Blackened teeth resulting from chewing betel nut. Betel nut is the nut
of the araca palm, sliced and wrapped in the leaf of the betel plant,
a climbing vine. It is a mild stimulant and is addictive. It has
cultural significance in Viet Nam.

Addendum: Apparently chewing betel nut does darken teeth
to a brown color, but there is a cultural practice of
intentionally blackening teeth.

Image ID 1971-72-559