Influence of light-exposure methods and depths of cavity on the microhardness of dual-cured core build-up resin composites

Abstract

ObjectiveThe purpose of this study was to evaluate the Knoop hardness number (KHN) of dual-cured core build-up resin composites (DCBRCs) at 6 depths of cavity after 3 post-irradiation times by 4 light-exposure methods. Material and MethodsFive specimens each of DCBRCs (Clearfil DC Core Plus [DCP] and Unifil Core EM [UCE]) were filled in acrylic resin blocks with a semi-cylindrical cavity and light-cured using an LED light unit (power density: 1,000 mW/cm2)at the top surface by irradiation for 20 seconds (20 s), 40 seconds (40 s), bonding agent plus 20 seconds (B+20 s), or 40 seconds plus light irradiation of both sides of each acrylic resin block for 40 seconds each (120 s). KHN was measured at depths of 0.5, 2.0, 4.0, 6.0, 8.0, and 10.0 mm at 0.5 hours, 24 hours, and 7 days post-irradiation. Statistical analysis was performed using repeated measures ANOVA and Tukey's compromise post-hoc test with a significance level of p<0.05. ResultsFor both DCBRCs, at 0.5 hours post-irradiation, the 20 s and 40 s methods showed the highest KHN at depth of 0.5 mm. The 40 s method showed significantly higher KHN than the 20 s method at all depths of cavity and post-irradiation times, except UCE at depth of 0.5 mm (p<0.05). The 120 s method did not result in significantly different KHN at all depths of cavity and post-irradiation times (p>0.05). In DCP, and not UCE, at 24 hours and 7 days post-irradiation, the B+20 s method showed significantly higher KHN at all depths of cavity, except the depth of 0.5 mm (p<0.05). ConclusionKHN depends on the light-exposure method, use of bonding agent, depth of cavity, post-irradiation time, and material brand. Based on the microhardness behavior, DCBRCs are preferably prepared by the effective exposure method, when used for a greater depth of cavity.

Bond performance of “Touch and Cure” adhesives on resin core systems

“…In these systems, dual cure (light and chemical) system was employed to avoid uncured core materials in deeper part of cavities, such as root canal 7,8) . However, there drawback is they tend not to adhere well between the adhesive and resin core material 9) . To overcome this, some systems include catalysts both in the adhesive and the core material.…”

The Effect of Touch-Cure Polymerization on the Conversion and Hardness of Core Build-Up Resin Composites: A Laboratory Study

“…For the hardness measurements, an IIT method was chosen to avoid optical and viscoelastic interferences such as the elastic recovery effect [26]. The profiles (top/bottom or cross-sectional) of the conventional hardness methods (Knoop, Vickers) initially introduced for the depth of the cure assessment in light-cured materials have been successfully employed for the testing of the self-curing capacity of dual-cured core build-up resin composites [2,5,27]. The moderate to strong correlations between the Martens hardness and the degree of conversion documented in the present experiment suggest that the differences in the Martens hardness per material can also be used as a curing indicator.…”

Influence Of Light Source And Photopolymerization Distance On Composite Resin Microhardness.

“…Esthet-X resin, which could have been explained by nanoparticle resin, which can attenuate the light spread 26 and consequently the effect of the distance it further and the light dispersion is less affected than the microhybrid resin.…”