title: Effect of production method on surface roughness, marginal and internal fit, and retention of cobalt-chromium single crowns.
abstract: BACKGROUND
  New production methods have been developed for metal-ceramic restorations. Different production methods may show different surface roughness and fit, which may affect retention and long-term success.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to examine 3 different production methods with regard to surface roughness, marginal and internal fit, and retention of cobalt-chromium alloy single-crown copings.
  
  
  METHODS
  A master abutment of a premolar mandibular tooth preparation with 4-mm height and a 0.6-mm deep 120-degree chamfer finish line with a 12-degree angle of convergence was replicated in die stone and scanned. Thirty-six cobalt-chromium alloy copings were produced using 3 different production techniques. Twelve copings were produced by laser-sintering, 12 by milling, and 12 by milled wax/lost wax. The surface microstructure of 2 copings in each group was analyzed using interferometry. The remaining 10 copings in each group were used to evaluate marginal and internal fit by using an impression material replica method, and retention was evaluated by using a uniaxial tensile force pull-off test. The copings from each test group were cemented with zinc phosphate cement onto resin abutments. Statistical analyses of differences in marginal and internal fit were performed using 1-way ANOVA and the Mann-Whitney U test. Differences in surface topography were analyzed with the Kruskal-Wallis and Mann-Whitney U tests for nonparametric data. Differences in retentive values were analyzed using the Mann-Whitney U test for nonparametric data (all α=.05).
  
  
  RESULTS
  Differences in surface microstructure were seen. The laser-sintered copings showed increased surface roughness compared with milled and milled wax/lost wax copings. Differences in marginal and internal fit were noted. Laser-sintered showed significantly smaller spaces between coping and abutment than milled wax/lost wax copings (P=.003). At the margins, laser-sintered copings showed significantly smaller spaces than either the milled wax/lost wax group (P=.002) or the milled group (P=.002). At the chamfer, laser-sintered copings showed significantly smaller spaces than milled wax/lost wax copings (P=.005). At the center of the axial walls, laser-sintered copings showed significantly smaller spaces than those in the milled wax/lost wax (P=.004) and milled copings (P=.005). No significant differences were noted between milled and milled wax/lost wax copings (P>.05). No significant differences were detected regarding retentive forces in the pull-off tests (P>.05).
  
  
  CONCLUSIONS
  Laser-sintered Co-Cr crown copings showed increased surface roughness and better internal and marginal fit than copings produced by milling or milled wax/lost wax technique. However, the crown pull-off tests did not reveal any significant differences.
authors.affiliation: Lecturer, Department of Materials Science and Technology, Faculty of Odontology, Malmö University, Malmö, Sweden.
authors.forename: Nils
authors.initials: N
authors.lastname: Lövgren
authors.affiliation: Graduate student, Department of Materials Science and Technology, Faculty of Odontology, Malmö University, Malmö, Sweden.
authors.forename: Rikard
authors.initials: R
authors.lastname: Roxner
authors.affiliation: Graduate student, Department of Materials Science and Technology, Faculty of Odontology, Malmö University, Malmö, Sweden.
authors.forename: Susanne
authors.initials: S
authors.lastname: Klemendz
authors.affiliation: Assistant Professor, Department of Materials Science and Technology, Faculty of Odontology, Malmö University, Malmö, Sweden. Electronic address: christel.larsson@mah.se.
authors.forename: Christel
authors.initials: C
authors.lastname: Larsson
mesh_terms: D001641:Bicuspid; D002858:Chromium Alloys / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D006801:Humans; D007834:Lasers; D008334:Mandible; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D018709:Statistics, Nonparametric; D013499:Surface Properties; D014885:Waxes; D015036:Zinc Phosphate Cement
chemical_list: D002858:Chromium Alloys; D003734:Dental Casting Investment; D003764:Dental Materials; D016876:Metal Ceramic Alloys; D014885:Waxes; D003035:Cobalt; D015036:Zinc Phosphate Cement