Chemical clues behind ancient smiles

The analysis of the tooth enamel uncovered unusually high levels of iron and sulfur—chemical signatures that point toward the iron–tannate mixtures long used in traditional practices. By matching chemical results with historical records and laboratory experiments, researchers identified a clear indication of tooth blackening without damaging the remains.

The evidence also suggests that the practice began during the era of the Dong Son Bronze Age culture and continued for centuries thereafter, serving as a shared expression of cultural identity among communities connected through exchange networks shaped by trade or travel.

The findings are published in Archaeological and Anthropological Sciences.

Tooth blackening has been documented from the late 19th century to today. The recipe for staining the pearly whites ranges from quick fixes like rubbing teeth with tannin-rich plants or coconut-shell soot to a remarkably refined process. The most advanced version follows a two-stage process that takes 20 days to transform off-white enamel into a deep, lasting black shade.

By the early 20th century, this practice had become widespread across Vietnam, embraced by major ethnic groups and many minority communities alike, irrespective of gender and social class.