Irradiance effects on the mechanical properties of universal hybrid and flowable hybrid resin composites

Objectives. A potential problem with high-intensity lights might be failure of polymer chains to grow and cross-link in a desired fashion, thereby affecting the structure and properties of the polymers formed. The purpose of this study was to evaluate mechanical properties of resin composites polymerized using four different light-curing units. Methods. A conventional quartz–tungsten–halogen (QTH) light, a soft-start light, an argon-ion laser, and a plasma-arc curing light were used to polymerize disk-shaped (9.0 mm diameter×1.0 mm high) and cylinder-shaped (4 mm diameter×8 mm high) specimens of a universal hybrid and a flowable hybrid composite. Biaxial flexure strength, fracture toughness, hardness, compressive strength, and diametral tensile strength were determined for each composite. Results. The use of the plasma-arc curing light, a high-intensity light, resulted in significantly lower hardness for the universal hybrid composite compared with the hardness obtained using the conventional QTH and the soft-start units. Hardness was the only mechanical property that was adversely affected by the use of a high-intensity light. Significance. High-intensity lights might affect some resin composite mechanical properties, but this effect cannot be generalized to all resin composites and all properties.