Micro-hardness evaluation of a micro-hybrid composite resin light cured with halogen light, light-emitting diode and argon ion laser

Abstract

This in vitro study aimed to determine whether the micro-hardness of a composite resin is modified by the light units or by the thickness of the increment. Composite resin disks were divided into 15 groups (n = 5), according to the factors under study: composite resin thickness (0 mm, 1 mm, 2 mm , 3 mm and 4 mm) and light units. The light activation was performed with halogen light (HL) (40 s, 500 mW/cm(2)), argon ion laser (AL) (30 s, 600 mW/cm(2)) or light-emitting diode (LED) (30 s, 400 mW/cm(2)). Vickers micro-hardness tests were performed after 1 week and were carried out on the top surface (0 mm-control) and at different depths of the samples. Analysis of variance (ANOVA) and Tukey tests (P < or = 0.05) revealed no statistically significant difference among the light units for the groups of 0 mm and 1 mm thickness. At 2 mm depth, the AL was not statistically different from the HL, but the latter showed higher micro-hardness values than the LED. In groups with 3 mm and 4 mm thickness, the HL also showed higher micro-hardness values than the groups activated by the AL and the LED. Only the HL presented satisfactory polymerization with 3 mm of thickness. With a 4 mm increment no light unit was able to promote satisfactory polymerization.

The effect of curing light and chemical catalyst on the degree of conversion of two dual cured resin luting cements

“…For conventional camphorquinone-based resin composites, no difference has been observed in the development of physical properties, such as the degree of conversion, when LED and QTH units are compared [13,31]. The argon ion laser has been described as a promising light source for curing resinous materials [21]. In spite of some benefits, such as an economic benefit of 25-33%, adequate depth of cure, and enhancement in resin physical properties after polymerization, the laser absorption peak is at 488 nm, displacing the camphorquinone absorption peak at 468 nm [32,33].…”

“…In spite of some benefits, such as an economic benefit of 25-33%, adequate depth of cure, and enhancement in resin physical properties after polymerization, the laser absorption peak is at 488 nm, displacing the camphorquinone absorption peak at 468 nm [32,33]. In some situations, this distance can make activation with the argon ion laser inefficient [21,34]. In this study, the argon ion laser, working with the same energy density as the QTH light, achieved an inadequate degree of conversion of Panavia F alone, due to the offset narrower spectral peak at about 488 nm, which could not initiate the photoinitiators present in this cement under the resin composite disk.…”

“…The argon ion laser has arisen as an alternative light source for polymerizing resin composites, resin luting cements, and for bleaching procedures [19][20][21]. For camphorquinone-based resins, the activation emits a blue light in the wavelength range 400-500 nm with peak values at about 468 and 480 nm, depending on the monomer formulation, and it has an irradiance at up to 2,000 mW/cm 2 [21][22][23][24].…”

“…For camphorquinone-based resins, the activation emits a blue light in the wavelength range 400-500 nm with peak values at about 468 and 480 nm, depending on the monomer formulation, and it has an irradiance at up to 2,000 mW/cm 2 [21][22][23][24]. Furthermore, the argon ion laser has certain characteristics, such as low beam divergence, collimation, monochromaticity, coherency, absorption selectivity and fiber delivery ability, that make it particularly suitable for clinical use to cure resinous materials with a greater degree of cure and improved physical and mechanical properties [22,23,25].…”

“…Furthermore, the argon ion laser has certain characteristics, such as low beam divergence, collimation, monochromaticity, coherency, absorption selectivity and fiber delivery ability, that make it particularly suitable for clinical use to cure resinous materials with a greater degree of cure and improved physical and mechanical properties [22,23,25]. Although these laser units may accelerate the cure of composites, they can promote a temperature increase at the light-curing tip [21].…”