Effect of number of uses and sterilization on the instrumented area and resistance of reciprocating instruments

Abstract

Objectives: This study evaluated the effect of repeated uses and autoclaving in the instrumented area, fracture resistance, and time of instrumentation of thermally treated nickel-titanium reciprocating systems.

Materials and methods: Two hundred simulated canals were instrumented using Reciproc Blue and WaveOne Gold. Each file was used up to 10 times or until fracture. The instrumented area was measured in pre- and post-operative images, using ImageJ software. Kaplan-Meier survival analysis evaluated the number of uses of instruments before fracture. Instrumented area and time of instrumentation were analyzed by Mann-Whitney U test and Kruskal-Wallis. Correlations among the number of uses and instrumented area were measured. The level of statistical significance was set at p < 0.05.

Results: Reciproc Blue presented a higher estimated number of uses in comparison with WaveOne Gold (p = 0.026), but autoclaving did not affect the resistance to fracture of instruments (p > 0.05). The instrumented area was different among the evaluated groups (p = 0.039), and the instrumented area along the uses of both tested instruments was reduced. With the time of instrumentation, there was also a significant difference among the evaluated groups; the groups without sterilization cycles were faster, in comparison to those submitted to autoclaving (p = 0.010).

Conclusions: Reciproc Blue was more resistant than WaveOne Gold, suffering later fracture. Additionally, the sterilization cycles did not influence the estimated number of uses of thermally treated reciprocating instruments, but the instrumented area of root canals was reduced along with the repeated uses of both instruments.

Keywords: Instrument fracture; Instrumentation; Reciproc Blue; Sterilization; WaveOne Gold.

Figure 1. Example of a pre-instrumentation image achieved, and transferred to ImageJ software (version 1.43; National Institutes of Health). The image of the root canal before and after instrumentation was selected and the number of pixels per millimeter was registered through the measure tool.

Figure 2. Image of the instruments achieved to illustrate fracture and locate morphological alterations before eventual fractures. (A) WaveOne Gold with no deformation or fracture; (B) Reciproc Blue after fracture.

Figure 3. Graphic representation of Kaplan-Meier survival analysis. The estimated survival (number of uses to fracture) of Reciproc Blue was 8.88 uses without sterilization, and 8.36 uses when autoclaved between the uses (p = 0.085); while WaveOne Gold presented an estimated survival of 7.05 without autoclaving, and 6.88 when submitted to sterilization (p = 0.853).

Figure 4. Graphic illustrating the reduction in the instrumented area (pixels per mm²) along the uses within the evaluated groups (WaveOne Gold and Reciproc Blue, with and without sterilization cycles).