title: Spectrophotometric evaluation of the optical influence of different metal alloys and porcelains in the metal-ceramic complex.
abstract: BACKGROUND
  Color matching between natural teeth, shade guides, and metal-ceramic restorations is a common clinical problem. Difficulties related to color matching arise from structural differences that exist between metal-ceramic crowns and natural teeth, the limited range of available ceramic shades, inadequate shade guides, different types of metal alloys, and varying compositions of ceramic materials.
  
  
  OBJECTIVE
  The aim of this study was to investigate the influence of various metal alloys and 2 porcelains on the final color of metal-ceramic complex. Material and methods Four commercial alloys for metal-ceramic restorations, a Ni-Cr (Thermobond), a Co-Cr (Wirobond), a Pd-rich noble (Cerapal-2), and a high noble Au-alloy (V-Delta) were combined with 2 porcelains (Vita Omega and Ceramco Silver) in metal-ceramic specimens with a standardized thickness of layers. Five disc-shaped (10 x 1 mm) specimens were prepared for each alloy/porcelain combination. Only opaque and dentin layers were applied (shade A3). The specimens were analyzed with a spectrophotometer, and data were obtained in the CIE Lab color system. The recorded data were analyzed with a 2-way multiple analysis of variance , a pair-wise comparison of group means (Student's t test), and finally, a categorical regression analysis of variance (CATREG) (alpha=.01).
  
  
  RESULTS
  The types of alloy substrate and overlying porcelain significantly affected the color (P < .01). Au and Co-Cr alloys were found to be brighter (higher L* values) than the Ni-Cr and the Pd alloys ( P <.01, SE 0.239). Ceramco porcelain was found to be most red (higher a* values) of all tested alloys ( P <.01). Gold and Pd alloys caused a yellow shift to the metal-ceramic color compared to the Ni-Cr and the Co-Cr alloys with both porcelains ( P < .01, SE 0.165). The detected color differences were visually perceptible for some alloy-porcelain combinations.
  
  
  CONCLUSIONS
  The final color of metal ceramic specimens was influenced both from the type of alloy substructure and from the type of overlying porcelain.
authors.affiliation: National and Kapodestrian University of Athens, 17121 Athens, Greece. stefkour@dent.uoa.gr
authors.forename: Stefanos G
authors.initials: SG
authors.lastname: Kourtis
authors.forename: Aris-Petros
authors.initials: AP
authors.lastname: Tripodakis
authors.forename: Asterios A
authors.initials: AA
authors.lastname: Doukoudakis
mesh_terms: D002858:Chromium Alloys / Q000737:chemistry; D003116:Color; D003722:Dental Alloys / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D016555:Matched-Pair Analysis; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D015999:Multivariate Analysis; D055095:Optics and Photonics; D010165:Palladium / Q000737:chemistry; D012044:Regression Analysis; D013053:Spectrophotometry; D013499:Surface Properties
chemical_list: D002858:Chromium Alloys; D003722:Dental Alloys; D006047:Gold Alloys; D016876:Metal Ceramic Alloys; D003776:Dental Porcelain; D010165:Palladium