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  • Effect of the load and thickness of resin cement on the light transmittance through zirconia onlays : an in vitro study
    Publication . Leduc, Smila; Pereira, Rita Cristina Pais Fidalgo; Souza, Júlio César Matias de
    Purpose: The objective of this study was to evaluate the light transmittance behavior of resin-matrix cement and zirconia onlays after cementation, subjected to two different loading magnitudes. Materials and Methods: Eighteen CAD-CAM fabricated 3Y-TZP zirconia onlays (1.5 mm thickness) were cemented onto zirconia disks following the APC protocol. Specimens were divided into two groups: Z20 (20 N load) and Z60 (60 N load), each applied for 60 seconds and analyzed in triplicate. All samples were cemented using a 73 wt% resin-matrix cement and light-cured at 900 mW/cm². Optical transmittance was assessed using a spectrometer with a monochromator before, during, and after polymerization, with additional real-time irradiance data from a MiniGig device. Post-cementation, specimens were sectioned perpendicularly and examined under optical microscopy for structural evaluation. Results: The highest light transmittance for uncemented zirconia onlays occurred near 300 nm, with increased transmission from 600 to 850 nm and peaks around 830–850 nm. Cemented specimens in the Z60 group exhibited higher light transmittance and radiant power at 840 nm than those in Z20, suggesting superior polymerization efficiency. MiniGig analysis revealed increased real-time irradiance and Rp/np ratios in Z60, while benchtop spectrophotometry showed no significant difference before and after curing. Both instruments provided complementary insights—absolute transmittance and dynamic irradiance, respectively. Conclusions: This study confirms that higher cementation loads (60 N) improve light transmittance and polymerization efficiency through 1.5 mm 3Y-TZP zirconia onlays. Increased pressure reduces cement layer thickness, minimizing light scattering. Both benchtop and in situ spectrophotometry validated the optical benefits of higher loads. Clinically, adequate cementation force is critical for optimal curing under opaque zirconia restorations. Standardized cementation protocols are recommended to enhance long-term restoration performance.
    2025-07-03Dissertação de mestrado Acesso embargado Ver mais