Authors: Weine FS, Healey HJ, Gerstein H, Evanson L.
Title: Pre-curved files and incremental instrumentation for root canal enlargement.
Journal: J Can Dent Assoc
Date: Apr 1970
Citation: 36(4):155-7
Category: Access and Canal Instrumentation
Evidence-based Ranking: 5
Discussion: A straight instrument should never be inserted into a curved canal because its tip may penetrate the comparatively soft dentinal wall and cause formation of a ledge or a perforation. This hazard is eliminated by precurving an instrument to approximate the configuration of the canal as determined by tactile sensation or with preoperative radiographs. When the radiograph indicates a root dilaceration or when an obstruction is encountered only the apical portion of the instrument is given a sharp curve. For all other cases, a gradual curve is used throughout the length of the instrumentÂ’s cutting edge. This is achieved by drawing an instrument over a metal ruler, cotton pliers or a fingernail. Also, during instrumentation, intermediate increments maybe established by trimming the tip of smaller instruments before using the next size. This is accomplished by cutting off 1mm of the tip with sharp scissors and then using a diamond fingernail file to re-establish the bevel and remove sharp edges from the tip. If 1 mm is trimmed from a size 10 that has a .02 taper, it becomes equivalent to a size 12 instrument. This method may be employed in any canal where the next larger instrument does not readily go to place.

ReviewerÂ’s comments: This article describes simple but very useful techniques that immensely aid canal instrumentation with stainless steel files.