Comparison of three different techniques on the efficacy of canal filling material removing using micro computed tomography

다국어 초록 (Multilingual Abstract)

Achieving high quality retreatment, the removal of previous filling materials is the first importance. Several techniques have been used to remove sealer and gutta-percha but none of them can completely clean the root canal walls, particularly in the apical third. That’s significant etiological factor for the success of nonsurgical retreatment. Recently studies showed that the passive ultrasonic irrigation (PUI) technique was only more effective than the conventional irrigation technique in removing residual root filling material in cervical and middle third of root canals. However, the action of the PUI may have been reduced in the apical third because the curvature in the root canals limited apical enlargement. Gentlefile Brush (GB) was invented to overcome the disadvantages of previous instruments, base on the effective of centrifuge force to remove the filling material from the apical third. Micro-CT system can evaluate the quality of the preparation and the quality of the endodontic retreatment in 3D manner nondestructively while preserving the specimen.
The aim of this study was to assess the quality of endodontic retreatment by three difference techniques after filled with gutta-percha cone and Well-root MTA sealer, by measuring the percentage of volume debris of gutta-percha and sealer remain intracanal for filling artificial molars with Micro-CT.
The filling material was removed from 30 plastic teeth by Nickel-titanium (Ni-Ti) rotary retreatment system. Final irrigation was performed with 2 mL of saline and 10 specimens was randomly allocated in conventional group (n = 10). In PUI group, irrigation with ultrasonic was added to the conventional group procedure for 10 specimens. In GB group, irrigation with GB was added to the conventional group procedure for 10 specimens. To measure the volume of the filling material remain after retreatment and the volume of root canal, Micro-CT (3D) images of the filling material were visualized by CT-Vol. When measuring the amount of filling material remain, a gray scale range between 124 and 255 was assigned as volume of the filling material (Vm), and a gray scale range between 0 and 124 was assigned as volume of empty root canal (Vc).
The results showed the total mean volume of residual filling material of an artificial tooth after retreatment in conventional group, PUI group and Gentlefile Brush group were 4.84896 mm3, 0.80702 mm3, and 0.05248 mm3, respectively. The volume of filling materials remain in apical area of GB group was significantly lower than conventional group and PUI group (p < 0.05). The volume of filling material remain in middle area and coronal area was significantly higher in conventional group, compare with PUI group and GB group (p < 0.05). In PUI group, the volume of filling materials remain was significant higher in apical area compared with middle area and coronal area (p < 0.05). Observation by stereo microscope demonstrate that the filling material remain stayed on the root canal wall. However, in PUI group, a large amount of filling materials was remained mainly focused in apical area.
The findings of this study indicated that the cleaning effect of GB system was superior to those of NiTi Retreatment files and PUI system in apical area. The cleansing effect of the GB is not impeded by the number of curvature of the root canal due to the GB's properties. GB is better than other techniques used in non-surgical retreatment to remove old root canal filling materials.