Source:Dental Materials
Author(s): William Germscheid, Louis Gosse de Gorre, Braden Sullivan, Catherine O'Neill, Richard B. Price, Daniel Labrie
ObjectiveTo determine the post-curing in six commercial contemporary resin-based composites (RBCs) using axial shrinkage, the degree of conversion, and Vickers hardness.MethodsFive Bulk Fill and one conventional RBCs from three companies were selected with a wide range of filler volume content. The axial shrinkage of samples that were 1.00mm thick by 9–10mm diameter was measured using a modified bonded disk method over a time between 15h and 19h at temperatures of 26°C and 34°C (mouth temperature). The degree of conversion (DC) was collected continuously for 10min using mid-infrared spectroscopy in the attenuated total reflectance geometry. Vickers hardness was measured at 1h post-irradiation using a load of 300gf. For all three tests, the samples were irradiated at five exposure times, 20, 5, 3, 1.5 and 1s with a light curing unit radiant exitance of 1.1W/cm2. Three samples (n=3) were used for each experimental condition.ResultsAfter light exposure, the axial shrinkage and degree of conversion exhibited a functional time dependence that was proportional to the logarithm of time. This suggests an out-of-equilibrium polymer composite glass that is transitioning to thermal equilibrium. At a sufficiently long time and among the RBCs investigated, the shrinkage related physical aging rate was found to vary between 1.34 and 2.00μm/log(t). The rate was a function of the filler content. Furthermore, 15h after light exposure, the post-curing shrinkage was estimated to be an additional 22.5% relative to the shrinkage at 100s for one RBC at T=34°C. The hardness in the photo-cured RBC was varied by using different light exposure times. The first two experimental techniques show that the higher the initial DC 10min after light exposure, the smaller is the post-curing shrinkage related and DC related physical aging rates. A direct correlation was observed between the shrinkage related and the DC related physical aging rates.SignificancePost-curing shrinkage should be evaluated for longer than 1h. The post-curing shrinkage 15h after light exposure in dental RBCs can be appreciable. The long-term development of built-in stress within the tooth wall structure may shorten the restoration's lifespan.
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