A toothache starts with inflammation entirely inside the tooth and is signalled to the brain by the nerve in the root of the tooth. Peculiarly, the pain may seem to come from a distant part, for example an inflamed molar back tooth may produce an earache. This is called referred pain and is an error of localization which we will discuss again in the section on heart attacks. It is different from the spread of pain just described in the twisted ankle.
If the inflammation spreads out of the tooth and involves the gums, the pain changes its quality and is precisely localized to where the problem is. It becomes obvious as an area of red, swollen and painful gum and face. A third pain may then appear with a quite different origin. The tissues of the body are drained by a massive network of little channels which converge into the lymph nodes. The lymph nodes that receive the drainage from the mouth are in the neck under the jaw. As the debris and bacteria from the inflamed tooth and gums are filtered by the lymph nodes, they too may become inflamed, swollen and painful. Finally, the breakdown products of the damaged cells may leak into the bloodstream and produce a fever with malaise and general aches. Local damage can evidently produce distant pain by these three mechanisms of referred pain, lymph nodes and fever.
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