Over the Australian summer (2012-2013) I was working with collections of human and nonhuman primate skeletons in Japan. At the National Science Museum in Tsukuba there is a very large collection of Edo Period (1603-1868) skeletons, that were recovered from a former cemetery as part of a salvage excavation in Tokyo. Excellent preservation makes this a very useful collection for studying aspects of growth, health, sexual dimorphism and anatomical variation in modern humans. An extremely useful source of forensic information, although without records of the age and sex of the deceased.
When studying the skeleton’s I noticed that a large proportion of them had black-coloured teeth, while others would have been useful in a Colgate commercial. There were at least two possible explanations. Firstly, there could have been some difference in the way the skeletons had been buried, for instance in a jar or a coffin, or in different parts of the cemetery (different types of soil), that could have produced chemical changes (mineral staining) in tooth enamel. Secondly, perhaps the blackened teeth were the result of a dietary or cosmetic process (accidental or intentional). For example, the chewing of areca nut and beetle leaf in parts of Asia and Melanesia can result in teeth that are red to dark brown in colour. Over lunch I consulted my Japanese colleagues. It turned out that the blackened teeth were not a surprise to them. Indeed, they were currently part of a research project by a leading Japanese dental anthropologist who was developing a method to identify faint traces of uhaguro through chemical changes in dental enamel.
In the Edo Period, up until the Meiji Restoration (1868-1912), married woman and some aristocrats, would dye their teeth black (Ohaguro) (Ai, et al., 1965). At least in the Edo period, and amongst Geisha, this was considered a sign of beauty. This custom appears to have had an extremely long history in Japan, with examples from the Kofun Period (250-358), and may have originated in China. In 1870 this practice was banned by the Japanese Government and it gradually died out. Today, it can only be seen in the Geisha quarters of Kyoto. The teeth were dyed using a dark-brown solution of ferric acetate called kanemizu (かねみず), made by dissolving iron filings in vinegar. When the solution was combined with vegetable tannins from sources such as gallnut powder or tea powder, it would turn black and become non-water soluble, in the same manner that iron gall ink is produced. Coating the teeth with this liquid also helped to prevent tooth decay and enamel decay, much as modern fissure-sealants do. The dye had to be applied once a day or once every few days. Where teeth have been stained black, or dark brown, through postmortem process (eg, iron manganese dissolved in ground water), usually both bones and dental enamel are darkened, not just the tooth crowns.
If you look at the detailed photographs of the blackened Edo incisor teeth, you can see that the part of the tooth crown closest to the alveolar bone, is not blackened. During life, this part of the tooth is covered by the oral soft tissues (gingiva), which would have prevented the dye from coming in contact with this part of the tooth. It is a clear indication that the teeth of this young woman had been stained during life, or at least before burial. Both sex and age can be determined by her skeleton, and the history of Ohaguro suggests that she was a married woman. She had died after recently dying her teeth (2-3 days), or her teeth had been dyed as part of the funeral preparations.
Betel nut staining of teeth
The areca nut is the seed of the areca palm (Areca catechu) and is often chewed wrapped in betel leaves. Betel is the leaf of a vine (Piper betle) belonging to the Piperaceae family, which includes pepper and kava. It is valued as a mild stimulant and is sometimes also chewed with a mixture of lime, tocbacco and spices (paan). During chewing a red stain is generated by the combination of ingredients. This can stain the teeth, lips and oral mucosa, with the archaeological evidence of stained teeth persisting for as long as 1000 years in parts of southeast Asia. Excavations of a cemetary on Motupore Island, Bootless Bay, Papua, in the 1970's (Allen et al., 1997), dating to around 400-500 BP, found many examples of betel stained teeth (I was responsible for cleaning and reconstructing the human skeletons in 1978-79). In the central incisor tooth (below) staining was present on the front (labial) surface of the crown but not on the rear of the tooth. The burial (below) contained large numbers of shell beads that were manufactured by the Motu residents of Motupore Island (Allen et al., 1997), and also had betel stains on incisor teeth. In contrast to ohaguru, both men and women chewed betel leaves, so betel staining is not an indication of a male or female burial.
References
Ai, S., Ishikawa, T., and Seino, A.1965. "Ohaguro" traditional tooth staining custom in Japan. International Dental Journal 15, 426-441.
Allen, J., Holdaway, S. and Fullagar, R. 1997. Identifying specialisation, production and exchange in the archaeological record: the case of the shell bead manufacture on Motupore Island, Papua. Archaeology in Oceania 32: 13-38