Microhardness of Self-adhesive Resin Cement Light-polymerized Through a Restorative Material

Objectives: Measure surface microhardness of a self-adhesive resin cement light polymerized through a zirconium oxide (Lava Plus shade A2; 3M Oral Care; Germany) material in 4 different thicknesses.
Methods: Methods: A self-adhesive resin cement (RelyX Unicem 2 automix; 3M Oral Care) was mixed according to manufacturer’s recommendation and dispensed into a 200µm thick ring. A glass slide as well as a transparent film was used in both top and bottom surfaces in order to separate the cement specimen after polymerization and allow testing. Specimens were separated into 5 groups: 1- control (led directly on to specimen); 2- lava plus 0.5mm; 3- lava plus 1.5mm; 4- lava plus 2.0mm and 5- lava plus 3.0mm. An LED lcu (Elipar Deep Cure Paradigm; 3M Oral Care) was used to polymerize the specimens and set for 20 seconds of exposure following manufacture’s recommendation. Surface microhardness was measured in a microhardness tester (M-400-G2; Leco, USA). Samples were stored in 100% humidity at 36 ^○C and measured 6 times after 10 minutes (immediate) and 24 hours. Means and standard deviations were calculated. Results were analyzed with ANOVA followed by Tukey HSD test (α=0.05).
Results: Results: Means and standard deviations microhardness (HV) are shown in Table 1. There was a statistical significant decrease in surface microhardness when cement specimens were polymerized through zirconium oxide thicker than 0.5mm (p<0.05). There was no statistical significant difference in microhardness between the control group and specimens polymerized through 0.5mm zirconium oxide. Surface microhardness increased after storing samples at 36 ^○C for 24h.
Conclusions: Conclusions: Within the limitations of this study, results determined that the energy delivered at cement specimens decreased when a zirconium oxide material was used in different thicknesses. Immediate Vickers hardness (HV) of light-polymerized specimens decreased with increasing thickness of the zirconium oxide material tested. Surface microhardness increased after storage at 36 ^○C for 24h, indicating that an efficient self-curing takes place. This is crucial for a reliable clinical outcome.