It has been shown that matrix metalloproteinases (MMPs), normally present in the oral fluids, can be active during carious breakdown of the organic dentin matrix. A number probably act in concert, after periods of low pH. The objective of this investigation was to determine whether the collagenolytic MMP-8 alone might attack demineralized dentin and thereby affect the potential for remineralization. Methods: dentin specimens from freshly extracted third molars were demineralized for 14 days in vitro and then remineralized for 7 days in the presence or absence of activated MMP-8. Control specimens were exposed to varying pH levels prior to remineralization in order to reveal the presence of any dentin-bound MMP-8 activity. Following treatment the mineral level of the specimens was assessed from the outer dentinal surface using Electron Probe Micro Analysis (EPMA). The results suggest that the addition of activated MMP-8 to the remineralizing solution may lead to reduced remineralization in the surface of the dentin. There appeared to be no effect on remineralization from MMP activity arising from the dentin itself. Conclusions: it appears that, even in the absence of co-functioning enzymes, MMP-8 may negatively influence the remineralization of demineralized dentin. This should be taken into consideration when designing in vitro systems for the study of de-and remineralizing processes occurring in vivo. hakonn@odont.uio.no

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