Deviation of apical foramen from the long axis of the anatomic apex is often undetectable on periapical radiographs. Use of electronic apex locators (EALs) in such cases might be prudent. Conflicting results have been reported regarding the influence of the position of an apical foramen in relation to the anatomic apex on the accuracy of EALs. This study was designed to shed further light on this potential influence. Fifty-six extracted human maxillary and mandibular molars were decoronated at the cementoenamel junction and canals were coronally flared with Gates-Glidden burs. Under 4X, Actual Canal Length (ACL) was determined by inserting K-file size 8 until its tip was leveled with the most coronal border of the apical foramen, file was withdrawn and measured with a digital caliper. This was done thrice and lengths were averaged to obtain ACL. Target Working Length (TWL) was obtained by deducting 0.5 mm from ACL. Teeth were embedded in freshly-mixed alginate. After irrigation with 2 mL 5% sodium hypochlorite, the blinded operator used Root ZX mini by attaching K-file size 8 to the file clip and apically advancing it to the APEX mark then withdrawing it to the 0.5 mark followed by file length measurement. This was done thrice and averaged to obtain Electronic Working Length (EWL). There was no significant difference between EWL and TWL neither in teeth with centered apical foramina (P=0.053) nor in teeth with deviated ones (P=0.246). The position of the apical foramen did not affect the precision of Root ZX mini.
