from The Dallas Morning News:

"Parallel grooves etched in the enamel of an ancient tooth found in
[Tanzania] may have come from a toothpick wedged between two teeth to
clean out stuck food. The toothpick must have been sharp - perhaps
a piece of bone or a gritty stick ..."
"A diet of meat not only sticks to your bones, it also sticks to
your teeth. Peter Ungar, a University of Arkansas anthroplogist
who found the grooves, said the the earliest toothpick use may have
coincided with the addition of meat to the diet of early humans."