Storage Time Effects on Flexural Strength and Modulus of Adhesives

Objectives: This study evaluated the biaxial flexural strengths and flexural modulus of four commercial adhesive systems (AS) (3M ESPE): one-step self-etching (Easy Bond - EB), two-step self-etching (Scotchbond SE - SE), two-step etch-&-rinse (Single Bond Plus - SB) and three-step etch-&-rinse (Scotchbond Multi-Purpose - MP) after distilled water storage. Methods: Adhesive resin discs of each product (0.5 mm thick and 6 mm in diameter) were prepared in silicon molds (n=10). The adhesive solutions were light-activated with a dental light-curing unit (Optilux 501, Demetron Research). Discs were water-stored for one week (1W), six months (6M) and one year (1Y) before testing to flexural failure (1.27 mm/min, Model 5844, Instron Corporation). Data were statistically analyzed by two-way ANOVA and Tukey's post hoc test (α=0.05). Results: The mean (SD) of flexural moduli values were (MPa): 1W/EB: 1374.6 (325.7); 1W/SE: 1850.9 (215.6); 1W/SB: 1308.2 (255.7); 1W/MP: 2132 (240.1); 6M/EB: 1358.6 (306.4); 6M/SE: 1619.9 (278); 6M/SBP: 1243.4 (379.4); 6M/MP: 2320.5 (344.8); 1Y/EB: 1574 (329.1); 1Y/SE: 1841.4 (399.4); 1Y/SB: 1670.5 (140.4); 1Y/MP: 2195 (241.5). The mean (SD) of flexural strength values were (MPa): 1W/EB: 73.07 (7.1); 1W/SE: 67.5 (15.4); 1W/SB: 58.6 (6.6); 1W/MP: 85.1 (9.3); 6M/EB: 74.4 (11.8); 6M/SE: 61.4 (21.4); 6M/SB: 59.1 (16.9); 6M/MP: 88.3 (29.2); 1Y/EB: 77.4 (6.2); 1Y/SE: 53.1 (13.5); 1Y/SB: 59.9 (3.2); 1Y/MP: 78.5 (8.1). No significant differences in flexural strength were observed among storage times for all AS. Significant statistical difference in flexural modulus was observed between 6M and 1Y only for SB. Conclusions: Water storage did not affect the flexural strength for the AS tested, while the flexural modulus was changed only for SB. (Acknowledgements: CAPES and CNPq #303587/2007-5).