The Role of MMP-Inhibitors on the Remineralization of Demineralized Dentin

Objective: Dentin matrices contain inactive preforms of proteolytic enzymes called matrix metalloproteinases (MMPs) that may be activated during demineralization. In this study, we tested the hypothesis that MMP-inhibitors preserve demineralized collagen fibrils and other constituents of the dentin matrix and thereby affect the potential for remineralization.

Method: Artificial carious lesions with lesion depths of 140 µm were created with 0.05 M acetatebuffer (pH=5.0, 66 hours), and remineralized using a polymer-induced-liquid-precursor (PILP) process (pH=7.4, 14 days) with CaP solution containing Poly-L-aspartate (27KDa) as the precursor inducing agent. De- and remineralizing procedures were performed in the presence or absence of MMP-inhibitors (benzamidine HCl, ɛ-amino-n-caproic acid, N-ethylmaleimide, and phenylmethylsufonyl fluoride). Ultrastructure and mechanical recovery of demineralized dentin following PILP remineralization were examined and measured in water with atomic force microscopy (AFM) and nanoindentation.

Result: AFM imaging showed the addition of MMP-inhibitors to the demineralizing solution prevented the breakdown and disintegration of dentin matrix as usually observed in the absence of MMP-inhibitors. Nanomechanical properties of hydrated artificial lesions had a low elastic modulus (Er=0.4 GPa) extending about 100 µm into the lesion, followed by a sloped region to about 140 µm depth where values reached normal dentin (18–20 GPa). In the presence of MMP-inhibitors, the hydrated artificial lesions exhibited higher elastic moduli (average 2.8 GPa) in the outer, more demineralized zone (Fig. 1). The improved mechanical response was attributed to preservation of collagen integrity by protease inhibitors. Collagen preservation may also lead to improved remineralization as dentin properties recovered at a more rapid rate, while in the absence of inhibitors mechanical recovery was delayed and not as elevated, as demonstrated in Figure 1.

Conclusion: It may be postulated that MMP-inhibitors during both de- and remineralization cycles may preserve the demineralized dentin collagen and thereby contribute to the nanomechanical recovery following PILP remineralization.