"As the authors [of the study] admit, encroaching on the [tooth's] pulp cavity would cause pain, and leaving these holes so close to the pulp cavity, where they would accumulate food and lead to infection and continue to cause pain, would hardly seem to be therapeutic."
Macchiarelli's team made the discovery while excavating a 9,000-year-old graveyard in Baluchistan, a region of Pakistan that borders Afghanistan and Iran (map).
The people of Mehrgarh, the site of the dig, were once nomadic hunter-gatherers who settled into a more sedate lifestyle, growing crops and raising cattle.
During the dig, the researchers identified nine individuals with a total of 11 drilled teeth.
"One individual had three drilled teeth, while another had a tooth that had been drilled twice," Macchiarelli said.
A closer look with a microscope revealed that at least in one case, not only had the tooth been drilled, but the resulting cavity had also been delicately reshaped.
And in all cases, the researchers noticed smoothening of the teeth. That meant the drilling had been conducted on living people who then continued to use the teeth for chewing food.
To make a hole on the relatively small surface of a tooth, Mehrgarh's dentists probably used a contraption quite similar to the one used in making a fire.
Rope from a bowlike device was looped around a slender piece of wood that was tipped with a sharp shard of flint. When the bow was moved sideways, it created a drill-like circular motion and pushed the flint into the tooth.
"It was very fast and also generated heat, enabling the dentist to drill holes smaller that 1 millimeter [0.04 inch] in diameter," said Macchiarelli, who created a replica of the drill by studying related artifacts.
He thinks that know-how for the early dentistry was probably transferred from artisans skilled at drilling holes in bead ornaments.
The researchers have yet to find evidence of dental fillings. Macchiarelli thinks that some sort of tarlike material or soft vegetable matter was stuffed into the tooth cavity. However, there is no evidence to prove the theory.
"[The fillings] could have degraded over time," he reasoned.
Out of Fashion
Though the dental manipulation lasted near Mehrgarh for about 1,500 years, the practice completely disappeared with the onset of the metal age about 7,000 years ago, Macchiarelli said.
"There is no evidence of this procedure in graveyards from much later periods, despite the continuation of poor dental health. We have no idea why it stopped," he said.
Schwartz, the Pittsburgh anthropologist, agreed the purpose of the drilling remains mysterious.
"In Pre-Columbian Mesoamerica, the lip-side surfaces of front teeth were drilled to receive semiprecious stones and gold, but that was clearly ornamental," he said.
"So I'm stumped as to why these holes were drilled."
Perhaps the pain caused the practice to lose popularity, he added.
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