Abstract
The aim of this study was to evaluate: (i) the absorption of photo-initiators and emission spectra of light curing units (LCUs); and (ii) the degree of conversion (DC) of experimental composites formulated with different photo-initiators when activated by different LCUs. Blends of BisGMA, UDMA, BisEMA and TEGDMA with camphorquinone (CQ) and/ or 1-phenyl-1,2-propanedione (PPD) were prepared. Dimethylaminoethyl methacrylate (DMAEMA) was used as co-initiator. Each mixture was loaded with 65 wt% of silanated filler particles. One quartz-tungsten-halogen - QTH (XL 2500, 3M/ESPE) and two lightemitting diode (LED) LCUs (UltraBlue IS, DMC and UltraLume LED 5, Ultradent) were used for activation procedures. Irradiance (mW/cm²) was calculated by the ratio of the output power by the area of the tip, and spectral distribution with a spectrometer (USB 2000). The absorption curve of each photo-initiator was determined using a spectrophotometer (Varian Cary 5G). DC was assessed by Fourier transformed infrared spectroscopy. Data were submitted to two-way ANOVA and Tukey's test (5%). No significant difference was found for DC values when using LED LCUs regardless of the photo-initiator type. However, PPD showed significantly lower DC values than composites with CQ when irradiated with QTH. PPD produced DC values similar to those of CQ, but it was dependent on the LCU type.
Highlights
Quartz-tungsten-halogen (QTH) light curing units (LCUs) have several drawbacks when compared with the light-emitting diodes (LEDs),[10] such as relatively shorter efficient working life span; heat production and filters degradation with time
The specific aims of this study were: 1. to evaluate the absorption of photo-initiators and emission spectra of light curing units; and 2. to evaluate the degree of conversion (DC), which determines the final properties of composites;[12] of experimental composites with different photoinitiators, photo-activated by LEDs and QTH
DC for composites formulated with CQ and CQ/PPD was not dependent on the LCU used
Summary
Since the introduction of visible-light activated composites camphorquinone (CQ) has been widespread used as the principal photo-initiator molecule.[1,2] CQ is a solid yellow compound and large amounts of it in resin formulations might lead to undesirable yellowing, which affects the final esthetic appearance of the cured material.[3,4,5] researchers have tested different photo-initiators in the organic matrix to substitute, or act synergistically with CQ.[4,6,7,8]The 1-Phenyl-1,2- Propanedione (PPD) has been suggested as a way to improve the polymerization kinetics and to reduce the “yellowing effect” of the photo-initiator. Since the introduction of visible-light activated composites camphorquinone (CQ) has been widespread used as the principal photo-initiator molecule.[1,2] CQ is a solid yellow compound and large amounts of it in resin formulations might lead to undesirable yellowing, which affects the final esthetic appearance of the cured material.[3,4,5] researchers have tested different photo-initiators in the organic matrix to substitute, or act synergistically with CQ.[4,6,7,8]. The absorption peak of this molecule is mainly in the near UV-Vis region and extends slightly into the visible region.[9] many LCUs are available on the market and each one emits light in different regions of the spectrum. Due to the narrow emission spectrum by second generation LEDs, some photo-initiators present in composites might not be activated. LEDs that emit wider spectrum have been developed.[11]
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