Bis-GMA co-polymerizations: Influence on conversion,flexural properties,fracture toughness and susceptibility to ethanol degradation of experimental composites

ObjectivesThe aim of this study was to evaluate the influence of monomer content on fracture toughness (K_Ic) before and after ethanol solution storage, flexural properties and degree of conversion (DC) of bisphenol A glycidyl methacrylate (Bis-GMA) co-polymers.MethodsFive formulations were tested, containing Bis-GMA (B) combined with TEGDMA (T), UDMA (U) or Bis-EMA (E), as follows (in mol%): 30B:70T; 30B:35T:35U; 30B:70U; 30B:35T:35E; 30B:70E. Bimodal filler was introduced at 80 wt%. Single-edge notched beams for fracture toughness (FT, 25 mm × 5 mm × 2.5 mm, a/w = 0.5, n = 20) and 10 mm × 2 mm × 1 mm beams for flexural strength (FS) and modulus (FM) determination (10 mm × 2 mm × 1 mm, n = 10) were built and then stored in distilled water for 24 h at 37 °C. All FS/FM beams and half of the FT specimens were immediately submitted to three-point bending test. The remaining FT specimens were stored in a 75%ethanol/25%water (v/v) solution for 3 months prior to testing. DC was determined with FT-Raman spectroscopy in fragments of both FT and FS/FM specimens at 24 h. Data were submitted to one-way ANOVA/Tukey test (α = 5%).ResultsThe 30B:70T composite presented the highest K_Ic value (in MPa m^1/2) at 24 h (1.3 ± 0.4), statistically similar to 30B:35T:35U and 30B:70U, while 30B:70E presented the lowest value (0.5 ± 0.1). After ethanol storage, reductions in K_Ic ranged from 33 to 72%. The 30B:70E material presented the lowest reduction in FT and 30B:70U, the highest. DC was similar among groups (69–73%), except for 30B:70U (52 ± 4%, p < 0.001). 30B:70U and 30B:35T:35U presented the highest FS (125 ± 21 and 122 ± 14 MPa, respectively), statistically different from 30B:70T or 30B:70E (92 ± 20 and 94 ± 16 MPa, respectively). Composites containing UDMA or Bis-EMA associated with Bis-GMA presented similar FM, statistically lower than 30B:35T:35U.SignificanceComposites formulated with Bis-GMA:TEGDMA:UDMA presented the best compromise between conversion and mechanical properties.