Comparison of working length determination with radiographs and two electronic apex locators

To evaluate the accuracy of the Root ZX and Elements-Diagnostic electronic apex locators when compared with radiographs for locating the canal terminus or minor foramen.

The canal terminus of 482 canals in 160 maxillary and mandibular teeth was located in vivo with both locators and radiographically. After extraction, the actual location of the minor foramen was determined visually and with magnification. A paired samples t-test, chi-square test and a repeated measure anova at the 0.05 level of significance were used to determine differences between the groups.

The Root ZX located the minor foramen correctly 68% of the time in anterior and premolar teeth, and 58% of the time in molar teeth. The Elements-Diagnostic located the minor foramen correctly 58% of the time in anterior and premolar teeth and 49% of the time in molar teeth. Radiographs located the minor foramen correctly 20% of the time in anterior and premolar teeth and 11% of the time in molar teeth. There was no statistically significant difference between the two locators, but there was a significant difference between them and radiographs. For all teeth, the measurements made by the apex locators were within +/-0.5 mm of the minor foramen 100% of the time, whereas for the radiographs, the measurements were within this range only 15% of the time. This difference was significant (P = 0.05).

Measuring the location of the minor foramen using the two apex locators was more accurate than radiographs and would reduce the risk of instrumenting and filling beyond the apical foramen.