Canal-centering ability of two rotary file systems

The ability of two nickel-titanium rotary file systems to maintain the original path of the canal were compared by using a new split-mold design (the Endodontic Cube). The mesial roots of 10 mandibular first- and second-molar teeth with separate canals from orifice to foramen were divided into two groups based on canal curvature and morphology. Working lengths for each canal were determined 1.0 mm short of where the file tip was visible on the external surface of the root. The teeth were embedded in composite resin by using the Endodontic Cube as a mold and sectioned into five pieces. ProFile Ni-Ti.06 taper Series 29 and ProFile GT rotary instrumentation techniques were randomly assigned to one of the canals and used in a crown-down fashion to a 0.217 ProFile and a 0.06 GT master apical file, respectively. Digital photographs were made of the middle three sections and software features of Adobe Photoshop were used to measure the movement of the canal centers by superimposing the images of the instrumented and uninstrumented canals. Data were analyzed using ANOVA. Both systems remained centered within the canal with minimal deviation from the original canal path. The largest mean movement was less than 0.15 mm. The Endodontic Cube was an effective tool for studying and comparing instrumentation techniques.