This article is currently trending all over social media and given the easy pass we give literature that tells us quicker and more profitable treatments are better, I thought it was worth a close look.

As those who have followed me for some time will know, I am doubtful about any pyramid scheme, including the hierarchy of evidence, and in particular, the way in which people neglect the inherent weakness of reviews and meta reviews.

The hierarchy of evidence was first outlined by Guyatt and Sackett in 1995 and has become a staple of academic discussions ever since, with very little in the way of critique.

The problem with pyramids, like the food pyramid, is that it allows a small number of elitist studies/opinion leaders, to massively influence dentistry.

If the evidence at the top of the pyramid is wrong, then it causes very large errors throughout the profession.

I prefer network or cloud type knowledge assembly. Wikipedia works in this way, with input from thousands or sources of varying knowledge base and has been unequivocally shown to be both more up to date than expert based encyclopaedias, but more accurate.

At its heart, the hierarchy of evidence does not meet its own criteria and whilst an interesting philosophy, should not be taken as the gospel.

Before reading meta studies, it is wort while noting the weakness that they can have.

Now lets look at this article:

Conflict of Interest

In this particular article the authors put faith in an eleven point process to distinguish conflict of interest or potential for bias. However they put too much faith in the self declaration of conflict of interest that authors put at the end of a paper. In my opinion, it is common for those who regularly get sponsored to speak, or get research grants to study materials from material manufacturers, to declare not conflict of interest because no one sponsored this particular study. Hence, a good way to start looking for conflict of interest is simple google search of the authors. In this case, a search did not show large numbers of sponsored lectures. A perusal of past papers of the authors in the paper above does show some research showing recurring products and areas of interest, but not enough to be suspicious of large commercial conflict of interest.

Confirmation Bias

Each of us will tend to like papers that confirm our treatment method or bias. So I should declare before I start that tend to favour single visit treatment where possible but will do two stage treatments in cases where I cannot get the canal dry due to blood or exudate, or in cases where I cannot achieve patency in the first visit due to time.

Ignore the abstract

The abstract is frequently undermined by the rest of the article in my experience. In general, it is best not to read it at all until you have finished the rest of the article. The abstract will frequently make claims that will bias the way you read the paper and often these claims are not supported by the actual research itself.

Opening claims

The first few paragraphs are usually where the author will declare their bias, or underlying assumptions. It claims that the single visit endo is a paradigm shift. I’m not sure in 2017 that single visit endo is still controversial or a paradigm shift. Driving cars was a paradigm shift in 1920, but perhaps not so much now.

We are then lead to a circular definition. This review only focusses on reviews because they are the highest level of evidence.

This is an assumption or an opinion and is not a fact. It is not proven that systematic reviews provide a clinician with better clinical outcomes especially when most of them end with the statement “insufficient evidence...”. A quick glance at some of the underlying reviews suggests that most of them finish with the statement “insufficient evidence” and hence, it is unlikely that a review of a whole lot of papers that claim insufficient evidence or lack of defined protocols, will suddenly produce information that does not also carry the underlying weakness. Hence, most systematic reviews are essentially the literature equivalent of the sub prime loan debacle.


The methodology sounds very fancy but essentially they searched for reviews on the topic at hand and then tried to weed out those that were particularly biased. What the methodology shows is why reviews are so popular. The total time and effort required to produce a paper from a review, and then be able to claim it as the highest level of evidence, is orders of magnitude lower than to do a clinical study that is both long enough, and with large enough sample sizes, to actually give some clinical insight that is useful. Reviews are cheap, quick, and far easier to carry out.

The bias analysis is good with the exception that google and pub med searches should be made of the authors in question so that you can gauge more accurately their level of sponsorship and risk of bias. Some of the authors in the low risk group are heavily sponsored speakers so I am a bit suspicious of the “no conflict of interest” claims. Overall, the authors have done a reasonable job weeding out bias.

Six articles were excluded for duplication but this is not explained well. Does it mean most of the underlying studies are duplicated? Would not all systematic reviews end up with much the same underlying studies?


The analysis is always fun because this is where we can interpret the review in multiple different ways. It is my gut feeling that the author favours single visit endo because of a number of claims that are not supported.

The first is the idea that there is a trend toward to single visit endo having less complications particularly in cases of apical periodontitis which come from the four papers above. These complications are suggested to be caused by;

  1. extrusion of contaminated debris
  2. changes of microbiota in the root canal
  3. incomplete preparation
  4. non establishment of patency
  5. intra canal medicaments

It is interesting these technical issues should be associated with multiple visit endo. It suggests that when doing a multiple visit endo, the canals may not be debrided as carefully or perhaps the dentist does not give themselves enough time in the initial visit. Or that the cases that most often tend toward multi-visit treatments are those that are the most difficult and then need a second visit for time reasons. These are not issues of the multi visit procedure but simple the rigour with which the technique is carried out. Perhaps when we know its a one shot deal, we try a bit harder to make sure we clean the canal good. What we can conclude is that the variations in technique in multi-visit treatment are far greater which makes comparing the two procedures basically impossible.

So I went and read the two papers that suggest greater success with single visit endo. The author has picked data that the previous papers said was not of statistical significance and included it in the above table. The Figini paper says that there is no difference radiographically but the above table says that there is.

It also says the exact opposite of what is claimed in the table above. It actually says single visit endo has higher risk of post op pain.

The Sathorn paper says the 6.3% difference is not significant but its inclusion in the above table creates the illusion to the cursory reader that single visit is superior, which is not supported. The other Sathorn paper shows that the intracanal medicament plays a huge role in post op pain and if we only look at those using calcium hydroxide, which is probably the most commonly used medicament in the world, the results for multi-stage are generally slightly better than single visit, but again, not statistically significant.

So what can we conclude from this review?

  1. The author probably slightly favours single visit. As do most dentists for its time efficiency.
  2. Dentists want studies that show their preferred method works, which they do.
  3. The paper above will confuse the cursory reader by making them think that single visit is in fact superior in patient post op comfort and outcome, which it is not. Since most dentists want studies that support their bias, this paper will probably be heavily quoted by those who have done a pub med search and only read the title or the abstract. :)))
  4. Reviews are very rarely the highest level of evidence as they simply collate a lot of evidence, that when inspected carefully, tends not to be that good. Worse, they tend to collate poor quality evidence and then present it as “the highest level of evidence” hence putting a AAA+ rating on evidence that is actually not that great.
  5. Reviews are a very cost efficient way to add a publication to your career or to get a PhD if going via the publication route (which is the most efficient way to get a PhD because you don’t have to rewrite your bibliography as often as if you go via thesis).
  6. Sometimes an author can make a typo which completely changes the meaning of a table.
  7. Never quote a study without reading it very carefully.

In my opinion

There is no evidence that single visit endo is better or worse than multi visit endo and the procedure is several orders of magnitude less important than the quality with which it is carried out. If you are more proficient at one of these options, you are likely to get better results with that option. The choice to do one or the other will probably come down to practical considerations like do I have enough time to complete this endo that I squeezed into my lunch hour. Further, long term outcomes will not likely depend on either of these factors and thus, in the long term you should probably devote more time and attention to not destroying the tooth during the endodontic andthe restorative process. Not fat files and fat chamfers please.