Working length radiograph, A file is placed carefully in the canal until it is within approximately 2.0 mm of the overall length. Before insertion the file should be precurved to the shape of the canal and gently manoeuvred into position, if necessary using a watchwinding technique and slight apical pressure. For accurate reading of the radiograph a size 15 file is usually necessary.
A silicone stop on the instrument shank is positioned against a reference point on the tooth, and both the length and the reference point should be noted in the records. When taking diagnostic radiographs, use should be made of the buccal object rule , where there are two or more canals present in the root (Figs 9 and 10). A second way of achieving the same result is to place a Hedstroem file in one canal and a K-file in the other, as the difference between the two is clear on the radiograph. The working length is calculated by measuring directly on the radiograph from the tip of the instrument to 1.0 mm short of the radiographic apex. It is only possible to
estimate this arbitrary position using this technique.
estimate this arbitrary position using this technique.