الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Nickel Titanium rotary files are greatly influenced by their metallurgical characteristics. Manufacturers have been struggling to increase the fracture resistance as well as the flexibility of the files to avoid file separation and increase the success rate of curved canal instrumentation. Multiple proprietary manufacturing procedures have been introduced to the dental market. These include surface, thermal and alloy treatments as well as several machining procedures to upgrade the mechanical properties of NiTi alloys. Therefore, this study aimed to evaluate the influence of these novel treatment modalities of NiTi rotary files on flexibility and cyclic fatigue resistance in comparison with the conventional NiTi rotary files. Three differently-treated NiTi rotary file systems were evaluated for their flexibility and cyclic fatigue. Results were compared to conventional non-treated NiTi rotary files (control). All 96 files were divided into four groups: group I: Conventional non-treated NiTi rotary file ProTaper Universal (Dentsply). group II: Treated NiTi rotary file ProTaper Gold (Dentsply), group III: Treated NiTi rotary file Hyflex EDM (Coltene) and group IV: Treated NiTi rotary file 2-Shape (Micro Mega). Each group was further divided into 2 subgroups according to the type of test conducted. Flexibility test was performed by means of a 3-point bending test using a Universal Testing Machine, while cyclic fatigue resistance was tested using a custom-made dynamic device with a 60-degree stainless-steel artificial canal. Time to Fracture (TTF) was recorded and the Number of Cycles to Fracture (NCF) was calculated. All data were tabulated and statistically analyzed. The results showed a statistically significant difference in flexibility between all groups except ProTaper Universal compared to 2Shape. Hyflex EDM had the best flexibility while 2Shape had the worst flexibility value. Regarding NCF, a statistically significant difference was present between ProTaper Universal and all three treated file groups. However, no statistically significant difference was observed among the remainder of the treated file groups. The highest cyclic fatigue resistance was recorded by
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2Shape followed by Hyflex EDM and then Protaper Gold. Protaper Universal had the least cyclic fatigue resistance. As a result, this study concluded that different treatment modalities for NiTi rotary files improve both flexibility and cyclic fatigue when compared with conventional NiTi rotary files.