Method: Different types of dental composites were chosen to test: a nanocomposite, Z350 Flowable; a hybrid composite, Z250; a packable composite, P60; and a low-shrinkage composite P90 (all from 3m/ESPE). For the static test, the composites were used to fabricate 30×5×1.5mm rectangular beam specimens. These specimens received a tensile test under six different loads after storage in artificial saliva for 30 days. Linearity of stress-strain relationship was examined, and the Poisson’s ratio was continuously measured in a half hour. For the dynamic test, 55×5×2mm rectangular beam specimens were tested immediately after curing or storage for 30days using a dynamic mechanical analyzer. The specimens were subject to a dynamic flexural loading condition with temperature increasing from 30 to 220°C. These data were used to create a master curve to observe time-dependent mechanical behaviors by the time-temperature-superposition principle (TTSP).
Result: The results of the static test represented the Poisson’s ratio nearly constant value and stress-strain shown the linear relationship under 14 MPa. For the dynamic test, the storage moduli decrease with temperature changes until the rubbery state at about 180°C, but P90 except. The modulus also decreased with the loading frequency for all resins. The orders of the storage modulus were: P60>Z250>P90>Z350 Flowable for both immediately test or stored for 30 days. The immediate test showed that Z350 Flowable, Z250, and P60 exhibited an abrupt storage modulus increase at 60°C.
Conclusion: Although the dental composites exhibit high filler contents, their matrix still dominate their mechanical behavior to be near liner viscoelasticity. The packable composites showed the highest storage modulus within the general chewing pattern. The TTSP may help to constitute the mechanical response of dental composites to temperature and dynamic loads.