An American scientist may have settled a conundrum that could have widespread implications about the customs, diet and oral health of early humans -- did they use toothpicks?

Curved grooves on the roots of teeth from ancient hominids suggest they were indeed concerned about dental hygiene and used implements to pick their teeth.

But critics of the hypothesis have pointed out that modern humans who regularly use toothpicks do not have similar grooves.

Leslea Hlusko, a paleontologist at the University of Illinois at Urbana-Champaign, believes grass stalks were used as toothpicks by early humans and made the distinctive dental grooves.

"Unlike wood, grass contains large numbers of hard, abrasive silica particles. This may explain the grooves seen on ancient teeth," New Scientist magazine said.

To prove the point, Hlusko ground a piece of grass along a tooth from a baboon and also on a human tooth.

"In both, the grass left marks almost identical to those seen in scanning electron microscopic images of early hominid teeth," the magazine said.

Dental grooves have been found on fossil teeth dating back 1.8 million years. If it was made by toothpicks it could qualify as the oldest human custom yet recorded, according to New Scientist.