Thursday, April 12, 2012

In vitro comparison of mechanical properties and degree of cure of bulk fill composites

DOI: 10.1007/s00784-012-0702-8

Abstract


Objectives  

The aim of our study was to measure and compare degree of conversion (DC) as well as micro- (indentation modulus, E; Vickers hardness, HV) and macromechanical properties (flexural strength, σ; flexural modulus, E flexural) of two recently launched bulk fill resin-based composites (RBCs): Surefil® SDR™ flow (SF) and Venus® bulk fill (VB).

Materials and methods  

DC (n = 6) was investigated by Fourier transform infrared spectroscopy (FTIR) in clinical relevant filling depths (0.1, 2, and 4 mm; 6 mm bulk, 6 mm incremental) and irradiation times (10, 20, 40 s). Micro- (n = 6) and macromechanical (n  = 20) properties were measured by an automatic microhardness indenter and a three-point bending test device after storing the specimens in distilled water for 24 h at 37°C. Furthermore, on the 6-mm bulk samples, the depth of cure was determined. A field emission scanning electron microscope was used to assess filler size. Results were evaluated using one-way analysis of variance, Tukey’s honest significance test post hoc test, a multivariate analysis (α = 0.05) and an independent t test. Weibull analysis was used to assess σ.

Results  

VB showed, in all depth, significant higher DC (VB, 62.4–67.4 %; SF, 57.1–61.9 %), but significant lower macro- (VB, E flexural = 3.6 GPa; σ = 122.7 MPa; SF, E flexural = 5.0 GPa; σ = 131.8 MPa) and micromechanical properties (VB, E = 7.3–8.8 GPa, HV = 40.7–46.5 N/mm²; SF, E = 10.6–12.2 GPa, HV = 55.1–61.1 N/mm²). Both RBCs showed high reliability (VB, m = 21.6; SF, m = 26.7) and a depth of cure of at least 6 mm at all polymerization times. The factor “RBC” showed the strongest influence on the measured properties (η 2 = 0.35–0.80) followed by “measuring depth” (η 2 = 0.10–0.46) and “polymerization time” (η 2 = 0.03–0.12).

Conclusions  

Significant differences between both RBCs were found for DC, E, σ, and E flexural at all irradiation times and measuring depths.

Clinical relevance  

Curing the RBCs in 4-mm bulks for 20 s can be recommended.

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