Essential oils can be used in oral hygiene in a number of ways. Many are, of course, used to flavor toothpaste and mouthwashes, but some have traditional uses that have therapeutic value as well. For instance, chewing on a clove or using a diluted solution of clove oil can relieve toothaches.
The common oils uses for flavoring are mint, fennel, cinnamon, and anise, but many other oils can be used if they are pure, meaning they are free of chemical contaminants and properly distilled using CO2 or steam. For flavor, peppermint would, of course, be the most familiar, but lavender is a bit more exotic and has many benefits as well. It can, of course, be blended with peppermint.