Endodontic Workshops, Critical Thinking and Common Sense Working Together

When conducting our hands-on endodontic workshops, the 3D printed teeth present degrees of difficulty, from fairly straight forward anatomy to the quite complex giving the dentists a range of challenges while demonstrating to the participants that the system we are teaching is highly adaptable to all these situations accomplishing the 3 goals of non-breakage, three-dimensional debridement?and non-distortion safely and consistently. More specifically, the primary advantage, non-breakage, is an absolute essential to give the dentists the freedom?to apply these oscillating stainless steel reamers against all the canal walls. Contrast this freedom with rotary NiTi’s need to stay centered throughout instrumentation.?

Greater tapered rotary instrumentation works well as long as the canals are reasonably round in cross-section. However, as the canal anatomy becomes more complex, the ability of a centered rotating NiTi instrument to cleanse all the canal surfaces decreases, a fact well-documented in the literature. Rotary systems cannot surmount the basic fact that to keep the instruments intact, they should deviate as little as possible from the centered least resistant pathway, a standard precaution to reduce the incidence of separation. This basic requirement compromises their ability to cleanse three dimensionally as the canals become more oval in cross-section and when isthmuses are present or for that matter any elongated flat anatomy.

Interestingly, if the wider dimensions of pulpal anatomy were present in the mesio-distal plane rather than bucco-lingually, the periapical x-ray would then have the ability to visualize the limitations of centered shaping. This, unfortunately, is not the case so the mesio-distal view obscures any deficiencies in debridement that may be present in the bucco-lingual plane. This fact is well known, but those advocating rotary systems ignore this inadequacy stating the answer to adequately cleansing resides is more effective irrigation systems. The implication of such a statement reiterates the reality?that rotary in itself is not suitable for adequate debridement compared to oscillating reamers, something that I have demonstrated in videos placed in previous posts.

In an attempt to improve three-dimensional cleansing, an undulating instrument was developed that can touch more of the walls. Because they are used in rotation it is necessary that this instrument not be subject to binding anywhere along length lest it encounter excessive torsional stresses. As a result it can only be used in canals that minimize a tight contact. Under these constricted conditions of use, the highly flexible undulating instruments will contact the canal walls and will immediately deflect as soon as resistance is encountered to resist the stresses that could lead to instrument separation. As micro-ct scans have shown, these instruments will debride those areas that are fairly wide open, but are totally ineffective when they encounter flat elongated anatomy such as isthmuses. As the video clearly demonstrates while the wider portions of the pulpal complex are debrided the pulp tissue residing in the flattened anatomy of isthmuses are untouched remaining as sources of potential continuing infection.

We can see case after case beautifully demonstrating non-distorted instrumentation and obturation in the mesio-distal plane, the beautifully flowing white lines to the apex and we use these examples as proof of rotary’s effectiveness further supported by what we are told is a high success rate logically resulting from such beautiful images. So, is that a reasonable response given the well-documented evidence of inadequate debridement in the bucco-lingual plane? For some, it evidently is especially given the fact that the cleansing deficiencies result from the precautions required to more safely employ rotary NiTi, their chosen instrumentation technique.

Given our human nature, one doesn’t like to talk about the deficiencies of a system one has chosen to use. While understandable, such a perspective is not an example of critical thinking. On the other hand, one might well counter that such an attitude makes perfectly good common sense given rotary’s high success rate. However, one should realize that common sense only derives from the information we have at hand. While overall success rates are high, these rates are selectively?effected by a host of factors including difficulty of the case, whether a periapical area was present at the start of treatment, the presence of a separated instrument, over instrumentations and overfills, the skill of the operator and the followup restorative treatment. In other words, while high there is still ample room for improvement.

Overtime, critical thinking will change the perception of common sense. Common sense cannot change critical thinking. If it did, it would nullify critical thinking with an authoritative cultural response degrading the process of critical thinking. In short critical thinking has a scientific basis. Common sense is cultural, responding to commonly held beliefs that may or may not be scientifically validated.

Regarding critical thinking versus common sense an interesting debate has been going on regarding the production of dentinal micro-cracks as a result of endodontic instrumentation. Many studies show this to be a consequence of rotary endodontics. More recent cadaver studies have concluded that whatever dentinal micro-cracks were present after rotary instrumentation were there before instrumentation implying that rotary NiTi is not the cause of micro-crack generation. Relying on these studies, one can come to the common sense conclusion that rotary NiTi is not associated with micro-cracks. However, a review of the consequences of instrumentation report significant incidences of instrument separation, a result of the impact of the canal walls on the rotary instruments. The canal walls and the instruments are mutually interactive. Yet, according to the cadaver studies, one must conclude that the damage is only inflicted on the instruments something the canal walls are evidently totally immune to. This is a contradiction of Newton’s Third Law of motion that states that two interactive bodies have an equal and opposite impact on each other. If one believes that the instruments can separate, a drastic form of metal defect, but the walls are impervious to defects then one must also believe that at times Newton’s Third Law is a one way street, a rather radical idea and a contradiction of a long established mechanical law.

Under these circumstances, critical thinking should be directed at the studies that reach this conclusion negating Newton’s Third Law rather than accepting these most recent studies as the most valid possibility, conclusions that are also in conflict with an overwhelming number of studies that note the direct relationships between rotary instrumentation and the production of dentinal defects. No one is challenging the honest intent of the researchers, but given its unique contradictory results it is worth challenging the research protocols the same way that those supporting rotary NiTi instrumentation challenge the studies demonstrating the production of dentinal micro-cracks via rotary instrumentation.

Regards, Barry