How would you explain the mechanism responsible for the formation of dental cavities by resident microorganisms?

Bacterial acids.: Bacteria on the tooth surface are living organisms. They eat and excrete. Their excretions are acids which remove the calcium from the tooth. This leaves behind the collagen fibers, or proteins, which the bacteria can now "eat" and viola- you've got a hole in your tooth!

Demineralization: The acids excreted by the bacteria dissolve the mineral matrix of the enamel which causes it to soften, resulting in decay.