Physical–mechanical evaluation of a microhybrid and a nanofilled composite light activated by quartz-halogen tungsten and light-emitting diode

Abstract

The aim of this study was to characterize organic and disperse phase of a microhybrid (Mh – Filtek Z250) and a nanofilled (Nf – Filtek Z350) dental composite and analyze the influence of two LCUs (QHT-quartz-halogen tungsten and LED – light-emitting diode) on its physical–mechanical properties (degree of conversion, polymerization shrinkage, Vickers hardness and diametral tensile strength). Surface morphology was studied by scanning electron microscopy. The disperse phase content was measured using thermogravimetric analysis (TGA) and the organic fractions were qualitatively analyzed by nuclear magnetic resonance spectroscopy. Physical–mechanical properties were analyzed varying dental composite and LCU: Mh-QHT, Nf-QHT, Mh-LED and Nf-LED. The degree of conversion was evaluated using Raman spectrophotometry and polymerization shrinkage was measured by water picnometry. Mechanical behavior was analyzed by Vickers microhardness and diametral tensile testing. Scanning electron microscopy analysis showed similar microstructure of the materials mainly composed with different-sized particles dispersed within methacrylate matrix. Thermogravimetric analysis shows 80.13% of inorganic fraction for microhybrid composite and 75.29% for nanofilled. Nuclear magnetic resonance analysis showed similar organic structure for composites and did not show the presence of the monomer TEGDMA. Different light sources did not influence the tested properties, but considering different composites, nanofilled showed the highest degree of conversion (Gr 2:77%, Gr 4: 79.4%). The study shows that when the optimum radiant exposure (24 J/cm2) was used for polymerization of composites, regardless of the polymerization source, the properties of these resin materials showed satisfactory and similar results in relation to the conversion of polymers, polymerization shrinkage and mechanical behavior.