Biaxial flexural strength and modulus of filled and unfilled adhesives

Objectives: The purpose of this study was to evaluate the effects of filler addition and storage conditions on the biaxial flexural strength and modulus of adhesive systems. Methods: The adhesive systems were classified as either unfilled (One Step (OS – Bisco Inc.)) or filled (One Step Plus (OP – Bisco Inc.)). Forty resin discs of each product (0.6 mm thick and 6.2 mm in diameter) were prepared in Teflon molds (n=10). The adhesive solutions were light-activated with XL 3000 curing unit (3M ESPE). The discs were stored dry (D), in water (W), in ethanol (E) or in mineral oil (O) in the dark for 3 months before biaxial flexure testing in a universal testing machine (1.27 mm/min - Instron 5844). Data were statistically analyzed by three-way ANOVA and Tukey's post-hoc test at a pre-set alpha of 0.05. Results: The flexural strength means (MPa) (SD) were: OS/D: 158(31), OS/W: 78(16), OS/E: 44(11), OS/O: 203(81), OP/D: 159(60), OP/W: 81(20), OP/E: 38(12), OP/O: 158(48). The modulus means (MPa) (SD) were: OS/D: 2325(455), OS/W: 1487(408), OS/E: 628(192), OS/O: 2621(456), OP/D: 1942(539), OP/W: 1621(277), OP/E: 458(149), OP/O: 2038(288). Water- and ethanol-storage significantly decreased the flexural strength and modulus for both adhesive systems. The presence of filler in the composition of adhesive system did not change the flexural strength and modulus. Conclusions: Storage in water and in ethanol reduced the flexural strength and modulus for OS and OP adhesives; however, ethanol-storage resulted in the lowest values. Commercial unfilled and filled adhesive systems exhibited similar flexural strength and modulus in the same storage media.

Supported by FAPESP (#06/57998-0) and FAEPEX-UNICAMP (#396/07).