Last Updated: Thursday, 8 April 2006, 12:33 GMT 13:33 UK

The researchers studied the drilled areas using an electron microscope

Stone age people in Pakistan were using dental drills made of flint 9,000 years ago, according to researchers.

Teeth from a Neolithic graveyard in Mehgarh in the country's Baluchistan province show clear signs of drilling.

Analysis of the teeth shows prehistoric dentists had a go at curing toothache with drills made from flint heads.

The team that carried out the work say close examination of the teeth shows the tool was "surprisingly effective" at removing rotting dental tissue.

A total of eleven drilled crowns were found, with one example showing evidence of a complex procedure involving tooth enamel removal followed by carving of the cavity wall.

Four of the teeth show signs of decay associated with the drilled hole.

"In all cases, marginal smoothing confirms that drilling was performed on a living person who continued to chew on the tooth surfaces after they had been drilled," the reserchers reported.

The form of dental treatment seen at Mehrgarh continued for about 1,500 years, before the practice was stopped in the area.

Flint drill heads are found abundantly at the Mehrgarh site, among assemblages of beads made of bones, shell and turquoise. Writing in Nature, the authors suggest that skills developed by bead craftsmen also worked well on teeth.

Mehrgarh straddles a route between Afghanistan and the Indus Valley to the south.