In this article some clinical operations preceding the preparation and filling of root canals are more thoroughly treated. Besides the technique for periapical X-ray photography the indication for photography at a mesial and distal angle is described here. Particular attention is paid to the reading of the apical foramen on the radiograph and the use of the diagnostic radiograph in determining the experimental working-length. This article ends with description and illustrations of the shapes of the entrances to endodontic cavities with the different tooth-elements.
