This week on the Blog I am joined by Badri Thiruvenkatachari, who has worked with me for several years, and was the lead author on our updated Cochrane Systematic Review, on the treatment of Class II malocclusion, published last week. This can be accessed on http://goo.gl/puzQR5. This is one of the largest and most cited orthodontic Cochrane Reviews and was first published in 2007. One of the requirements of carrying out a review for Cochrane is that you have to commit to update the findings periodically. This means that as new knowledge from studies becomes available, this is included into the reviews. In effect, the review is a “living document” and the conclusions may change with time. This is one of the great advantages of Cochrane reviews compared to the more static conventional literature. The downside is that you are committed to updating your reviews for as long as you are working!
This update allowed us to include several new studies and evidence that has become available. It also resulted in several of the established studies being reassessed for the quality of evidence, and new statements made on the strength of evidence in the review.
So what did we find?
The review included 17 studies with data derived from 721 participants.
- Three trials compared early treatment with functional appliances (2 Phase) with treatment provided in adolescence only (1 Phase).
- Two trials compared early treatment with headgear to one phase adolescent care.
- Six trials compared different types of functional appliances when used in one phase adolescent treatment.
- Finally, one trial compared treatment with functional appliance against no treatment
What did we conclude?
I found it very interesting and important to find that adding newly available data resulted in a change in the conclusions from the first version of the review. This was relevant to the role of early Class II treatment in preventing incisal trauma Our overall conclusions were
“providing early orthodontic treatment for a child with Class II malocclusion is more effective in reducing the incidence of incisal trauma than providing one course of treatment in adolescence. There was no other advantage in providing early treatment”.
“When one course of treatment was provided in adolescence, no functional appliance was better than another. Any change in skeletal pattern when compared to a control was not clinically significant”.
It was also important to consider that the overall quality of evidence was low, apart from the findings on trauma, where the quality of evidence was moderate. This may be interpreted by considering confidence in the results. So where evidence is low quality, this may be defined as “further research is very likely to to have an important impact on our confidence in the findings’. When the level of evidence is moderate this means that “further research is likely to have an important effect on our confidence”. I have discussed this issue of confidence in a previous blog post. Sense about science: Dealing with uncertainty in orthodontic research.
How strong are the conclusions for Class II orthodontic treatment?
If I build on my post of last week. It is clear that when we consider most of the findings of this review, we must appreciate that the quality of the evidence is low because of bias in the studies. We also need to remember that Cochrane is pretty unforgiving in this assessment! The reasons for this classification are clearly stated in the review and I shall address this assessment in a future post.
Nevertheless, when we consider the important findings on trauma, we can have some confidence that this is a clinically important finding. At this point, we should examine the data concerned with the potential reduction in trauma. This data is shown in the paper in the summary of findings table 1 for the main outcomes. This reveals that 29% of patients with new trauma were in the 1 phase adolescent treatment group compared with only 20% of those patients receiving early treatment. The odds ratio was 0.59(CI 0.35 to 0.99). This is a clinically significant finding, but we need to appreciate that the CI is wide and almost contains 1. We also need to consider how to interpret the odds ratio. As with several statistical tests this is not straightforward and I had to look this up. I found this explained well in this blog http://goo.gl/lDWlI8. They explain odds ratio in this way…
“When you are interpreting an odds ratio (or any ratio for that matter), it is often helpful to look at how much it deviates from 1. So, for example, an odds ratio of 0.75 means that in one group the outcome is 25% less likely. An odds ratio of 1.33 means that in one group the outcome is 33% more likely.”
If we now look at the OR we found (0.59) this means that in the early treatment group (functional appliance) the chance of trauma was 41% less likely than for the group whose treatment was provided when they were in adolescence.
So what does this mean clinically?
Whenever, I give a course or speak to trainees, I stress that one we have read a paper we need to consider the “so what” question and whether we are going to change our practice based on the results of the study. It is clear from this review that moderate level of evidence suggests that providing early Class II treatment with functional appliances reduces incisal trauma. This means that when I see an 8 year old child with an increased overjet, I will explain to them that early treatment will result in a transient increase in their self esteem and that they will be 40% less likely to have trauma than if we waited to provide treatment when they are older. They can then decide. I suspect that we will be providing more early treatment…
Thiruvenkatachari B, Harrison JE, Worthington HV, O’Brien KD (2013). Orthodontic treatment for prominent upper front teeth (Class II malocclusion) in children Cochrane Database of Systematic Reviews (11) Other: CD003452.