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Effect of intrinsic and extrinsic moisture on bond strength to dentine
1Department of Conservative Dentistry, Periodontology and Pedodontics, University of Ulm, Ulm, Germany. karl-heinz.moll@medizin.uni-ulm.de
Objectives:
The aim of this in vitro study was to investigate the effects of simulated pulpal pressure (PP) and moist bonding (MB) on the shear bond strength of three different dentine bonding systems (DBSs).
Methods:
Dentine surfaces were exposed on 120 extracted human molars and bonded with one out of three restorative systems (A. R.T. Bond/Brilliant, OptiBond FL/Herculite XRV, Scotchbond 1/Z100). In one-half of the specimens, the DBSs were applied under hydrostatic pulpal pressure of 30 cm H2O (PP). Forty specimens were prepared for each DBS according to the following experimental groups (each n=10): no PP/no MB; with PP/no MB; no PP/with MB; with PP/with MB. Shear bond strengths after 24 h were measured in a universal testing machine (Zwicki 1120) and statistically analysed by 2-way ANOVA. Fractured surfaces were investigated for the type of failure under an optical stereomicroscope and by SEM.
Results:
In all DBSs, pulpal pressure resulted in a decrease of dentinal bond strength. This effect was significant in A.R.T. Bond and OptiBond FL (P<0.001), but not in Scotchbond 1 (P=0.060). Moist bonding significantly increased the bond strength of Scotchbond 1 (P<0.001), significantly decreased the bond strength of A.R.T. Bond (P=0.032), but had no effect in the case of OptiBond FL (P=0.691). In A.R.T. Bond, the combination of hydrostatic pulpal pressure and moist bonding resulted in complete failure of most of the specimens prior to the debonding tests. The fracture patterns as detected by SEM fracture analyses were typical for each DBS and specific bonding condition and consistent with the results of the bond strength measurements.
Significance:
The results indicate that continuous intrinsic moisture in the form of hydrostatic pulpal pressure adversely affects the efficacy of DBSs, while limited extrinsic moisture by moist bonding is acceptable or even essential. The effect of moist bonding on the efficacy of DBSs seems to depend not only on the monomers used and the solvents per se, but also on the water content of the dentine primer and the self-priming adhesive, respectively.