No haven't heard of specialdatabases. But infousa.com is the mailing list database I'm familiar with. And as far as I know, the largest. You can pick any category of businesses or individuals by their professions, ages, income levels, the magazines they read, etc.
They may even have a list of the members of the American Medical Association. Or maybe you can contact AMA directly. (but that may be more expensive)
Have you tried freedentistfinder.com?? You can find the great database of USA dentist where people come and find dentist according to their need.