AMA, ADA and in particular ask about their past conference registration lists. They may have asked if the registrant consents to receive marketing materials from these organizations and other third parties. If the physician or dentist consented then this authorization to contact would transfer to you as a purchaser of the list. Also the contact info on a conference registration might be more direct to the physician.
Also if you actually have strong data, you might want to be an exhibitor or speaker at a conference.