Addition of upconversion phosphors in dental resin cements to enhance polymerization

Abstract

Light-cured (LC) composite resins are widely used in dental restorations and are also applied as luting cements Dental resin cements are polymerized by blue light irradiation thus they are easily controlled and fast cured in a short time However the polymerization of resin cements by blue light is hampered by the reduced transmission through the ceramics Recently research reveals that Infrared (IR) light exhibits high transmission through dental ceramics Our previous study also showed that the addition of upconversion phosphors (UPs) into LC composites could enhance the degrees of polymerization under NIR irradiation The purpose of this study is to investigate if the addition of Ups into dental resin cements might enhance polymerization The specific aims are to examine the thickness and type of dental ceramics different combinations of blue light and IR on the new polymerization pathway The experimental material was Ups which absorbs NIR laser to emit blue light First the spectrum and irradiance of NIR laser and blue light emission were measured by a spectrometer To examine the light transmission through ceramics transmission of blue light and NIR through two ceramics (lithium disilicate ceramics and zirconia discs) of four thicknesses (0 3 0 5 0 8 1 0 1 5 and 2 0 mm) were measured by a powermeter The experimental cement was prepared by adding 5% UPs into LC resin cement (VariolinkⅡA3 base) A multiphoton excitation microscopy was used to examine the excitation and emission lights of Ups and the particle distribution in resin cements Subsequently the blended cements were cured under two ceramics of different thickness with four blue light and adjunctive NIR combinations The microhardness of cured cements was measured by a Knoop hardness test The result shows that the NIR-UP conversion rate was 10 8% NIR light exhibited about 1 8 time transmitted power of BL through both ceramics at 0 5 mm and 1 7 time of BL power through 2 mm thick ceramics The lithium disilicate ceramic allowed more light transmission than zirconia did The UPs particle distributed homogeneously from top to bottom layers of the cement From the microhardness test NIR60 did not polymerize the cement to detectable hardness Both BL40+NIR20 and BL20s+NIR40s showed higher hardness than BL60s did The lithium disilicate ceramic groups exhibited higher surface hardness than zirconia When increased NIR irradiation time from 20s to 40s and decreased BL from 40s to 20s there were no significance difference in surface hardness The application of this new materials and light curing technique on clinical ceramic cementation well improve the adhesion strength and quality significantly

Date of Award	2016 Jul 28
Original language	English
Supervisor	Shu-Fen Chuang (Supervisor)