Abstract
The aim of this in vitro study was to evaluate the hardness and shrinkage stress (SS) of six bulk-fill resin composites. To evaluate microhardness (MH), ten 6 mm specimens were prepared using a metal mold for each selected bulk-fill resin composite and irradiated from the top side for 40 s using an LED light. After 24 h of storage, Vickers MH was evaluated on the upper, lower and lateral sides of the specimens. SS evaluation was then performed with a universal machine, which evaluated the contraction force generated by a bulk-fill composite specimen placed between two metal cylinders during and after light curing. The results were evaluated with a one-way ANOVA test with a post-hoc Bonferroni test and linear regression analysis (p < 0.05). All materials showed a significant MH decrease between the top and bottom surfaces. However, the bulk-fill materials tested performed differently when considering lateral depth progression. ANOVA tests for SS evaluation showed that both SDR and Venus Bulk Fill had significantly lower stress during irradiation than other tested materials. Further, MH decrease became significantly lower from the top surface at different depths in each tested group. Among the different resins, Venus Bulk Fill and SDR showed not only inferior hardness, but also a significant reduction in SS.
Highlights
For most resin-based composite materials, incremental layering techniques have been accepted and are widely used, especially in high C-factor cavities [1,2]
ANOVA tests for SS evaluation showed that both SDR and Venus Bulk Fill had significantly lower stress during irradiation than other tested materials
The size of the indentation left by the tip was calculated with the aid of a microscope; the Vickers number (VHN) was calculated according to the following formula: specimen, 6 measurements were performed on the top and the bottom surfaces and 18 measurements were performed on the lateral surface, three for each millimeter, starting from the surface in contact with the curing light tip
Summary
For most resin-based composite materials, incremental layering techniques have been accepted and are widely used, especially in high C-factor cavities [1,2]. Previous findings [14] showed that the Young modulus, Vickers hardness, and indentation modulus classified some bulk-fill materials (SureFil SDR, Venus Bulk Fill and Filtek Bulk Fill) between hybrid and flowable composites For this reason, bulk-fill composites with increased viscosity were more recently produced to overcome the mechanical limitations and increase clinical indications. A recent study showed that bulk-fill materials, both flowable and non-flowable, resulted in a similar proportion of gap-free marginal interface when compared to a conventional composite [16]. The purpose of this in vitro study was to evaluate the hardness and SS of six bulk-fill resin composites. The null hypothesis was that (1) the decrease in hardness is not directly related to the increment thickness, and that (2) SS is not comparable among the various composites tested
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