If you get Dr Clark's oregano oil -- BE SURE TO DILUTE IT -- I was using usa oils and was placing drops of it directly on a couple of teeth. It finally cleared up the infections.
But then I ordered form Dr Clark and a drop of the oil burned the outside layer of skin out of my entire mouth. Tongue and all.
Now, I use it in baking soda very minutely to make my own tooth powder. It works just as well as the cheaper oils in full strength drops.
Also, I put a few drops in an empty capsule and swallow for sinus congetstion. Clears of the sinuses quickly.