To sum up the caries process on both enamel and root surface:

Coronal Caries: Root Surface Caries:
88 vol. % mineral 45 vol. % mineral
plaque related plaque and recession related
acid dissolves subsurface "white spot" acid dissolves surface subsurface "sticky"
complete dissolution=cavitation complete dissolution=surface contour changes
until cavitation occurs, remineralization is possible with collagen in place, remineralization is possible
once collage is destroyed, no framework for remineralization to occur

At every given moment, when the pH drops below the critical threshold for caries, for every tooth surface, no matter the age or location of the surface, it will undergo an acid challenge...a tug of war.

Fluorides become an integral part in the prevention of dental decay for every tooth surface, no matter the age or location...and fluorides play a major role in our practices today.

Animation of the demineralization/remineralization process.