Microhardness Evaluation of Resin Composites Polymerized by Three Different Light Sources

Abstract

This study examined the surface microhardness of four kinds of resin composites with different fillers and resin matrices. Ten specimens of 2 mm thickness and 4 mm diameter of each resin composite were polymerized using a halogen light, a blue light-emitted diode, and a plasma arc unit. Microhardness evaluation was performed at top and bottom surfaces for each specimen using a Vickers microhardness tester. Furthermore, morphologies of the polished top surfaces of composites cured with blue light-emitted diode were observed using scanning electron microscopy. Results indicated that composites cured with halogen or blue light-emitted diode light yielded higher microhardness values, although it also appeared to depend on the type of composite cured. Plasma arc curing according to manufacturer' s instructions yielded the lowest microhardness values for all the materials. Among the materials tested, the nanofilled resin composite displayed the highest microhardness values for each curing regime.

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

“…The lowest hardness and elastic modulus values were found on composite's bottom surface. Previous studies had also found similar results 12,21,24,25 . During photopolymerization, there is a considerable reduction of irradiance in deeper regions through the bulk of the composite, due to absorption and scattering of light by the resin matrix and particles filler 25 .…”

“…lower power densities and longer periods of time slow down the formation of a rigid polymer chain, which allows for more efficient polymerization. Continuous exposure to light helps maintain the activation of the camphorquinone molecules near to the surface 24 , increasing the material's degree of polymerization on top surface 33 . On the other hand, studies demonstrate that very high power densities applied in a shorter time do not increase the DC of composites 32,34 .…”

“…Hardness of the bottom is mostly affected by light intensity, and is therefore considered a more accurate parameter for evaluating the effectiveness of curing 24 , and consequently the performance of the LCUs. Considering only the bottom surface, L468 generated the highest results for hardness and elastic modulus.…”

Post-irradiation vickers microhardness development of novel resin composites

“…In the contrary, it has been shown previously that nanofilled resin composite gave the highest VHN compared to mirofilled and microhybrid composites. This may be attributed to the presence of small agglomerated or non-agglomerated nanofillers that occupy the spaces between the slightly larger particles resulting in increased filler load in the composite 40 . The composite materials showed higher hardness values on the top surface than the base one in all test groups.…”

“…Moreover, after polymerization, the solidified polymer matrix that is formed plays a role in hardness development. It has been shown previously that monomers have not participated in polymerization reactions lead to a decrease in hardness 16 . Therefore, the purpose of this study was to determine the effect of post-irradiation dry aging on Vickers microhardness of some novel composites based on differ-ent resin matrices over periods of time after polymerization; at two common temperatures.…”