The hybrid concept of nickel–titanium

The development of nickel–titanium (NiTi) rotary instruments is undoubtedly a quantum leap for the field of endodontics. Nevertheless, those who have gained some experience in the use of such instruments will confirm that each file system has its own special advantages and dis-advantages and that particular rules for its usage need to be followed. With most NiTi systems, it is easy to reach working length and prepare the apex to a small size such as International Standards Organization (ISO) size 20. When the apex is prepared to larger sizes, however, the limits of a particular system quickly become apparent. The idea of the hybrid concept is to combine instruments of different file systems and use different instrumen-tation techniques to manage individual clinical situations to achieve the best biomechanical cleaning and shaping results and the least procedural errors. The hybrid concept combines the best features of different systems for safe, quick, and predictable results. Nickel–titanium rotary instrument systems Some NiTi rotary instrument systems that presently can be used for this hybrid concept are introduced here, and their main features are described. Among these systems, two main categories of NiTi rotary instruments need to be differentiated: active and passive instruments. Active instruments have active cutting blades similar to the K-FlexoFile (Fig. 1A), whereas passive Dent Clin N Am 48 (2004) 183–202instruments have a radial land between cutting edge and flute (Fig. 1B). The radial land touches the canal wall on its entire surface, guiding the instrument—stable and balanced—within the canal. In general, activ