ROEN0110

36 I I research _ working length _We would like to start the second part of our article with a quotation: “Adequate radiographs, knowledgeofanatomy,andtactilesenseandnotapex locators will help to determine apical constriction.”2 We found this statement provocative enough to give electronic locators a chance. As is well known, apex locators actually locate the foramenandnottherootapex.Astheforamenisusu- allynotontherootapex,thetermelectronicforamen locators (EFLs) is more accurate. Electronic root- canallengthmeasuringdevices or similar descriptive terms are also incorrect, since the root-canal length doesnotappearonadisplay,particularlynotinsome standardised units. EFLs are usually classified into different genera- tions. The following classification of EFLs based on their functional properties is useful for dentists who, besidesdesiringthelatestandbestmodels,wouldlike to know how a particular device works and why it is better than another model: 1. resistance-based devices (Generation I) 2. low frequency based devices (Generation II) 3. high frequency (capacitance) based devices (Gen- eration II) 4. capacitanceandresistancebaseddevices(Genera- tion IV) 5. voltage gradient devices 6. two frequency (impedance difference) based de- vices (Generation III) 7. two frequency (impedance ratio quotient) based devices (Generation III) 8. multi frequency based devices (Generation III). The authors of this classification give perhaps the mostappropriatecomment:“TheuseofGenerationX to describe and classify these devices is unhelpful, unscientific and perhaps best suited to marketing issues.”5 Marketing firms and manufacturers often cooperatetoincreaseturnover,whichiswhy,insome cases,youcanfindtwoidenticaldevicesthataresold under different brand names (Figs. 1a & b). _In vitro studies A remarkable number of studies have been con- ducted in the last 20 to 30 years on the use of EFLs. A majority were conducted in vitro, with all research conditionsandvariablescontrolledandstandardised. Webelieveitwouldbeusefultopointoutanumberof variablesthatinfluencetheaccuracyofEFLsininvitro studies. Embeddingmediasimulateperiodontalligaments through their physical and electrical properties and thus could affect the results if those media vary from the natural tissue. Electrical properties of intra- canal solution, particularly with extremes of electro- conductivityandionconcentration,cansignificantly influence the EFLs’ accuracy. The discrepancies vary amongst the different EFL models. roots1_2010 Determining working length, or how to locate the apical terminus (Part 2) Authors_Prof Vladimir Ivanovic & Dr Katarina Beljic-Ivanovic, Serbia Figs. 1a & b_Two identical EFLs sold under different brand names. Fig. 1a Fig. 1b