Filler Content, Surface Microhardness, and Rheological Properties of Various Flowable Resin Composites.

OBJECTIVES: The objectives of this study were to determine the filler content, the surface microhardness (at baseline and after immersion in water for 2 years), and the rheological properties of various flowable resin composites. METHODS: Three flowable resin composites (Grandioso Heavy Flow [GHF], Grandio Flow [GRF], Filtek Supreme XTE Flow [XTE]), one pit and fissure sealant resin composite (ClinPro [CLI]), and three experimental flowable resin composites with the same matrix and a variable filler content (EXPA, EXPB, EXPC) were tested. The filler content was determined by calcination. The Vickers surface microhardness was determined after polymerization and then after immersion in distilled water at 37°C for 7, 60, 180, 360, and 720 days. The rheological measurements were performed using a dynamic shear rheometer. RESULTS: The determined filler contents differed from the manufacturers' data for all the materials. The materials with the highest filler content presented the highest microhardness, but filler content did not appear to be the only influencing parameter. With respect to the values recorded after photopolymerization, the values were maintained or increased after 720 days compared with the initial microhardness values, except for GHF. For the values measured after immersion for 7 days, an increase in microhardness was observed for all the materials over time. All the materials were non-Newtonian, with shear-thinning behavior. At all the shear speeds, GRF presented a lower viscosity to GHF and XTE. CONCLUSIONS: GRF presented a low viscosity before photopolymerization, associated with high filler content, thereby providing a good compromise between spreadability and mechanical properties after photopolymerization.

High-resolution tomography study of the porosity of three restorative resin composites.

OBJECTIVES: The aim of this study was to analyze the porosity of three photopolymerizable resin composites: one high-viscous resin composite (Filtek™ P60®, 3 M™ ESPE™), one moderate-viscosity resin composite (Grandio®, VOCO™), and one low-viscous resin composite (Filtek™ Supreme XTE®, 3 M™ ESPE™). MATERIALS AND METHODS: A total of 36 cylindrical samples with a height of 2 mm and a diameter of 2 mm were prepared using PTFE molds. Eighteen cylinders were prepared by two incremental applications of 1 mm into the molds, then polymerized (group 1). For the other 18 samples (group 2), the first increment was polymerized before the second addition was made. The average porosity percentage and the average porosity volume were evaluated by high-resolution tomography (Nanotom M® - Phoenix X-Ray(TM), Wunstorf, Germany). The impact of incremental applications in terms of porosity was also evaluated. RESULTS: Irrespective of the protocol used, the low viscous material presented an average porosity percentage and an average porosity volume significantly greater than those of the other materials. Incremental application (group 2 samples) led to an increase in the average porosity percentage and volume irrespective of the material compared to the group 1 samples. CONCLUSIONS: High-resolution tomography appeared to be a particularly suitable tool for studying the porosity of resin composites. The viscosity and the handling of these materials seemed to be influential factors on their porosity. CLINICAL RELEVANCE: The presence of porosities in dental resin composites remains an objective reality, especially with low-viscous resin composites. Since the intrinsic porosity of the materials can be neither controlled nor modified by the operator, rigorous and iterative clinical protocols still remain the best way to limit inclusion of porosities in the resin composites.