Dentin matrix component solubilization by solutions of pH relevant to self-etching dental adhesives

To evaluate the potential for phosphoric acid solutions - common constituents of dental adhesive systems - of varying pH to solubilize dentin matrix components (DMCs) from human dentin.

Human dentin chips were ground under liquid nitrogen to a powder (ca 100 µm) and incubated at 4°C with agitation in phosphoric acid of pH 1, 2, 3, 4, 5, and 6 (1 g/4 ml; n = 4) for six days with solution changes each day. Estimates of daily protein release were made by UV spectrophotometry at 280 nm. Extract solutions were dialyzed for 7 days in reverse osmosis water, lyophilized, and weighed. Non-collagenous proteins (NCPs) and glycosaminoglycans (GAGs) were quantitated by dye-binding assays. 1D-PAGE for preliminary protein characterization and sandwich ELISA for presence of TGF-ß1 were performed. The results were analyzed by ANOVA and regression (α <= 0.05).

Protein release was drastically reduced after the first few days, with the highest amounts obtained from pH 1. There was no significant difference in the quantity of DMCs solubilized by the different pH levels, but there was a significant logarithmic relation between release and pH, suggesting that greater DMC solubilization occurs with higher hydrogen ion concentrations. Dye binding assays confirmed the release of NCPs and GAGs at all pH levels. There were only subtle differences in protein bands observed between the different pH levels (1D-PAGE). Significant levels of TGF-ß1 were identified from extraction at all pHs.

Acids at pH levels relevant to those used in commercial dentin adhesives are capable of solubilizing human DMCs, with release being related to hydrogen ion concentration.