February 27, 2012
The following is an interview with a world-renowned endodontist on the introduction of a new “file system” to the endodontic armentarium; Q: A general practitioner might get the impression that the WaveOne system makes root canals easy. Do you think encouraging this view might be cause for concern amongst endodontists? A: Well, I have read this argument about making root canal treatment simple. Many colleagues struggle with the complexities of root-canal treatments and I do not see why we can’t make it simpler. Any competent dentist has good manual skills. If we can simplify the treatment procedure for general dentists and thereby improve their skills in completing more root canal treatments to a higher standard, our patients will surely benefit. If you look at the majority of root canal instruments and the many preparation systems available in today’s market, as many as three to five files may be needed to produce a perfectly shaped canal. However, with WaveOne, one file is needed to get to that shape. It’s so simple! It’s simple to understand, it’s simple to use and it’s simple to teach (2).
I was intrigued by the suggestion that root canal therapy can be made “simpler” and chose to test this postulation. The rationale behind his theory focused solely on the mechanics of the endodontic procedure and the architecture rendered by the instrumentation; could the success of endodontic treatment outcomes be improved by “shape” alone (the only variable addressed)? My interest was peaked further on reading an article by the interviewee and others (1) wherein, the following was included in the conclusions as a caveat; “WaveOne files only shape the canal, extremely quickly in many cases. It is the duty of teachers and clinicians and manufacturers to emphasize the role and importance of irrigation as a major determinant of endodontic success.” Dr. Webber chose to address shape only in his interview and irrigation in passing in the article; as such, the analysis of the considerations on shape will be challenged, the glaring omission of irrigation as an equal if not more significant partner will come in a future posting.
The root canal system is an arborizational, anastomotic, byzantine, labyrinthine complexity, morphologically comparable to the passages of a maze. While primary canals exist, the tributaries, accessory branches and lumina of the dentinal tubuli harbor extensive tissue and microflora, which if left untreated remain vectors for persistent and refractory pathology. Carabelli documented the first description of these vast and capacious pathways in 1842. Since then, Muhlreiter (1870), G. V. Black (1890), Preiswerck (1901), Fischer (1907), Dewey (1916), Hess (1917), Okumura (1918-1926), Davis (1923), Barret (1925), De Deus (1960) among others studied the “magical mystery tour” of root canal anatomy. The quest continues to this day with the use of micro-computed tomography. (http://rootcanalanatomy.blogspot.com/) (http://endodontiafobusp.wordpress.com/)
The presence of multiple foramina, accessory/auxiliary canals, fins, deltas, inter- and intra-canal connections, loops, C-shaped and ovoid canals are the reality of pulpal anatomy. The morphology of the apical region of a root exhibits myriad ramifications, inclusive of accessory canals formed as a result of entrapment of periodontal vessels in Hertwig’s epithelial root sheath during calcification, areas of resorption and repair, attached, embedded and free pulp stones, varying amounts of irregular dentin, inter-canal connections that may become exposed and single foramen which may become multiple (11). Added to these are varying degrees of root curvature especially in the apical portion. All these intricacies mandate that instruments used to chart the course of the root canal system be operated at the highest level of pilotage and stewardship of navigation.
Contrary to common clinical belief, studies suggest that instruments sizes 10 to 20 often do not have any friction at the physiological foramen area, but rather encounter resistance elsewhere because of root canal irregularities or curvatures. The fact that coronal flaring of the root canal increases the size of the initial apical file that binds at the apex and consequently also increases the size of the master apical file supports this assumption. This is commonly referred to as coronal flaring or coronal enlargement (3). The failure to embrace this primary component of the crown-down approach to debridement and shaping can have catastrophic consequences. The sense that apices can be treated with a one size fits all approach can only result in diminishing degrees of success.
Harmeet Walia was the first to recognize the potential of nickel-titanium (NiTi) alloy for endodontic files. He showed that it’s low elastic modulus, torsional ductility and stress-induced thermoelastic transformation made it suitably adjunctive to machined stainless steel instruments for instrumentation of the root canal system (4). Since the 1990’s, nickel titanium instrumentation has been shown to result in sufficient cleanliness and acceptable preservation of the principal root canal anatomy. The centering ability and the decreased straightening of the root canal space is superior with NiTi techniques in comparison to the manual techniques using stainless steel instruments. However, the apical region shows similar or fewer remnants of debris after manual instrumentation (5).
