Retreatment of Root Fillings with Four Nickel-titanium Instrument Systems

OBJECTIVES: Evaluation of the efficacy of four rotary nickel-titanium instrument systems regarding residues of gutta-percha and sealer by means of light microscopy.

METHODS: Fourty-four root canals were prepared to apical size 40 taper .04 with FlexMaster instruments (VDW Dentsply, Munich, Germany). Root canals were filled with AH Plus (DeTrey/Dentsply, Konstanz, Germany) and laterally condensed gutta-percha. After 1 week, canals were retreated using the instrument systems according to the sequence recommended by the manufacturers. Teeth were randomly assigned to four groups (n=11) and root fillings were retreated with: group1; ProFile (Dentsply-Maillefer, Ballaigues, Switzerland); group2: AlphaSystem (Brasseler, Lemgo, Germany); group3: Mtwo (VDW); group4: Liberator (Miltex, York, PA, USA). Apical preparation size was limited to size 40 taper .04 for comparability reasons because Mtwo instruments and Alpha System instruments were not available in larger sizes. Retreatment time was recorded. Roots were fractured longitudinally and light microscopic images were taken from each specimen. Coded images were investigated for residues of gutta-percha and sealer according to the classification of Hülsmann et al. (J Endod 1997;23:301-6) modified for residues of root fillings. Statistics were computed with SPSS 14.0 software (SPSS Corporation, Chicago, IL, USA).

RESULTS: Presence of residues revealed significant differences between groups (t-test, P<0.05). The percentage of residue-coated canal surface in all specimens was significantly greater in the apical third (ANOVA, P<0.05). Retreatment was significantly faster with Liberator and Mtwo instruments (t-test, P<0.05).

CONCLUSION: Within the limits of this study, none of the tested instrument system allowed complete removal of residues. Further enlargement is recommended to sufficiently remove sealer and gutta-percha residues, especially in the apical part of the root canal.