Abstract: Objective To study the influence of different endodontic situations on the measurement accuracy of Root ZX and ProPex. Methods 30 extracted teeth were selected, after measurement of the actual working length （L）, the working length of root canal were measured using Root ZX（LR） and ProPex（LP） in 3% H2O2 solution, 0.9% NaCl solution, 2.5% NaClO solution or dry root canal, which was compared with the actual working length of root canal. The actual working length of root canal was obtained by the micro-observation of root apex（D） and means of software calculation. Results In four different environments, there was no statistically significant difference between the measuring length using Root ZX or ProPex and the real length of root canal（P>0.05）. But the measuring deviation between Root ZX and ProPex had statistical significance（P＜0.05） when the same endodontic situation was used. If the measurement error was ±0.5 mm, the differences between the measurement accurate ratio of Root ZX and ProPex had no statistical significance（P>0.05）. Conclusion The accuracy of measurement of Root ZX or ProPex was not influenced by root canal media and had no relation to the dry or moist root canal. There was no statistically significant difference between the accuracy of the two electronic apex locators.

Key words: Root ZX, ProPex, working length of root canal, endodontic irrigation