Caries is the appropriate medical terminology.

Source: wife is a dentist.

Neat! Thanks for teaching me something today!

I always assumed caries was the generic term for tooth decay of any severity, while cavities are the holes you get if caries isn't stopped.

We use caries in Australia as well.

We do? I've never heard it used in place of cavities.

We definitely use both.

I hear professionals use 'caries' when talking professionally, and 'cavities' when talking to layfolk. I've not heard non-professionals use caries much here in Aus. Mileage may vary, I guess.

source: not a dentist, but have had a bunch of dental work done...