Other than being thought as beautiful, other guesses include that they want to maintain dental health and protecting ugly tooth as such.
Besides, a woman who has black teeth is obviously a married woman and no man should try to woe her.
Chronological Facts of Ohaguro:- Heian period (References to ohaguro exist in the Genji Monogatari and Tsutsumi Chuunagon Monogatari) Ohaguro was practiced by aristocratic men and women who have reached puberty and celebrated their genpuku or mogi, Tairas and other samurai, members of the imperial family who had finished their hakamaza, a ceremony where a child is fitted with a hakama and pages working at large temples.
At this period, they even shaved off their eyebrow and painted their eyebrow instead.
To crop the hair, decorate the body, rub pigment into arms and fasten garments on the left side are the ways of the Ba and Yue (southern barbarians).
In the country of Daiwu* the habit is to blacken teeth, scar cheeks, and wear caps of sheepskin stitched crudely with an awl.
*** Interesting Japanese custom: Ohaguro or black teeth writes on the historical practice of through the ages: Yellow teeth are a real turn off, but black teeth are a major turn on, for the ancient Japanese people at least. It is an old Japanese custom that was so popular centuries ago in Japan, and up to the Meiji period at the end of the 19th century.
In Japan, it existed from ancient times, and it was seen among the civilians up until the end of the Meiji period.perhaps you’ll wonder why would the wife of the samurai would dyed their teeth black?
The practice is dwindling among the younger women, but remains prevalent in older women among certain of the hill tribes.