If by crowdsource you mean have multiple dentists look at every image set, then maybe. But if you're suggesting that a random selection of people look at dental x-rays and guess where the cavities are... that would be an interesting experiment, but I wouldn't expect too much.

In either case, I doubt you'd find much traction since looking at dental x-rays isn't something most people are going to want to do on a regular basis without being compensated.