Currently, there are approximately sixty NiTi systems¶ in the marketplace. Important mechanical features include the variability of the taper (constant, increasing or decreasing) and the rake angle (direction of the cutting edge). The latter can be negative, neutral or positive. Other feature are cross-sectional geometry (triangular, triple helix, asymmetrical, S-shape, U flute design), tip configuration (rounded and non-cutting tip, cutting tip), design of blades (radial lands), helical angle (angle between the cutting edge and the long axis of the file) and pitch (distance between cutting edges). Newer systems incorporating advanced metallurgical composition further minimize the potential for fracture of these instruments. ……….
A recent study concludes that fast and reliable mechanical enlargement of the root canal space can be predictably produced with an automatized single-ﬁle approach (6). In other words, a tapered preparation can be achieved quickly. It is noteworthy that this contrasts with the envelope of motion concept of cleaning and shaping advocated by Schilder (7, 8). Dr. Schilder’s crown-down approach involved the tooth as partner in debridement and architectural rendering of the design of the root canal space. Through the use of repeating, sequential and blended instrumentation, a unique rheologic mold was established through the root canal system under treatment. It did not imprint a shape on the canal space, rather it enabled the tooth to re-establish its native anatomical canal system morphology; the shape was not imprinted by the file(s) used.
However, true cleaning is a function of irrigation and the irrigants require considerable time to do their task. Time is a factor that is often overlooked in clinical and pseudo-clinical trials. In the context of root canal debridement and disinfection, faster is not necessarily better (9). To state the matter differently, after only a few minutes of mechanical instrumentation, the root canal space can now be enlarged properly with an approach such as the single-ﬁle F2 ProTaper (WaveOne) technique, but a minimum standard of debridement is unlikely to be reached. The focus of the present laboratory investigation was clearly on the quality of the ﬁnal canal shape. DOUBLE CLICK ON IMAGE BELOW….
Overall, abstracts, not unlike interviews are unable to show the real take-home message of the studies. Thus, we are presented with a highly problematic situation wherein achieving a balanced and accurate overview can in actuality misstate. Additionally, commentary on one variable does not validate the incorporation of reciprocal movement into the endodontic protocol. In the study cited, µm-CT was used to compare the effect of reciprocation versus rotary movement in some mechanicals parameters; changes in dentin volume, (percentage of shaped canal walls) and degree of canal transportation. As time required to reach working length in each system was the only variable compared this study was restricted in just compare the overall mechanical efficacy in enlarging the root canal space. It means, quality of the mechanical shaping procedure (personal communication).
What struck me the most about the interview cited at the beginning was the circular reasoning manifested by the contributor. Circular reasoning, or in other words, paradoxical thinking, is a type of formal logical fallacy in which the proposition to be proved is assumed implicitly or explicitly in one of the premises. For example: “Only an untrustworthy person would run for office. The fact that politicians are untrustworthy is proof of this.” or Root canal shape is the principal component of treatment outcome success. Simplification of the procedures for root canal shape should prove primarily responsible for successful treatment outcomes. Such an argument is fallacious, because it relies upon its own proposition — “shape alone engenders success” — in order to support its central premise. Essentially, the argument assumes that its central point is already proven, and uses this in support of itself. Circular reasoning is different from the informal logical fallacy “begging the question”, as it is fallacious due to a flawed logical structure and not the individual falsity of an unstated hidden co-premise as begging the question is.
The strange thing about controversies is that the logic of the text often loses out to the power of context. The myth of science has, as its ideal a value-free truth, a fact free from the colours of ethnicity, ideology or market interest. Controversies in science do not always follow the ideal. The objective of this blog in the long term is to encourage evidence, NOT EMINENCE based science to come to the forefront. That requires active not passive participation. It’s never enough to read an op-ed piece; it’s goal in the purest sense is to create emotional, visceral and psychological response resulting in putting paper to pen or fingers to mouse and keyboard. Wherever we go, there we are, provided we chose the path to be followed and not to be led along a faux course.