Proving prehistoric man's ingenuity and ability to withstand and inflict excruciating pain, researchers have found that dental drilling dates back 9,000 years. Primitive dentists drilled nearly perfect holes into live but undoubtedly unhappy patients between 5500 B.C. and 7000 B.C., an article in Thursday's journal Nature reports. Researchers carbon-dated at least nine skulls with 11 drill holes found in a Pakistan graveyard. That means dentistry is at least 4,000 years older than first thought — and far older than the useful invention of anesthesia. This was no mere tooth tinkering. The drilled teeth found in the graveyard were hard-to-reach molars. And in at least one instance, the ancient dentist managed to drill a hole in the inside back end of a tooth, boring out toward the front of the mouth. The holes went as deep as one-seventh of an inch (3.5 millimeters). "The holes were so perfect, so nice," said study co-author David Frayer, an anthropology professor at the University of Kansas. "I showed the pictures to my dentist and he thought they were amazing holes." How it was done is painful just to think about. Researchers figured that a small bow was used to drive the flint drill tips into patients' teeth. Flint drill heads were found on site. So study lead author Roberto Macchiarelli, an anthropology professor at the University of Poitiers, France, and colleagues simulated the technique and drilled through human (but no longer attached) teeth in less than a minute. "Definitely it had to be painful for the patient," Macchiarelli said. Macchiarelli and Frayer said the drilling was likely done to reduce the pain of cavities. Macchiarelli pointed to one unfortunate patient who had a tooth drilled twice. Another patient had three teeth drilled. Four drilled teeth showed signs of cavities. No sign of fillings were found, but there could have been an asphalt-like substance inside, he said.