Electronic Apex Locators and Conventional Radiograph in Working Length Measurement

The success of endodontic treatment is highly dependent on the adequate three-dimensional cleaning, shaping, disinfection, and obturation of the root canal system. It is universally accepted that the correct determination of the working length (WL) is one of the crucial steps in the process of a successful treatment. It is believed that root canal preparation and filling should be kept inside the root canal system to prevent damage to the periradicular tissues. On the other hand, selecting a point shorter than apical constriction may leave infected tissue apically, which may cause the persistence of the disease (Schilder, 1967; Seltzer et al., 1969). The glossary of endodontic terminology of the American Association of Endodontists (American Association of Endodontists 2003) defines the WL as “the distance from a coronal reference point to the point at which canal preparation and obturation should terminate.” In order to define an apical end point during a course of root canal therapy, it is imperative to know the anatomy of the apical portion of the root. Several anatomical landmarks exist at the apical segment of each root (Figure 14.1; Table 14.1). Traditionally, radiographic images were extensively used to help locate the apical end of the roots. The radiographic apex, which was believed to commonly coincide with apical foramen and was easy to detect radiographically, was considered as the end of the root canal. However, several investigators (Green, 1956, 1960; Kuttler, 1955; Pineda and Kuttler, 1972) have shown that less than 50% of the time, the apical foramen coincides with the anatomical apex (Figure 14.1). Such variations are not easily detectable in two-dimensional radiography, even with minimum distortion. Therefore, considering the radiographic apex as the terminus seems not ideal. Although two different anatomical entities, traditionally, the apical constriction is known as the cementodentinal junction (CDJ) (Grove, 1928, 1930; Kuttler, 1958). However; the location of the apical constriction that coincides with CDJ is known to be variable (Dummer et al., 1984). The apical constriction is easily detectable in histological sections. It is a challenge to detect it clinically or radiologically. Moreover, the apical constriction varies in its