Radiographic reproduction of endodontic "working length" comparing the paralleling and the bisecting-angle techniques.

The reproduction of a metal indicator simulating a root canal instrument at the apex of a tooth was examined as a function of paralleling, modified paralleling, and bisecting-angle radiographic techniques. Radiographs exposed according to the paralleling and modified paralleling principles demonstrated good correlation between the radiographic position of the metal indicator and its position on direct inspection. The bisecting-angle technique, either correctly or incorrectly angulated, produced the least accurate results. The apical location of the metal indicator was significantly more reliable with the paralleling principle than with the bisecting-angle technique (p less than 0.05).