title: The effect of ceramic thickness and number of firings on the color of two all-ceramic systems.
abstract: BACKGROUND
  All-ceramic restorations have been advocated for superior esthetics, and various materials have been used to improve ceramic core strength, but there is a lack of information on how color is affected by different core substructures and fabrication procedures.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the effects of various dentin ceramic thicknesses and repeated firings on the color of lithium disilicate glass-ceramic (IPS e.max Press) and zirconium-oxide (DC-Zirkon) all-ceramic systems.
  
  
  METHODS
  Thirty disc-shaped specimens, 4 mm in diameter with a 1-mm core thickness, and 0.5-, 1-, or 1.5-mm dentin ceramic thicknesses, were made from each of 2 ceramic systems (n=10). Repeated firings (3, 5, 7, or 9) were performed, and the color of the specimens was compared with the color after the initial firing. Color differences among ceramic specimens were measured using a spectrophotometer (VITA Easyshade), and data were expressed in CIELAB system coordinates. Repeated measures ANOVA was used to analyze the data (number of firings, ceramic composition, and ceramic thickness) for significant differences. The Tukey HSD test and paired 2-tailed tests were used to perform multiple comparisons (alpha=.05).
  
  
  RESULTS
  L*a*b* values of the ceramic systems were affected by the number of firings (3, 5, 7, or 9 firings) (P<.001), ceramic composition (DC-Zirkon or IPS e.max Press) (P<.001), and ceramic thickness (0.5, 1, or 1.5 mm) (P<.001). Significant interactions were present in L*a*b* values between the number of firings and ceramic composition (P<.001) and between the number of firings and ceramic thickness (P<.001). Significant interactions were present between the number of firings and ceramic thickness and ceramic composition (P<.05) in L* and b* values, but not for the a* value (P=.068). As the ceramic thickness increased, significant reductions in L* values (P<.01) were recorded for IPS e.max Press and DC-Zirkon specimens. For IPS e.max Press specimens, there were significant increases in a* and b* values (P<.01). For DC-Zirkon specimens, significant increases in a* values were observed; however, no significant differences were recorded for b* values.
  
  
  CONCLUSIONS
  The analysis revealed that there were significant changes in L*a*b* color data as the number of firings increased, which resulted in perceptual color changes in L*a*b* color parameters.
authors.affiliation: Department of Prosthodontics, University of Ankara, Faculty of Dentistry, Ankara, Turkey. ozgeozturk11@hotmail.com
authors.forename: Ozge
authors.initials: O
authors.lastname: Ozturk
authors.forename: Bulent
authors.initials: B
authors.lastname: Uludag
authors.forename: Aslihan
authors.initials: A
authors.lastname: Usumez
authors.forename: Volkan
authors.initials: V
authors.lastname: Sahin
authors.forename: Gozde
authors.initials: G
authors.lastname: Celik
mesh_terms: D000704:Analysis of Variance; D003116:Color; D003124:Colorimetry; D003442:Crowns; D003735:Dental Casting Technique; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D003804:Dentin / Q000033:anatomy & histology; D006358:Hot Temperature; D017797:Prosthesis Coloring; D013053:Spectrophotometry; D018709:Statistics, Nonparametric; D015040:Zirconium
chemical_list: C508050:IPS e.max Press; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide