Restor Dent Endod.  2023 Feb;48(1):e10. 10.5395/rde.2023.48.e10.

Buckling resistance, torque, and force generation during retreatment with D-RaCe, HyFlex Remover, and Mtwo retreatment files

• Kim Y
• Chang SW
• Oh S

• KMID: 2548167
• DOI: http://doi.org/10.5395/rde.2023.48.e10

Abstract

Objectives
This study compared the buckling resistance of 3 nickel-titanium (NiTi) retreatment file systems and the torque/force generated during retreatment.
Materials and Methods
The buckling resistance was compared among the D-RaCe (DR2), HyFlex Remover, and Mtwo R25/05 retreatment systems. J-shaped canals within resin blocks were prepared with ProTaper NEXT X3 and obturated by the single-cone technique with AH Plus. After 4 weeks, 4 mm of gutta-percha in the coronal aspect was removed with GatesGlidden drills. Retreatment was then performed using DR1 (size 30, 10% taper) followed by DR2 (size 25, 4% taper), HyFlex Remover (size 30, 7% taper), or Mtrwo R25/05 (size 25, 5% taper) (15 specimens in each group). Further apical preparation was performed with WaveOne Gold Primary. The clockwise torque and upward force generated during retreatment were recorded. After retreatment, resin blocks were examined using stereomicroscopy, and the percentage of residual filling material in the canal area was calculated. Data were analyzed using 1-way analysis of variance with the Tukey test.
Results
The HyFlex Remover files exhibited the greatest buckling resistance (p < 0.05), followed by the Mtwo R25/05. The HyFlex Remover and Mtwo R25/05 files generated the highest maximum clockwise torque and upward force, respectively (p < 0.05). The DR1 and DR2 files generated the least upward force and torque (p < 0.05). The percentage of residual filling material after retreatment was not significantly different between file systems (p > 0.05).
Conclusions
NiTi retreatment instruments with higher buckling resistance generated greater clockwise torque and upward force.

Keyword

Buckling resistance; Root canal retreatment; Torque; Upward force

Figure

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  Figure 1 Experimental setup for the (A) buckling resistance test and (B) retreatment.

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  Figure 2 Results of tests for (A) buckling resistance, (B) maximum clockwise torque, and (C) maximum upward force.The different lowercase letters in each figure indicate significant differences between nickel-titanium retreatment instruments.

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  Figure 3 Representative graphs of the upward force and torque generated during retreatment. The upward force is presented as a positive value in the graph for force vs. time. Clockwise torque is shown as a positive value in the graph for torque vs. time. The coronal level of the resin block was considered point zero, and downward movement toward the apex was described as a negative value in the vertical direction.

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  Figure 4 Representative stereomicroscopic images of resin blocks after retreatment. (A) Retreatment using DR1, DR2, and WaveOne Gold Primary. (B) Retreatment using HyFlex Remover and WaveOne Gold Primary. (C) Retreatment using Mtwo R25/05 and WaveOne Gold Primary.

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