EFFECTS OF FOOD ORAL SIMULATING FLUIDS ON MICROSTRUCTURE AND STRENGTHOF DENTIN BONDING AGENTS/

This Study evaluated the effect a food simulating solution, 75% v/v et hanol/water, and an artificial saliva, Moi-Stir, have on the microstru cture and on the diametral tensile strength (DTS) of three dentine bon ding agents (Tenure, Scotchbond Multi-Purpose and Optibond). The micro structure was examined by using a scanning electron microscope (SEM). The DTS data were analysed using ANOVA and the Tukey LSD test. The mic rostructural observations were compared with changes in DTS. The SEM o bservation revealed deterioration of all bonding agents due to conditi oning in the solutions for 30 days. The different solutions appeared t o cause different reactions in the bonding agents. However, these effe cts may be exaggerated due to the presence of an air-inhibited surface layer. Those conditioned in Moi-Stir showed swelling. The presence of filler particles in the Optibond bonding agent appears to decrease th e deterioration resulting from soaking. Materials conditioned in ethan ol exhibited both dissolution and thinning. Diametral samples of each bonding material were tested after being conditioned in the above-ment ioned solutions for 1, 7, 14 and 30 days. Conditioning significantly d ecreased the DTS of all bonding agents, except Optibond in Moi-Stir. F illed Optibond maintained its DTS longer than did the two unfilled bon ding agents. The decrease in DTS of all the ethanol-conditioned groups is a function of the square root of time (P < 0.001) and conforms to Fick's laws of diffusion. The filled Optibond showed a lower ethanol d iffusivity (0.5 x 10(-5) cm(2) s(-1)) than the other two unfilled bond ing agent systems (average 1 2 x 10(-5) cm(2) s(-1)) (P < 0.05). The h igh ethanol diffusivities were thought to be due to the presence of HE MA, a hydrophilic resin, in the bonding agent. These results also sugg est that solution uptake occurred through the resin matrix. Filler par ticles may therefore play an important role in weathering resistance o f these materials to oral environment solutions. The physical appearan ce and strength of dentine bonding agents are significantly altered by exposure to oral environment solutions.