Effect of a Diode Laser (445 nm) on Polymerization Efficiency of a Preheated Resin Composite Used for Luting of Indirect Composite Restorations
The aim of this study was to evaluate the polymerization efficiency of a preheated resin composite used as a luting agent for indirect restorations light-cured by a blue diode laser (445 nm). Bronze molds were used to prepare cylindrical specimens of a laboratory composite (Ceramage) with dimensions 2, 3, and 4 mm in height and 8 mm in diameter. The molds had additional height of 120 μm for the placement of the preheated resin composite. A nanohybrid resin composite (Enamel Plus HRi) was preheated at 55°C to use as a luting agent. Photopolymerization was followed for 20 seconds using three light sources: a diode laser emitting at 445 nm (SiroLaser Blue) and two light-emitting diode (LED) units (Bluephase Style and Valo). Degree of conversion (DC) of the preheated resin composite was evaluated using Fourier transform infrared spectroscopy. The results indicated that the main effects of the analysis were significant for both material thickness (p<0.001) and polymerization method (p<0.001). The preheated resin composite was not polymerized under 4-mm-thick specimens, independent of the light-curing unit. For 2-mm material thickness, there was no difference among the three light-curing units (p=0.383), while 3-mm Bluephase Style presented very low DC. Diode laser (445 nm) achieved better polymerization efficiency at the same fluence compared to the LED unit at 3-mm depth, implying a better mechanical behavior and potential improved adhesion of the luting material to dentin.SUMMARY
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Schematic design of the experiment of the study. Abbreviations; BLU, Bluephase Style; CER, Ceramage; EPH, Enamel Plus HRi; SIR, SiroLaser Blue; VAL, Valo; FTIR, Fourier transform infrared.
Typical ATR-FTIR spectrum of the uncured resin focused on wavenumber range 1800-1580 cm−1. Abbreviations: ATR-FTIR, attenuated total reflectance - Fourier transform infrared; C=C, carbon-to-carbon double bond.
Representative ATR-FTIR spectra of the uncured resin and 3-mm-thick specimens light-cured with the laser device SiroLaser Blue (445 nm) and the two LED units Bluephase Style (1100 nm) and Valo (1400 nm) focused on wavenumber range 1800-1580 cm −1 . The shaded areas indicate the areas under the aliphatic and aromatic C=C absorption peaks that determine the degree of conversion. Abbreviations: ATR-FTIR, attenuated total reflectance - Fourier transform infrared spectroscopy; LED, light-emitting diode; C=C, carbon-to-carbon double bond.
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