March 04, 2024

Is there an association between sleepiness and malocclusion?

It’s about time that we had some interesting papers on sleep disorders, orthodontics, and malocclusion. These topics have been discussed a lot on this blog, but the research covered so far has been low quality. Moreover, the evidence quoted in discussions and social media has been almost nonsensical. Therefore, this new paper on childhood sleepiness comes as a breath of fresh air.

Studies have estimated that 4-11% of children suffer from sleep-disordered breathing, which may be associated with their craniofacial morphology. Typically, treatment is done in collaboration with an otolaryngologist, and the first step is the removal of the tonsils and adenoids (or watchful wait!). However, this approach is not always effective, and we should consider the possible association of severe malocclusion and breathing problems.

A well-known team from Copenhagen, Denmark, has explored this subject in a new research paper. The AJO-DDO published the paper. This paper is open-access, so that anyone can read it!

sleepiness Copenhagen

Sleepiness in children with severe malocclusion compared with children with neutral occlusion

Sanne Nygaard Bruun, Camilla Hansen, Liselotte Sonnesen

American Journal of Orthodontics: Advance access

What did they ask?

In this study, they wanted to:

“Examine daytime sleepiness and sleep in children with severe malocclusion before orthodontic treatment compared to children with neutral occlusion”.

What did they do?

The team did a cross-sectional study of children with and without severe malocclusion.  I will go through their sample selection in detail because this is integral to our interpretation of this paper.  

They identified two samples.

Severe Malocclusion

They approached all the children with severe malocclusion who were referred for orthodontic treatment to the postgraduate clinic at the Dental School, University of Copenhagen. General practitioners had referred the children following the child screening protocols to identify those with health risks from malocclusion.  This was based on the risks outlined by Solow. (reference). This procedure is established and was a forerunner to the Index of Orthodontic Treatment Need (IOTN).  They identified a group of 120 children (73 girls and 47 boys) with a mean age of 11.96 years.

Neutral Occlusion

They enrolled this group of children from another study. These were recruited these children from the Copenhagen dental services. They had a neutral occlusion, according to Bjork. (reference). In effect, they had no indications for orthodontic treatment.  This sample comprised 35 children (18 girls and 17 boys) with a mean age of 11.97 years.

They did a sample size calculation based on a difference of 60% in the Epworth Sleepiness Score.

The participants completed the Epworth Sleepiness Score and the Berlin Questionnaire. They did this with their parents.

They then recorded the occlusion in three planes of space from the study models. Finally, they took cephalograms on the severe malocclusion group and analysed them.

Their statistical analysis was relevant and complex to consider several cofounders. They did a regression analysis to take age, gender, and BMI into account.

What did they find?

I thought that these were the main findings.

There were no differences in the age and gender of the groups.

This is the main data on EES scores.

VariableMalocclusionNeutral occlusion
EES score4.03 +/-3.492.6 +/-2.5

When they adjusted their statistics for age, gender, and BMI, daytime sleepiness occurred more often, and the ESS scores were 1.5 times higher for the malocclusion group than the normal occlusion group. The 95% CI was 1.069-1.85).

The team looked at single malocclusion traits with malocclusion. They found a significant difference in daytime sleepiness with children with deep bite having 1.6 times EES (95% CI 1.054-2.5) than children with neutral occlusion. Similarly, children with open bite had 1.71 times higher EES (95% CI 1.012-2.9) than those with neutral occlusion.

Interestingly, they did not find any differences concerning sagittal and transverse occlusal discrepancies.

There were no differences in terms of hours of sleep between the groups.

Their overall conclusions were

“Daytime sleepiness occurs more often in children with severe malocclusion than those with neutral occlusion, and an association between daytime sleepiness and craniofacial morphology may exist”.

What did I think?

The method and results of this study are very interesting and add to our knowledge.  This paper has made me think hard about the study.  As with all studies that look at a cross-sectional sample of people, we need to look carefully for any issues with the method of population selection.

This study examined patients referred for orthodontic treatment due to severe malocclusion, according to an established formal classification. Therefore, we can conclude that these patients required treatment for health-related reasons.

They selected the control group using established criteria for not having malocclusion.

The research team utilised two appropriate outcome measures. It is worth noting that the two questionnaires were insufficient to diagnose sleep-disordered breathing, as this was not the study’s primary objective. However, the team highlighted that daytime sleepiness could indicate a sleep disorder. I thought it was also interesting to see an orthodontic breathing study that measured an outcome that had meaning to patients, as opposed to some measurements taken from radiographs or a CBCT.

It was also good to see investigators use multivariate statistics to take cofounders into account.


I would like to discuss the interpretation of our results. The first point to consider is that the outcome measures that they used.

I wasn’t entirely familiar with the EES, so I looked up the clinical symptoms relevant to the scores on the ESS website. According to the website, scores ranging from 0 to 5 indicate normal daytime sleepiness, while scores between 6 and 10 indicate higher-than-normal daytime sleepiness. 

When I looked at the data from the study, I found that the children had “normal” sleepiness scores. I contacted the authors about this. They got back to me and informed me that while EES scores below 10 are non-pathological for adults. Nevertheless, at present, there are no such thresholds for children.

.However, the group with malocclusion had significantly higher scores than those with neutral occlusion, suggesting a trend towards higher scores with malocclusion.

We can now look at the malocclusion features associated with daytime sleepiness. These were trends towards increased and decreased overbite.  These are similar to findings in earlier research.  We also need to remember that “association is not causation”. Therefore, we cannot assume that malocclusion causes daytime sleepiness, nor can we assume that daytime sleepiness causes malocclusion! This concept is well-explained in a blog post by Students 4 Best Evidence.

What can we conclude?

Due to the low EES values, I’m unsure if I can draw a solid conclusion from this paper. Nevertheless, the paper does indicate a potential link between daytime sleepiness and the vertical component of malocclusion, indicating a trend. However, it’s crucial to remember that this is simply a correlation and doesn’t prove causation.

I thought that it was important that there was no association between maxillary transverse discrepancies and sleepiness, which contradicts the expansion philosophy of treating breathing problems.

The paper presented raises numerous questions that require further research. It is a well-conducted study that suggests a possible link between sleepiness and malocclusion. However, more in-depth research is necessary to explore this important area. Although it may sound repetitive, surely there is a research team that can take up this crucial work.

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Have your say!

  1. Hi Kevan, I’m interested in your view here: Is there a specific numbers of studies that must indicate a “correlation” before this is taken seriously by orthodontists? Is it 5? 15? 30 studies? I hear more studies are needed, but how many is enough for orthodontists to believe mouth breathing and SDB are linked to most malocclusions?

    • Thanks for the comment. As I said in the conclusion to my post “It is a well-conducted study that suggests a possible link between sleepiness and malocclusion”. However, we need more research because association is not causation. But, it is a pointer that there may be an effect either way. I think that current knowledge is that there may be a link between malocclusion and breathing (or between breathing and malocclusion). Nevertheless, the real question is whether orthodontic treatment influences breathing. This can be answered by doing a trial. If I could turn back time and have my career again, I would do this trial. It is an important question, we have uncertainty about treatment and I would think that a funding body would support it. Unfortunately I have retired.

      • Hi Kevan

        I know you have a lot of sway and you may inspire some orthodontist to do the trial. But please keep in mind that orthodontics is just one piece of the entire puzzle. Has the aao white paper said some forms of orthodontics have been shown to be helpful in the treatment of sleep disorders.

        But orthodontics alone cannot correct sleep disorders because it is a multi-factorial problem. Neither can delegation to an ENT doctor either. Numerous techniques must be employed in order to treat the entire problem even in some cases weight loss and diet change.

        So if you are trying to inspire anyone to do this trial you have to ensure that they use orthodontics as part of a multi-factorial treatment. Your question of whether orthodontics helps with breathing has to be answered by combining orthodontics with rhinology myofunctional therapy and breathing retraining then also organizing for any other factors that are impacting the presence of breathing problems for example diet.

        It is definitely possible but it won’t be easy to run such a trial. I hope somebody runs it and consults with the people who are doing it every day in their private practices before publishing anything or creating a study protocol.

        I’m am aware that you didn’t answer my question above when I asked you how many studies do you require that show a correlation before you start to think that orthodontics has a role to play in the correction of breathing problems is it a number or is it mainly a question of quality?

        Best wishes

        • You are correct a study into this subject will need a multidisciplinary research team. But any good academic research centre can put this together. The AAO white paper stated that RME may help but the evidence was not strong.

          • Thanks for acknowledging. I will be happy to assist any researchers as well.

            Do you have an answer to my question? How many studies are needed until you are convinced?

          • Sorry I did not make myself clear. Firstly, it is not the number of studies that should influence this subject. The most important factor is the quality of the research. There are now a few studies that use relevant outcomes and they appear to show a trend towards a link between some malocclusions and breathing problems. However, this does not mean that orthodontic treatment can cure breathing disorders. This can only be done with a trial. I think that we are in a position to do this, so we don’t need anymore studies to look for an association. We need to move to answer the real question.

  2. This is an interesting study but I’m not sure I would classify it as ‘high’ quality. First, no overnight sleep studies were taken, so it’s impossible to differentiate between sleep debt, insomnia, narcolepsy and sleep apnea as the cause of daytime sleepiness. Second, there was no definition of ‘severe’ malocclusion in the paper. Third, ‘maxillary prognathia’ is almost unheard of in craniofacial dysostoses since the cranio-caudal gradient of development dictates that the mandible follows the maxilla (and the cranial base) – not the other way round, which in part highlights the inappropriateness of lateral cephalometry. Having said all that, I feel this study is a step in the right direction.

    • Yes, I agree it is step in the right direction and the authors should be congratulated. Lets see if someone takes the next step and does a trial in this area.

  3. Kevin, I like that you are choosing to bring more discussion on airway related topics. This is an important topic that demands greater attention, analysis, and debate – so I enjoy reading the various perspectives presented.

    If we are choosing studies to support/refute a link between poor jaw development and airway problems, this is not a very useful paper.

    Firstly, excessive daytime sleepiness is a far from ideal choice of outcomes to measure. A child with SDB and unrestorative sleep is more likely to present with symptoms of inattention, hyperactivity, difficulties sitting still, poor impulse control, etc rather than falling asleep. The use of an alternative measure such as PSQ scores would have been more useful to look at.

    Secondly, the definitions of malocclusion are purely dental. The neutral occlusion groups had no lateral cephalograms taken. We do not know for instance if any of these children were bimaxillary retrusive. It is the AP relationships of the jaws, not the dental relationships that would be more impactful to explore from an airway development perspective.

    Similarly – the absence of crossbite does not imply lack of transverse deficiency. The work of Miner et al has demonstrated that patients without crossbites can have significant dental compensations that may mask a transverse deficiency warranting treatment. We really need to start looking at hard palate measurements including palate width or depth, or even intermolar width if no imaging is available.

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