Zinc-Inhibited MMP-Mediated Collagen Degradation after Different Dentine Demineralization Procedures

<b><i>Background:</i></b> Dentine matrix metalloproteinases (MMPs) play an important role in the dentine caries process. <b><i>Aims:</i></b> To determine if MMP-mediated collagen degradation of acid-demineralized dentine may be inhibited by zinc or zinc chelators. <b><i>Methods:</i></b> Human dentine specimens were demineralized by phosphoric acid (PA), ethylenediaminetetraacetic acid (EDTA), Clearfil SE Bond primer (SE), or Xeno V (XE) and stored in artificial saliva. Chlorhexidine digluconate (CHX), doxycycline, EDTA, or ZnCl₂ was added. C-terminal telopeptide determinations (ICTP) were performed by radioimmunoassay after 24 h and 4 weeks. <b><i>Results:</i></b> Collagen degradation was prominent in PA-demineralized (ICTP values from 74.01 µg/l at 24 h to 202.46 µg/l after 4 weeks) and EDTA-demineralized dentine (ICTP values from 83.93 µg/l at 24 h to 158.82 µg/l after 4 weeks) stored in artificial saliva. Doxycycline fully blocked proteolysis. CHX and EDTA reduced collagen degradation only at 24 h. Zinc in excess strongly inhibited hydrolysis of collagen in all tested groups (ICTP values were: PA, 13.56 µg/l; EDTA, 11.21 µg/l; SE, 1.52 µg/l, and XE, 2.37 µg/l) and its effect was maintained for up to 4 weeks, except for EDTA-treated dentine (ICTP values were: PA, 40.76 µg/l; EDTA, 79.15 µg/l; SE, 5.29 µg/l, and XE, 6.38 µg/l). <b><i>Conclusion:</i></b> EDTA and CHX exerted time-limited MMP inhibition, and excess zinc served as an effective inhibitor of MMP-mediated collagen degradation in strong or mildly demineralized dentine. MMP degradation of collagen was reduced in resin-infiltrated dentine; the presence of excess zinc chloride exerted an additional protective effect.