thats not the reason why primary care physicians make less than dentists.... it all boils down to 1 principle: Insurance.
Primary care docs are getting hit pretty hard with insurance reimbursements.
Dentistry on the other hand, and alot of times, its a pay-per-service and cash/credit cards are more widely used in a dental office than a primary care. You walk into a dentist's office, he offers you an extraction for $80 or a root-canal treatment for $600-900. Either option you take, you'll probably just pay it cash and walk out.... and if your customer service skills are up to the task, you'll be able to convince many patients to take the more "expensive" option (i.e better).