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).
Keywords: Acid etch, Collagen, Dentin, Dentin bonding agents and MMPs
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