A method and system are disclosed for detecting an apical position depending on the change in the impedance between a first electrode inserted into the root canal of the tooth of a patient and a second external electrode applied to a body surface of the patient. According to some embodiments, a regulated current such as an alternating current having a substantially constant amplitude is supplied between the two electrodes, and this current serves as a measurement signal. Alternatively or additionally, the frequency of the time varying (e.g. alternating) current is at least 50 KHZ, and/or at most about 300 KHZ. In some embodiments, the presently disclosed device includes a processing unit which determines a capacitance-governed function when the first electrode is in the apical region, and which determined a function at least moderately governed by resistance when the electrode is in the dental neck region. Optionally, the first electrode inserted into the root canal is a dental file or reamer.