Effect of filler-morphology on stability of composites under dynamic loading

Objectives: To investigate the effect of variation in filler particle size, morphology and wet conditioning on the viscoelastic stability of resin-composites under dynamic loading. Materials and Methods: Eight experimental light cured resin-composites (RZD series) were selected. All of them had a same matrix (BisGMA, UDMA and TEGDMA, with 0.33% camphoroquinone) and the same filler volume fraction – 56.7%. The filler particles were either spherical or irregular in shape and were either unimodal or multimodal in size-distribution. For each of the eight resin-composites, ten cylindrical specimens (4x6 mm), divided into two subgroups (n=5) were prepared from a divisible stainless steel mould. Specimens were thoroughly cured from all sides. Group 1 and 2 were loaded dynamically after 1 d of dry storage and one week of wet storage respectively. A cyclic load between 1 MPa and 50 MPa was applied for both groups at a frequency of 0.25 Hz for 30 min to obtain the “dynamic” creep strain (%). Data was analysed by univariate ANOVA and multiple pair wise comparisons: a Tukey post-hoc test was used to establish homogenous subsets (at p=0.05) for wet conditions and a post-hoc Games-Howell test was used for dry conditions. Results: Under dry conditions “mean dynamic” creep strain (%) values for unimodal and multimodal resin-composites were in the range of 1.04 to 1.98 (%) and 1.03 to 2.18 (%) respectively. Whereas, in wet conditions these values ranged from 0.93 to 2.33 (%) and 0.82 to1.42 (%) for multimodal and unimodal resin-composites respectively. Conclusions: Irregular filler shape particles in both unimodal and multimodal resin-composites were more resistant to dynamic creep under both dry and wet conditions and showed higher stiffness.