Flute and Shank Dimensions of Reciprocating Instruments before and after Simulated Root Canal shaping.

AIM

This study analyzed the effect of the dimensions of the flute and shank in the first 4 mm of instrument tips on the deformation and dimensional changes of reciprocating instruments after root canal shaping (RCS).

MATERIALS AND METHODS

The reciprocating instruments used were Reciproc R25, R40, and R50; WaveOne Small, Primary, and Large; and Unicone #20, #25, and #40. Scanning electron microscopy images of the first 4 mm of the tip were acquired at 30× magnification before and after simulated curved root canals were shaped. Each instrument was used only once. The images were transferred to the AxioVision software to measure the flute area (μm), shank area (μm), flute length (μm), and cross-sectional diameter (μm). Student's t test for paired samples was used to compare differences before and after RCS, and analysis of variance followed by the Tukey test, to compare differences between instruments of similar sizes. The instruments were classified according to deformations after RCS.

RESULTS

Reciproc instruments had larger flutes and smaller shanks. The Reciproc R40 had significant differences in cross-sectional diameter at 0.5 mm from the tip. Reciproc had no plastic deformations. Unicone #20 instruments had significant differences in cross-sectional diameter at 1.5 and 3.0 mm from the tip, and #25 instruments had differences at 1.5 and 3.0 mm and in length of the second and third flutes. One #20 and three #40 instruments had plastic deformations. The differences in length of the first and fourth flutes of WaveOne Primary and in cross-sectional diameter at 2.0 mm from the tip of WaveOne Large were significant. Two of three WaveOne Large instruments had plastic deformations.

CONCLUSION

Reciproc instruments had greater flute areas and lengths and smaller shanks than Unicone and WaveOne instruments of similar sizes. Reciproc instruments had a greater flute-to-shank ratio. WaveOne instruments had the lowest flute-to-shank ratio. Unicone instruments had the most plastic deformations. Instruments with larger flutes and smaller shanks had fewer plastic deformations after curved RCS.

CLINICAL SIGNIFICANCE

The knowledge of mechanical behavior before choosing the endodontic instrument may avoid fracture, regardless of the clinical condition, and it is essential to the success of root canal treatment.