The concept of a tooth-worm, which according to popular belief, caused caries and periodontitis, has existed in diverse cultures and across the ages. During the Enlightenment, however, the theory of the tooth-worm was assigned by medical doctors almost exclusively to superstition. Even so, the idea that toothache was caused by gnawing worms held on even into this century. There were many different ideas with regard to the appearance of tooth-worms. In England, for instance, it was thought that the tooth-worm looked like an eel. In Northern Germany, people supposed the tooth-worm to be red, blue, and gray and in many cases the worm was compared to a maggot. The gnawing worm was held responsible for many evils and, in particular, was blamed for toothache provoked by caries. The question is discussed of how the belief in the existence of the tooth-worm in former times can be explained. In popular medicine, numerous therapies were applied in order to eradicate the tooth-worm. In addition to the fumigations with henbane seeds, which allowed the "tooth-worm" to develop in the form of burst seeds, there were also magical formulas and oaths.