Use of NIR light and upconversion phosphors in light-curable polymers

Objective. Light-curable polymers are commonly used in restorative surgery, prosthodontics and surgical procedures. Despite the fact of wide application, there are clinical problems due to limitations of blue light penetration: application is restricted to defects exposed to the light source, layered filling of defect is required. Methods. Combining photo-activation and up conversion allows efficient polymer hardening by deep penetrating near-infrared (NIR) light. The prerequisite 450 nm blue light to polymerize dental resins could be achieved by filler particles, which absorb the incident NIR irradiation and convert it into visible light. Results. The on spot generated blue light results in uniform polymer hardening. Composite samples of 5 mm thickness were cured two times faster than pure polymer cured by blue light (30 and 60 s, respectively). Overall degree of monomer conversion resulted in higher values of more than 40%. The enhanced transmission of NIR light was confirmed by optical analysis of dentin and enamel. The NIR transmittance surge in the 800-1200 nm window could improve sealing of complex and deep caries lesions. Significance. We demonstrate faster curing and an improved degree of polymerization by using upconversion filler particles as multiple light emission centers. This study represents an alternative approach in curing dental resins by NIR source. (C) 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.