A SEM study of in vivo accuracy of the Root ZX electronic apex locator.

Twenty-nine unprepared, vital teeth were used to evaluate the accuracy of the Root ZX in locating the root canal foramen. After extraction of the teeth, a scanning electron microscope analyzed the relation of the file tip to the foramen. The sample was divided into two groups (Group A and Group B) according to the presence of a normal apical foramen (along the root main axis) or of a lateral foramen (deviating from the root main axis). With a tolerance level of +/- 0.5 mm, a clinical accuracy rate of 82.75% was recorded in the total sample. With a +/- 1.0-mm tolerance level, an accuracy of 100% was found. The error in locating the apex was significantly smaller in cases with a normal apical foramen (Group A) than in cases with a lateral foramen (Group B) (p < 0.001). An accuracy of 100% at the +/- 0.5-mm tolerance level was registered in Group A.