Using NIR activated phosphors to enhance polymerization of light-curable dental composites

Abstract

Light-curing composite resins have been widely used in restorative dentistry for several decades Despite the fact of their wide application there are clinical problems due to limitations of blue light penetration in 2-3 mm depth Their applications are restricted in cavities exposed to the light source where layered filling is still required The near-infrared light may penetrate tissue deeper than blue light does A novel resin polymerization reaction has been proposed by adding upconversion phosphor (UP) particles into dental composite and conversion via the excitation of near-infrared light The purpose of this study is to examine the novel curing pathway of dental composites and to compare its property of polymerization with traditional light-cured dental composites The efficacy of UPs in upconverted luminous intensity of the fluorescence was first characterized The UP particles were ground into sizes of 1 8 0 5 and 0 3 μm The excitation spectra of these UPs were examined and their mixtures with dental composite were evaluated thus to determine the proper UP particle size With the result 0 5-μm UP was chosen as adjunct filler for further examination UP was mixed into Z100 microhybrid composites at different conditions to generate three composites: Z100 (0% UP) UP5 (the mixture of 5 wt% UP) and UP10 (the mixture of 10 wt% UP) To examine the effect of curing protocols UP5 received either 3-10 min NIR irradiation or the combination with BL (BL+NIR) and subsequently received a microhardness test to compare the degree of conversion of composites at different depths The depths of cure in different composite materials were also evaluated These materials also received FTIR analysis for degrees of conversion A temperature analysis was performed to measure the temperature rise during NIR irradiation Finally these UP tuned composites were evaluated about their applications to enhance the polymerization under tooth substances (enamel dentin and enamel + dentin bilayer) For the proper UP ratio UP5/BL+NIR showed higher microhardness at each depth compared to UP10/BL+NIR and Z100 The adjunct NIR increased the depths of cure about 1 mm compared to blue light alone For the curing protocol 10-min NIR significantly improved the top microhardness However 10-min NIR alone showed the lowest top microhardness The temperature analysis showed NIR irradiation on UP5 for 10 min raised temperature about 12 oC and 7 1 oC at 2mm and 4mm depth in metal mold The temperature raised was about 16 4 oC in teeth mold For the polymerization under tooth substances the enamel + dentin bilyaer affected the blue light penetration most compare with enamel and dentin The BL600 irradiation group was higher than others under enamel dentin and enamel + dentin bilyaer According to these findings NIR activated phosphors could be a new way to cure the dental composite deeply to enhance the degree of conversion Accordingly this study will provide some information for the future development in another direction of the dental composites

Date of Award	2014 Sept 2
Original language	English
Supervisor	Jui-Che Lin (Supervisor)