Researchers have found nine skulls with 11 drill holes in a Pakistan graveyard proving that dentistry is at least 4,000 years older than first thought.

An article in Thursday's journal Nature reports that primitive dentists drilled nearly perfect holes into live but undoubtedly unhappy patients between 5500 B.C. and 7000 B.C.As it was much before the useful invention of anesthesia.

Researchers figured that a small bow was used to drive the flint drill tips into patients' teeth as flint drill heads were found on site.

Researchers say drilling was likely done to reduce the pain of cavities. No sign of fillings were found, but they believe there could have been an asphalt-like substance inside.