The effect of rapid high-intensity light-curing on micromechanical properties of bulk-fill and conventional resin composites

Abstract

Rapid high-intensity light-curing of dental resin composites is attractive from a clinical standpoint due to the prospect of time-savings. This study compared the effect of high-intensity (3 s with 3,440 mW/cm²) and conventional (10 s with 1,340 mW/cm²) light-curing on micromechanical properties of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing. Composite specimens were prepared in clinically realistic layer thicknesses. Microhardness (MH) was measured on the top and bottom surfaces of composite specimens 24 h after light-curing (initial MH), and after subsequent immersion for 24 h in absolute ethanol (ethanol MH). Bottom/top ratio for initial MH was calculated as a measure of depth-dependent curing effectiveness, whereas ethanol/initial MH ratio was calculated as a measure of crosslinking density. High-intensity light-curing showed a complex material-dependent effect on micromechanical properties. Most of the sculptable composites showed no effect of the curing protocol on initial MH, whereas flowable composites showed 11-48% lower initial MH for high-intensity curing. Ethanol/initial MH ratios were improved by high-intensity curing in flowable composites (up to 30%) but diminished in sculptable composites (up to 15%). Due to its mixed effect on MH and crosslinking density in flowable composites, high-intensity curing should be used with caution in clinical work.

Figure 1

Schematic representation of the study design.

Figure 2

Initial microhardness (mean values ± standard deviation). Same letters denote statistically homogeneous groups within each material.

Figure 3

Plots of initial microhardness measured on top specimen surface vs. filler content (left: weight percentage; right: volume percentage) and results of Pearson correlation analysis. Error bars represent ± 1 standard deviation. Dashed lines represent statistically significant correlation functions.

Figure 4

Bottom/top ratios for initial microhardness (mean values ± standard deviation). Same letters denote statistically homogeneous groups. Dashed red line denotes the 80% bottom/top MH threshold.

Figure 5

Ratio of microhardness measured after ethanol immersion and initial microhardness (mean values ± standard deviation). Same letters denote statistically homogeneous groups within a specimen surface.