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I 41 research _ working length I roots1_2010 Contradictory and controversial results and statements about certain factors that influence the accuracy of EFLs when tested in vivo (both with sta- tistical and/or clinical significance) still exist, parti- cularly with regard to vital and necrotic cases. Reports vary from higher precision in teeth with vital pulp to higher precision in cases with necrotic/ infected pulp or even no difference at all. Whether EFLsdemonstratebetterresultsinmoistordrycanals is yet another controversial issue. Here, the type of EFL used is most often the determining factor. The same can be concluded for the type of irrigant used, considering its conductivity and ion concentration. Thefollowingfactorsadverselyaffecttheaccuracy of all tested EFLs: 1. presence of peri-apical lesions associated with periodontal ligament and bone destruction that have destroyed both the anatomical foramen and apical constriction; 2. wide-open apical foramen in immature teeth; and 3. extremes in conductive properties of the irrigating solution in the canal, such as saline versus distilled water. According to the literature, the precision of EFLs tested in clinical conditions varies between 15 and 100%. Evidently, additional factors or variables that influence clinical results must exist. In general, measurements of an extracted tooth with a revealed apicalsegmentoftherootcanaltakenusingamicro- scope and software programmes are more precise comparedtomeasurementstakenusingradiographs ofatoothunderclinicalconditions.Furthermore,the range of tolerance or targeted interval from approx- imately 0.5 to 1.0 and 1.5mm significantly affects accuracy: the higher the value of tolerance is, the higher the percentage of precision is. Thedisplaymarkselectedtobetheapicalterminus for measuring the electronic working length may influence clinical results of the accuracy of EFLs. In reality,eachoperatorwillselecthis/herpreferreddis- playmarkandthereforeselecthis/herpersonalapical terminus. The anatomical landmark selected to measure the distance from the file tip also varies and can sig- nificantly affect the results. The cemento-dentinal junction and the apical constriction are not reliable reference points. However, the apical anatomical foramen and, even more so, the anatomical apex are well defined and easy to distinguish, even without magnification. The type of EFL used also influences the results. Generally, the more sophisticated and newer the modelis,themoreaccuratethemeasurementswillbe. Manufacturers constantly strive to improve their models in order to make our work easier and more precise. However, all instruments are handled and results interpreted by practitioners, which leaves room for random and unforeseeable errors. In the early 1980s, we conducted a number of studiesattheDepartmentofRestorativeOdontology and Endodontics in the School of Dentistry at Bel- grade University using two EFLs—DIAPEX (DiaDent) and Odontometer (Goof). The results achieved with Odontometer demonstrated 77% precision in locat- ingtheapicalconstriction,checkedbythesameradi- ographic criteria as explained before. Significantly less overestimation was found than with the tactile sense and the radiographic method. Similar results wereachievedwiththeForamatron(Parkell,Inc.)sev- eralyearslater,withmeasurementdeviationsofupto -1.0mm. Traditionally, the accuracy of EFLs has been cor- roboratedwithradiographs,butanycorrectionofthe file position according to radiographic projections would invariably lead to overextension. Comparing electronic foramen locator mean (+/- SD) beyond AF MedicNRG-XFR 0.148 (0.079) Dentaport ZX 165 (0.222) +0.076 +0.131 ProPex I 0.169 (0.149) +0.226 (0.102) Raypex 5 0.187 (0.142) +0.119 +0.208 +0.075 ApexPointer+ 0.189 (0.168) +0.129 electronic foramen locator from – to (in µm) range (in µm; resolution/subtlety) Raypex 5 0 – 508 – 701 193 (300) ProPex I 0 – 354 – 705 351 (340) MedicNRG-XFR 0 – 305 – 380 75 (48) Dentaport ZX 0 – 367 – 674 307 (350) ApexPointer+ 0 – 143 – 312 169 (202) 2; 9; 3; 1; Ø 0.0 -0.0 Apex Apex AP EX 0.25 0.1 0.0 0.1 Table 2 Table 1