Mechanical root canal preparation with NiTi rotary instruments: Rationale,performance and safety. Status Report for the American Journal of Dentistry

The growing use of NiTi rotary instruments in dental practice demands a goo d understanding of their concept of alloy and design in relation to improve d properties and inherent limitations. Nickel titanium's super elasticity a llows more centered canal preparations with less transportation and a decre ased incidence of canal aberrations. Furthermore, the production of files w ith increased taper became possible. This is of special importance because of concerns on the achievement of adequate irrigation and close adaptation of the filling material during endodontic treatment. Unique shaft and tip d esigns should permit the use of a rotary handpiece allowing different tacti le awareness. On the other hand, special attention is paid to maximize cutt ing efficiency and cutting control throughout instrumentation. NiTi rotary instruments are generally used in a crown-down approach and a continuous re aming motion. Consequently, rounder root canal preparations, with less stra ightening and a smaller amount of apical extrusion is achievable. In spite of their increased flexibility, separation is still a concern with NiTi fil es. The phenomenon of repeated cyclic metal fatigue and the variable of tor sional loading are two important factors in instrument fracture. However, w ith awareness of the appropriate manipulation and special attention to the equipment used, NiTi systems are safe with a minimal incidence of instrumen t failure.