# In Vitro Accuracy of Two Different Electronic Apex Locators Under Various Conditions
## 4 Discussion  
Studies have reported the accuracy of EALs for in vitro models using various canal irrigants [7, 17, 18, 20, 22, 24, 25, 26, 27, 28, 29, 30]. In the presence of dried canals and a tolerance level of \(\pm\)0.5 mm, the Raypex showed an accuracy of 80%, 82.07%, and 85.59% with instrument sizes 08, 10, and 15, respectively [31]. Measurements within the \(\pm\)0.5 mm clinical tolerance range are considered to be highly accurate. We agree that a tolerance of \(\pm\)0.5 mm can be permitted, because this accuracy level cannot be reached with any other working length determination method in clinical practice [34]. Our results showed that the Raypex EAL was accurate in the range of \(\pm\)0.5 mm between 55% and 87.5%, depending on the canal irrigant. Additionally, the Ipex showed a similar accuracy of 55% to 82.5% within the \(\pm\)0.5 mm range, depending on the canal irrigant. If a tolerance of \(\pm\)1 mm was allowed, the accuracy reached 96.5%, 95.14%, and 96.88% with instrument sizes 08, 10, and 15, respectively [34]. No statistically significant differences were observed between the Raypex 5 and ApexDal for all intracranial media tested (2% chlorhexidine solution, gel and 2% NaOCl). In this study, good results were achieved only when canals were filled with CHX solution or CHX gel. The measurement accuracy was 79.3% and 86.2%, respectively, for the devices. Measurements that were made in canals irrigated with 2% NaOCl were correct only in 53.2% and 48.2% of cases for Raypex 5 and ApexDal EAL, respectively [35]. In the presence of saline and 17% EDTA, measurements were closer to the AL, while those performed in dry canals or in the presence of xylol were shorter than the AL [18]. The authors concluded that EDTA and saline can be considered reliable solutions for electronic measurements. In the present study, 0.9% saline solution and 3% NaOCl (Chlorcid) showed the most accurate readings within a tolerance of \(\pm\)0.5 mm for both EALs. Chlorcid, or 3% NaOCl according to the manufacturer's composition data, also showed the smallest discrepancies for both EALs between the ACL and ECL. Another study concluded that the NaOCl concentration had no effect on the accuracy of the Root ZX EAL [29]. One study reported that chlorhexidine gave the least variability in EAL performance [20]. Another study concluded that there were no differences in canal measurements in the presence of chlorhexidine (0.2%) or NaOCl. One published paper showed that the accuracy of neither the Ipex nor the Root ZX EAL was affected by 2.5% NaOCl or 2% CHX. Yet, the study reported that chlorhexidine digluconate (2%) showed the best results, in contrast to 3% NaOCl and 2% lidocaine, but the results were not significant [21]. In newer generations of EALs, multiple frequencies are used to determine WL, resulting in a more precise WL measurement in the presence of different electrolytes. However, the presence of highly electroconductive irrigants, such as saline, local anesthetic solution, CHX, blood, hydrogen peroxide, EDTA, irrigating fluids, and NaOCl, may compromise the accuracy of the EAL's performance [33]. However, significant differences were observed between the readings of the Ipex and Root ZX, irrespective of whether 2.5% NaOCl or 2% CHX was used as the irrigant [36]. These results were not similar to those found in our study, but can be explained by the different chlorhexidine concentrations (0.1% and 0.2% versus 2%) or by the in vivo or in vitro conditions used. Chlorhexidine digluconate is an antiseptic and has an affinity for hydroxyapatite. Another study showed that 0.8% CHX and RC Prep may not be clinically acceptable because of measurement error, in contrast to NaOCl and EDTA [7]. Despite the fact that third-generation EALs can work under chelating canal irrigants, measurement errors are still possible. An explanation could include dentine conductivity changes caused by the chelating ability of canal irrigants, which could have an impact on the impedance of the EALs.