title: Effects of repeated firing on the marginal accuracy of Co-Cr copings fabricated by selective laser melting.
abstract: BACKGROUND
  Selective laser melting (SLM) is a technique used to fabricate Co-Cr dental restorations; however, because marginal accuracy is important for the long-term success of restorations, the marginal accuracy of SLM after repeated firings must be considered.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the marginal accuracy of dental Co-Cr alloy copings fabricated by SLM and to investigate the effects of repeated firing on the marginal fit of these copings.
  
  
  METHODS
  SLM-fabricated and cast Co-Cr alloy copings (n=15) were prepared for a zirconia die. The marginal gap widths of each group were evaluated with a silicone replica technique after the first, third, fifth, and seventh firing cycle. The thickness of the reference point was measured with a stereomicroscope with ×100 magnification. Analysis of variance was used to evaluate the effect of repeated firing on the marginal accuracy of the 2 alloys. The Student t test was used to compare the marginal gap widths of the SLM-fabricated and cast Co-Cr alloy copings after repeated firing (α=.05).
  
  
  RESULTS
  The marginal gap width values between the 2 groups at all firing periods were statistically significant (P<.05). The mean marginal gap width values for SLM-fabricated copings were 36 μm, 37 μm, 38 μm, and 38 μm after the first, third, fifth, and seventh firing, while the mean marginal gap width values for cast copings were 67 μm, 71 μm, 72 μm, and 73 μm at the same number of firings. The marginal gap width values within the 2 groups were not statistically different from each other with additional firing (P>.05).
  
  
  CONCLUSIONS
  The SLM copings demonstrated superior marginal accuracy at all firings. Repeated firing had no significant influence on the marginal accuracy of both copings, and the marginal fit of both copings after repeated firing was within a clinically acceptable range.
authors.affiliation: Intern Doctor, Department of Prosthodontics, Stomatology Special Consultation Clinic, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zeng
authors.affiliation: Technician, Department of Technical, Shanghai Foshion Medical System Co Ltd, Shanghai, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Technician, Department of Technical, Shanghai Foshion Medical System Co Ltd, Shanghai, China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Professor, Department of Prosthodontics, Stomatology Special Consultation Clinic, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China. Electronic address: weibin0328@hotmail.com.
authors.forename: Bin
authors.initials: B
authors.lastname: Wei
mesh_terms: D002858:Chromium Alloys / Q000737:chemistry*; D017076:Computer-Aided Design; D003442:Crowns; D003735:Dental Casting Technique; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D007834:Lasers; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000295:instrumentation; D015040:Zirconium / Q000737:chemistry
chemical_list: D002858:Chromium Alloys; D003764:Dental Materials; D016876:Metal Ceramic Alloys; D015040:Zirconium; C028541:zirconium oxide