Comparison of Two Rotary Instruments to Preserve Root Canal Morphology

Background. Proper cleaning and shaping of root canal systems cannot be determined by post operative radiographs of root filled teeth as radiographs are two dimensional images of three dimensional objects. There are currently two methods in which canal morphology of teeth can be studied before and after instrumentation; Cube Methodology and the use of the CT scan. The Cube Methodology was used in this study. Objective. To compare the ability of two rotary instruments to preserve the morphology of the root canals of human molar teeth. Methods. A pre-existing collection of extracted human first and second molar teeth (n = 25) radiographically demonstrating a Vertucci type IV canal configuration with two separate canals from orifice to foramen were used. The teeth were embedded in composite resin using the endodontic cube as a mold (Kuttler et al., JOE 2001;27:533-6). Each of the embedded teeth was cut into transverse slices. The slices were re-assembled into complete teeth using the endodontic cube. In each tooth, one root canal was cleaned and shaped using the 06 ProFile (Dentsply, Maillefer, Ballaigues, Switzerland), and the other canal with the K3 g-pack (SybronEndo, West Collins, CA) rotary instruments according to manufacturers’ guidelines, with all groups being prepared to size 25 and then to 40 apical file. The working lengths for each canal were determined 1mm short of the apex using a #15 file. The tooth slices were digitally scanned before and after preparation, and image analysis software was used to assess changes in the morphology of the root canals. The data was analyzed by ANOVA and Scheffe post-hoc statistical tests (p values) at a significance of 95%. Results. The use of different files created different deviations of the center-line of the root canal (p = 0.0001) and different root canal areas (p = 0.000). The ProFile 25 06, 40 06 and the K3 equivalents cut very similar root canal centerlines (p \u3c 0.05). The area of root instrumentation was lower with the Profile 25 06 compared to the K3 25 06 (p = 0.0004), while both the Profile 40 06 and K3 40 06 area were similar (p = 0.3389). These results suggest ProFile 25 06 instruments are better at retaining the morphology of molar root canals than the K3 25 06 instruments, but the larger files have the same effects. Conclusion. The K3 and ProFile 25 06, 40 06 files were able to maintain the original root-canal morphology. The ProFile 25 06 removed less dentin tooth structure than the K3 25 06. The K3 25 06 and 40 06 files removed a similar amount of dentin tooth structure. This could be due because the K3 file system has coronal files of different taper sizes; .12, .10 and 0.8