Evaluation of the accuracy of three electronic apex locators using glass tubules

AIM: To evaluate the accuracy of three different electronic apex locators (EALs) using glass tubules. METHODOLOGY: Forty-eight glass tubules with different diameters and an agar model were used to mimic root canals. A size 15 stainless steel K-file was used as the measuring electrode. The Root ZX, Propex and Neosono Ultima EZ were used to measure the tubule length with tubules dry, or filled with 0.9% NaCl, 3% H(2)O(2), 2.5% NaOCl or 17% EDTA. The distance between the real length (RL) and measured length (ML) of the tubules was recorded. The range of RL +/- 0.5 mm and RL +/- 1 mm was used to evaluate the accuracy of the EALs. Results were subject to correlation analysis and Friedman's test. RESULTS: In dry tubules, the accuracy of Root ZX was 75-91.7% for RL +/- 0.5 mm and 100% for RL +/- 1 mm, whilst the measurements of the other two EALs were all within the RL +/- 0.5 mm. No influence from the increase in tubule diameter on the accuracy of all three EALs was observed in dry tubules. In tubules filled with electrolyte, the accuracy of the Root ZX decreased as tubule diameter increased (R(d) > 0, P < 0.05). The RL-ML distance recorded by Propex was inversely related to the tubule diameter (R(d) < 0, P < 0.05). The accuracy of Propex was 75-100% for RL +/- 0.5 mm and 100% for RL +/- 0.5 mm when the tubule diameter was not more than 0.80 mm, but decreased in tubules with diameter over 0.80 mm and filled with 2.5% NaOCl or 17% EDTA. Nearly, all the measurements (except for six tubules) using Neosono Ultima EZ were within 1 mm shorter than RL despite the contents in tubules and the increase of tubule diameter. CONCLUSIONS: The accuracy of the Root ZX decreased as the tubule diameter increased when tubules were filled with electrolytes. The electrolytes in the tubules decreased the accuracy of Propex when the tubule diameter was large. The electrolytes in tubules and tubule diameter had no influence on the accuracy of Neosono Ultima EZ. The Propex and Neosono Ultima EZ were more accurate than the Root ZX under various conditions in this laboratory study.