Effect of conditioning solutions containing ferric chloride on dentin bond strength and collagen degradation.

OBJECTIVE: To investigate the effects of conditioning solutions containing ferric chloride (FeCl3) on resin-dentin bond strength; on protection of dentin collagen against enzymatic degradation and on cathepsin-K (CT-K) activity. METHODS: Conditioning solutions were prepared combining citric acid (CA) and anhydrous ferric chloride (FeCl3) in different concentrations. The solutions were applied to etch flat dentin surfaces followed by bonding with adhesive resin. Phosphoric acid (PA) gel etchant was used as control. The microtensile bond strength (µTBS) was tested after 24h of storage in water and after 9 months of storage in phosphate buffer saline. Dentin slabs were demineralized in 0.5M EDTA, pre-treated or not with FeCl3 and incubated with CT-K. The collagenase activity on dentin collagen matrix was examined and characterized by SEM. Additional demineralized dentin slabs were treated with the conditioning solutions, and the amount of Fe bound to collagen was determined by EDX. The activity of CT-K in the presence of FeCl3 was monitored fluorimetrically. Data were analyzed by ANOVA followed by post-hoc tests as required (α=5%). RESULTS: Slightly higher bond strengths were obtained when dentin was conditioned with 5% CA/0.6% FeCl3 and 5% CA-1.8%FeCl3 regardless of storage time. Bond strengths reduced significantly for all tested conditioners after 9 months of storage. Treating dentin with 1.8% FeCl3 was effective to preserve the structure of collagen against CT-K. EDX analysis revealed binding of Fe-ions to dentin collagen after 15s immersion of demineralized dentin slabs into FeCl3 solutions. FeCl3 at concentration of 0.08% was able to suppress CT-K activity. SIGNIFICANCE: This study shows that FeCl3 binds to collagen and offers protection against Cat-K degradation. Mixed solutions of CA and FeCl3 may be used as alternative to PA to etch dentin in resin-dentin bonding with the benefits of preventing collagen degradation.