Storage effect on dentine structure and on resultant composite bond strengths

This study evaluates the effects of a food simulating solution (75 vol% ethanol/water) and an artificial saliva (Moi-Stir) on dentine structure and chemistry, using scanning electron microscopic examination and Fourier transform infra-red (FTIR) microscopic characterization. The effect on the bonding of composites to the conditioned dentine were evaluated by shear bond strength (SBS) tests. Three adhesive/composite systems were examined: Tenure/Marathon One, Scotchbond Multi-Purpose/Z100, and Optibond/Herculite XRV. Control specimens were stored in either distilled water or tested without storage. Dentine surface exposure to ethanol resulted in partial loss of the smear layer and of plugs, as well as possible perturbation of collagen. Dentine surfaces exposed to artificial saliva or to distilled water had no evidence of any change from normal appearance of the smear layer. The measured FTIR spectra for most specimens conditioned in these two liquids appeared to be similar to those obtained from fresh dentine. SBS data were analysed using ANOVA and the Tukey LSD test. The SBS value for the non-preconditioned control (23.0 +/- 3.7 MPa) or for the dentine preconditioned in distilled water (22.9 +/- 4.2 MPa) was significantly higher (P < 0.05) than that for dentine pre-conditioned in ethanol (20.0 +/- 3.5 MPa). The SBS (13.3 +/- 3.4 MPa) of all bonding systems was reduced by 40-50% (P < 0.001) when artificial saliva pre-conditioned dentine was used. The failure mode at the dentine-bonding agent interface for the artificial saliva group was adhesive in nature. This is in contrast to the complex cohesive fracture mode found in the control groups and in most ethanol conditioned groups. Dentine structure and chemistry, shear bond strength, and the subsequent debonded mode can be significantly affected by exposure to oral environment prior to conditioning.