In other words, dentine, enamel and cementum are electrical insulators, soft tissue, including the periodontal ligament, is a conductor. The device established a circuit in the mouth that originated in the device, ran through an endodontic file via the attached probe, and extended down the canal out of the foramen and into the periodontal ligament. The circuit continued through the patient’s mucosa and eventually completed the loop by running into the lip clip that was connected to the device through a return wire.