Ohaguro

Ohaguro (お歯黒^?) is a custom of dyeing one's teeth black. It was most popular in Japan until the Meiji era, as well as in the southeastern parts of China and Southeast Asia. Dyeing was mainly done by married women, though occasionally men did it as well. It was also beneficial, as it prevented tooth decay, in a similar fashion to modern dental sealants.

In Japan, it existed from ancient times, and was seen among the civilians until the end of the Meiji period. Pitch black things such as glaze like lacquer were seen as beautiful.