Measurement of the Distance Between the Minor Foramen and the Anatomic Apex by Digital and Conventional Radiography

The purpose of this study was to determine the distance between the minor foreman and the anatomic apex from digital and conventional radiographs. Thirty permanent single-canal teeth with mature root apex were used. After access preparation, a K-file was inserted into the canal until the tip of the file was just seen at the minor foramen under a ×40 stereomicroscope. The file was fixed in the canal by filling the access with composite resin. The teeth with files in the canals were radiographed using a Schick CDR digital system and conventional radiography with E-speed film. For digital radiographs, the distance between the file tip and the center of radiographic apex was directly measured from the computer screen by using Schick CDR measurement software. For conventional radiographs, the distance was measured under a stereomicroscope at a magnification of ×10 with a calibrated millimeter ruler. The mean distance was 0.494 mm measured from conventional radiographs and 0.594 mm from digital radiographs. These results agree with the current conception that endodontic working length should terminate 1 mm from the radiographic apex. There was a significant difference between the measurements on digital radiographs and those on conventional radiographs (p < 0.05, paired t test). However, the 0.1-mm difference has no clinical significance, because clinically, the working length is generally measured to the nearest 0.5 mm.