Why? Because, not knowing how germs work, they believed it was the actual bad smell that carried disease.
Almost all dental care in Medieval England was about smells. This practice even made it into the Canterbury Tales, where Chaucer’s characters chew cardamom and licorice to keep their breath smelling clean. A mixture of aniseed, cumin, and fennel was sometimes recommended to women.
What dental problems were they living with while focusing mainly on breath? Fortunately, there wasn’t much sugar to cause cavities in the diet of Medieval England. Unfortunately, small particles of stone would get into their bread from the millstones they used to grind flour, and that caused severe erosion. Most adults would lose four to six teeth in their lifetimes.
Things got really weird if you ever had a toothache. Physicians believed they were caused by tiny worms, and remedies included myrrh and opium. Those were expensive, though, so a cheaper option was to burn a candle very close to the tooth so the alleged worms would fall out into a basin of water.