Devices which operate on the basis of electrical charges are increasingly being used in stomatology, such as in cariology for the detection of invisible caries lesions or for the measurement of canal lengths during patient treatment. The majority of these devices now emit a current of alternating frequency. The aim of the work was to explain how the electrical devices of labile frequency commonly used in stomatology influence the vessels of the tooth pulp. Teeth extracted for orthodontic reasons were investigated with the use of a transmission electron microscope. The teeth were treated with current emitted by a specially constructed device. The control group comprised 4 teeth. No changes were found in the electron microscopic studies in the slides of the teeth treated with low charges of current. However, in the specimen treated with current charges of 9600 μC or more flattened endotheliocytes were found together with exudation in the vessel lumen. Cases are referred to in which the duration of the work was 2 or 3 times longer than normal and in which a current of constant intensity was emitted uninterruptedly.