Effect of intrinsic and extrinsic moisture on bond strength to dentine

Objectives: The aim of this in vitro study was to investigate the effects o f simulated pulpal pressure (PP) and moist bonding (MB) on the shear bond s trength of three different dentine bonding systems (DBSs). Methods: Dentine surfaces were exposed on 120 extracted human molars and bonded with one ou t of three restorative systems (A.R.T. Bond/Brilliant, OptiBond FL/Herculit e XRV, Scotchbond 1/Z100). In one-half of the specimens, the DBSs were appl ied under hydrostatic pulpal pressure of 30 cm H2O (PP). Forty specimens we re prepared for each DBS according to the following experimental groups (ea ch n=10): no PP/no MB; with PP/no MB; no PP/with MB; with PP/with MB. Shear bond stengths after 24 h were measured in a universal testing machine (Zwi cki 1120) and statistically analysed by 2-way ANOVA. Fractured surfaces wer e investigated for the type of failure under an optical stereomicroscope an d by SEM. Results: Ln all DBSs, pulpal pressure resulted in a decrease of d entinal bond strength. This effect was significant in A.R.T. Bond and OptiB ond FL (P < 0.001), but not in Scotchbond 1 (P=0.060). Moist bonding signif icantly increased the bond strength of Scotchbond 1 (P < 0.001), significan tly 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 h ydrostatic pulpal pressure and moist bonding resulted in complete failure o f most of the specimens prior to the debonding tests. The fracture patterns as detected by SEM fracture analyses were typical for each DBS and specifi c bonding condition and consistent with the results of the bond strength me asurements. Significance: The results indicate that continuous intrinsic mo isture in the form of hydrostatic pulpal pressure adversely affects the eff icacy of DBSs, while limited extrinsic moisture by moist bonding is accepta ble 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 adhesi ve, respectively.