Advances in Working Length Determination Publisher



Nekoofar MH¹ Show Affiliations
Source: Endodontic Advances and Evidence-Based Clinical Guidelines Published:2022

Abstract

There is general consensus that root canal procedures should be limited within the confines of the root canal, with the logical endpoint for preparation and filling being the narrowest part of the canal, the so-called apical constriction. It is not possible to predictably detect the position of the apical constriction clinically; indeed, the constriction is not uniformly present or may be irregular. Equally, it is not logical to base the endpoint of root canal procedures on an arbitrary distance from the radiographic apex as the position of the apical foramen is not related to the apex of the root. Electronic root canal length measuring devices (ERCLMDs) offer a means of locating the most appropriate endpoint for root canal procedures, albeit indirectly. The principle behind most ERCLMDs is that human tissues have certain characteristics that can be modelled by means of a combination of electrical components. Then, by measuring the electrical properties of the model (e.g. resistance, impedance), it should be possible to detect the canal terminus. Thus, most modern ERCLMDs are capable of recording the point where the tissues of the periodontal ligament begin outside the root canal, and hence from this, a formula can be applied to ensure that preparation is confined within the canal. Most reports suggest that 0.5 mm should be subtracted from the length of the file at the point when the device suggests that the file tip is in contact with the PDL (zero reading). This does not mean that the constriction is located; rather it means that the instrument is within the canal and close to the PDL. It is not appropriate to rely on any device reading 0.5 mm short of the foramen as this will often be inaccurate. The use of generation X to describe and classify these devices is unhelpful, unscientific, and perhaps best suited to marketing campaigns. This chapter describes the fundamental operating principles of ERCLMDs and classifies them on this basis. Initially, a review of basic electronics is presented in order to provide an understanding of electronic devices and circuits. The electronic function and clinical application of ERCLMDs is then discussed. © 2022 John Wiley & Sons Ltd. All rights reserved.