Dentin matrix metalloproteinases (MMPs) are involved in collagen degradation of resin-dentin interfaces. This study evaluated if collagen degradation can be prevented by chlorhexidine after different dentin demineralization procedures. Human dentin demineralization was performed with phosphoric acid (PA), EDTA, or acidic monomers (ClearfilSEBond and XENOV). Specimens were stored (24 h, 1 wk or 3 wk) in the presence or absence of chlorhexidine. In half of the groups, active MMP-2 was incorporated into the storing solution. C-terminal telopeptide determination (ICTP) was performed in the supernatants. Collagen degradation was higher in PA and EDTA-demineralized dentin. Chlorhexidine reduced collagen degradation in these groups only for 24 h. When dentin was demineralized with SEBond or Xeno, collagen degradation was reduced up to 30%, but addition of exogenous MMP-2 significantly increased collagen degradation. In self-etchant treated dentin the inhibitory effect of chlorhexidine on MMPs lasted up to 3 wk. Treating dentin with EDTA, PA or self-etching agents produces enough demineralization to permit cleavage of the exposed collagen. Monomers infiltration may exert protection on demineralized collagen, probably through immobilization of MMPs. The partial inhibitory action of CHX on MMP activity produced by self-etching adhesives was prolonged compared to the short-acting in PA or EDTA-treated dentin.

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The aim of the study was to ascertain whether the addition of zinc to adhesives may decrease metalloproteinase-mediated collagen degradation without affecting bonding efficacy. Human dentin beams were treated with phosphoric acid, with Clearfil SE Bond Primer or with Clearfil SE Bond Primer plus ZnCl(2) (2 wt%). Acid-etched dentin was infiltrated with Single Bond, Single Bond plus ZnCl(2) (2 wt%), or Single Bond plus ZnO nanoparticles (10 wt%), and Clearfil SE Bond-primed dentin was infiltrated with Clearfil SE Bonding resin, Clearfil SE-Bonding resin with ZnCl(2) (2 wt%), or Clearfil SE-Bonding resin with ZnO nanoparticles (10 wt%). The C-terminal telopeptide concentrations were determined 24 h, and 1 and 4 wk after treatment. Microtensile bond strength to dentin was determined for the tested adhesives. Matrix metalloproteinases-mediated collagen degradation occurred in acid-etched and SE-primed dentin. Resin infiltration decreased collagen degradation. Lower collagen degradation was found for SE Bond than for Single Bond. Zinc-doped Single Bond resin always reduced collagen degradation, the ZnO particles being more effective than ZnCl(2) . Zinc-doped SE Bond reduced the liberation of C-terminal telopeptide only at 24 h. Bond strength to dentin was not decreased when Zn-doped resins were employed, except when ZnCl(2) was added to SE Primer. Zinc-doped resin reduced collagen degradation in Single Bond hybrid layers, but did not affect bond strength. The addition of zinc to SE Bond had no beneficial effects.