Mechanical properties of bulk fill compared to universal composites.

Abstract

Objectives: Bulk fill composites are becoming increasingly popular due to claimed facilitated placement and curing. Varying results on the mechanical properties and depth of cure have been reported, however. The aim for the present study was to compare flexural strength, E-modulus, secant modulus, Knoop hardness and depth of cure of bulk fill and universal composite materials, subjected to different storage times and artificial aging. Materials and methods: Two bulk fill (1 low and 1 high viscosity) vs. 2 universal composite resin based materials were subjected to mechanical and depth of cure testing. Evaluation was performed according to ISO4049:2009 with slight modifications regarding mould size and storage time/temperature. To simulate aging, increased storage temperature was used for additional analysis. Three groups were made of each material, 37°C (24 hours and 7 days) and 57°C (7 days). Mechanical testing was performed after assigned storage time. Micro CT was used for complimentary evaluation on 2 randomly selected samples. All data were tested for normality and analyses were performed with a 95% confidence interval. Conclusion and significance: There were significant differences in mechanical properties among the tested materials. Storage and aging affected the materials in a dissimilar manner. The low viscosity bulk fill composite evaluated showed lower moduli and hardness due to filler loading in comparison to the other materials tested, but a significant higher flexural strength and depth of cure with increased storage temperature in comparison. The increase could be explained by the monomer composition in the material. The result indicates that the term “bulk fill” seems irrelevant since it is not a discriminating factor for assessment of different mechanical properties. More relevant information concerning filler loading and monomer content should be given and assessed. Negative effects on the mechanical properties can be obtained due to voids within the materials.