title: The effect of occlusal surface relief of dies on marginal adaptation of metal-ceramic casting copings.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the impact of occlusal relief of dies on internal adaptation of metal-ceramic casting copings.
  
  
  METHODS
  Standardized preparations were made on 80 extracted third molar teeth. Impressions were made with poly(vinyl siloxane), and stone dies were prepared. Dies were covered with four layers of die spacer, covering the entire preparation together with the occlusal surface excluding the apical 0.5 mm of the preparation in group 1 (40 specimens), and covering the same area excluding the occlusal surface in group 2 (40 specimens). Copings were cast using nickel-chromium-based metal ceramic alloy and cemented using zinc phosphate cement. The specimens were sectioned along the long axis. Internal discrepancies were recorded with a 0.001-mm resolution stereoscope at 6 points: the middle of the occlusal surface (MO), middle of the lingual wall (ML), middle of the buccal wall (MB), middle of the buccal shoulder finish line (MSH), middle of the lingual chamfer finish line (MCH), and middle of the buccal bevel finish line (MBL). Student's t-test was used for statistical analysis. Significance level was set at p < 0.05.
  
  
  RESULTS
  The marginal discrepancies of group 1 were higher than those of group 2. Significant differences in discrepancies were found on MO (p < 0.0001), MSH (p = 0.012), and MBL (p = 0.035). The bevel margin showed the least marginal discrepancy following occlusal surface of the die with no relief.
  
  
  CONCLUSIONS
  Leaving the occlusal part of the die uncovered with the die spacer improved the crown seating considerably in the occlusal surface as well as shoulder and bevel margins.
authors.affiliation: Dental Research Center, Department of Prosthodontics, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Fariba Saleh
authors.initials: FS
authors.lastname: Saber
authors.forename: Nader
authors.initials: N
authors.lastname: Abolfazli
authors.forename: Farhang
authors.initials: F
authors.lastname: Mahboub
authors.forename: Fariba Emadian
authors.initials: FE
authors.lastname: Razavi
mesh_terms: D002484:Cementation / Q000379:methods; D002858:Chromium Alloys / Q000737:chemistry; D003442:Crowns; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique; D018772:Dental Marginal Adaptation; D017267:Dental Prosthesis Design / Q000295:instrumentation*; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D003765:Models, Dental; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000295:instrumentation / Q000379:methods; D015036:Zinc Phosphate Cement / Q000737:chemistry
chemical_list: D002858:Chromium Alloys; D003734:Dental Casting Investment; D016876:Metal Ceramic Alloys; D015036:Zinc Phosphate Cement