Abstract
The aim of this study was to compare three different light-curing-units (LCUs) and determine their effectiveness in the adhesive cementation of indirect composite restorations when a light-curing resin cement is used. Two resin composites were selected: Enamel Plus HRI (Micerium) and AURA (SDI). Three thicknesses (3 mm, 4 mm and 5 mm) were produced and applied as overlays and underlays for each resin composite. A standardized composite layer was placed between underlay and overlay surfaces. Light curing of the resin-based luting composites was attained through the overlay filters using LCUs for different exposure times. All specimens were allocated to experimental groups according to the overlay thickness, curing unit and curing time. Vickers Hardness (VH) notches were carried out on each specimen. Data were statistically evaluated. The curing unit, curing time and overlay thickness were significant factors capable of influencing VH values. The results showed significantly decreased VH values with increasing specimen thickness (p < 0.05). Significant differences in VH values were found amongst the LCUs for the various exposure times (p < 0.05). According to the results, a time of cure shorter than 80 s (with a conventional quartz–tungsten–halogen LCU) or shorter than 40 s (with a high-power light-emitting diode (LED) LCU) is not recommended. The only subgroup achieving clinically acceptable VH values after a short 20 s curing time included the 3 mm-thick overlays made out of the AURA composite, when the high-power LED LCU unit was used (VH 51.0). Composite thickness has an intense effect on polymerization. In clinical practice, light-cured resin cements may result in insufficient polymerization for high thickness and inadequate times. High-intensity curing lights can attain the sufficient polymerization of resin cements through overlays in a significantly shorter time than conventional halogen light.
Highlights
optimum micro-hardness (OM) values were calculated for each composite in the two control hardness on theanalysis specimen surface [16,22]
VHofvalues were statistically by the curing time, the overlay thickness deep cavityclinically is considered to be acceptable if its hardness is above 80% of the maximum considered and the light-curing units (LCUs) (p < 0.05)acceptable
Despite the limitations of the present in vitro study, it can be concluded that all three investigated light sources were efficient, but light transmission through composite overlays seems to be more efficient using a high-power LCU
Summary
Several types of resin-based luting composites (RBLCs) are currently used to bond indirect restorations. RBLCs may be classified based on their adhesive features (etch-and-rinse, self-etch and self-adhesive systems) and their polymerization initiation mode (self-curable, light-curable and dual-curable) [1]. For the placement of indirect restorations, a dual-curable RBLC is adopted to safeguard effective cement polymerization. Light-curable RBLCs have several advantages: improved handling (formulated as a single paste that does not require mixing), extended working time, simplification of surplus cement elimination procedures and, as a consequence, an easier full sitting of the restoration [2]. Light-curable RBLCs generally contain an increased amount of filler than traditional dual-cure RBLCs, enabling higher intrinsic mechanical properties [3]
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