Effect of a multi-layer infection control barrier on the micro-hardness of a composite resin

Objective: the aim of this study was to evaluate the effect of multiple layers of an infection control barrier on the micro-hardness of a composite resin. material and methods: one,two,four,and eight layers of an infection control barrier were used to cover the light guides of a high-power light emitting diode (led) light curing unit (lcu) and a low-power halogen lcu. the composite specimens were photopolymerized with the lcus and the barriers,and the micro-hardness of the upper and lower surfaces was measured (n=10). the hardness ratio was calculated by dividing the bottom surface hardness of the experimental groups by the irradiated surface hardness of the control groups. the data was analyzed by two-way anova and tukey's hsd test. results: the micro-hardness of the composite specimens photopolymerized with the led lcu decreased significantly in the four-and eight-layer groups of the upper surface and in the two-,four-,and eight-layer groups of the lower surface. the hardness ratio of the composite specimens was <80% in the eight-layer group. the micro-hardness of the composite specimens photopolymerized with the halogen lcu decreased significantly in the eight-layer group of the upper surface and in the two-,four-,and eight-layer groups of the lower surface. however,the hardness ratios of all the composite specimens photopolymerized with barriers were <80%. conclusions: the two-layer infection control barrier could be used on high-power lcus without decreasing the surface hardness of the composite resin. however,when using an infection control barrier on the low-power lcus,attention should be paid so as not to sacrifice the polymerization efficiency.