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EXTRACT WHY? EXTRACT WHY NOT? THE AIRWAY. PART 3

The effect of orthodontics on the airway has been a debated topic, further complicated by the effect of orthodontics on Sleep Disorder Breathing (SDB), resulting in one of the most controversial topics in orthodontics. In this blog, we will look specifically at the effect of extractions on the airway and sleep disorder breathing. There has been significant research within the last decade exploring this topic.

How can extractions cause airway changes?

 

In orthodontics extractions have been considered by some as causative factors of sleep disorder breathing due to a reduction in the airway space. The orthodontic audience is split, when questioned about extractions in a hypothetical patient with reduced airway space, 42% of orthodontists changed their treatment plan due to this clinical finding Cumming 2018.

To understand the process, the mechanism of how extractions can cause changes to the airway needs to be explored as it is not a direct process. The proposed process is of extractions reducing the arch length, and therefore reducing the volume in the oral cavity. The tongue and soft palate are displaced posteriorly, reducing the airway space (defined as the nasopharynx, oropharynx and laryngopharynx/hypopharynx) through the effect of these soft tissues.

How to measure effects of extractions on the airway

The use of a CBCT has become a common method of assessing the airway space. A CBCT allows 3D shape and size analysis of both hard and soft tissues, replacing 2D radiographs, which did not account for the 3D shape of the airway. However, as we explore CBCTs it will emerge that 3D imagery is limited in assessing changes to the airway. CBCT’s are used in two ways to assess the airway: 1/ Overall volume of the airway space, 2/ Narrowest cross section. The narrowest cross-section may sound odd, after all it is a 2D measurement, however some consider the mean cross sectional area (MCA) of the narrowest aspect of the airway as the ‘bottle neck’, and therefore a cause of sleep disordered breathing.

CBCTs are able to give more data than we previously had on airway analysis, however the reliability of this data is poor. If we take two different CBCTs on the same patient there is low reproducibility (ICC 0.61-0.95), and an approximate maximum error of 16.9% Ryan 2018*. A CBCT can only generate data of the airway in a snapshot of a breathing cycle, which does not inform us of how well the airway is functioning. Different times of the day, orientation and posture can all affect the airway function, and therefore the volume, simply lying down can reduce the airway volume by 40% Battagel 2012. Information of susceptibility of soft tissues to collapse is the key outcome to analysis in predicting impeding function of the airway, which a CBCT cannot assess. The gold standard for assessment of the airway, is to see it in action, a polysomnography study assessing the number of ‘malfunctions’ through apnoea or hypopnea events, as well as monitoring of oxygen, airflow and 5 other parameters (all non-ionising, to labour the point).   

The discussion of imaging for sleep disorder breathing is detailed in the excellent White Paper from the AAO Behrents 2019, which concluded a CBCT “should not be used to diagnose sleep apnea or any other SRBDs, because such imaging currently does not represent a proper risk assessment technique or screening method.

So, what do extractions actually do to the airway?

There have been several retrospective studies assessing the changes to the airway of extraction and non-extraction orthodontic treatment. Some studies have shown a reduction in airway volume in incisor retraction cases with extractions, and other studies have shown an increase in airway volume from mesial molar movement following extractions Hu 2015. 

Overall however the findings were of non-significant changes to the airway volume through extraction orthodontic treatment. There is one paper to single out in the quest to answer the question, by Larsen 2015 published in the Journal of Clinical Sleep Medicine. 5584 patients were assessed with matched extraction and non-extraction orthodontic treatment. They found 10.7% of patients missing premolars and 9.6% of non-extraction patients developed Sleep Disorder Breathing, a non-significant finding OR 1.14 (95% CI: 0.96–1.37). Therefore patients who have extraction orthodontic treatment have no greater risk of developing Sleep Disorder Breathing than patients who undergo non-extraction treatment.

*Ryan 2018 – data was re-analysed from this study.

Conclusions

The effects of extractions on the airway are unclear due to CBCT data not being a reliable method of assessment of airway function. One could even say volume changes to the airway are irrelevant as they do not relate to airway collapsibility or function. A statement from Larsen’s 2015 adeptly described volume based studies of the airway as being of significant “limitation… (as) none examined this relationship to OSA”. In research terms the endpoint of pathology has been overlooked in these studies.

Even if extractions had demonstrated a reliable reduction in airway volume (it hasn’t for those who scrolled to the conclusions), there is yet no evidence which supports a reduction in airway volume increasing collapsibility, so the function of the airway is not affected by extractions Hu 2015.

 

Contributions

Contents: Kerolos AlHakeem

Contents: James Andrews 

Edited/contents: Farooq Ahmed

We hope you have enjoyed this blog, This blog started with a conversation between Kerolos AlHakeem, Farooq Ahmed and James Andrews, to follow more conversations, clinical tips and commentaries on orthodontics please check us out on Instagram / facebook

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