Most toothaches are caused by cavities (tooth decay). Some toothaches are caused by a tooth abscess or by inflammation of the gum around the crown of a tooth (pericoronitis). Much less commonly, toothaches result from inflammation of the nasal sinuses (sinusitis).
If several upper teeth hurt when a person is chewing or is bending down (for instance, to tie a shoe), the cause is probably sinusitis—especially if the toothache develops while the person has or recently has had a cold. Additional symptoms suggesting sinusitis are headache and tenderness and swelling of the skin above the affected sinus.
Last full review/revision October 2008 by David F. Murchison, DDS, MMS