Influence of energy density of different light sources on knoop hardness of a dual-cured resin cement

Abstract

The purpose of this study was to evaluate the Knoop hardness of a dual-cured resin-based luting cement irradiated with different light sources as well energy density through a ceramic sample. Three light-curing unit (LCUs) were tested: tungsten halogen light (HAL), light-emitting diode (LED) and xenon plasma-arc (PAC) lamp. Disc-shaped specimens were fabricated from a resin-based cement (Enforce). Three energy doses were used by modifying the irradiance (I) of each LCU and the irradiation time (T): 24 Jcm-2 (I/2x2T), 24 Jcm-2 (IxT) and 48 Jcm-2 (Ix2T). Energy doses were applied through a 2.0-mm-thick ceramic sample (Duceram Plus). Three groups underwent direct irradiation over the resin cement with the different LCUs and a chemically-activated group served as a control. Thirteen groups were tested (n=10). Knoop hardness number (KHN) means were obtained from cross-sectional areas. Two-way ANOVA and the Holm-Sidak method were used for statistical comparisons of activation mode and energy doses (α=5%). Application of 48 J.cm-2 energy dose through the ceramic using LED (50.5±2.8) and HAL (50.9±3.7) produced significantly higher KHN means (p<0.05) than the control (44.7±3.8). LED showed statistically similar performance to HAL. Only HAL showed a relationship between the increase of LCU energy dose and hardness increase.

Effect of High-Irradiance Light-Curing on Micromechanical Properties of Resin Cements

“…This finding corroborates numerous previous studies on degree of conversion and mechanical properties of not only light-cured, resin-based materials [1–7], but also of dual-curing resin cements [17, 19, 20]. The fact that the dual-curing resin cements reacted similarly to purely light-curing, flowable resin composite reflects that most dual-curing resin cements rely to a large extent on effective light-curing [10, 16, 17, 21].…”

“…Overall, there was a linear correlation between radiant exposure and H V or E IT . Thus the “exposure reciprocity law” or “total energy principle” was generally corroborated, dictating that, at a certain radiant exposure, all combinations of irradiance and exposure duration result in comparable material properties, for example, degree of double bond conversion [2, 3, 25, 26], hardness [19, 23, 27], and modulus of elasticity [3, 28, 29]. Despite the general, significant correlation between radiant exposure and micromechanical properties and due to the significant interaction found between resin-based material and irradiation protocol, variation in the light-curing mode did not have the same impact on all four materials.…”

Color stability, opacity and degree of conversion of pre-heated composites

“…In order to increase the longevity of restorations, new composites and the use of novel techniques for application of these materials are currently being investigated to allow for the development of new types of monomers, 21 load particles of different sizes and configurations, 22 improvement of adhesive systems, 23 and refinement of photoactivation. 24 Nanocomposites comprise a class of materials with nanoscale inorganic fillers finely dispersed within the resinous matrix. 25 In comparison with microfilled composites, these materials have been reported to exhibit improved properties, such as elasticity modulus, mechanical strength, heat resistance and color stability.…”

Water interaction with dental luting cements by means of sorption and solubility

“…Since polymerization of light-cured or dual-cured luting cements commonly implies in an interposition of the tooth structure or the restoration material between the cement and the light-activation unit tip, this study was conducted using an usual ceramic material disk in order to reproduce a clinical situation [23,24].…”