Effectiveness Of Different Instrumentation For Root Canal Retreatment Using Three-Dimensional Models Based On Micro-CT Data

Aim:To establish the three-dimensional model of human permanent premolar based on Micro-CT data to facilitate clinical research of Endodontics, using which as a quantitative research method to evaluate the effectiveness of different methods for retreatment of root canals.Methods:1. The establishment of three-dimensional model:One permanent premolar was scanned by using Micro-CT. With the NRecon software,1121 images obtained from the scan were reconstructed to illustrate the 2-D slices in the format of BMP. Mimics software was used for the 3-D reconstruction.2. The effectiveness of different methods for retreatment of root canals:Forty permanent premolars were collected and prepared by using ProTaper nickel-titanium files. Access into the canals was carried out and the work length was determined. During the preparation,0.5% sodium hypochlorite, saline and EDTA were used as irrigants. All canals were dried with paper points and filled by using cold lateral condensation with Gutta-percha and Cortisomol. Glass ionomer and nail polisher were used to seal the subjects. After incubation in 100% humidity at 37℃for 72 hours, subjects were scanned by using Micro-CT. Forty teeth were randomly divided into two groups that were allocated a retreatment technique by using K-flexo file or ProTaper Universal Retreatment system. Then all subjects were scanned again and the mean percentage of remaining filling material and the scores of the appearance of materials presented in upper, middle and apical 1/3 were calculated.Results:A three-dimensional model was obtained, providing a 3-D platform for the clinical research of Endodontics. Mean volumes of the remaining filling material by K-flexo file were lower than ProTaper Universal Retreatment system (P<0.05). The scores demonstrated that K-flexo file had greater effectiveness than ProTaper Universal Retreatment system when retreating the apical 1/3 of canals (P<0.05).Conclusion:Micro-CT with its high spatial resolution, wide ranges of voxels, smaller voxel of volumes and low radioactivity, is rapidly becoming the most essential components of academic research in the realm of Endodontics. The present study showed that both techniques could not remove filling materials completely. In this case, a combination of these two techniques and a further shaping of canals might result in a more effective removal of filling materials.