RESUMO
OBJECTIVE: The aim of this study was to evaluate the precision of working length determination of 3 electronic apex locators (EALs): Root ZX, RomiApex D-30, and Ipex at 0.0 mm, at the apical foramen (AF), and at 1.0 mm short of the AF. METHODOLOGY: Thirty-eight mandibular premolars had their real lengths previously determined. Electronic measurements were determined at 1.0 mm, followed by measurements at 0.0 mm, performed in triplicate. RESULTS: Precision of devices at 1.0 mm and 0.0 mm were: 94.7% and 97.4%, respectively (Root ZX); 78.9% and 97.4% (RomiApex D-30); and 76.3% and 97.4% (Ipex). Although no statistical differences were observed between the EALs at 0.0, at 1.0 mm Root ZX performed significantly better than the others. CONCLUSION: The EALs had acceptable precision when measuring the working length at the AF. However, when used at levels short of the AF, only Root ZX did not suffer a significant negative effect on precision.