Ex vivo evaluation of the ability of the ROOT ZX II to locate the apical foramen and to control the apical extent of rotary canal instrumentation.

Aim: To evaluate the capacity of the ROOT ZX II to locate the apical foramen and to control the apical extent of rotary instrumentation.
Methodology: Sixty-five extracted human single rooted teeth were selected and measured directly using a size 15 K-Flexofile introduced in the canal until the tip was visible at the major foramen (direct length, DL). The teeth were then measured electronically (EL1) with the ROOT ZX II when used passively, that is without rotation. To test the auto reverse function, the root canals were instrumented with nickel titanium rotary instruments. Instrumentation was carried out apically until rotation was reversed by the automatic apical reverse (AAR) function at different levels (2, 1 and 0.5). The instrumented length at each level was measured and registered as AAR2, AAR1 and AAR0.5, respectively. After instrumentation, a second passive electronic measurement was conducted and noted as electronic length 2 (EL2). All measurements were expressed in millimetres with accuracy set to 0.5 mm. Percentages of acceptable measurements for each electronic reading were calculated and compared using the proportions test. The Wilcoxon's signed rank test was used to compare the differences between DL/EL1 and DL/EL2, and to compare EL2 with the different AAR measurements. The critical value of statistical significance was 5%.
Results: EL1 and EL2 measurements were coincident to DL in 56 (86%) and 54 (83%) of the cases, respectively. The proportions test showed no statistically significant difference between these percentages (P > 0.05). The Wilcoxon's signed rank test did not show any differences (P > 0.05) when comparing the mean difference between DL with EL1 (0.03) and DL with EL2 (0.10). Statistically significant differences were observed when comparing EL2 with AAR2 and with AAR1.
Conclusions: The ROOT ZX II reliably located the major apical foramen, but was not an accurate method for controlling the apical extent of rotary instrumentation. Rotary instrumentation with the automatic apical reverse feature was always closer to the foramen than expected.