title: Translucency of zirconia copings made with different CAD/CAM systems.
abstract: BACKGROUND
  Zirconia cores are reported to be less translucent than glass, lithium disilicate, or alumina cores. This could affect the esthetic appearance and the clinical choices made when using zirconia-based restorations.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the translucency of zirconia copings for single crowns fabricated using different CAD/CAM systems, using lithium disilicate glass ceramic as a control.
  
  
  METHODS
  Using impressions made from a stainless steel complete-crown master die, 9 stone cast replicas were fabricated, numbered, and distributed into 8 ceramic ZrO(2) CAD/CAM system groups (Lava Frame 0.3 and 0.5, IPS e.max ZirCAD, VITA YZ, Procera AllZircon, Digizon, DC Zircon, and Cercon Base) and to a lithium disilicate glass-ceramic control group (IPS e.max Press) using a simple computer-generated randomization method. From each die, the manufacturer's authorized milling centers supplied 5 copings per group without applying any dying technique to the ceramic base material. The copings were prepared to allow for a 40-mum cement layer and were of different thicknesses according to system specifications. Translucency was measured by the direct transmission method with a digital photoradiometer mounted in a dark chamber. The light source was a 150-W halogen lamp beam. Measurements were repeated 3 times for each specimen. Data obtained were analyzed using 1-way ANOVA and the Bonferroni multiple comparison test (alpha=.05).
  
  
  RESULTS
  Among ZrO(2) copings, Lava (0.3 mm and 0.5 mm thick) showed the highest (P<.05) values of translucency measured as light flow units (3.572 + or - 018 x 10(3) lx and 3.181 + or - 0.13 x 10(3) lx, respectively). These values represent 71.7% and 63.9%, respectively, of the glass-ceramic control group (4.98 x 10(3) lx).
  
  
  CONCLUSIONS
  All ZrO(2) copings demonstrated different levels of light transmission, with the 2 Lava specimens showing the highest values. Translucency of zirconia copings was significantly lower (P=.001) than that of the lithium disilicate glass-ceramic control.
authors.affiliation: Alma Mater Studiorum University of Bologna, Department of Oral Sciences, Section of Prosthodontics, Via S. Vitale 59, 40125 Bologna, Italy. paolo.baldissara@unibo.it
authors.forename: Paolo
authors.initials: P
authors.lastname: Baldissara
authors.forename: Altin
authors.initials: A
authors.lastname: Llukacej
authors.forename: Leonardo
authors.initials: L
authors.lastname: Ciocca
authors.forename: Felipe L
authors.initials: FL
authors.lastname: Valandro
authors.forename: Roberto
authors.initials: R
authors.lastname: Scotti
mesh_terms: D002516:Ceramics / Q000737:chemistry; D017076:Computer-Aided Design / Q000145:classification; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D006801:Humans; D008027:Light; D008422:Materials Testing; D055620:Optical Phenomena; D010783:Photometry; D011874:Radiometry; D015040:Zirconium / Q000737:chemistry*
chemical_list: C508050:IPS e.max Press; C493120:lithia disilicate; D003776:Dental Porcelain; C023506:Glass ceramics; D015040:Zirconium; C028541:zirconium oxide