Inductive and Deductive Reasoning: Seeking Better Explanations In Endodontics

In deductive?reasoning we start with a theory generally from inductive evidence, specific data and pattern recognition, and develop a hypothesis and then see how it holds up in examining the claims that it makes using various research tools and clinical experience. In endodontics, one hypothesis is that rotary NiTi is more efficient and effective than other means of instrumentation. The data that supports that hypothesis comes from studies?comparing the debriding of canals using rotary NiTi to the manual use of K-files. Both research studies and clinical experience confirm that rotary NiTi is, indeed, a good deal more efficient, taking less time to perform the debriding procedures while also reducing hand fatigue. Other studies confirm that in many situations rotary NiTi cleansed the canals more thoroughly and produced less distortions when shaping curved canals.These studies confirm rotary’s superiority in terms of efficiencies, reduction in distortions and in simple anatomy improved debridement. In short rotary’s superiority over the manual use of K-files is supported by a good explanation given the data supplied.

Now when it comes to progress, a process of replacing good explanations with better explanations is never ending. The original good explanation does not have data that includes rotary’s function in oval canals and thin isthmuses especially when the canals are also significantly curved. Nor does the original explanation include any comparable data on systems other than the manual use of K-files. Explanations that include this new data make for a more encompassing better explanation because it expands our understanding of how rotary functions in the presence of complex pulpal anatomy and how it compares to systems other than the manual use of K-files.

In terms of more complex pulpal anatomy, many studies demonstrate inadequate debridement in the longer dimension of oval canals, a direct result of applying the precaution of staying centered, the least resistant pathway to the apex, a necessity?that increases as canal anatomy becomes more complex to reduce the incidence of instrument separation. With the original explanation replaced by one that includes more complex pulpal anatomy the superiority of rotary that was obvious with its application in simple anatomy in terms of debridement is no longer present.?

The better explanation regarding instrumentation also includes comparisons to other systems, one being an engine-driven 30o oscillating system using relieved stainless steel twisted reamers. Incorporated in this explanation is data that confirms that confined to short arcs of motion the instruments are invulnerable to breakage even at frequencies of 3000-4000 cycles per minute. Given their invulnerability to breakage the precaution of staying centered is not a requirement giving the dentist the freedom to apply the instruments vigorously against all the canal walls. This new explanation given the data it is based on, confirms the increased safety of the 30o oscillating approach that automatically leads to superior debridement that is also data supported.

In the same way that complex anatomy illustrates the weakness of rotary NiTi, it has been suggested that 30o oscillating reamers used with an up and down motion produce inordinate amounts of apically extruded debris that negatively impacts outcomes. The data that supports this explanation comes from in vivo studies that note an increased amount of extruded debris when the manual use of K-files are used with a push/pull stroke. The push/pull stroke of K-files consistently produces the greatest amount of apically extruded debris, a not surprising result considering the predominantly horizontal flute orientation that shaves the dentin away on the pull stroke and tends to impact and drive any dentin debris present in the canal apically on the push stroke. There is data that demonstrates that even instruments designed as reamers with predominantly?vertical flutes also have the potential to extrude debris apically, but these smaller amounts are common to any flutes system that employs up and down strokes, systems that include rotary NiTi as well as 30o oscillating relieved stainless steel reamers.

In the quest for better explanations, it is also important to include data that sheds light on the impact of extruded debris. One of the weaknesses of explanations is that data may be included that is not as relevant to outcomes as was believed. In the case of apically extruded debris, it has generally been accepted as conventional wisdom that the more debris extruded the poorer the prognosis. Yet, that viewpoint has no support in any in vivo studies. Complicating issues such as host response, virulence of the bacteria, the amount of tissue remaining in the canals after instrumentation have not been evaluated in any study to date undermine the conventional wisdom that extruded debris is what determines outcomes.

From a common sense perspective, we know infected pulpal tissue can lead to periapical abscesses and major inflammation. No debris in these situations has been mechanically extruded apically. In like manner, we all know that the missed mb2s can also produce apical periodontitis without the mechanical extrusion of apical debris. The complicating factors of what is left in the canals is obviously at least an issue in any conclusions that are reached regarding apically extruded debris.?

Incorporating this logic makes for a far more subtle explanation furthering our understanding of the impact of various instrumentation systems, including insights that are compatible with reality and tempering those that even though widely accepted are not supported by any existing data. In that light, controversy ensued when I posted the Pappen study that created a protocol where varying amounts of infected and non-infected debris were placed into cavities drilled into the femurs of rats. Within 60 days all the defects healed. The conclusion of the authors was that dentinal debris alone does not negatively impact outcomes.?

A criticism of the study was that any protocol that did not include teeth’s not valid because it does not reflect what would happen if teeth were present. That criticism misses the point. To determine the impact of any single factor in bone repair, that factor must be isolated. That was the object of this study, to determine the impact of extruded debris in bone repair. That such bone repair would likely not happen if teeth were present suggests that the facts negatively impacting bone repair originate from the tooth and not the extruded debris. Again there is no specific research isolating these other factors to date. That lack of data in no way undermines the misdirection of conventional wisdom that associates extruded debris with decreased success rates. So while apically extruded debris is not a plus, this study provides balance in terms of its impact on endodontic outcomes and indirectly suggests that a good deal more research focused on the remaining elements in the teeth impacting apical healing should be done.

Progress proceeds with even better explanations. That includes relevant data and the removal of unsupported opinions. Opinions (hypotheses) are a good starting point, but like all opinion they will be challenged or supported by data. We must also realize that data itself is subject to challenge?to ensure to the best of our ability it is valid. Please note that this entire discussion is limited to the goal of greater understanding. As such it is completely divorced from marketing, a practice that cares little about data other than using it selectively to sell product. For me personally, I have enough confidence in the endodontic instrumentation systems we advocate to defer to the data that is produced by the various research institutions.?

Of course, we should not be naive to the invasive potential of marketing by the major companies and their impact on research efforts. It’s a complicated world when commercial enterprises become the source of research funding, an increasing trend as government funding has drastically reduced over the years. In order for any society to function properly, there must be trust. Today we live in a country where trust in all aspects of our government are highly diminished leaving a vacuum for further chaos. The solution to these trends is the same as it is for research. By using the standard for what is good for society with the goal of every citizen reaching his/her full potential whatever it might be, we have a measuring rod to adopt policies that are in line with that goal and eliminating those that are not. Personally, I would like to see major efforts to eliminate monopolies, reintroduce a level playing field for competition, a requisite for a functioning democratic capitalist society.

Regards, Barry