Stiffness effect of using polywave or monowave LED units for photo-curing different bulk fill composites

We investigated three bulk fill composites (Mat1, Mat2, Mat3) cured by two polywave (Poly1, Poly2) and one monowave (Mono) lamps. We used infrared spectroscopy, nanoindentation and atomic force microscopy to assess degree of conversion (DC), stiffness, and roughness after polishing, respectively. Mat2 exhibited the highest DC with Poly1 and second highest with Mono, however was the less stiff. Both Mat1 and Mat3 showed highest DC with Poly2, while Poly1 scored better than Mono. Mat3 scored better than Mat1 and was the third highest when cured with Poly2. For each composite cured by different lamps the stiffness ranked same as the DC. However, roughness did not correlate with hardness. Absolute stiffness value depends on composite formulation. Polywave lamps work better than monowave but not in all cases, as Mat2 showed higher DC with Mono than with Poly2. However, all lamps guarantee a DC≥50% but Mono for Mat1.