Working Width in Endodontics -1

Root canal shaping is one of the most important steps in canal treatment. It is essential to determine the efficacy of all subsequent procedures, including chemical disinfection and root canal obturation and is the basis for successful endodontic treatment, aiming to debride the root canal, to remove contaminated dentin, and to create an ideal canal shape for three-dimensional filling . The main objective of a clinician is to mechanically and chemically cleanse the root canal system thoroughly, making it free of microorganisms and their substrates. The canal surface irregularities require proper instrumentation for adequate root canal filling. For this purpose, working length, various cleaning and shaping techniques, and instrument motions have gained importance in endodontics.

The root with a graceful tapering canal and a single apical foramen has long been established as an exception rather than the rule. Bifurcating canals, multiple foramina, fins, deltas, loops, cul-de-sacs, intercanal links, C-shaped canals, and accessory canals have most commonly been faced by the investigators in most teeth . Microbes are found in all parts of the root canal system, including fins and anastomoses, and at varying depths (up to 300 μm within the dentinal tubules) . However, after instrumentation, they have been reported at less than 34 μm of dentin removal (depending on the type of canal cross section) .

The instrumentation of the apical matrix to a large size leads to more anatomical irregularities and increases irrigant exchange in the apical third. Apical enlargement during canal cleaning and shaping procedures increases the likelihood of achieving maximum elimination of bacteria from root canal system , though a major part of the canal remains uncleaned even after thorough cleaning and shaping . It is very difficult even for the most proficient clinician to predict the exact site and number of root canals present in any tooth before the beginning of the treatment. Even the smallest uncleaned part of the canal significantly affects the success rate of the treatment .

Until recently, most investigations have involved counting the number of canals and foramina and categorizing how the canals join or split. Majority of studies have tried to evaluate the shape of the canal systems and its clinical implications than to evaluate the actual preoperative size of the canal .

The main aims of instrumentation are as follows:

1. To remove heavily infected dentine from all regions of apical canal wall.
2. To facilitate placement and replacement of the irrigating solution .
3. To facilitate placement of intracanal medication.
4. To create an apical stop that facilitates reduced leakage and material extrusion.
5. To facilitate obturation procedures.

However, it is recommended not to widen the root canal to a larger extent to avoid unnecessary weakening of the root and increased risk of fracture. Regarding modern concepts, the final canal allows adequate irrigation and close adaptation of the filling material during obturation . Working width (WW) is relatively new concept, which involves perceiving a root canal in both perpendicular (working length) and horizontal (WW) dimensions. Thus, endodontic ―working width‖ has always remained unforgotten dimension during root canal procedure without solid scientific evidence; however, it is still not clear ―how large is enough.‖

The concept of working width (WW) was given by Dr. Yi-Tai Jou, Department of Endo, University of Pennsylvania, Philadelphia, PA , which is defined as “the initial and post-instrumentation horizontal dimensions of the root canal system at working length and other levels.” WW is best understood by studying the cross sections of apical canals. If the greater diameter of the original canal is measured, the correct WW is an instrument size slightly bigger than that dimension. It is incorrect to determine the final apical instrument size (master apical file) by measuring the size of constriction. The instrumentation is not aimed to match the size of the final instrumentation with that of the constriction. Smaller size increases the canal diameter by removing hard tissue but barely removing the vital pulp tissue, which causes inflammation of remaining tissues. This concept ignores the fact that most canals enlarge so significantly coronal to the constriction that standard tapered instruments (0.02, 0.04, 0.06, 0.08) are adequate in this region, resulting in underprepared apical canals. It is not always feasible to achieve ideal WW. However, even in such cases, we should try to clean as best as we can.