Abstract
Background: Limited curing depth and its effect on the degree of conversion are among the challenges of working with light-cure composite resins. The use of bulk-fill composites is one strategy to overcome these limitations. Methods: Ever X Posterior (EXP), Filtek Bulk-Fill Posterior (FBP), Sonic Fill 2 (SF2), Tetric N-Ceram Bulk-Fill (TNB), and X-tra Fil (XF) bulk-fill and Filtek Z250 conventional composite were evaluated in this in vitro experimental study. Six samples for the assessment of microhardness and three samples for the evaluation of DC were fabricated of each composite. After light curing and polishing, the samples were incubated at 37°C for 24 hours. Microhardness was measured by a Vickers hardness tester three times and the mean value was calculated. DC of the top and bottom surfaces was determined using Fourier-Transform Infrared Spectroscopy (FTIR). Data were analyzed using one-way ANOVA and Tukey’s test. Results: Microhardness and DC were significantly different among the groups (P<0.001). XF and Z250 equally showed the highest bottom-to-top surface microhardness ratio (0.97 ± 0.01) and significantly higher DC in the top (P<0.001) and bottom (P<0.005) surfaces compared to other groups. TNB showed the lowest microhardness ratio (0.88 ± 0.04) and DC (68.66 ± 1.52 and 61.00 ± 2.00); the difference in DC of the bottom surface was statistically significant (P<0.003). Conclusion: It appears that bulk-fill composites evaluated in this study are adequately polymerized at 4 mm depth. Their DC was optimal and within the range of conventional composites.
Highlights
The application of composite resins has greatly increased due to their optimal physical, mechanical, and esthetic properties
This in vitro, experimental study was performed on composite samples fabricated of five bulk-fill composites namely Ever X Posterior (EXP), Filtek Bulk-Fill Posterior (FBP), Sonic-Fill 2 (SF2), Tetric-N-Ceram Bulk-Fill (TNB), and X-tra fil (XF) and one conventional composite namely Filtek Z250 using a mold
The null hypothesis of this study was rejected because the results showed that the bulk-fill composites tested were well polymerized at 4 mm depth and their Degree of Conversion (DC) was above the standard threshold of 55-65%
Summary
The application of composite resins has greatly increased due to their optimal physical, mechanical, and esthetic properties They still have drawbacks that limit their application [1]. Polymerization of composite resins includes conversion of carbon double bonds to carbon single bonds which determine the DC. Factors such as the size of filler particles, polymer matrix, the radiating light, its intensity, wavelength, and duration of radiation, the size of tip of device, type and amount of photo-initiators, and color of composite resins can all affect the DC and subsequently the mechanical properties, wear resistance, and color stability of composite resins [4, 6]. The use of bulk-fill composites is one strategy to overcome these limitations
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