An in vivo evaluation of the auto apical reverse function of the Root ZX II

To evaluate in vivo the accuracy of the Root ZX II (J. Morita) apex locator in controlling the apical extent of rotary instrumentation when using the Auto Apical Reverse (AAR) set at the levels 0.5, 1.0 and 1.5.

Thirty single-rooted premolar teeth scheduled for extraction were divided into three groups (n = 10), according to the AAR setting 0.5, 1.0 and 1.5. The root canals were prepared using ProTaper (Dentsply Maillefer). After rotary instrumentation, the last file used (F3) was manually introduced into the extent of the root canal preparation and fixed before tooth extraction. The apical third of the root was dissected until exposure of the file. The distance from the file tip to the major apical foramen was obtained.

Measurements within the range -1.0 to 0.0 mm were obtained in 30% of the teeth with AAR 0.5, 50% with AAR 1.0 and in 0% with AAR 1.5. The proportions test revealed a significant difference between the AAR settings 1.0 and 1.5 (P = 0.0188). Overinstrumentation occurred in 70% of the teeth with AAR 0.5 and in 40% with AAR 1.0. The measurements short of the acceptable range occurred in 10% of the teeth with setting AAR 1.0 and in 100% of the cases with AAR 1.5. A significant difference was found when comparing the percentage of teeth in which the file tip was short and beyond the established range between groups, except when comparing AAR 0.5 and AAR 1.0.

The AAR function of the Root ZX II was not an accurate method for controlling the apical extent of rotary instrumentation in vivo. The setting 0.5 presented overinstrumentation in most of the canals, the setting 1.5 was short in all cases, and the setting 1.0 provided an adequate working length in only 50% of the teeth.