Influence of light energy and power density on the microhardness of two nanohybrid composites

Abstract

The purpose of this study was to investigate the role of light parameters on nanohybrid composite curing. Two nanohybrid resins were cured by two light-emitting diode (LED) devices and by one quartz-tungsten-halogen (QTH) device using different combinations of energy density and power density (8 J cm(-2) and 400 mW cm(-2); 8 J cm(-2) and 1,000 mW cm(-2); 16 J cm(-2) and 400 mW cm(-2); and 16 J cm(-2)-1,000 mW cm(-2)). The effects of these combinations on polymerization were assessed by measuring the Vickers microhardness. Data differed for the two composites and varied according to the light parameters and the nature of the curing device. For both resins, an energy density of 16 J cm(-2) yielded the best microhardness values at both the top and the bottom of the sample, independently of the power density. When using a lower energy density of 8 J cm(-2), a modulated power density was required to achieve proper curing at the bottom of the sample: 8 J cm(-2) and 400 mW cm(-2) induced greater values at the bottom surface. At an energy density of 16 J cm(-2), the power density was not relevant (no significant differences were found between 400 and 1,000 mW cm(-2)), except when the emission spectra of the light-curing units (LCUs) did not match exactly with the absorption spectra of the photoinitators included in the resins (greatest values with 16 J cm(-2) and 1,000 mW cm(-2)). These results suggest that above a certain energy density threshold, the power density may not significantly influence the polymerization kinetics.

Knoop microhardness and FT-Raman evaluation of composite resins: influence of opacity and photoactivation source

“…22 Moreover, above an irradiance of 10 J/cm², there is a tendency for the DC to stabilize. 24 However, higher DCs lead to concerns because they promote higher shrinkage stress during polymerization, and there might be an increased risk of adhesive failures.…”

“…Table 2 presents the energy density calculated after multiplying the power density by the exposure time recommended by the manufacturers. 22 …”

An alternative specimen preparation technique for 3-point bending tests on dual-cured dental resin cements

“…A reduction of approximately 75% in the energy density when the tip is positioned at 10 mm from the sample has been reported (PRICE, et al 2011). This significant reduction in the energy density reduces the polymerization of resin cement and its mechanical properties, explaining the lowest values observed when only one point was used to light-cure the samples (HALVORSON, et al 2002;BAEK, et al 2008;GRITSCH, et al 2008). The use of the other two additional points for light-curing increases the energy available to polymerize the resin cement.…”

Wavelength of Experimental LEDS: Hardness, Elastic Modulus, Degree of Conversion and Temperature Rise of a Microhybrid Composite

“…Emami et al 32 , Peutzfeldt & Asmussen 17 and Gritsch et al 22 showed that lower power densities can be compensated for by increasing the photopolymerization time, which increases the energy density, and thus induces a higher degree of polymerization. They justify this finding by the kinetics of polymerization, i.e.…”

“…However, there is little data about the performance of experimental LED LCUs with different wavelength peaks evaluated through DC, hardness and the elastic modulus of the cured composite. Moreover, authors found LED LCUs whose wavelength peak is below the optimum value for activation of camphorquinone 21,22 . The aim of this study was to evaluate the effect of different peak wavelengths of experimental LED LCUs on the hardness, elastic modulus, degree of conversion and temperature rise of a composite.…”