«NanoEst» — professional small-sized device for root canal working length measurement (localization of apical constriction) at the time of endodontic treatment. The device localizes the apical constriction by complex electrical resistance measuring between two electrodes. One of the electrodes is a metal hook (lip clip), placed on patient’s lip and the other electrode (file clip) is connected to the metallic part of the endodontic file, placed into the tooth root canal. Advantages of the device: -Guaranteed accuracy and stability of measurements in any mediums; -Tiny dimensions and small weight; -The possibility of device fixing on the patient’s protective apron by means of clasp owing to which device is always located within operational zone of the dentist.