Working width, a deserted aspect of Endodontics

Understanding the complexity of the root canal system and the aim to provide successful endodontic treatment has led to the development of newer techniques, instruments, and materials. These recent developments have greatly enhanced the clinician’s ability to achieve biologically-based objectives of root canal treatment. In order to achieve these objectives, it is imperative to accurately determine the endodontic working length (WL) and working width (WW) of each root canal. The term ‘Working Width’ aims to address the horizontal dimension of a root canal and was first coined by Jou et al. to describe the diameter of the canal that corresponded to the tip size of the final instrument used up to WL. Inadequate determination of the width of the canal and subsequently the WW amplifies the possibilities of its insufficient cleaning and shaping. A thorough search of the literature failed to express what an optimal preparation size might be, and it still remains a subject of uncertainty. Early protocols suggested apical enlargement to be two or three sizes greater than the first binding file at the apex. These techniques have been demonstrated to be inadequate for bacterial elimination, thus undermining success of the treatment. Furthermore, there is no evidence that the first binding instrument truly reflects the diameter of the canal at the apex, and it remains unclear as to where this binding occurs along the entire length of the canal. Variability in instrument design, cross-section, size and taper, canal anatomy, crosssection, calcifications, and the concept of pre-flaring and the instrument utilized for pre-flaring have significantly affected gauging the first apical binding file. Thus, these early-proposed concepts were without reliable and reproducible scientific method, and also lacked the support of literary evidence to accurately determine the WW of the canal. Subsequent in vitro studies exploring specially designed instruments, mathematical and photographic analyses, and micro-computed tomography (μ-CT) imaging have been attempted to ascertain the appropriate WW of canals in different teeth. Wider apical preparation of six to eight sizes larger than previously recommended sizes has been proposed to allow for adequate apical canal surface instrumentation. However, increased apical enlargement of curved canals (20 50) was shown not to result in a complete apical preparation, whereas it did lead to the unnecessary removal of dentin. Newer innovative cleaning and shaping methods like the ‘S-curve’ design of the TRUShape (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA) or the hollow core selfadjusting file (SAF, Redent-Nova, Ranaa, Israel) that distorts externally and internally based on the canal shape and dimension, attempt to incorporate the WW concept. ISSN 2234-7658 (print) / ISSN 2234-7666 (online) http://dx.doi.org/10.5395/rde.2015.40.4.334 Letter to editor