Nanofiller loading level: influence on selected properties of an adhesive resin

Objectives: To evaluate the effect of the filler content in the cohesive strength (sigma), Weibull modulus (m) and degree of conversion (DC) of an experimental adhesive system. Methods: A HEMA/Bis-GMA/TEGDMA-based adhesive was formulated and filled with silica nanofillers in the following weight percentages (wt%): R0 = 0%; R1 = 1%; R3 = 3%; R5 = 5% and R10 = 10%. The adhesive of Adper Scotchbond Multi-Purpose (SBMP) system was used as a commercial reference. Twenty dumbbell-shaped specimens with cross-sectional area of 0.5 mm(2) were made per group and tensile tested with a crosshead speed of 0.5 mm/min until fracture. The cohesive strength was calculated in MPa. DC was obtained through FTIR after light curing for 25 s. Data were submitted to one-way ANOVA and Tukey's test (alpha = 0.05) and to Weibull analysis. Results: Mean a results were: R0 = 65.4 +/- 8.4; R1 = 73.2 +/- 8.8; R3 = 72.0 +/- 8.4; R5 = 73.1 +/- 9.7; R10 = 85.5 +/- 13.1 and SBMP = 79.0 +/- 11.0 MPa. R10 presented the highest sigma, while R0 showed the lowest. R5 and SBMP did not differ significantly (p < 0.05). Weibull analysis revealed no significant difference in structural reliability between groups. The experimental adhesives presented similar results of DC, which, in turn, were significantly higher than the SBMP. Conclusions: The addition of 10% filler in weight improves the cohesive strength of the adhesive, not interfering in the structural reliability or the degree of conversion. (C) 2009 Elsevier Ltd. All rights reserved.