Translucency Parameter and Transmittance Relationship in Zirconia at Different Shades
Objectives: The effect of zirconia shade and thickness on the translucency and transmittance of the prosthesis is being studied. The investigation will significantly value the understanding of bonding zirconia CAD to tooth structure using light-cure and dual-cure resin cement. Methods: Ceramics specimens from Zirconia CAD (Katana UTML) in A1, A2, and A3 shades and their corresponding enamel shades (EA1, EA2, EA3) were used. IPS e.max CAD blocks in A1, A2, and A3 were used as control groups. 150 square-shaped e.max and zirconia specimens were prepared from CAD-CAM material blocks and discs, respectively. The samples were cut and then polished by a polisher machine (EcoMet1000, Buehler). The e.max CAD specimens were sintered in a furnace (Programat CS; Ivoclar Vivadent AG) and zirconia in another furnace (Sintra Pro; Shenpaz) and polished into final thicknesses of 1, 1.25, 1.50, 1.75, and 2.00 mm. A spectrophotometer (CM-2600D; Konica Minolta Sensing Americas, Inc) measured the translucency parameter (TP) at the center of all specimens A spectrophotometer (MARC Resin calibrator; Bluelight Analytics, Inc) and LED unit (Bluephase) were used to measure light transmittance. A regression analysis was used by plotting the natural log of transmittance against thickness to find each shade's absorption coefficient and reflectance. Results: Coefficient of absorption ranges from 0.616 to 0.948 (mm-1) were found in the zirconia group. Higher coefficient of absorption, lower TP, and lower transmittance were found in each shade compared to the corresponding enamel shade groups. A linear relationship between the translucency parameter and transmittance for each shade from both materials was found to fall on the same curve in a shade-dependent fashion. Conclusions: A linear relationship between the translucency parameter and transmittance for each shade from both materials further confirmed our previous study using a different zirconia material. The fundamental physics behind the correlation will be further explored.