[Treatment of curved canals: from stainless steel to nickel titanium]

Endodontic treatment of curved canals is always more difficult than straight canals, especially for the apical zone preparation: root canals may present several curvatures in different space directions. From an anatomical point of view root canals with accentuated curvatures are a very frequent event (more than we might think); radiological exams, in fact, give us only a 2D image, and we can observe mesial or distal curvatures but not those in the oral or buccal direction. However, all root canals have curvatures of some degrees; even those that appear straight. Because of this, endodontitis have made many attempts to overcome these problems and manage to have a good preparation in curve canal. The authors analyse all endodontic techniques (step back, step down, crown down, balanced forces) codified in the course of the years, to prepare curved canals; they both in shape or in materials. It's fundamental for the endodontist to have a specific technique to treat curved canals to allow a good, wide preparation; in this way it's possible to make a better and tridimensional filling of the endodontic space above all in the tipical zone.