Correlation of filler content and elastic properties of resin-composites

Objectives The aim was to determine the Youngʹs modulus (E), bulk modulus (B), shear modulus (G) and Poissonʹs ratio (ν) of a series of composite restorative materials and to correlate them with their filler volume-fractions. Methods Twelve model resin-composite formulations, with systematically varied volume-fraction (Tokuyama), a flowable resin-composite (Point 4 flowable, Kerr) and two hybrid resin-composites (Filtek Supreme XT, 3M-Espe & X-tra Fil, Voco) were investigated. Twelve cylindrical specimens (5 mm × 6 mm) were prepared from each material. Six were free to expand radially under axial compressive loading, and were used to calculate the Youngʹs modulus (E). The other six were radially constricted in a rigid stainless steel ring during loading, from which the bulk modulus (B) was calculated. Compression loading was performed at 1 mm/min. The Youngʹs and bulk moduli were determined using equations of elasticity. Poissonʹs ratio from ν = 0.5 − (E/6B) and shear modulus from G = E/2(1 + ν). Results Youngʹs moduli ranged from 2.19 to 7.15 GPa, bulk moduli from 12.79 to 22.43 GPa and shear moduli from 0.74 to 2.47 GPa. Poissonʹs ratio ranged from 0.45 for the stiffer to 0.47 for the more compliant composites. Statistically significant differences (ANOVA and Bonferroni at p = 0.05) were found depending on filler volume-fraction. Significance Elastic moduli varied significantly and a positive correlation existed between elastic moduli and filler volume-fraction (r2: 0.905–0.992 and 0.940–1.000 for Youngʹs and bulk moduli, respectively).