SuttaCentral
Some suttas are just hillarious and just too authentic 
AN 5.208: Bhikkhus, there are these five dangers in not brushing one’s teeth. What five? It is bad for one’s eyes; one’s breath stinks; one’s taste buds are not purified; bile and phlegm envelop one’s food; and one’s food does not agree with one.
such tidbits have significance for anthropological research
on the one hand it tells that as early as around the Buddha time Indians had idea about teeth brushing, on the other hand it tells that apparently not a few people were neglecting this hygienic procedure if a sutta had to be composed to specifically tout it
Ven Bodhi translates using the modern idiom “brushing teeth”. But while toothwoods, or as more widely known, chew sticks (= dantakaṭṭha), are somewhat obscure, they are a distinct means of cleaning the teeth; they didn’t have colgate.
I learned how to make and use chew sticks in Thailand. In the forest tradition, they are still the traditional gift for one’s teacher. And they have their own wikipedia page!
Check out the study here, which indicates that they are as good or better than toothbrushes:
In India I’ve seen people using sticks from the adored neem tree in a similar way. First I was like ‘äh??’ but then was pretty fascinated
This was one part of Indian Buddhism that had to be imported when it came east to China. If I remember correctly, Yijing wrote that (unlike in China) the people in India rarely experienced toothaches because they cleaned their teeth with a neem twig. One of the most interesting things about the neem is that it has antibacterial properties.
Of course, the neem tree is not native to East Asia. Instead, Chinese monks used a willow twig. In translations as well, all the instances of “neem” were translated as “willow.” The interesting thing about the willow is that it has similar medicinal properties. Obviously there was some knowledge of traditional medicine informing the whole matter.
To this day, if you go to some temples in China, you can see statues of Avalokitasvara holding a (healing) willow branch. Perhaps it is derived from similar iconography in India, in which the bodhisattva would instead be holding a neem branch?
In any case, cleaning one’s teeth with a neem twig also comes up in Mahāyāna sūtras as part of ritual purity. When translated into Chinese, the instances of neem were simply translated to willow. This is a teaching given by one monk from India:
Accept and maintain this mantra dharma in the six periods of the day and night, thirty-seven times at each. In the morning and at night, one should bathe, rinse his or her mouth, and chew a willow twig. Make proper offerings of incense before an image, kneeling with palms joined, and recite this mantra thirty-seven times. Persist in this way every day, and it will annihilate the four grave acts, the five terrible crimes, and the ten evils. Every sort of offense can be eliminated. Being without the many evil ghosts and spirits of anger and confusion, at the end of one’s life, rebirth will be assigned in the land of Amitābha.
from THE BUDDHIST RELIGION AS PRACTISED IN INDIA AND THE MALAY ARCHIPELAGO (A.D. 671-695) By I-TSING (pp. 33 - 35)
CHAPTER VIII.
USE OF TOOTH-WOODS.
EVERY morning one must chew tooth-woods, and clean the teeth with them, and rub off the dirt of the tongue as carefully as possible. Only after the hands have been washed and the mouth cleansed is a man fit to make a salutation; if not, both the saluter and the saluted are at fault. Tooth-wood is Dantakashtha in Sanskrit—danta, tooth, and kashtha, a piece of wood. It is made about twelve finger-breadths in length, and even the shortest is not less than eight finger-breadths long (i.e. ’ angula ’ = one twenty-fourth hasta. In Kullavagga V, 31, 2, the length of a tooth-stick is limited to eight finger-breadths.) Its size is like the little finger. Chew softly one of its ends, and clean the teeth with it. If one unavoidably come near a superior, while chewing the wood, one should cover the mouth with the left hand.
Then, breaking the wood, and bending it, rub the tongue. In addition to the tooth-wood, some toothpicks made of iron or copper may be used, or a small stick of bamboo or wood, flat as the surface of the little finger and sharpened at one end, may be used for cleaning the teeth and tongue; one must be careful not to hurt the mouth. When used, the wood must be washed and thrown away.
Whenever a tooth-wood is destroyed or water or saliva is spit out, it should be done after having made three fillips with the fingers, or after having coughed more than twice (Kasyapa, quoting the Samyuktavastu, chap, xiii, says that the Buddha did not allow a tooth-wood or anything to be thrown away without making some noise beforehand for a warning.); if not, one is faulty in throwing it away. A stick taken out of a large piece of wood, or from a small stem of a tree, or a branch of an elm, or a creeper, if in the forest; if in a field, of the paper mulberry, a peach, a sophora japonica (’ Huai’), willow-tree, or anything at disposal, must be prepared sufficiently beforehand (The Dantakashthas were bits of sweet-smelling wood or root, or creeper (Gataka I, 8o; Mahavawja, p. 23), the ends of which were to be masticated as a dentifrice, not rubbed on the teeth, and not ‘tooth-brushes’ as Childers translates. See Kullavagga V, 31, 1 (S.B. E.), note; Brihat-samhita LXXXV; Sujruta II, 135.) The freshly-cut sticks (lit. wet ones) must be offered to others, while the dry ones are retained for one’s own use.
The younger priest can chew as he likes, but the elders must have the stick hammered at one end and made soft; the best is one which is bitter astringent or pungent in taste, or one which becomes like cotton when chewed. The rough root of the Northern Burr-weed (Hu Tai) is the most excellent; this is otherwise called Tsang-urh or Tsae-urh, and strikes the root about two inches in the ground. It hardens the teeth, scents the mouth, helps to digest food, or relieves heart-burning. If this kind of tooth-cleaner be used, the smell of the mouth will go off after a fortnight. A disease in the canine teeth or tooth-ache will be cured after a month. Be careful to chew fully and polish the teeth cleanly, and to let all the mouth-water come out; and then to rinse abundantly with water. That is the way. Take in the water from the nose once. This is the means of securing a long life adopted by Bodhisattva Nagarjuna. If this be too hard to put in practice, to drink water is also good. When a man gets used to these practices he is less attacked by sickness. The dirt at the roots of the teeth hardened by time must all be cleaned away. Washed with warm water, the teeth will be freed from the dirt for the whole of life. Tooth-ache is very rare in India owing to their chewing the tooth-wood.
It is wrong to identify the tooth-wood with a willow-branch. Willow-trees are very scarce in India. Though translators have generally used this name, yet, in fact, the Buddha’s tooth-wood-tree (for instance) which I have personally seen in the Nalanda monastery, is not the willow. Now I require no more trustworthy proof from others than this, and my readers need not doubt it. Moreover, we read in the Sanskrit text of the Nirvana-sutra thus: ’ The time when they were chewing tooth-woods.’
Some in China use small sticks of willow which they chew completely in their mouth without knowing how to rinse the mouth and remove the juice. Sometimes it is held that one can cure a sickness by drinking the juice of the tooth-wood. They become impure, in so doing, contrary to their desire for purification. Though desirous of being released from a disease, they fall into a greater sickness. Are they not already aware of this fact ? Any argument would be in vain ! It is quite common among the people of the five parts of India to chew the tooth-wood. Even infants of three years old are taught how to do it.
The teaching of the Buddha and the custom of the people correspond on this point, and help each other. I have thus far explained the comparative merit of the use of the tooth-wood in China and India. Each must judge for himself as to whether he will adopt or reject the custom.