Effect of two lasers on the polymerization of composite resins: single vs combination.

Abstract

The selection of a light-curing unit for the curing composite resins is important to achieve best outcomes. The purpose of the present study was to test lasers of 457 and 473nm alone or in combination under different light conditions with respect to the cure of composite resins. Four different composite resins were light cured using five different laser combinations (530mW/cm(2) 457nm only, 530mW/cm(2) 473nm only, 177mW/cm(2) 457 + 177mW/cm(2) 473nm, 265mW/cm(2) 457 + 265mW/cm(2) 473nm, and 354mW/cm(2) 457 + 354mW/cm(2) 473nm). Microhardness and polymerization shrinkage were evaluated. A light-emitting diode (LED) unit was used for comparison purposes. On top surfaces, after aging for 24h, microhardness achieved using the LED unit and the lasers with different conditions ranged 42.4-65.5 and 38.9-67.7Hv, respectively, and on bottom surfaces, corresponding ranges were 25.2-56.1 and 18.5-55.7Hv, respectively. Of the conditions used, 354mW/cm(2) 457nm + 354mW/cm(2) 473nm produced the highest bottom microhardness (33.8-55.6Hv). On top and bottom surfaces, microhardness by the lowest total light intensity, 354 (177 × 2) mW/cm(2), ranged 39.0-60.5 and 18.5-52.8Hv, respectively. Generally, 530mW/cm(2) at 457nm produced the lowest polymerization shrinkage. However, shrinkage values obtained using all five laser conditions were similar. The study shows the lasers of 457 and 473nm are useful for curing composite resins alone or in combination at much lower light intensities than the LED unit.