What gives us a toothache?

A toothache is when you have irritation to the nerve supply to a tooth. The most common experience is sensitivity to cold, when you have sensitive teeth, but often it's because you have a hole in your tooth - a carie.

Caries, or holes in teeth, are caused by bacteria, usually streptococcal bacteria, metabolising sugars in your diet into acids, which then drill holes in teeth. Teeth are made of calcium phosphate, and so can be dissolved by acid.

When the hole becomes big enough, the bacteria can start to change the chemical environment inside the tooth, and you can get abscesses. These are painful because they cause inflammation and swelling, or just because of the change in chemistry.

Another less common, but very serious, cause of toothache can be an infection in a sinus. The nerves that supply your teeth run through, for example, the floor of the maxillary air sinus, the sinus behind your cheek. An infected sinus could make you feel that you have a toothache, when there's nothing wrong with your teeth.