The effect of load cycling on nanoleakage of deproteinized resin/dentin interfaces as a function of time.

OBJECTIVES: To evaluate the effects of cyclic loading on nanoleakage as a function of time at resin-dentin interfaces with and without removal of collagen.

METHODS: Bovine flat mid-coronal dentin received one of the following surface treatments: (1) acid-etch or (2) acid etched+5% NaOCl for 2m. The teeth were then bonded with Single Bond (3M ESPE), Scotchbond Multi-Purpose (3M ESPE), One-Step Plus (Bisco) or All-Bond 2 (Bisco) adhesive systems and restored with Z250 composite. Half of the bonded teeth were randomly assigned to receive 200,000 cycles of loading at 50 N. Teeth were sectioned into 1 mm x 1 mm thick slices and stored in distilled water for 24h and 6 months. After water storage, beams were prepared for nanoleakage evaluation and observed under the SEM. Data were statistically analyzed using three-way ANOVA and Fisher's PLSD test (p<0.05).

RESULTS: Use of NaOCl did not affect nanoleakage at the interface of all adhesive systems (p>0.05) when compared to their respective controls. After 6 months of immersion in water, except for One Step Plus, collagen-depleted groups and control groups presented similar leakage values. After cyclic loading, the deproteinized group revealed a higher degree of silver nitrate deposits when compared to the control group (p<0.05). All four adhesive systems presented a high degree of silver nitrate deposits after 6 months of water storage.

SIGNIFICANCE: The hybrid layer is important as a stress-absorbing layer and it may not represent the weak link for initiation of the nanoleakage phenomenon.