Pain in the tooth occurs when the nerve is irritated. The most common causes are infection, gum disease, plaque, decay, injury, or loss of a tooth, including extractions.
Sometimes there is a problem in an ancillary area that will make the mouth hurt as well. Examples are TMJ (tight jaw syndrome) or ear problems.
If the sensation is mild, that is pretty common. If the pain is severe and lasts longer than 15 seconds, this is a warning that there could be something very serious going on. If the pain radiates to the cheek, ear or jaw, this is very serious.