Ohaguro is the custom of dyeing one's teeth black. It was most popular in Japan until the Meiji era. Tooth painting was also known and practiced 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.Text and image via Deformutilation, where there are additional images.
In 1873, the empress of Japan made a radical beauty statement, appearing in public with white teeth. For centuries, tooth blackening, known as ohaguro, signified wealth and sexual maturity especially for women in Japanese society, and they would drink an iron-based black dye tempered with cinnamon and other aromatic spices to achieve the lacquered look.