Localization of matrix metalloproteinases (MMPs-2, 8, 9 and 20) in normal and carious dentine. 
Dentine matrix metalloproteinases (MMPs) may participate in the destruction of dentine following demineralization by bacterial acids.  This study investigated the localization of MMPs in carious dentine.  Frozen sections of dentine caries were prepared without demineralization and immersed in monoclonal antibody against MMP-2, -8, -9 and -20.  The sections were labelled by IgG conjugated with gold colloidal particles, and observed under FE-SEM.  Labelling indexes (number of gold particles/mum(2)) of outer and inner carious dentine, respectively, with and without bacterial infection, were compared with that of normal dentine.  MMP-2 was distributed in both carious and normal dentine; the level of MMP-2 showed no significant difference among the outer caries, inner caries, and normal dentine.  The labelling indexes of MMP-8 and MMP-9 both significantly decreased at the inner carious dentine compared with the level of normal dentine, but intensified again at the outer caries region.  The labelling index of MMP-20 was the highest at normal dentine.  The localization of MMPs was visibly detected using immunogold labelling.  The localization of MMP-2 showed no significant difference among the three regions, while MMP-8 and MMP-9 showed significant reduction at the inner caries layer, and MMP-20 reduced toward the outer caries.