Macro-, micro- and nano-mechanical investigations on silorane and methacrylate-based composites.

OBJECTIVES: Cationic ring-opening monomers with a reduced shrinkage stress--silorane--are being used as matrix resins for recently introduced dental composites. Since shrinkage and mechanical properties are generally opposite properties, our study aimed to analyze the mechanical behavior of the silorane-based composite in comparison to six homologous clinical successful methacrylate-based composites.
METHODS: Mechanical properties were determined at macro- (strength and modulus of elasticity), micro- (hardness, modulus of elasticity and creep) and nano-scale (nano-dynamic-mechanical parameters: complex, storage, loss modulus and tandelta) after storing the materials for 24 h in distilled water as well as after aging (thermocycling and storing for 4 weeks in water, saliva or alcohol).
RESULTS: The strongest influence on the mechanical properties at macroscopic scale was exerted by the storage media although the influence of the material was also significant. At micro- and nano-scale, the material itself influenced the mechanical properties stronger than the storage. By comparing the four storage conditions, a multivariate analysis revealed a significant decrease in all measured mechanical properties by storing for 4 weeks in water, saliva or alcohol, when compared to the 24 h storage. The strongest effect was exerted through the alcohol storage, whereas the effect of storing for 4 weeks in water or saliva was comparable. The nano-composites were more degraded by a 4-week storage in water and saliva than the micro-hydrids, whereas the effect of storing in alcohol was material depended. The tested silorane-based composite revealed good mechanical properties. The material was very stable in all applied solvents and more reliable by storing in alcohol solutions than the measured methacrylate-based composites. SIGNIFICANCE: From the point of view of the mechanical properties measured at macro-, micro- and nano-scale, the silorane-based composite was comparable to clinically successful methacrylate-based composite materials, encouraging the clinical use of the new composite material.