Impact of the distance of light curing on the degree of conversion and microhardness of a composite resin

Abstract

Objective. This study evaluated the impact of the distance between the light guide tip of the curing unit and material surface on the degree of conversion and Knoop microhardness of a composite resin. Materials and methods. Circular samples were carried out of a methacrylate micro-hybrid resin-based composite and light cured at 0, 2 and 4 mm distance. Monomer conversion rate was measured using a Fourier-transform Raman spectrometer and Knoop hardness number was obtained using a microhardness tester on the top and bottom surfaces. Data were statistically analyzed by analysis of variance and Tukey’s test (α = 0.05). Results. Overall, the increase of curing distance reduced the microhardness (p ≤ 0.05), but did not influence the carbon double bond conversion rate (p > 0.05) of the composite resin tested; and the top surface showed better properties compared to the bottom (p ≤ 0.05). Conclusions. The light curing at distance can reduce mechanical properties and could affect long-term durability of the composite restorations. Thus, the use of a curing device with high irradiance is recommended.