287 Int. J. Odontostomat., 13(3):287-291, 2019. Accuracy of Four Electronic Apex Locators During Root Canal Length Determination Precisión de Cuatro Localizadores de Ápice en la Determinación de la Longitud de Trabajo Pablo Betancourt 1 ; Daniela Matus 2 ; Javiera Muñoz 2 ; Pablo Navarro 1 & Scarlette Hernández 3 BETANCOURT, P.; MATUS, D.; MUÑOZ, J.; NAVARRO, P. & HERNÁNDEZ, S. Accuracy of four electronic apex locators during root canal length determination. Int. J. Odontostomat., 13(3):287-291, 2019. ABSTRACT: The apical limit of tooth roots for instrumentation and obturation is a controversial subject due to the high morphological complexity presented by the apical zone of the root. The development of electronic apex locators (EALs) has made working length (WL) determination more predictable, producing more accurate results; however, the interpretation mechanisms of different devices may affect measurements taken under different clinical conditions. One hundred premolars were used to compare the effectiveness of Propex II, Raypex 6, Propex Pixi and Root ZX II in locating the apical foramen (AF). No statistically significant differences were observed when the accuracy of measurement was compared between the different groups of EALs, however Root ZX II and Raypex 6 presented the best overall performance. KEY WORDS: tooth root, anatomy, endodontics, electronic apex locator. INTRODUCTION The success of endodontic treatment depends on the correct mechanical enlargement, disinfection and sealing of the root canal system (D'Assunção et al., 2007). These objetives can only be achieved with accurate determination of the working length (WL) (Ding et al., 2010). The WL is defined as “the distance from a coronal reference point on the tooth to the point where canal preparation and obturation should terminate” (American Association of Endodontists, 2003). An error in determining the WL may lead to insufficient debridement of the root canal, delaying healing and increasing postoperative pain (Duran- Sindreu et al., 2012). The apical limit of tooth roots for instrumentation and obturation is a controversial subject due to the high morphological complexity presented by the apical zone of the root. Various authors have suggested that determining the exact location of the apical constriction is extremely complex because it is not present in all teeth (Martínez-Lozano et al., 2001; Lee et al., 2002; de Vasconcelos et al., 2014). As a result the apical foramen (AF) has been described as the most stable anatomical reference point for taking the measurement (Somma et al., 2012; Oliveira et al., 2017). The development of electronic apex locators (EALs) has made WL determination more predictable, producing more accurate results (Haffner et al., 2005; Altunbas¸ et al., 2014). Their action mechanism is based on a resistance in the electrical conductivity between the tissues which surround the root apex and the interior of the root canal (Custer, 1918). One of the main advantages is that it reduces the patient's exposure to ionising radiation by reducing the number of radiographies (Tampelini et al., 2017). A large number of different models of EALs have been developed in recent years, however, although they work on the same principle, they operate with different mechanisms. Some use the impedance quotient principle, such as Root ZX II (J Morita, Tokyo, Japan) (Altunbas¸ et al., 2014). The Propex II (Dentsply 1 Research Centre for Dental Sciences (CICO), Endodontic Laboratory, Dental School, Universidad de La Frontera, Temuco, Chile. 2 Dental School, Universidad de La Frontera, Temuco, Chile. 3 Faculty of Medicine, Austral University of Chile, Valdivia, Chile.