INTRODUCTION:

This study compared the effect of different phases (M– wire, NiTi, R phase) of rotary systems to VRF instrumented with ProTaper Next (PTN, Dentsply Maillefer), Revo s (MicroMega, Besancon, France) and Twisted File (SybronEndo, Orange, CA) systems and obturated with compatible gutta–percha system and a resin sealer and tested under Universal testing machine to measure the force that is required to fracture the teeth in Newton’s (N).

METHODOLOGY:

This study included 40 single rooted premolar teeth. The coronal portions of all teeth were removed with a diamond‑coated bur under water cooling, leaving roots approximately 13 ± 1 mm in length, the roots then covered with additive silicone and placed in Eppendorf tubes which were then filled with self–cure acrylic. The tubes were then evenly distributed to three experimental groups and one control group (n = 10), based on their weights and the homogeneity of the group:

GROUP I:Control Group

GROUP II: Instrumented with ProTaperNext

GROUP III: Instrumented with TF

GROUP IV:  Instrumented with   REVO S

The teeth will be prepared according to manufacturer’s instruction till apical size 25/.06And then teeth will be taken under universal testing machine under cross head speed of 1mm/ N

RESULT: Group II was more Resistant to fracture and group I was least resistant. The difference between group I and II was statistically significant.

Conclusion: The teeth Instrumented with PTN were least resistant than those with TF which were More resistant to VRF