The canals were prepared and shaped with one file (25/~) and finished with 40/.04 using crown down technique. Torque controlled endodontic motor was used with a rotational speed of 500 rpm and torque of 2.5Ncm (25 Nm).

The canals were prepared and shaped with one file (25/~) and finished with 40/.04 using crown down technique. Torque controlled endodontic motor was used with a rotational speed of 500 rpm and torque of 2.5Ncm (25 Nm).

Canals were prepared and shaped with single rotational file system One Shape with the sequence of Endoflare (12, 0.12), One G (18, 0.03) and One Shape (12.06) connected to endodontic motor with rotational speed of 400rpm and 4 Ncm torque as recommended by manufacturer.

In the control group, no endodontic instrumentation and shaping was done in the canals. Only the necrotic pulp tissue was extirpated from the canals with the help of barbed broaches and then the specimens were analyzed for fracture testing.

Root canal shaping procedures were performed. Irrigation was done after each three pecks of endodontic file. After instrumentation (Groups 1-3), the canals were dried with sterile paper points. The dentinal walls were then coated with Sealapex. For vertical root fracture resistance testing, sample preparation was done in acrylic blocks. Then roots were coated with polyvinylsiloxane impression material. After that roots were inserted again into acrylic resin blocks. The acrylic blocks with the vertically aligned roots were mounted in the Instron testing machine. 0.5 mm diameter round tip stainless-steel rod was fixed to the universal testing machine. The universal testing machine was adjusted and vertical compressive force was applied at a crosshead speed of 1mm/min. The Instron tester applied a slowly increasing force, until the root fractured. The maximum amount of force necessary to fracture every sample was recorded in Newton (N).

The acrylic blocks with the vertically aligned roots were mounted in the Instron testing machine one at a time. 0.5 mm diameter round tip stainless-steel rod was fixed to the upper stage of the universal testing machine (Instron, Canton, MA, USA). The rod was centered over the canal orifice of each root. The universal testing machine (Instron) was adjusted and vertical compressive force was applied at a crosshead speed of 1mm/min. The Instron tester applied a slowly increasing force, at a rate of 1.0 mm per min, until the root fractured. This point was verified by the computer monitoring the Instron testing machine; at the same time the crack was heard, the monitor showed a sharp drop in force. The test was terminated at this point and the force applied was recorded. The maximum amount of force necessary to fracture every sample was recorded in Newton (N).

crack pattern is complete/incomplete