Abstract
The main aim is to evaluate the cyclic fatigue resistance of blue heat-treated instruments with different kinematics. Twenty-four endodontic instruments of the same brand were used for each of three experimental groups: VB (Vortex Blue 40/0.04), RB (RECIPROC Blue 40/0.06), and XB (X1 Blue 40/0.06). The instruments were randomly distributed and subjected to temperatures of 20°C and 37°C. The fatigue test was performed using a stainless steel device. Data were analysed using the Shapiro–Wilk test, Student's t-test, the F test, and Tukey's and Tamhane tests at significance level P=0.05. The instruments' cyclic fatigue resistance at both temperatures differed significantly for each instrument type (P < 0.001). The RB instruments displayed greater cyclic fatigue resistance at the tested temperatures compared with the VB and XB instruments (P < 0.001). Reciprocating kinematics positively influenced cyclic fatigue resistance. Blue heat-treated instruments showed decreased cyclic fatigue resistance as the temperature increased (P < 0.001).
Highlights
Cyclic fatigue is one of the main mechanisms leading to nickel titanium (NiTi) instrument fracture in root canals [1,2,3,4]. is type of fatigue is caused by alternating tensile and compressive stresses when the instrument is inside a curved canal, and the instrument typically fractures in the area of maximum curvature [5, 6]
Per their manufacturers, when subjected to blue thermal treatment, the instruments Vortex Blue (VB; DENTSPLY Tulsa Dental, Tulsa, Oklahoma, USA), RECIPROC Blue (RB; VDW, Munich, Bayern, Germany), and X1 Blue (XB; MK Life, Porto Alegre, Rio Grande do Sul, Brazil) are indicated when better cyclic fatigue resistance is desired. us, the present study evaluated the cyclic fatigue resistance of instruments with blue thermal treatment and different kinematics, continuous, and reciprocal rotation (Vortex Blue, RECIPROC Blue, and X1 Blue) at 20°C (±0.5°C) and 37°C (±0.5°C) simulating room temperature and the temperature inside the root canal, respectively
Discussion e results of the present study showed that decreased temperatures increased the cyclic fatigue resistance of blue heat-treated instruments. ese instruments are the result of the oxidation that heating and cooling induce on their surface, making the NiTi alloy more martensite, giving it better fatigue life [18]
Summary
Cyclic fatigue is one of the main mechanisms leading to nickel titanium (NiTi) instrument fracture in root canals [1,2,3,4]. is type of fatigue is caused by alternating tensile and compressive stresses when the instrument is inside a curved canal, and the instrument typically fractures in the area of maximum curvature [5, 6]. The mean time to fracture is not directly proportional to the increase in the number of reciprocations required for a complete rotation (360°) probably because the resulting speeds are not directly proportional [26] Per their manufacturers, when subjected to blue thermal treatment, the instruments Vortex Blue (VB; DENTSPLY Tulsa Dental, Tulsa, Oklahoma, USA), RECIPROC Blue (RB; VDW, Munich, Bayern, Germany), and X1 Blue (XB; MK Life, Porto Alegre, Rio Grande do Sul, Brazil) are indicated when better cyclic fatigue resistance is desired. Us, the present study evaluated the cyclic fatigue resistance of instruments with blue thermal treatment and different kinematics, continuous, and reciprocal rotation (Vortex Blue, RECIPROC Blue, and X1 Blue) at 20°C (±0.5°C) and 37°C (±0.5°C) simulating room temperature and the temperature inside the root canal, respectively. E mean fragment length (4.62–5.40 mm) did not differ significantly among the instruments tested at 20°C or 37°C (P > 0.05)
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