Effects of acids and additives on the susceptibility of human dentine to denaturation

The purpose of this study was to evaluate the efficacy of a number of additives to acid conditioners at reducing the denaturation of dentine collagen. Dentine collagen is normally not very susceptible to trypsin attack. After denaturation, however, it becomes more susceptible to the action of trypsin. Slabs of human dentine were dipped in water or acidic conditioners (10% citric acid or 37% phosphoric acid) containing no additives, 5 or 10% NaCl, 3 or 6% ferric chloride or 50% hydroxyethylmethacrylate (HEMA) for 15 or 60 s, followed by rinsing. The slabs were then exposed to trypsin for 24 h to solubilize any denatured collagen. The solubilized collagen was hydrolysed to liberate hydroxyproline that was quantitated spectrophotometrically. The amount of hydroxyproline (HOP) liberated was indicative of the amount of dentine collagen that was denatured by the test solutions. The only additive that consistently reduced HOP release was 50% HEMA, and this only occurred in the 60 s exposure group. Thus, the use of salt additives to acidic conditioners has little protective effect.