Establishing the working length is an important step in endodontic treatment as inaccurate length determination may lead to failure. There is an ongoing debate regarding the extent of the apical limit of root canal preparation. This controversy is based upon different clinical opinions concerning the distance between the end point of the root canal preparation and the periodontal tissues. In this paper, we review the different schools of thought for working length determination, and how apex locators work and how they must be used for optimal accuracy. The reliability of these devices has been proven; the price is moderate and apex locators are now part of the basic armamentarium in the achievement of quality and predictable endodontic treatment. Simon et al. 2009

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Apical Limit and Working Length in Endodontics