Effect of food and oral simulating fluids on structure of adhesive composite systems

This work evaluates the degradation of three adhesive/composite systems (Tenure/Marathon One, Scotchbond Multi-Purpose/Z100 and Optibond/Herculite XRV) upon immersion in 75% ethanol solution and in an artificial saliva (Moi-Stir). Shear bond strength (SBS) and diametral tensile strength (DTS) specimens were employed for this study. For the SBS specimens, the bonded interface and composite were exposed to food and oral simulating fluids at 37 °C for up to 30 days. A similar control series was stored in air. DTS specimens were stored in 75% ethanol at 37 °C for up to 30 days. The SBS specimens were sheared to failure. Small quantities of bonding resin were removed from the tooth side of the fractured surface and from the non-fractured end of the composite for Fourier transform infrared microscopic evaluation. Similar scrapings were taken from DTS specimen surfaces. The infrared absorbance intensity (AI) of the major peaks was measured as a function of storage time and ratioed against the aromatic CC (1609.4 cm^-1) peak. The data were analysed using ANOVA and the Tukey LSD test. The AI of major peaks was similar for the materials stored either in air or in Moi-Stir for all testing periods. Storage in ethanol caused the AI of aliphatic CC (1638 cm^-1) and of OH (~3500 cm^-1) bonds to significantly decrease (30-50%) for specimens of bonding resin while the AI of CO bonds (1730 cm^-1) increased (60-120%). In both composite specimens, there were similar 25-45% reductions in aliphatic CC and in OH, while CO increased 50-90% after the same treatment. The decrease in aliphatic CC bonds or OH bonds correlates to increased C O groups for both bonding resins and composites (P < 0.001). The increase in CO bonds was a power function of time (i.e. (time)^x, where x varied from 0.12 to 0.23 (P < 0.001)). This suggests a complex, rate-determining process, such as hydroperoxidation or transesterification. An increase in AI (4-6 times) versus the control occurred between 1300 and 900 cm^-1. The increase was attributed to the exposure of filler material as the resin degraded.