This article illustrates the conceptual basis and the operative procedures of the zone technique and explains the specific instruments used in each phase. The zone technique defines two regions of the root canal: the coronal zone (the area above the curvature of the canal) and the apical zone (the area below the curvature). Whether the root canal possesses a significant curvature must first be determined. The instruments and procedures are separated into four different steps. In the first phase, the distance of the curvature from the apex is determined. The area above the curvature of the canal (coronal zone) is then shaped with NiTi rotary flare instruments. In the third phase, a stepback sequence is used to enlarge the area below the curvature (apical zone) with ISO size (#)20 taper .02, #25 .02, #25 .04 and #25 .06 NiTi rotary instruments. During the final phase, finishing #30 .06 or #35 .06 NiTi rotary instruments are used to shape the apical third of the canals.
Keywords: curved root canal, NiTi instruments, root canal preparation, shaping