The mini-implants fractures had the center of twist out of their
geometric center due to the shape of their thread. This condition
shows that the shear stresses were developed in the plane of fracture
and the thread is a stress concentration area. To accomplish this, the
center of twist is displaced away from the geometric center, along a
diameter perpendicular to the direction of the applied force. Helical
dimples followed the twist deformation on the cylindrical portion of
the mini-implant. These dimples are similar to the dimples typically
observed in a ductile material subjected to pure torsional loading. All
of the mini-implants had similar fracture process and the torsion resistance
was higher in nTi and Ti-6Al-4 V mini-implants.