Teeth blackening was the custom of dyeing one's teeth black with various tannin-rich plant dyes. It was practiced throughout almost the entire range of Austronesia, including Island Southeast Asia, Madagascar, Micronesia, and Island Melanesia, reaching as far east as Malaita. However, it was absent in Polynesia. It also existed in non-Austronesian populations in Mainland Southeast Asia and Japan. The practice was primarily preventative, as it reduced the chances of developing tooth decay similar to modern dental sealants. It also had cultural significance and was seen as beautiful. A common sentiment was that blackened teeth separated humans from animals.