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38 I I research _ working length One of the first questions the study aimed to address was: are differences between real values of distances from the file tip to the referent point and those shown on a EFL display clinically significant? Usingahigh-techelectronicmicrometer,withmeas- uring precision at 0.1µm, the distances from the file tip to the reference point (anatomical foramen) were measured. We tested and gained almost identical results for all four EFLs. Thefindingsofthisstudycanbesummarisedthus: a) Figures or marks on the display of the EFL scales do not represent strict values in mm. b) Thedifferencebetweentherealvaluesandthoseon thedisplayissmallerthan0.5mm(Figs.2a&b),and thus may be considered clinically insignificant, owing to our manual inability to distinguish such short movements of the canal instrument. c) We may tolerate small differences between real values on a high-tech measuring instrument and thoseonthedisplayoftheEFLsbecausetheyarenot even detectable by the hand of a practitioner, since theyareapproximately300µmandsmallerandare therefore acceptable in clinical work (Figs. 3 & 4). While taking measurements, we sometimes no- ticed a slight bouncing on the scale of the EFL, even whenthefiletipwasnotmovingintherootcanal.This wasduetoaslightmixingofelectrolytesandchanges in ion concentrations between the embedded media outside and solution inside the root canal at the level of the apical foramen. Therefore, in clinical use wait- ing for three to four seconds for a stable reading is recommended. Following this study, Prof Moshonov wished toaddressamoredetailedandprofoundquestion:to what extent do the readings on a display correspond to the real values on a high-tech measuring instru- ment? In addressing this question, he examined two models of mini-EFLs: the MedicNRG-XFR and the MedicNRG-Blue. The MedicNRG-XFR displayed extra fine reso- lution with very small values of distortion from the real measurements—only 12 to 38µm in instances in whichtheEFLindicated0.25mmfromthemark‘apex’ (Fig. 5a) and 22 to 65µm at the 0.5mm mark from the ‘apex’ on a EFL display (Fig. 5b). The MedicNRG-Blue enables users to connect to their PC via a Bluetooth connection. Prof Moshonov compared the value on the EFL itself with a scheme on the screen of a PC. He found that there was no Figs. 5a & b_The MedicNRG-XFR displays extra fine resolution and very small values of distortion from the real measurements: from 12 µm (a) to 65 µm (b). Fig. 4_Tolerable difference of 300 µm between the real value and that shown on the Raypex 5. roots1_2010 Fig. 4 Fig. 5a Fig. 5b

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