Farkli niti alaşımlarından yapılmış döner aletlerin döngüsel yorgunluk direncinin, bükülme direncinin, ve mikrosertliğinin in vitro değerlendirilmesi

In Vitro Evaluation of Cyclic Fatigue Resistance, Bending Resistance, and the Microhardness of Different NiTi Alloy Rotary Instruments. Yeditepe University Institute of Health Sciences. Faculty of Dentistry, Department of Endodontic, PhD Thesis, Istanbul. This study was conducted to compare the mechanical properties of the Protaper Next (PTN), Hyflex CM, EdgeFile, and XP -endoShaper, and to analyze the influence of the temperatures, sodium hypochlorite (NaOCl) immersion, and sterilization on the cyclic fatigue resistance of these instruments in a single and double (S- shape) canal curvatures. Four types of Nickel-Titanium (NiTi) rotary instruments: Protaper Next- X3 (30/0.07), Hyflex CM (30/0.04), EdgeFile- X7 (30/0.04), and XP-endoShaper (30/0.01) were evaluated. Each brand of the NiTi instruments was divided into 4 groups (n=20/each group; 10/subgroup) during the cyclic fatigue test as followed: Group 1 (control group) was composed of new instruments without immersed in NaOCl or subjected to autoclave sterilization at room temperature. Group 2 was composed of instruments with immersed in 5% NaOCl solution without sterilization at body temperature, Groups 3 was composed of instruments with immersed in 5% NaOCl solution and 1-time sterilization at body temperature. Groups 4 was composed of instruments immersed in 5% NaOCl solution with 5-times sterilization at body temperature. The number of cycles to failure (NCF) was calculated. The fracture surface of instruments was assessed by using a scanning electron microscope (SEM). The files were tested for bending resistance by using a cantilever- bending test (n=20/each brand). Vickers microhardness was measured on the cross-section of instruments with 300-g load and 15-second dwell time (n=20/each brand). Statistical analysis was carried out using a three-way analysis of variance (ANOVA) and Bonferroni's post hoc analysis for cyclic fatigue test, and one-way analysis of variance (ANOVA) and Games-Howell post hoc analysis for bending resistance and microhardness tests. The statistical significance level was established at p < 0.05. The results show that, the difference in the NCF of all the instruments was statistically significant (p < 0.05). The NCF of EdgeFile and XP -endoShaper were higher than Hyflex CM and PTN (p < 0.05) in all tested groups. The NCF was significantly influenced by the file types (p < 0.05) in all tested groups, angle and curvature locations (p < 0.05) in all tested files except PTN (p > 0.05), and surrounding medium conditions (p < 0.05) in all tested files except PTN and Hyflex CM (p > 0.05). No statistical difference in the length of the separated part at all tested groups (p > 0.05) except at angle and curvature locations (p < 0.05). The ranking in bending resistance values was as follows: PTN > HCM > EdgeFile > XP-endoShaper. The order of the microhardness test from lowest to highest values was as follows: Hyflex CM < XP-endoShaper < PTN and EdgeFile, and there was no statistical difference between PTN and EdgeFile (p > 0.05). In conclusion, EdgeFile significantly outperforms other brands in terms of fatigue resistance, followed by XP-endoShaper. All files except PTN showed a significant decrease in NCF in more challenging canals. The NCF of both EdgeFiles and XP-endoShaper is harmed by body temperature and NaOCl immersion, whereas sterilization has a favorable influence on EdgeFile's NCF but a detrimental one on XP- endoShaper's. In comparison to the other brands examined, XP-endoShaper demonstrated the most flexibility, followed by EdgeFile. When compared to other brands, PTN and EdgeFiles showed greater wear resistance. Keywords: Mechanical properties, NiTi rotary instruments, body temperature, irrigation, sterilization.