E Jalalian, Ar Banifatemeh, A Zarbakhsh, A Eskandari Damaneh, E Hashemi, M Shariaty,
Volume 4, Issue 2 (6-2019)
Abstract
Background and Aim: Screw loosening is a common problem with both screw-retained and cemented implant restorations. It is assumed that the abutment diameter affects detorque value and screw loosening. We aimed to determine the effect of two different abutment diameters on detorque value using cyclic loading and thermocycling.
Materials and Methods: This in-vitro experimental study was conducted on sixteen Morse-taper implants (4×10 mm) with two different diameters (3.9 and 5.2 mm) installed with a 25-Ncm torque (n=8). Eight screws from each group (3.9- and 5.2-mm abutments) were maintained for a month in a stable state while the rest of the screws underwent cyclic loading for 10,000 cycles with the frequency of 1 Hz and force of 75 N/cm. Then, thermocycling was done at 5-55°C. Detorque value was determined using the torque meter used for screw tightening. Removal torque values were recorded. Maximum deformation force and fracture resistance were documented. Data were analyzed according to Student's t-test using SPSS 21.0 software.
Results: Detorque values were 18.25±1.91 and 21.13±1.46 Ncm with 3.9- and 5.2-mm abutments, respectively. Detorque loss value was 15.50±5.83% with 5.2-mm abutment and 27±7.63% with 3.9-mm abutment. The mean difference between the two abutment diameters was 2.87±0.85 Ncm. Significant differences were observed on torque loss with 3.9-mm- compared to 5.2-mm-diameter abutments (P=0.004).
Conclusion: The results suggested that torque loss was lower with 5.2-mm abutment diameter.
M Sedigh-Shams, R Ebrahimi, B Asheghi, F Eskandari,
Volume 7, Issue 1 (2-2022)
Abstract
Background and Aim: Despite the advantages and conveniences that NiTi files offer, their main drawback is their catastrophic fracture due to cyclic and torsional fatigue leading to instrument separation. This study aimed to compare the cyclic fatigue resistance of two single file engine-driven instruments, HyFlex EDM and NeoNiTi A1, in simulated curved canals.
Materials and Methods: In this experimental study, NiTi endodontic instruments with a similar tip size of 0.25 mm were investigated in two groups of 20: HyFlex EDM (group A) and Neoniti A1 (group B). Evaluation of cyclic fatigue was conducted in a stainless steel artificial canal with a 60° angle and 5-mm radius curvature. HyFlex EDM and Neoniti A1 instruments were operated based on the instruction for use provided by the manufacturers. All instruments were rotated (at 400 rpm) until fracture, and the number of cycles to fracture (NCF) and the length of the fractured tip were documented. Means and standard deviations of NCF and fragment length were determined for each system and compared using the Mann-Whitney test (P<0.05).
Results: A statistically significant difference was detected when comparing the NCF, and time until fracture of HyFlex EDM and Neoniti A1 instruments (P=0.001). HyFlex EDM instruments showed significantly greater mean NCF in comparison with Neoniti A1 instruments (2984.75 ± 576.14 vs. 839.55 ± 305.5 NCF). No statistically significant difference was found in the mean length of the fractured fragments between the instruments (P=0.683).
Conclusion: HyFlex EDM instruments showed significantly greater cyclic fatigue resistance compared with Neoniti A1 instruments.
