Phosphoric acid (PA) etching used in etch-and-rinse adhesives is known to activate host-derived dentinal matrix-metalloproteinases (MMPs) and increase dentinal permeability. These two phenomena will result, respectively; in degradation of dentine-adhesive bond and leaching of some monomers especially 2-hydroxyethyl methacrylate (HEMA) into the pulp that would negatively affect the viability of pulpal cells. This study is the first to investigate the inhibitory effect of non-protein thiols (NPSH); namely reduced glutathione (GSH) and N-acetylcysteine (NAC) on dentinal MMPs and compare their effects on HEMA cytotoxicity.

Dentine powder was prepared from human teeth, demineralized with 1% PA and then treated with 2% GSH, 2% NAC or 2% chlorhexidine (CHX). Zymographic analysis of extracted proteins was performed. To evaluate the effect of GSH, NAC and CHX on HEMA cytotoxicity, solutions of these compounds were prepared with or without HEMA and rat pulpal cells were treated with the tested solutions for (6 and 24 h). Cells viability was measured by means of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cytotoxicity data were analysed by one-way ANOVA and Tukey post hoc tests (p < 0.05).

The inhibitory effect of GSH and NAC on dentinal MMPs was confirmed. GSH showed similar effectiveness to NAC regarding HEMA cytotoxicity inhibition.

NPSH were effective to inhibit dentinal MMPs and HEMA cytotoxicity.

The tested properties of NPSH provide promising clinical use of these agents which would enhance dentine-bond durability and decrease post-operative sensitivity.