Replacement of glass particles by multidirectional short glass fibers in experimental composites: Effects on degree of conversion, mechanical properties and polymerization shrinkage

ObjectiveTo test the null hypothesis that the replacement of a small fraction of glass particles with random short glass fibers does not affect degree of conversion (DC), flexural strength (FS), fracture toughness (FT) and post-gel polymerization shrinkage (PS) of experimental composites.MethodsFour experimental photocurable composites containing 1 BisGMA:1 TEGDMA (by weight) and 60 vol% of fillers were prepared. The reinforcing phase was constituted by barium glass particles (2 μm) and 0%, 2.5%, 5.0% or 7.5% of silanated glass fibers (1.4 mm in length, 7–13 μm in diameter). DC (n = 4) was obtained using near-FTIR. FS (n = 10) was calculated via biaxial flexural test and FT (n = 10) used the “single edge notched beam” method. PS at 5 min (n = 8) was determined using the strain gage method. Data were analyzed by ANOVA/Tukey test (DC, FS, PS) or Kruskal–Wallis/Dunn's test (FT, alpha: 5% for both tests).ResultsDC was similar among groups (p > 0.05). Only the composite containing 5.0% of fibers presented lower FS than the control (p < 0.001). FT increased significantly between the control (1.3 ± 0.17 MPa m0.5) and the composites containing either 5.0% (2.7 ± 0.6 MPa m0.5) or 7.5% of fibers (2.8 ± 0.6 MPa m0.5, p < 0.001). PS in relation to control was significantly reduced at 2.5% fibers (from 0.81 ± 0.13% to 0.57 ± 0.13%) and further reduced between 5.0% and 7.5% (from 0.42 ± 0.12% to 0.23 ± 0.07%, p < 0.001).SignificanceThe replacement of a small fraction of filler particles with glass fibers significantly increased fracture toughness and reduced post-gel shrinkage of experimental composites.