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Received Jan 18, 2018; Revised Mar 5, 2018; Accepted Mar 15, 2018
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1. Introduction
Photopolymerization [1] has become an essential tool in three-dimensional (3D) printing [2] and photolithography [3], in the construction of polymer electronics [4], optical materials [5], membranes [6], and coatings, and in surface modifications. The most common photopolymerization monomers are cyclic or linear epoxides (cationic) and acrylate-based monomers (radical) [1]. Acrylate-based photopolymers are important materials for cardiovascular applications [7], for in vivo drug delivery [8], and for minimally invasive procedures. Dimethacrylate-based resins have many applications in restorative dentistry, being used as adhesives and pit-and-fissure sealants, can be combined with silane-coated glass fillers to render the most widely used esthetic direct restorative material, and can be used as cementation agents and veneering materials [9–12]. Photopolymerization starts with exposure to a light source, the operation wavelength of which depends on the photoinitiator added. For the photopolymerization process to be effective, the spectral radiant power of the light-curing unit must fall within the spectral range required to activate the photoinitiator present in the resin [13].
Several types of light-curing units are available for photoactivation of photopolymerizable dental resins. The contemporary technologies include quartz-tungsten-halogen lights (QTH), plasma arc lights, high-intensity QTH lights, and light emitting diodes (LED). The most common photoinitiator in dental practice is camphorquinone (CQ) in combination with tertiary amines as coinitiators [14]. CQ has a relatively broad absorption in the ultraviolet (UV) region and an absorption band in the visible region with a maximum wavelength
To overcome the relatively low initiation efficiencies, other high-performance visible photoinitiators have been developed for resins used in specialty applications, such as direct laser imaging, holography, or photopolymerization color printing [17]. Fluorinated diaryl...