Abstract
Blue light (BL) curing on dental resin composites results in gradient polymerization. By incorporating upconversion phosphors (UP) in resin composites, near-infrared (NIR) irradiation may activate internal blue emission and a polymerization reaction. This study was aimed to evaluate the competency of the NIR-to-BL upconversion luminance in polymerizing dental composites and to assess the appropriate UP content and curing protocol. NaYF4 (Yb3+/Tm3+ co-doped) powder exhibiting 476-nm blue emission under 980-nm NIR was adapted and ball-milled for 4–8 h to obtain different particles. The bare particles were assessed for their emission intensities, and also added into a base composite Z100 (3M EPSE) to evaluate their ability in enhancing polymerization under NIR irradiation. Experimental composites were prepared by dispensing the selected powder and Z100 at different ratios (0, 5, 10 wt% UP). These composites were irradiated under different protocols (BL, NIR, or their combinations), and the microhardness at the irradiated surface and different depths were determined. The results showed that unground UP (d50 = 1.9 μm) exhibited the highest luminescence, while the incorporation of 0.4-μm particles obtained the highest microhardness. The combined 20-s BL and 20–120-s NIR significantly increased the microhardness on the surface and internal depths compared to BL correspondents. The 5% UP effectively enhanced the microhardness under 80-s NIR irradiation but was surpassed by 10% UP with longer NIR irradiation. The combined BL-NIR curing could be an effective approach to polymerize dental composites, while the intensity of upconversion luminescence was related to specific UP particle size and content. Incorporation of 5–10% UP facilitates NIR upconversion polymerization on dental composites.
Highlights
Photopolymerization of resin-base composites (RBCs) with blue lights (BL) was introduced in the 1980s [1]
The BL irradiance significantly attenuates in the composite materials to cause gradient polymerization, which means that the degree of conversion (DC) decreases with the depth of cavities [4]
The NIR-to-BL upconverted photoluminescence was examined for its efficacy in curing dental RBCs
Summary
Photopolymerization of resin-base composites (RBCs) with blue lights (BL) was introduced in the 1980s [1]. BL irradiation activates the photosensitive initiator camphorquinone to react with a tertiary amine accelerator and generate primary free radicals. These radicals react with the dimethacrylate monomer and break the C=C double bonds to start a crosslinking reaction [2]. This process denoted a great advance for restorative dentistry since the operators have sufficient time to manipulate the RBC materials and solidify them on demand. The BL irradiance significantly attenuates in the composite materials to cause gradient polymerization, which means that the degree of conversion (DC) decreases with the depth of cavities [4]. Complete and homogeneous polymerization of RBC restorations remains a goal to accomplish
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