The MC1R gene belongs to a family of receptors that include pain receptors in the brain, and as a result, a mutation in the gene appears to influence the body’s sensitivity to pain. A 2004 study showed that redheads require, on average, about 20 percent more general anesthesia than people with dark hair or blond coloring. And in 2005, researchers found that redheads are more resistant to the effects of local anesthesia, such as the numbing drugs used by dentists. (NY Times)
As a result, Red Heads have a statistical tendency to avoid dentistry.
As an aside, when I was at the hospital I noted that pain management was often a weak spot in medical care. Doctors are often nervous about prescribing narcotic pain killers, even in a hospital setting. God help you if someone writes "drug seeking" on your chart! I remember one doctor who became suspicious of a patient simply because that patient asked for a specific drug with a specific dosage, never mind that this person has a painful chronic condition and had been through hospitalizations enough to know what worked to control his pain, in this case knowledge worked against him. There have been a lot of studies that have concluded that many (by no means all) doctors under-prescribe to treat pain, probably because there are no objective metrics clinically available to quantify pain. As a result, they end up asking that "On a scale of 1 to 10" question, which honestly seems lame to me. People have no reference point. Better to ask, "Do you think you are in more pain today or less?"
Honestly, I was also very suspicious of the class and racial bias that may exist in pain management. I knew a black woman with Charcot Marie-Tooth that has some real horror stories of what it was like to present herself at an emergency room asking for help with pain from her condition. She is currently working on a timely documentary about how race affects medical care in this country.