I've worked IT for a few dental offices. It's know as "drilling at shadows". (the dark spots on the xray are likely candidates for decay) Some dentists are more aggressive than others who take a "wait and see" approach. (You do go every 6 months right?)

Dentists will often drill and fill these dark spots "just to be sure". This is the first time I've ever really considered the financial angle and the perverse incentive that may also be at work.

The proliferation of digital xrays with instant networkable images creates a fascinating opportunity here. There's probably a startup in instant second opinions...