Low pH and heat treatment may also directly lead to MMP
activation (Davis, 1991; Gunja-Smith and Woessner, 1993).
The change in pH can alter the conformation of the propeptide
and induce the cysteine switch, which represents a critical step
in the activation process. During caries activity, the release of
acids by bacteria rapidly decreases the pH, and the acidic
environment can then activate host-derived pro-MMPs from
both dentin and saliva.