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Attenuation Coefficient and Degree of Conversion Achieved by Blue Light Passing Through Polycrystalline Dental Ceramics
Purpose: To evaluate the transmission of blue light through zirconia ceramic disks as the attenuation coefficient, as well as investigate the degree of conversion (DC) of dual-cure resin cements with different thickness zirconia ceramic disks. Materials and Methods: Five brands of zirconia ceramic disks and lithium disilicate with four different thicknesses (0.65, 1.15, 1.65, and 2.15 +- 0.06 mm) were prepared. The transmission of light through the disks was measured in the visible blue light range using a spectrophotometer, and then the attenuation coefficient was calculated using the Beer-Lambert equation. The DC of two dual-cure resin cements (RelyX Ultimate and Panavia F2.0) were measured using Fourier transform infrared spectroscopy (FT-IR), and calculated based on the ratios of aliphatic to aromatic carbon double bond IR absorption peaks before and after polymerization. DC was measured uncured and at 0, 3, and 6 minutes (based on manufacturer recommendations). The data was analyzed using repeated measures ANOVA (alpha = .05). Results: The attenuation coefficient (mu) of each ceramic was plotted against the wavelength of light. The data showed Sirona CEREC Zirconia and 3M Chairside Zirconia had the highest attenuation coefficients and converged with each other in the 480-485 nm range, while ZirCADLT, ZirCAD Multi MT, and e.max CAD LT had lower values and also converged in the 480-485nm range. The attenuation coefficient of Katana STML diverged away from the other ceramics near 480 nm to a lower value than the rest. RelyX Ultimate was found to have higher DC values than Panavia both after the initial cure and 6 minutes. The DC achieved for both cements was lower when the ceramic was thicker. The attenuation coefficient was found to have no correlation with the degree of conversion of RelyX Ultimate or Katana STML Zirconia for either cement.
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