Toothache. The cause of toothache may be thus explained : - Within the tooth is a cavity filled with a nervous pulp - of course highly sensitive - and under the influence of injury, exposure, and disease, affords one of the sources of " toothache." The roots of the tooth are surrounded by a membrane, a similar one to which lines the socket into which they are planted.- Inflammation in these membranes is another source of toothache. They become filled with blood, but cannot expand, and consequently compress the nerve with the power, almost, of an hydraulic press, causing most severe agony.