Polymerization Shrinkage and Hardness of Three Bulk Fill Flowable Resins

Objectives: This study evaluated polymerization shrinkage and surface hardness of 3 flowable composites using the scraping method and Knoop hardness test. Methods: Three flowable composites were used: Surefil SDR, Venus Bulk Fill and Filtek Supreme Flow (control). For polymerization shrinkage 10 2mm samples were made for each composite, cured for 20 seconds and measured with a Kaman linometer. Ten specimens of each composite were made in a 10 x 10mm mold and cured for 20 seconds; the bottom surface was scraped according to ISO #4049. Hardness samples were prepared at 2, 3, 4 and 5mm thick x 14mm diameter, cured for 20 seconds and polished. After 24 hours of dry storage, Knoop hardness was conducted with 100g load for 11 seconds. Three readings were made on top and bottom of each specimen and the average was calculated. One-way ANOVA, Tukey and t-Tests were used to determine significant differences among materials. Results: Polymerization shrinkage values were 3.43±0.51, 3.57±0.63, 4.4±0.79% for Filtek, SureFil and Venus respectively, Venus being significantly greater (p<0.05). Scraping method values were significantly lower for Filtek (2.98±0.22mm) than Surefil and Venus (>5.0mm). Top hardness values at 2mm were: Venus 21.55±2.39, Filtek 44.62±1.93, and Surefil 29.17±0.76, which were similar for 3, 4 and 5 mm thicknesses within each material. Ratio for bottom/top values for 2, 3, 4 and 5mm were: Venus: 0.8±0.1, 0.78±0.03, 0.67±0.10, 0.59±0.07 respectively. Surefil; 0.74±0.08, 0.72±0.08, 0.69±0.18, 0.62±0.08 respectively. Filtek: 0.56±0.08 at 2mm, 0.40±0.08 at 3mm. The B/T ratio was .80 or less at all depths. Conclusion: Filtek had the lowest shrinkage; the highest top hardness after curing, but the lowest B/T ratio at all depths. Surefil and Venus showed similar depths of cure up to 5mm, which did not correlate well with the ISO scraping test.