Do orthodontic extractions change soft tissue profiles?
Do premolar extractions influence soft tissue profile in Class II cases?
As we all know the extraction/non-extraction debate continues in orthodontic and dental circles. My feeling is that most of the opinions on either side tend to lack an evidence base, because there is a dearth of research on orthodontic extractions. I was, therefore, pleased to see this systematic review published in the European Journal of orthodontics. I thought that this would be a good start to my blog posts for this New Year. Sadly, I was wrong, but read on…
Janson, G., Mendes, L. M., Helena, C., Junqueira, Z., & Garib, D. G. EJO doi:10.1093/ejo/cjv083
The authors pointed out in the literature review that the extraction debate, particularly for class II malocclusion, is important. This is because there are concerns that premolar extractions might cause greater lip retrusion than other methods, for example, functional appliances and headgear.
What did they do?
The aim of the review was to evaluate the soft tissue changes after orthodontic treatment with premolar extractions in class to Division I malocclusion is. I felt that this review was important because any evidence that is derived will fuel the debate. They adopted systematic review methodology in an attempt to provide high-level evidence. Their inclusion criteria in the form of a PICO was:
I would like to point out that they included retrospective studies and I will return to this later.
They classified the risk of bias in the studies using the Cochrane Collaboration tool for assessing risk of bias.
What did they find?
After the usual filters based on the PICO they obtained the final sample of 13 papers. Of these, eight were retrospective, three were prospective and two were unclear.
They provided a large amount of data in supplementary tables and I looked at these studies closely. I found that only one study was a randomised clinical trial. As a result, we have a systematic review that includes only one RCT out of 13 papers. This is important.
They did not combine any of the data and simply listed various cephalometric measures derived from individual papers. They discussed these in a long discussion that I struggled to understand. They finally concluded “that according to studies with high scientific evidence that when class II malocclusion is treated with extractions there are various levels of upper lip retrusion”.
What did I think?
I was disappointed in this paper and I am sorry to be critical. However, this review attempted to answer a controversial clinical problem and was published in a high-quality journal. There is also a danger of misinterpretation of the quality of this paper and hence the results.
I have several points that I think are important:
- The whole purpose of a systematic review is to systematically review the high-quality evidence. This means that the systematic review should be confined to prospective controlled clinical trials or randomised clinical trials, in which bias is minimised. If the reviewers include retrospective studies, that are poorly controlled, biases are introduced and the findings of the review are not high quality. In effect, by including studies of high risk of bias and low quality all that is happening is a recycling of low levels of evidence. When this is then repackaged in a systematic review readers, may be less critical and the review may have undeserved impact.
- The authors used the Cochrane Collaboration risk of bias tool to evaluate bias in the final sample of papers. This is designed for use with randomised trials and I cannot see how they used this for retrospective studies. This is a major problem and I have checked and rechecked the paper to be absolutely clear on their methodology. I’m not sure how the EJO referees did not raise this as an issue.
- They suggested that the studies provided a high level of evidence, yet they included eight studies that they classified as high risk of bias ( although I do not know how this was calculated).
In summary, I cannot help thinking that this paper exhibited significant problems and to be honest it does not add to our knowledge. I have covered “how to read a systematic review” in a previous blog post and my previous comments are relevant to this review.
We also need to be cautious in interpreting studies that evaluate the non-extraction/extraction decision. This is because it may have been a clinical decision to use mechanics that open the naso labial angle. We should always remember that the effects of treatment are a combination of the treatment decision and our mechanics. Simply combining data from a mixture of studies completely ignores the “real world’ clinical situation.
Finally, I would like to call on journal editors to be more critical when assessing some of the systematic reviews that are submitted. The use of this methodology is widely accepted and we should welcome the publication of good review. However, we should make sure that the standards are high. I do worry that there is a danger of the systematic review becoming the cephalometric analysis review of the 1980s; a lot of data meaning very little.