The Effects of Irradiation Distances and Energy Densities on the Nanomechanical Properties of Dental Composites

This study evaluated the influence of changing light energy density, as a result of the use of different distance levels of irradiation, on the nanohardness and modulus of elasticity of four composite materials. Two nano-composites (Filtek Z-350 XT; Tetric-N-Ceram), a submicron hybrid composite (Spectrum TPH3) and a microhybrid composite (Filtek P90) were used. Eighteen composite discs were fabricated from each material and divided into three groups. Samples were light-cured at three distance levels: direct contact (44 J/cm(2)), 2 mm distance (32.8 J/cm(2)) and 4 mm distance (19.2 J/cm(2)). Samples were then subjected to nanomechanical testing by means of a Berkovich indenter probe. Although, at higher energy density, nano-based composites showed the highest nanohardness values, no significant differences among the materials were found at all three levels of distance (p > 0.05). However, all materials, except STPH3, showed significant differences in elastic modulus values between 4 mm and other levels of irradiation (p < 0.05). Therefore, moving the tip of an LED unit, with 1100 mW/cm(2), 4 mm away may affect the modulus of elasticity and, therefore, the longevity of the restorations.