Can 100 percent clove oil be used for toothache?

It can be used but the effect is shortlived. Clove oil should not be used on a regular basis, as a substance naturally found in cloves, called eugenol, is known to cause cancer. (This compound is greatly concentrated in the oil form of cloves.) Using clove oil could increase your risk of cancer in the mouth, and in other parts of your body as well.

If you have continued toothache, see your dentist! It could cause worse damage to your teeth by ignoring it.