Effects of acid-etching on endogenous MMP activity of EDTA-demineralized dentin

Objectives:   Previous studies suggest that acid-etching dentin with 37% phosphoric acid (PA) inactivates MMPs by denaturing them.  Some think that the MMPs are temporarily covered by CaHPO₄-reaction products that mask the MMPs.  The purpose of this work was to completely demineralize dentin beams with 0.5 M EDTA pH 7.4, and then “acid-etch” the matrix with increasing concentrations of PA to see if they can decrease dentin MMP activity.  Methods:   Control beams (n=10) were incubated in a simulated body fluid (SBF, 1 mL); experimental beams were incubated in 2 mM APMA 1 hr; PA experimental beams were dipped in 1, 10 or 37% PA for 15 min or 37% PA for 15 sec, rinsed and then incubated in 1 mL of SBF for 1 day or 1 week.  Aliquots of the SBF were analyzed for C-terminal telopeptides (ICTP) using an ELISA kit.  Results:   in ng/mg dentin are:

	Treatments		Phosphoric acid 15 min			PA 15 sec
	Control SBF	APMA	1%	10%	37%	37%
1 day	8.5±2.1A	3.1±1.0B	6.5±2.0A	10.6±2.3A	15.8±3.5D	10.8±2.1A
1 wk	8.6±2.0A	10.2±2.5A	3.2±1.1B	3.8±0.9B	7.3±0.7	4.1±1.9B

Conclusions:   These results clearly show that 1, 10 and 37 mass % PA do not lower endogenous MMP activity in dentin matrices that are free of buffer.  Instead, 10-37% PA increases endogenous MMP activity of dentin matrices demineralized in EDTA above that produced by APMA at 1 day, suggesting that acids activate these MMPs better than the traditional APMA activator.  Supported, in part, by R01DE015306 from the NIH/NIDCR to DHP (PI) and by grant #8126472 from the Academy of Finland to AT-M (PI).