Influence of light source and extended time of curing on microhardness and degree of conversion of different regions of a nanofilled composite resin

Abstract

Objectives:The aim of this study was to evaluate the effects of different light sources and curing time on the degree of conversion and microhardness of two surfaces within a nanofilled composite resin.Methods:Four experimental groups (n=10) were formed in accordance with the light source (quartz-tungsten halogen (QTH – 600mW/cm2), or light-emitting-diode (LED - 800mW/cm2)) and the time of curing (20 s or 40 s). The specimens were prepared with a circular mould (5 mm ∅ and 2 mm thick), according to the respective protocol, and the Knoop microhardness and degree of conversion was measured at the top and the base of the specimens. The degree of conversion was evaluated by the Fourier transform infrared spectrometer (FTIR). The results were analyzed by ANOVA two-way repeated measures and Tukey’s test (α=,05).Results:Both the degree of conversion and microhardness were higher at the top than at the bottom of the specimens. The QTH light source presented better values on the degree of conversion evaluation, but this result was not observed in the microhardness evaluation. Although forty seconds of curing promotes an increased level of microhardness, it did not influence the degree of conversion.Conclusion:It could be concluded that increasing the time of curing to 40 s promotes an increase in microhardness, but it does not influence the degree of conversion of a nanofilled composite resin. QTH promote better monomeric conversion; however, the microhardness values are similar to LED curing. For all situations tested, the bottom of the specimens presented lower results than the top.

Effect of Preoperative Occlusal Matrices on the Vickers Microhardness of Composite Disks Polymerized with QTH and LED Lamps

“…Due to the lack of interference with light transmission, it is reasonable that the T surfaces of the composite discs registered significantly higher VMH values than did the respective B surfaces in most of the experimental subgroups, as occurred in previous research (Table ). Since light passes through the mass of the matrix and the composite, its intensity is greatly decreased due to the light absorption and spreading by the restorative material, reducing its potential to cure .…”

“…Recently marketed LEDs are still compared with conventional QTHs, as the latter are considered the gold standard for LCUs. Whereas some studies attribute better top and bottom VMH values to resin composites polymerized with LEDs, other studies, including our experiment, confirm that the type of LCU does not affect the composite VMH . The QTH resulted in a higher B VMH than the LED only when polymerizing 2‐mm high composite samples in the absence of a matrix (Table ).…”

“…Whereas some studies attribute better top and bottom VMH values to resin composites polymerized with LEDs, 7,20 other studies, including our experiment, confirm that the type of LCU does not affect the composite VMH. 21,22 The QTH resulted in a higher B VMH than the LED only when polymerizing 2-mm high composite samples in the absence of a matrix ( Table 2). Differences in the spectral emission of both lamps may produce variations in light scattering, which in turn may cause differences in the depth of penetration.…”

Effect of a third‐generation LED LCU on microhardness of tooth‐colored restorative materials

“…LED units also generate minimal heat and do not require cooling fans, so they are smaller and lighter in weight than other technologies. Nevertheless, LED technology has two main drawbacks: First, because first‐ and second‐generation LEDs emit light matching the absorption spectrum of camphorquinone (430–500 nm), they may not provide adequate curing of composite resins containing alternative initiators. Second, the manufacturers of LED units recommend irradiation times of 20 s and 40 s, whereas shorter curing times are always preferable in clinical conditions.…”

Effects of radiant exposure and wavelength spectrum of light-curing units on chemical and physical properties of resin cements

“…As previously demonstrated, radiant exposure, irradiance, wavelength, and distance of the light-curing tip can influence the degree of conversion (DC) of resin materials 11141516…”