CYCLIC FATIGUE RESISTANCE OF NEWLY INTRODUCED SURFACE AND THERMAL TREATED NICKEL-TITANIUM ROTARY FILES

Objectives The main objective of the present study invitro was to evaluate the cyclic fatigue resistance and metallurgic properties of newly thermal treated (CM wire) rotary Ni-Ti files with different surface treatments.
Materials and Methods: A total of one hundred and twenty rotary files were used from three different rotary systems with the same thermomechanical treatment – controlled memory wire (CM Wire) and different surface treatment technique using rotation motion. Groups were set as Group 1: M3 Pro Gold (United Dental, Shanghai, China) (CM Wire) size (25/0.04), Group 2: AF F One Blue (Fanta Dental Material Co., Shanghai, China) [controlled memory wire (CM Wire)] size (25/0.04) and Group 3: Hyflex EDM (25/ 0.04). These files were tested for cyclic fatigue resistance using a custom-made static cyclic fatigue testing apparatus with various angles and radius (angle 60 radius 2.5mm and 5mm radius and angle 90 radius 2.5mm and 5mm). Each rotary file was coated with EDTA after its attachment in handpiece supported in stainless steel cylinder apparatus. M3 Pro Gold rotary files, AF F one blue and Hyflex EDM rotary files were rotated at 500rpm 2.5N/cm torque according to manufacture instructions. Digital watch was used to record the time taken until file fracture in seconds and the (NCF) number of cycles till fracture were calculated. Scanning electron microscope SEM image of the fractured surface were taken. Statistical analysis was performed using one-way analysis of variance and Tukey’s test at the 95% confidence level (P = 0.05).
Results: After comparing the cyclic fatigue resistance of AF F One Blue and M3 Pro Gold by recording time till the file fracture was ranged between 670s to 1180s in all groups at angle 60 degree with different radius and 10s to 815s in all groups at angle 90 degree with different radius. There were no significant differences between the M3 Pro Gold and AF F One Blue rotary files at angle 60 degree and 90 degree in both radius 2.5mm and 5mm ( P> 0.05), while there were significant differences between the Hyflex EDM and M3 Pro Gold and AF F One Blue rotary files at angle 60 degree, radius 2.5mm ( P> 0.05). Hyflex EDM have the highly significant differences M3 Pro Gold and AF F One Blue rotary files at angle 90 degree, radius 2.5mm (P < 0.001).
Conclusions: All new thermomechanical treatment technique - controlled memory CM-Wire rotary systems represented great performance and remarkable enhancement in cyclic fatigue resistance but the Hyflex EDM rotary files had the highest cyclic fatigue resistance among the M3 Pro Gold and AF F one Blue rotary files. Also surface treatment of the rotary files enhancing the cyclic fatigue resistance by decreases surface micro cracks and the tendency to fracture.