title: Effects of multiple firings on metal-ceramic bond strength of Co-Cr alloy fabricated by selective laser melting.
abstract: BACKGROUND
  Selective laser melting (SLM) is a new technique for fabricating dental restorations, but the metal-ceramic bond strength of the restorations after multiple firings must be considered because adequate bond strength is a clinical requirement for long-term performance.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the effects of repeated firing on the metal-ceramic bond strength of an SLM Co-Cr alloy.
  
  
  METHODS
  Thirty-six SLM-fabricated (Group SLM) and conventional lost wax cast (Group Cast) Co-Cr metal bars were prepared. Eighteen bars from each group were molded into dimensions of 25×3×0.5 mm, following International Organization for Standardization (ISO) standard 9693:2012. In the center of each bar, a 1.1-mm thickness of porcelain was fused onto an 8×3-mm rectangular area. In each group, specimens were divided into 3 subgroups based on the number of firing cycles (3, 5, 7) for the veneering process. Metal-ceramic bond strength, fracture mode analysis, and area fraction of adherence porcelain (AFAP) of each subgroup was evaluated with a 3-point bend test and by measuring the Si content of specimens with scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). The results were statistically analyzed first with the Shapiro-Wilk test, where a P value of .364 was considered normally distributed, and then with the Student t test to determine significant differences (α=.05).
  
  
  RESULTS
  Student t test results showed no statistical differences between the metal-ceramic bond strength of SLM and that of conventionally cast groups after firing 3, 5, and 7 times (P>.05). However, after SEM/EDS analyses, the SLM group showed significantly more porcelain adherence than that of the control group (P<.05) after 5 or 7 firings.
  
  
  CONCLUSIONS
  The SLM group showed superior metal-ceramic bond strength that exceeded ISO 9691:1999 (E) requirements at all firing periods. Also, the bond showed better behavior in terms of AFAP than the conventional cast group, especially after 5 or 7 firings.
authors.affiliation: Intern, Department of Prosthodontics, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China.
authors.forename: Xiao-Wei
authors.initials: XW
authors.lastname: Ren
authors.affiliation: Intern, Department of Prosthodontics, 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: Graduate, Shanghai World Foreign Language Middle School, Shanghai, China.
authors.forename: Zi-Ming
authors.initials: ZM
authors.lastname: Wei
authors.affiliation: Intern, Department of Prosthodontics, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China.
authors.forename: Xian-Zhen
authors.initials: XZ
authors.lastname: Xin
authors.affiliation: Professor, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Electronic address: weibin0328@hotmail.com.
authors.forename: Bin
authors.initials: B
authors.lastname: Wei
mesh_terms: D002516:Ceramics; D002858:Chromium Alloys; D001840:Dental Bonding; D003735:Dental Casting Technique; D003776:Dental Porcelain; D008422:Materials Testing; D016876:Metal Ceramic Alloys; D013499:Surface Properties
chemical_list: D002858:Chromium Alloys; D016876:Metal Ceramic Alloys; D003776:Dental Porcelain