Successful root canal treatment depends on thorough cleaning & shaping and 3- dimensional fluid impervious obturation of tooth within the confines of canals. To achieve this objective  the apical constriction must be detected accurately during canal preparation and precise  control over  working length  during the  procedure must  be maintained.  There are  many methods  of working length determination including  radigraphs  and electronic method(apex locator). Introduction of apex locators  have definitely served  as an effective adjuvant  to radiographs. 

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