Effect of removal of canal filling materials with different instruments

Objectives: To compare the ability of removal of filling materials with different instruments in re-treatment of filled root canals. Methods: 48 canals from single-rooted maxillary anterior teeth were instrumented by a standardized method to an apical ISO size 40. They were obturated with iodoform paste and laterally condensed gutta-percha, divided into four groups. Re-treatment was performed with the following techniques: K-files(groupI); H-files(groupII); K-files with reciprocal(groupIII); H-files with reciprocal(groupIV). Chloroform was used in all groups. The time required to achieve the working length was recorded. The teeth were subsequently split longitudinally, photographs were taken with a digital camera and the remnants within the root canals after re-treatment were examined. The amount of filling materials been pushed out of apex was also recorded. The results were compared by means of ANOVA test and Chi square test among the four groups. Results: Group IV was significantly faster than other groups (P<0.01)to achieve the working length. All groups left gutta-percha inside the canal, and there was no significant difference among them in the coronal and middle third of canal. But in the apical third of canal, Group IV was clearer than other groups(P<0.05). There was a perforation in group III. Conclusions: H-files removed the filling materials faster and cleaner than other instruments. Reciprocal instruments could lighten the working intensity. But there was a risk of perforation. It's necessary to clean and shape the root canal subsequently.