Method: Composites containing (in weight) 29.4% of matrix (59.0% of BisGMA, 39.4% of TEGDMA, 0.5% of camphorquinone, 1.0% of co-initiator EDMAB and 0.1 of BHT) and 70.6% of inorganic filler (65.6% of 0.7µm-average size barium glass and 5% of silica nanoparticles) were used. Fillers were previously treated with either 1% or 3% of 3-methacryloxypropyltrimethoxysilane. Unsilanated filler was used in the control composite. Degree of conversion was obtained by NIR spectroscopy, with the evaluation of the area under the peak corresponding to the peak centered at 6165cm-1. The biaxial flexural strength (n = 10) was determined on discs (15 mm-diameter X 1 mm-thick) using a piston on three balls device attached to a universal testing machine. Fracture toughness was obtained in bars of 25.0 mm x 5.0 mm x 2.8 mm (n = 15) using the single-edge notched beam method. All the samples were stored in destilled water at 37°C for 24h before testing. Data were analyzed using 1-way ANOVA and Tukey test (α = 0.05).
Result: There was no statistically significant difference in degree of conversion among the composites (control:78.3±0.8%A, 1%: 77.4±3.3%A, 3%:77.8±4.0%A, p=0.933).The biaxial flexural strength of formulation with 3% silane (112.5±19.2 MPaA) was higher than 1% (95.2±9.3 MPaB), which was higher than the unsilanated control ( 77.9±11.4 MPaC) (p<0.001). Fracture toughness did not vary significantly between silane concentrations, and both were higher than the control (3%: 1.22±0.24A,1%:1.09±0.15A, control:0.85±0.13B, p<0.001).
Conclusion: Increasing the silane content from 1% to 3% increased the biaxial flexural strength by 18%. Fracture toughness was not significantly affected by silane content. Silane content also had no effect on composite degree of conversion.