title: The effect of variations in translucency and background on color differences in CAD/CAM lithium disilicate glass ceramics.
abstract: OBJECTIVE
  The purpose of this study was to compare the effect of variations in translucency and background on color differences (ΔE) for different shades of computer-aided design and computer-aided manufacturing (CAD/CAM) lithium disilicate glass ceramics.
  
  
  METHODS
  A pilot study suggested n = 10 as an appropriate sample size for the number of lithium disilicate glass ceramic cylinders per group. High-transparency (HT) and low-transparency (LT) cylinders (diameter, 12 mm; length, 13 mm) were fabricated in three ceramic shades (BL1, A2, C3) using CAD/CAM technology and were cut into specimen disks (thickness, 1.2 mm; diameter, 12 mm) for placement on Natural Die (ND1 and ND4) backgrounds. Four combinations of translucency and background color were evaluated in terms of color differences for the three ceramic shades: group 1 (HT ND1, reference), group 2 (HT ND4), group 3 (LT ND1), and group 4 (LT ND4). A spectrophotometer was used to measure the color differences. Nonparametric tests (Kruskal-Wallis tests) were used to evaluate the color differences among the tested groups, and Mann-Whitney U tests with Bonferroni correction were used as post hoc tests. Furthermore, for each ceramic shade, the HT groups were compared to the LT groups using the Mann-Whitney U test.
  
  
  RESULTS
  Significant differences were present among the tested groups of the same ceramic shade (p < 0.001). The highest ΔE values were observed in the HT ND4 group for BL1, while the lowest ΔE values were found in the LT ND1 group for both A2 and C3. Further, the HT groups and the groups with a darker background (ND4) showed increased ΔE values compared with the other groups (p < 0.001).
  
  
  CONCLUSIONS
  Within the limitations of this study, the results suggested that the translucency and background color significantly influenced the lithium disilicate glass ceramic color among the BL1, A2, and C3 ceramic shades. Changing the underlying color from a lighter background to a darker background resulted in increased color differences.
authors.affiliation: Department of Prosthodontics and Operative Dentistry, Tufts University School of Dental Medicine, Boston, MA.
authors.forename: Abdulaziz
authors.initials: A
authors.lastname: Al Ben Ali
authors.forename: Kiho
authors.initials: K
authors.lastname: Kang
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Finkelman
authors.forename: Roya
authors.initials: R
authors.lastname: Zandparsa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hirayama
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D003116:Color; D017076:Computer-Aided Design; D003460:Crystallization; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D006358:Hot Temperature; D008027:Light; D008422:Materials Testing; D013053:Spectrophotometry / Q000379:methods; D013499:Surface Properties
chemical_list: D003764:Dental Materials; C520133:IPS e.max CAD LT; C493120:lithia disilicate; D003776:Dental Porcelain; C023506:Glass ceramics
keywords: All-ceramic materials; Natural Die; abutment color; lightness