Abstract: A method and device are described for preparing an endodontic filler for a root canal whereby the minimum diameter of the prepared root canal is determined and a filler for the root canal formed exterior to the canal so that it has a terminal diameter which corresponds to the minimum diameter of the prepared root canal and a shape which is appropriate for adaptation to the configuration of the canal. The invention further includes a gauge for forming the endodontic root canal filler and which comprises a unitary member having a plurality of calibrated, elongated, tapered cavities one of which is adapted to receive an elongated instrument which has the terminal diameter corresponding to the minimum diameter of the root canal. A second calibrated cavity has an appropriate form to receive the elongated instrument or a filler material and a linear scale corresponding to calibration on the first cavity.