February 1, 2006
by Rich Mounce, DDS
Recently I received e-mail from a reader asking me to comment on negotiation of canals with hand files. I had mentioned in a previous column that, all things being equal, small K files should be “precurved and placed into the given canal third” prior to the use of rotary nickel titanium files (RNT). The reader also wanted to know if apically curved files were supposed to be introduced into canals that don’t yet have the diameter to support their entry. An interesting question and a question worthy of discussion.
For our purposes here, small K files are defined as 6-10 K files. The particular brand of K files used is not of primary importance, and frankly, neither is the cross sectional pattern. Neither the cross sectional design nor the brand are particularly relevant because of the function (use) of the files (to be discussed below). In these sizes, stiffness is an asset and as a result, I am not an advocate of nickel titanium hand files. Flexibility of such small K files, in my empirical opinion, is not a desirable feature, despite some product advertising. Stiffness in lieu of flexibility provides a better tactile sense as well as allowing a greater force (albeit a very gentle and deliberate force) that can be placed upon the tip of the file to traverse a particularly challenging canal.
Primarily, small K files are used as negotiators and glide path creators to pave the way for RNT. A glide path refers to opening the given third of the canal to at least a 15 K file before any given rotary file is used. Negotiation in the context of endodontic treatment refers to placing small K files that have been precurved into a given canal third that are then used to determine the length, diameter, patency, calcification, curvature, and to some degree the content of a given canal (content in this context means determining if there are large volumes of pulp tissue-vital or necrotic-within the canal, or a canal that may appear to be empty). Both this negotiation and glide path creation can be achieved with equal efficiency with almost any cross section and brand of stainless steel K file, in these smaller sizes, 6-10.
While not all canals in every third will require the use of small K files for negotiation first before the use of RNT files, many do. Said differently, the greater the use of small K files to establish canal patency through careful canal negotiation and ultimately a creation of a glide path, the greater the efficiency with which RNT files can later be used. Such safety stems from less torsional stress that the given RNT is subsequently asked to carry as well as providing a pathway (glide path) for the instrument to track down. The curvature placed on such small K files can be done with either an EndoBender pliers (SybronEndo, Orange, CA, USA) or it can be placed by hand (for a gentle curvature) or done with a cotton pliers. Cotton pliers are acceptable for placing such a curvature but they tend to place a kink or acute bend in the file rather than a true curvature. With practice this can be overcome, but the convenience of the EndoBender is unrivalled.
Such negotiation with hand files is done always with lubrication, be it sodium hypochlorite, a viscous EDTA gel such as Glide (Dentsply Tulsa Dental, Tulsa, OK, USA) or chlorhexidine (2% solution, Vista Dental Products, Racine, WI, USA). If a small K file does not want to advance, do not force it. Use a smaller file or if a #6 file won’t advance, change the orientation of insertion into the canal to see if the file can ease its way apically. Curvatures that are imprinted onto a hand file upon its removal can give significant information to the clinician. If a file has, for example, a three-dimensional curvature imprinted upon it, when removed, the clinician will possess a very definite idea of the canal curvature and direction. Alternatively, because RNT files are super elastic and the metal rebounds to its original shape after use, one cannot get an impression of the canal that might guide subsequent RNT insertion.
Part II of this article will appear in the March 2006 issue of Oral Health.
Dr. Richard Mounce is in private endodontic practice in Portland, OR, USA. Dr. Mounce is the author of a comprehensive DVD on cleansing, shaping and packing the root canal system for the general practitioner.