Chaucer's Miller's Tale is written in the 14th century and set in Oxford. The story uses the French fabliaux style to in many ways burlesque the preceding serious and chivalrous Knight's Tale.

There are two competing lovers trying to seduce the wife of an old carpenter. One, who is successful in his seduction, is an astrologer and student at Oxford renting a room in the carpenter's house, and the other is the local parish clerk. The clerk, who attempts to flirt with a number of parishioners, is described as fancying himself as a courtly lover (i.e a knight coming to win the lady). He is described as "effeminate" and "squeamish" and highly concerned with his appearance. A modern parallel may be the whole "lumber jack-beard model" where these very rugged "looks" are appropriated into something "fashionable." The "metrosexual" trend also might have some parallel.

When Absolon, the clerk, gets all gussied up as he sets out to "win" his lover via serenade, he pays careful attention to his breath and oral hygiene. I won't ruin what is perhaps the greatest comedic twist ending in the English Language, but this attention to oral hygiene serves the comedic finale well.

• Whan that the firste cok hath crowe, anon

• When the first cock has crowed (about midnight), at once

• Up rist this joly lovere Absolon,

• Up rises this elegant lover Absolon,

• And hym arraieth gay, at poynt-devys.

• And dresses himself handsomely, in every detail.

• But first he cheweth greyn and lycorys,

• But first he chews cardamom and licorice,

• To smellen sweete, er he hadde kembd his heer.

• To smell sweet, ere he had combed his hair.

• Under his tonge a trewe-love he beer,

• Under his tongue he had a true-love herb,

• For therby wende he to ben gracious.

• For thus he thought he would be gracious.

Absolon's attention to oral hygiene using an herbal solution is representative of a widespread use of spices for this purpose. A great and readable book on spices that contains mention of their use (along with other plants and herbs) in dental and oral health is Out of the East: Spices and the Medieval Imagination by Paul Freedman.

Various ways depending on time and location. Common ways include brushing with various types of brushes and masking bad breath with fragrant herbs and spices.

During the Middle Ages in western Europe, for example, proscription for dental hygiene included brushing with the end of a frayed stick as a sort of primitive toothbrush and chewing on various herbs and spices, including specifically fennel seeds.

One thing to note, though, is that dental problems, especially tooth decay, correlates strongly with access to refined sugars. Less refined sugars, less tooth decay. That's not to say cut all sugars and have perfect teeth, though. I know of one archaeological find from Medieval Wales; poor guy had thick mineralized tartar buildup on his teeth.

edit mineralized, not generalized. Darn spellcheker