Abstract
ObjectiveThis study evaluated the surface hardness of a resin cement (RelyX ARC) photoactivated through indirect composite resin (Cristobal) disks of different thicknesses using either a light-emitting diode (LED) or quartz tungsten halogen (QTH) light source.Material and MethodsEighteen resin cement specimens were prepared and divided into 6 groups according to the type of curing unit and the thickness of resin disks interposed between the cement surface and light source. Three indentations (50 g for 15 s) were performed on the top and bottom surface of each specimen and a mean Vickers hardness number (VHN) was calculated for each specimen. The data were analyzed using two-way ANOVA and Tukey-Kramer test was used for post-hoc pairwise comparisons.ResultsIncreased indirect resin disk thickness resulted in decreased mean VHN values. Mean VHN values for the top surfaces of the resin cement specimens ranged from 23.2 to 46.1 (QTH) and 32.3 to 41.7 (LED). The LED curing light source produced higher hardness values compared to the QTH light source for 2- and 3-mm-thick indirect resin disks. The differences were clinically, but not statistically significant. Increased indirect resin disk thickness also resulted in decreased mean VHN values for the bottom surfaces of the resin cement: 5.8 to 19.1 (QTH) and 7.5 to 32.0 (LED). For the bottom surfaces, a statistically significant interaction was also found between the type of curing light source and the indirect resin disk thickness.ConclusionsMean surface hardness values of resin cement specimens decreased with the increase of indirect resin disk thickness. The LED curing light source generally produced higher surface hardness values.
Highlights
Due to their excellent esthetic and superior mechanical properties, resin cements are considered the material of choice to be used with metal-free restorations10
For both types of curing light sources, the mean Vickers hardness number (VHN) values for the top surface of the resin cement specimens decreased as the indirect resin disk thickness increased
The VHN of the top surface of the resin cement was 22.5% lower when a 3mm-thick indirect resin disk was used compared to when a 1-mm-thick indirect resin disk was used for the light-emitting diode (LED) unit, and 49.7% lower for the quartz tungsten halogen (QTH) light source
Summary
Due to their excellent esthetic and superior mechanical properties, resin cements are considered the material of choice to be used with metal-free restorations. The mechanical properties and biocompatibility of resin cements are directly related to the degree of monomer conversion. Several studies have demonstrated that the degree of monomer conversion determines the surface hardness and wear resistance of the resin materials. The amount or degree of conversion of the resin cement may vary, especially with bulky restorations thereby compromising the retention of the crown or inlay restoration. If a photo-cured or dual cured resin material does not receive a sufficient number of photons at the correct wavelength, the amount of polymerization and degree of conversion will be inadequate. Other studies have reported an inverse relationship between the thickness of ceramic inlays and the surface hardness of light-cured and dual cured resin cements
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