Current concepts of canal preparation.

Canal preparation is a complex procedure, performed with inadequate instruments and chemicals in a restricted environment. With these limitations, it is surprising that the success rate for root canal treatment is good, although not as high as is commonly reported. The preparation of the canal is divided into two actions, cleaning and shaping. Both are quite different and require different criteria for evaluation. Specifically, cleaning is debridement, whereas shaping is preparing the canal for obturation. Cleaning (debridement) depends on straight-line access, and requires the action of both intracanal instruments and irrigants. Files should contact and plane as many walls as possible to loosen debris. This is followed by irrigation, which has the primary function of flushing debris from the canal space. The chemical action of the irrigant is less important, but is an aid in total debridement. Shaping of the canal depends on the obturating material and the condensing instruments. Because gutta-percha is the preferred material, and lateral condensation the most common technique (although not necessarily superior), preparations should be flared. It has been shown that the taper should be sufficient to permit deep penetration of the spreader or plugger alongside the gutta-percha during lateral condensation. Hand instrumentation remains the preferred approach for canal preparation. There are variations including standardized and flaring, with the flaring (or step-back) the most commonly taught and used. The step-back approach encourages a small apical preparation with larger instruments used at successively decreasing lengths to create a taper. An advantage is that this method tends to minimize procedural errors such as transportation, ledging, and apical perforation. Automated techniques continue to be of interest as the dentist searches for easier, faster, and generally more efficient techniques. Ultrasonic and sonic devices have generated considerable interest. Research has not demonstrated these instruments to be as effective as hand techniques unless employed in a special manner. Other types of engine-driven instruments are generally not indicated and may in fact be dangerous.