A mains electricity (AC-powered) device designed to measure resistance to the flow of electric current across teeth for the diagnosis of early stage dental caries and/or to monitor the progress of caries (carious areas being less resistant due to higher concentrations of fluid). It typically consists of a probe with an electrode placed in contact with the tooth to be tested and a second counter electrode, separate from the probe, which is placed in contact with another part of the patient's body to complete an electrical circuit; and an electronic control unit that quantifies the resistance. This procedure is also known as electronic caries monitoring/measurement (ECM).