Radiographic "working length" revisited

The desired "working length" for the biomechanical preparation and resultant obturation of the root canal system is one of the most important phases of endodontics. Traditionally, radiographs are used to confirm working length of the root length and to evaluate the subsequent obturation of the root canal system. This study attempts to determine if radiographs are an accurate method of root length determination in a period when electronic apex locators are proposed as their replacement. Eight-seven vital and 24 nonvital teeth were accessed and files placed to and the radiographic working length before the file and teeth were extracted for sectioning. Results showed that the radiographic distance of the file from the apical vertex was 0.7 mm shorter than the actual file position. This discrepancy can lead the clinician to try to get closer to the radiographic apex, when in reality the end of the file is closer to the vertex than is suspected. The average distance short of the vertex as established by Kuttler should be increased to lie between 1.5 and 2.0 mm from the apical vertex to prevent overfilling the root canal.