الفهرس 
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Abstract
The aim of the present study was to compare the fracture resistance of mandibular molar roots following instrumentation using TruNatomy versus ProTaper Next rotary files.
The current study was conducted on 30 permanent mandibular molars. Teeth were randomly distributed into two equal groups. Decoronation of the crown was done and the distal root was sectioned from the mesial root. Study group I: Fifteen mesial roots (MB and ML canals) were instrumented using TruNatomy (TRN) rotary files up to the prime file (26/.04). Study group II: Fifteen mesial roots (MB and ML canals) were prepared using ProTaper Next (PTN) rotary files up to X3(30/.07). Control Group: The distal root of each tooth.
Irrigation protocol was standardized for all the samples. For both groups, EDTA gel was used as a chelating agent during the instrumentation along with 2ml of 2.5% NaOCL irrigating solution. A 30-gauge side vented needle was used for the PTN and a special two side vented irrigating needle was used for the TRN. For the smear layer removal, the canals were irrigated with 5 ml of 17% EDTA for one minute followed by a final flush of 5 ml of 2.5% NaOCL. All specimens were kept moist throughout the instrumentation procedure and were stored in saline after completing the instrumentation procedure. Teeth were then embedded in acrylic resin blocks and mounted on a universal testing machine. A four mm ball diameter was used to apply force in the center of the roots at speed of 1mm⁄min till fracture.
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Results were statistically analyzed using IBM SPSS for Windows (Version 23.0). Comparison of fracture resistance between the two study groups was done using independent samples t-test, while comparison of the mesial and distal roots within each group was done using paired t-test. Significance was set at p value <0.05.
Results showed that roots prepared with TRN were significantly more fracture resistant than roots prepared with PTN. In addition, the intact distal roots were significantly more fracture resistant than instrumented mesial roots in both groups.