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Objectives Verify the influence of different filler distributions on the subcritical crack growth (SCG) susceptibility, Weibull parameters ( m and σ 0 ) and longevity estimated by the strength–probability–time (SPT) diagram of experimental resin composites. Methods Four composites were prepared, each one containing 59 vol% of glass powder with different filler sizes ( d 50 = 0.5; 0.9; 1.2 and 1.9 μm) and distributions. Granulometric analyses of glass powders were done by a laser diffraction particle size analyzer (Sald-7001, Shimadzu, USA). SCG parameters ( n and σ f0 ) were determined by dynamic fatigue (10 −2 to 10 2 MPa/s) using a biaxial flexural device (12 × 1.2 mm; n = 10). Twenty extra specimens of each composite were tested at 10 0 MPa/s to determine m and σ 0 . Specimens were stored in water at 37 °C for 24 h. Fracture surfaces were analyzed under SEM. Results In general, the composites with broader filler distribution (C0.5 and C1.9) presented better results in terms of SCG susceptibility and longevity. C0.5 and C1.9 presented higher n values (respectively, 31.2 ± 6.2 a and 34.7 ± 7.4 a ). C1.2 (166.42 ± 0.01 a ) showed the highest and C0.5 (158.40 ± 0.02 d ) the lowest σ f0 value (in MPa). Weibull parameters did not vary significantly ( m : 6.6 to 10.6 and σ 0 :170.6 to 176.4 MPa). Predicted reductions in failure stress ( P f = 5%) for a lifetime of 10 years were approximately 45% for C0.5 and C1.9 and 65% for C0.9 and C1.2. Crack propagation occurred through the polymeric matrix around the fillers and all the fracture surfaces showed brittle fracture features. Significance Composites with broader granulometric distribution showed higher resistance to SCG and, consequently, higher longevity in vitro.

Objectives The aim of this study was to determine the Weibull and slow crack growth (SCG) parameters of bulk-fill resin based composites. The strength degradation over time of the materials was also assessed by strength-probability-time (SPT) analysis. Methods Three bulk-fill [Tetric EvoCeram Bulk Fill (TBF); X-tra fil (XTR); Filtek Bulk-fill flowable (BFL)] and a conventional one [Filtek Z250 (Z250)] were studied. Seventy five disk-shaped specimens (12 mm in diameter and 1 mm thick) were prepared by inserting the uncured composites in a stainless steel split mold followed by photoactivation (1200 mW/cm 2 /20 s) and storage in distilled water (37 °C/24 h). Degree of conversion was evaluated in five specimens by analysis of FT-IR spectra obtained in the mid-IR region. The SCG parameters n (stress corrosion susceptibility coefficient) and σ f0 (scaling parameter) were obtained by testing ten specimens in each of the five stress rates: 10 −2 , 10 −1 , 10 0 , 10 1 and 10 2 MPa/s using a piston-on-three-balls device. Weibull parameter m (Weibull modulus) and σ f0 (characteristic strength) were obtained by testing additional 20 specimens at 1 MPa/s. Strength–probability–time (SPT) diagrams were constructed by merging SCG and Weibull parameters. Results BFL and TBF presented higher n values, respectively (40.1 and 25.5). Z250 showed the highest (157.02 MPa) and TBF the lowest (110.90 MPa) σ f0 value. Weibull analysis showed m (Weibull modulus) of 9.7, 8.6, 9.7 and 8.9 for TBF, BFL, XTR and Z250, respectively. SPT diagram for 5% probability of failure showed strength decrease of 18% for BFL, 25% for TBF, 32% for XTR and 36% for Z250, respectively, after 5 years as compared to 1 year. Significance The reliability and decadence of strength over time for bulk-fill resin composites studied are, at least, comparable to conventional composites. BFL shows the highest fatigue resistance under all simulations followed by TBF, while XTR was at par with Z250.

This study evaluated the effect of the combination of two dimethacrylate-based monomers [bisphenol A diglycidyl dimethacrylate (BisGMA) or bisphenol A ethoxylated dimethacrylate (BisEMA)] with diluents either derived from ethylene glycol dimethacrylate (ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate) or 1,10-decanediol dimethacrylate (D3MA) on network characteristics and mechanical properties of neat resin and composite materials. The degree of conversion, maximum rate of polymerization and water sorption/solubility of unfilled resins and the flexural strength and microhardness of composites (after 24 h storage in water and 3 months storage in a 75 vol% ethanol aqueous solution) were evaluated. Data were analyzed with two-way ANOVA and Tukey’s test (α = 0.05). The higher conversion and lower water sorption presented by BisEMA co-polymers resulted in greater resistance to degradation in ethanol compared with BisGMA-based materials. In general, conversion and mechanical properties were optimized with the use of long-chain dimethacrylate derivatives of ethylene glycol. D3MA rendered more hydrophobic materials, but with relatively low conversion and mechanical properties.