Do high translucency zirconia shades contribute to the degree of conversion of dual-cure resin cements

Objective:The opacity of the zirconia ceramic restoration may influence the degree of conversion (%DC) of dual-cured resin cements. The aim of this study was to evaluate the degree of conversion of resin luting agents photocured under different high translucency zirconia shades. The opacity of each ceramic shade was evaluated. Method and materials:The opacity per-centage of Lava Frame and three Lava Plus High Translucency Zirconia ceramic shades (W1, A2, and B4) was determined. A spectrophotometer MiniScan was used to measure the opacity percentage of each specimen (0.7 mm thick) and then the opac-ity was calculated. Specimens from three different resin cements (Panavia F2.0, RelyX Unicem 2 Automix Self-Adhesive, and Per-maFlo DC) were prepared with 100-mu m thickness. The speci-mens were photocured according to the manufacturers'instruc-tions under a ceramic block (0.7 mm thick). Specimens photo-cured without the ceramic block were used as control. Fifteen groups (n = 3) were evaluated. Micro-ATR/FTIR (micro-attenu-ated total reflectance/Fourier-transformed infrared spectros-copy) spectrometry was used to evaluate the extent of poly-merization of all specimens after 24 hours. The %DC was deter-mined using experimentally polymerized versus maximally polymerized composite. Results: The opacity percentages (mean +/- SD) of W1, Lava Frame, A2, and B4 ceramics were 72.41% +/- 0.04%, 74.24% +/- 0.09%, 77.63% +/- 0.11%, and 78.17% +/- 0.12%, respectively. There was a statistically significant differ-ence in %DC among the different cements investigated (P = .003) and a statistical difference in %DC was also found among the different ceramic shades studied (P = .030). For the Lava Frame and A2 ceramic blocks, the resin cements tested presented the lowest %DC except for the RelyX Unicem resin cement. Conclu-sions: The %DC of RelyX Unicem 2 cement under low zirconia opacities (W1 and Lava Frame) was greater compared to high zirconia opacities (A2 and B4). For the Panavia F2.0 cement, no effect on the %DC under different high translucency shades was observed. The highest %DC of PermaFlo cement was exhib-ited when the ceramic shade W1 was used. Clinical implica-tions: Dual-cured resin cements exhibited different degrees of conversion depending on the opacity of the zirconia restoration. However, different brands demonstrated higher or lower de-pendency of the light transmittance on their degree of conversion.