059605:Dental Implant-Abutment Design; D003761:Dental Impression Technique; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry*; D019094:Dental Prosthesis, Implant-Supported; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation; D003830:Denture, Partial, Fixed; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D008855:Microscopy, Electron, Scanning; D013314:Stress, Mechanical; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D002858:Chromium Alloys; D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide