November 28, 2013

Orthodontic treatment and trauma to the front teeth: Are the risks reduced?

Early orthodontic treatment for Class II malocclusion reduces the risk of trauma to the front teeth:  How do we interpret this data; Odds, Risk and Numbers needed to treat?

In my last blog, I described the results of our Cochrane Systematic review into the effectiveness of treatment for Class II malocclusion (  In the review we concluded that the only benefit of providing treatment when a child was 8-10 years old was a reduction in trauma to the front teeth.  I also pointed out my interpretation of the odds ratio for the data we presented was

 “the odds of trauma for patients who were treated early was 41% less likely than for the patients treated in adolescence only”.

What does all this mean?

I have received several comments on this conclusion and this has led me to explore these findings further and attempt to come to a clear conclusion on what we should be doing for our young patients with prominent incisors.  I have leant heavily on these three main sources.

  1. The module on dichotomous data from the Cochrane Collaboration open learning material for reviewers,
  2. The effect size by Nick Pandis
  3. Risk ratio vs odds ratio by Nick Pandis

You may also like to refer back to my previous post on reducing uncertainty in orthodontic treatment

I have based all my calculations on Table 1.6 in the review and a shortened version is included here:

Spacing between teeth21.5
Shape or colour of teeth20.6
Prominent anterior teeth19.6
Anterior open bite14.1
Crowding of teeth7.6


How do we quantify the risk?

I first calculated the risk of trauma for each group, this revealed that for the early treatment group it was 19.7% and for the adolescent group it was 29.7%.  The difference in risk was, therefore, 9.6%. Meaning that if we treated early there was a reduction in trauma of 9.7% compared to if we treated in adolescence.


The next measure that I considered was relative risk or risk ratio. This is the risk in one group (early treatment) divided by the risk in the other (adolescent treatment).  I calculated this to be (34/172)/(54/185)=0.67

This means that providing early treatment reduced the risk of trauma by 33% of what it was when the treatment was provided in adolescence. Again an interesting finding.

The last important measure is the numbers needed to treat (NNT)  This gives us the number of children we would have to treat early to prevent one episode of trauma.  This calculation is easy, is it 1/Risk difference. For this data 1/0.1.  Therefore, the number needed to treat is 10 with a very wide 95% confidence interval of (6-175).

If you want to calculate similar values for other datasets this can be done easily by using this web calculator.


What can we conclude?

 One of the important factors of which I have become more aware, is that is it is up to us to interpret the data and we should not all simply “go along” with the authors conclusions. So, the decision to treat early is up to you.  You need to consider the following main points if we treat early


1          The chance of incisal trauma is reduced by 10% compared to a group of patients treated in adolescence

2          The odds of trauma will be 41% less likely than in the adolescent group

3          The risk of trauma will be reduced by 33% compared to the risk in the adolescent group

4          To prevent one episode of trauma, you will need to treat 10 patients.

How certain are you of this data? You need to remember that the confidence intervals are very wide.

 So what would I do?

 I think that I am influenced mostly by the reduction in trauma of 10% and the numbers needed to treat of being high.  I would not treat early for the sole aim of reducing trauma. What would you do?

I would like to acknowledge the help of Badri Thiruvenkatachari and Nick Pandis with this one!



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Have your say!

  1. dont forget this data is an extrapolation from a sample to a population, hence a confidence range. As clinicians we need to interpret from a population to an individual. For example a young sporty child with teeth that stick out will not have an average risk of trauma, so the advice given to a 9 year old rugby player will be different than that to someone who is not so active and at risk

    • Thanks, you have made a good point, and we all need to remember that this data represents the average effect of treatment for the average patient. However, we must also be careful of potentially not taking notice of research because of our own perceptions of risk. However, in some cases it is logical to consider the patients circumstances. In the example that you put forward, it could be argued that a mouth guard may be more effective than early treatment in providing protections. But this study does provide information that should allow our patients and parents to take part in a fully informed treatment decision

  2. Knowing what you know would the answer be the same if it was your son or daughter? My suspicion is that you would treat, when you set the numbers aside you go with what you would do for your own children.

    • Good point! But we need to remember the number needed to treat to prevent one episode of trauma and the potential harms of providing treatment early. In our Class II study we showed that the overall quality of treatment in the group that had early treatment was not as good as in the group that had one course of treatment. So if the patient was my son or daughter, I would not treat…

  3. Hello, Kevin. Please assist with my confusion. In this review you are opposed to intervention, ” I think that I am influenced mostly by the reduction in trauma of 10% and the numbers needed to treat of being high. I would not treat early.” However, in your November 21, 2013 review of what appears to be the same article, 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 ………you state, “This means that when I see an 8year 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…”
    This leaves me unclear as to where you stand.
    Gerry Samson

    • Hi Gerry, thanks for the comment. You are correct in drawing attention to some confusion in my posts. I suppose that this is a great illustration on the fact that clinical orthodontics is full of uncertainty! In my first post I interpreted my closing comments as I would provide the information to our patients and their parents and more of them will choose to have early treatment.

      In my second posting on the same subject I concentrated solely on the need to provide early treatment to reduce trauma. I am fairly sure that for most children I would not routinely provide early treatment with the aim of only reducing trauma. If the patient was also having problems being teased at school then I would provide treatment. But,If they were playing contact sports then I would also treat them. The most important part of the discussion on early treatment that we need to have is that we do need to routinely treat everyone early but we need to consider the individual patient.

      I hope that I have addressed your question

      Best wishes: Kevin

      • Hello, Kevin and thanks for your reply. Routinely, I inform parents of all sides of the overjet and trauma issue – providing adequate information for them to decide what is best for themselves and their children. Overall, I favor the view,”Statistical data has little value for the patient with a problem”.

  4. Dear Kevin, you ask at the end :

    ” So what would I do?
    I think that I am influenced mostly by the reduction in trauma of 10% and the numbers needed to treat of being high. I would not treat early for the sole aim of reducing trauma. What would you do?”

    I do suggest – ask the Patient/Parents. How does she/they percepts this risk? Is it a male or female? Is the child more or less acitve. Make the decision shared and so on. Different People different values.
    One of the most frequent fallacies done by doctors in decision making is the confusion of evidence- with value question. Value question however is where patients must be involved. Here:
    The 10% reduction of Trauma is the scientific evidence.
    But how the Trauma is valued- this is subjective and different among personalties.

    • Yes, this is a good way forwards. When I see patients with a large overjet, I give them the information that I have outlined and they decide whether they want early treatment or delay. The thing that seems to influence them the most is whether their child plays contact sports and they feel that there is a real risk of trauma. Thanks for your comments

  5. Sorry – best regards from Germany!
    Alexander Spassov

  6. I thought I would follow on from Gerry’s comments about confusion with the Odds ratio and its interpretation. Odds ratios I feel are misleading as it is not the way most of us and especially patients and their families would interpret risk in everyday life. As an example, an odds ratio of 2 indicates a risk is 100% more likely but if the condition is only a low risk, say 2%, then the risk elevated by 100% is still only 4% – it does not sound like such a big deal now does it? As you pointed out (although my math came out slightly differently), the risk of trauma with Early Treatment was 19.8% (34/172) and with Late Treatment it was 29.2% (54/185) so only a 9.4% additional risk of trauma. As discussed, this sounds less ominous and may sway some to delay treatment but some of the more active subjects or those not willing to bear the risk would still seek early treatment. However I then feel you need to factor in the type of trauma. The UNC trial alluded to the fact that most of the trauma was minor while the Florida trial quantified it. They found 80% of the trauma was in the enamel only while 19% involved dentine and only 1% had a pulpal involvement. If we then consider major trauma to be only the dentine and pulpal involvements (and I assume any avulsions) this is only ~20% of all trauma. This then gives us 20% of 9.4% which is only a 1.9% additional risk of a major trauma if delaying treatment. I suspect some families would then make a different informed choice?

    • Hello, Peter and thanks for your valuable input. Except for being an odd fellow myself, the mathematics of “odds ratios” is beyond my one-celled mind. From a practical standpoint, routinely I inform parents of all sides of the overjet and trauma issues – providing adequate information for them to decide what is best for themselves and their children. Overall, I favor the view,”Statistical data has little value for the patient with a problem”.

  7. Kevin
    Would it be unreasonable to suggest that a mouthguard might be the treatment of choice here until adolescent treatment is available? I suspect a study that included that option might decrease the risk of trauma significantly and make orthodontic intervention even less justified.

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