Dynamic and static moduli of elasticity of resin-based materials

Objectives: The purpose of this study was to assess and compare the elastic moduli of 34 resin-based materials using a dynamic and a static method. The effect of water storage was also studied up to 6 months. Methods: Five samples of each material were prepared according to ISO-4049. The dynamic moduli were first determined non-destructively from the fundamental period of the vibrating specimen, then the static moduli were determined by a three-point bending test. The percentages of fillers by weight were determined by ashing in air at 900°C. Results: Low values were obtained with flowable composites as well as with two packable resin composites. Correlations were found between the static and the dynamic modulus of elasticity (r=0.94; p=0.0001) as well as between the weight percentage of fillers and the moduli of elasticity (r=0.82; p<0.05 for static modulus and r=0.90; p<0.05 for the dynamic modulus) both at 24 h. Water storage significantly affected both static and dynamic moduli of elasticity (ANOVA two factors; p<0.05). Significance: The low moduli of the flowable composites do not allow their use in posterior cavities under high stress. However, this does not exclude their use for minimally-invasive Class I cavities when the opposing tooth is stabilized to a large amount on the natural enamel.The Grindosonic method is very useful and simple for determining the dynamic moduli although it gives higher values than the static one. The elastic modulus evolution of resin-based materials after water storage is unpredictable since different patterns were observed as a function of time.