Efficacy, cleaning ability and safety of different rotary NiTi instruments in root canal retreatment

To evaluate the efficacy, cleaning ability and safety of three different rotary nickel-titanium instruments with and without a solvent (eucalyptol) versus hand files in the removal of gutta-percha root fillings.

Eighty extracted single-rooted anterior teeth were enlarged to size 35 and obturated with laterally condensed gutta-percha using AHPlus as the sealer. Removal of gutta-percha was performed with the following devices and techniques: FlexMaster, GT Rotary, ProTaper and Hedström files. All techniques were used with and without the solvent eucalyptol. The following data were recorded: time taken to reach the calculated working length and time required for the removal of gutta-percha. The teeth were split longitudinally and photographed. Cleanliness of the root canal walls was scored using the projected slides with a total magnification of approximately 70x. Statistical analysis was performed using the two-way anova (P < 0.001) for the analysis of working time.

The technique that reached the working length most rapidly was that using ProTaper instruments and eucalyptol (+E), followed by FlexMaster + E, ProTaper, FlexMaster, Hedström files + E, GT Rotary + E, Hedström files, and GT Rotary. No significant differences were found for retreatment with or without a solvent in all groups. ProTaper and FlexMaster worked significantly more rapidly than Hedström files and GT Rotary (anova, P < 0.001). Time for complete removal of gutta-percha was again shortest with ProTaper + E, followed by FlexMaster + E, ProTaper, FlexMaster, GT Rotary + E, Hedström files + E, Hedström files, and GT Rotary. ProTaper and FlexMaster again worked significantly faster than the other techniques (anova, P < 0.001). There was no visible filling material extruded apically. Root canal cleanliness proved best following the use of FlexMaster + E, and Hedström files + E, followed by ProTaper + E, and GT Rotary + E.

Under the experimental conditions, FlexMaster and ProTaper NiTi instruments proved to be efficient and time-saving devices for the removal of gutta-percha. The use of eucalyptol as a solvent shortened the time to reach the working length and to remove the gutta-percha, but this was not significant.