Auto-degradation of collagen matrices occurs within hybrid layers created by contemporary dentin bonding systems, by the slow action of host-derived matrix metalloproteinases (MMPs). This study tested the null hypothesis that there are no differences in the activities of MMP-2 and -9 after treatment with different etch-and-rinse or self-etch adhesives. Tested adhesives were: Adper Scotchbond 1XT (3M ESPE), PQ1 (Ultradent), Peak LC (Ultradent), Optibond Solo Plus (Kerr), Prime&Bond NT (Dentsply) (all 2-step etch-and-rinse adhesives), and Adper Easy Bond (3M ESPE), Tri-S (Kuraray), and Xeno-V (Dentsply) (1-step self-etch adhesives). MMP-2 and -9 activities were quantified in adhesive-treated dentin powder by means of an activity assay and gelatin zymography. MMP-2 and MMP-9 activities were found after treatment with all of the simplified etch-and-rinse and self-etch adhesives; however, the activation was adhesive-dependent. It is concluded that all two-step etch-and-rinse and the one-step self-etch adhesives tested can activate endogenous MMP-2 and MMP-9 in human dentin. These results support the role of endogenous MMPs in the degradation of hybrid layers created by these adhesives.

Matrix metalloproteinases (MMPs) bound to dentin contribute to the progressive degradation of collagen fibrils in hybrid layers created by dentin adhesives. This study evaluated the MMP-inhibiting potential of quaternary ammonium methacrylates (QAMs), with soluble rhMMP-9 and a matrix-bound endogenous MMP model. Six different QAMs were initially screened by a rhMMP-9 colorimetric assay. For the matrix-bound endogenous MMPs, we aged demineralized dentin beams for 30 days in calcium- and zinc-containing media (CM; control), chlorhexidine, or QAMs in CM to determine the changes in dry mass loss and solubilization of collagen peptides against baseline levels. The inhibitory effects of QAMs on soluble rhMMP-9 varied between 34 and 100%. Beams incubated in CM showed a 29% decrease in dry mass (p < 0.05), whereas beams incubated with QAMs showed only 0.2%-6% loss of dry mass. Significantly more solubilized collagen was detected from beams incubated in CM (p < 0.05). It is concluded that QAMs exhibited dentin MMP inhibition comparable with that of chlorhexidine, but required higher concentrations.