Computer-assisted photomicrographic evaluation of root canal morphology after removal of the filling material during retreatment.

AIM: The purpose of this study was to evaluate the morphology of the apical third of the root canal and the effectiveness of rotary instrumentation for the removal of lateral condensed gutta-percha during endodontic retreatment. MATERIALS AND METHODS: Thirty roots with canals with regular morphology were prepared to apical size #30 and were filled with gutta-percha/AHPlus using lateral condensation. Digital radiographs of teeth were captured. After two weeks, canals were retreated to size 40 using ProTaper rotary instruments, without solvent. Roots were embedded in resin blocks and reduced incrementally at four different apical levels (at 0.5, 1.0, 1.5 and 2.0 mm from the apical foramen). The sectioned surfaces were observed under a metallographic optical microscope and digital micrographic images were captured and processed. Perimeter covered with root-filling residue was expressed as percentage of total canal perimeter for all specimens. RESULTS: Residue percentage was greater at 2.00 mm from apical level than at other levels. Most residue of filling material in all specimens was observed at 0.5 and at 2.0 mm from apex. The use of ProTaper instruments allowed the removal of gutta-percha and AHPlus sealer in the apical 2 mm in average 50% of the cases. CONCLUSIONS: The resulting morphology of the prepared canals allowed root fillings performed with gutta-percha and AHPlus sealer that were efficiently removed by using rotary instruments. More material residue was found adhering to the canal walls in the apical segments of canals. The removal of this residue was enhanced by apical enlargement beyond the diameter of the canal before retreatment.