Correcting posterior crossbites changes the palatal morphology!
There are many ways to correct dental posterior crossbites. But do any of them change the morphology of the palate? This new trial provides us with great information.
I have posted several times about crossbite correction. My most recent post was about a new study from Sweden that was done in the “real world” of specialist and general practice. This showed that specialists were more effective than general practitioners in treating crossbites.
This newly published paper is an extension of their study. It provides information on changes in the morphology of the palate following crossbite correction.
Most previous research into the correction of crossbites has concentrated on dental changes. Indeed, many of the claims about orthopaedic change are based on analysis of 2D radiographs. Importantly, they involve case series with limited comparisons between appliances or untreated controls. This new study addresses this deficiency in our knowledge.
A team from Malmo, Sweden, did this study. The EJO published it.
Ola Sollenius et al
EJO: Advanced access. doi:10.1093/ejo/cjz054
What did they ask?
They did the study to ask this question:
“What are the effects of correcting unilateral posterior crossbites with expansion plates or quad helices on the palatal volume and area”?
What did they do?
They did an ambitious trial in specialist and general dental practice. The PICO was
Participants: 135 children who were between 8-10 years old with unilateral posterior crossbites and a functional shift.
Interventions: Quad helix (QH) or removable expansion (EP) treatment done by specialists or general practitioners
Control: A delayed treatment control
Outcome: Change in palatal surface and volume changes.
They also identified a “normal” control group of children who were in the mixed dentition between 8 and 10 years old. These children had no malocclusion with an IOTN of 1or 2.
They randomised the participants to have treatment in general dental practice with either a QH or EP or in specialist clinics with a QH or EP. They also randomised to an untreated (delayed treatment by 1 year) control group.
The randomisation was pre-prepared, and allocation was concealed in sealed envelopes. They took study models before and after treatment and scanned the models to construct 3D scans. They made similar records for the untreated control and the “normal” group.
Finally, they calculated the palatal surface volume and shell volume from the 3D scans. Blinded examiners recorded all the data.
What did they find?
They presented a large amount of data, and I have concentrated on the most essential information from the paper. These were
At baseline.
- All the crossbite groups had significantly less palatal surface and area compared to the normal group.
- There were no differences between the crossbite groups.
At the end of treatment (observation).
- The surface area and volume increased in the four treatment groups.
- There was no change in the untreated and normal occlusion groups.
- The QH(specialist) QH (generalist) and EP(specialist) groups had higher surface and volume area than the control or normal group.
- It appeared that the QH treatment was more effective than the EP treatment in changing palatal morphology.
Their overall main conclusion was:
“Unilateral posterior crossbite correction results in a normalisation of the palatal structures in terms of palatal area and volume”.
What did I think?
I thought that this was an ambitious and well-carried trial. The randomisation, concealment and sample size was clear. Importantly, they recorded the data blind. I also thought that it was important that the study was carried out in a real-world setting, as opposed to a dental school clinic. This means that the trial has generalisability. Overall, their methodology was excellent.
When I looked at their findings, I was unsure whether the changes that they reported were clinically significant. For example, the post treatment difference in maxillary surface area for the QHS and control was 77 mm2 . Nevertheless, it was important to see that the changes they detected were more significant than the untreated or normal control group. I feel that we can conclude that the palatal morphology had been normalised.
I was a little unclear on the source of their control group, and it would have been nice to have information on this. Furthermore, it would have been beneficial to have information on any changes in sleep-disordered breathing etc. However, this trial was started in 2013, and I am not sure that the new role of orthodontics in SDB had been put forward at this time.
Summary
Finally, this was a nicely done trial that provides us with reassuring information about the effect of simple treatment mechanics on palatal morphology. I am not sure where this leaves the TAD supported expanders etc. But this can be easily studied using a similar methodology.
Emeritus Professor of Orthodontics, University of Manchester, UK.
Interesting article. Pity it was only a shot-term assessment of changes to the palatal volume. Is the change stable? Why should all individuals have the same palatal volume? Should they also have the same sized teeth, arch length or stature?
The most important question should be, “is treatment required for unilateral posterior crossbites with a slide in the mixed dentition?”
Is there evidence of damage if it is left untreated? Does it cause future TMJ problems?
Does it cause asymmetrical facial growth? If it does, then why is there a slide? Surely this asymmetrical growth would eliminate the side? A functional appliance is merely a method of creating a large anterior slide, then waiting for growth to eliminate it. Why do lateral slides, generally on the primary canines, persist at recall appointments when the interference is not removed?
Thanks Kevin for looking at this. Assuming that the measurement is 77 square mms this is about 2mm expansion per side by my guess. If the teeth are moved buccally would you not expect more palatal mucosa to have formed next to the tooth? After all if you move a single palatal tooth into position then presumably there is a greater surface area of palate at the end. As well structured as this study is I’m not sure it’s really telling me anything that is surprising or useful. If the teeth have moved then the palatal area must increase since the posterior teeth are further apart (as must the volume). As for morphology, you don’t say what the morphological changes were but I expect the palate to be a bit shallower, again because the posterior teeth have moved buccally and probably tipped a bit. In summary is the paper not just saying that of you move teeth then bone follows?
Good Study, especially from the methodological point of view. As reported earlier by Burstone, the upper molars are excessively palatally inclined, on the cross bite side, compared to the normal side, in unilateral posterior crossbite cases (as a compensatory phenomenon?). Once they become upright/normally torqued during and after correction(normal biting force), naturally archwidth increases in the molar region. This might be the logical/possible explanation for the results?
These are interesting findings that support our previous results in adults. Note that there is no such thing as “3D palatal surface area”. By definition area is measured in 2D. I did not have access to the full paper but I assume the ‘shell’ measurement refers to 3D volumetric measurements. Also, altho’ the total sample size was 135, this was not the analysis performed against the control group. It appears there were 25 subjects in each comparison, which I believe might satisfy a power calculation for the minimal sample needed for statistical significance. In any case, these data support the idea that the craniofacial sutures may provide a niche for mesenchymal stem cells, as predicted by the Spatial Matrix hypothesis. Happy Labor Day everyone!
Singh GD, Heit T, Preble D. Changes in 3D midfacial parameters after biomimetic oral appliance therapy in adults. J Ind Orthod Soc. 48(2), 104-108, 2014.
Singh GD, Heit T, Preble D, Chandrashekhar R. Changes in 3D nasal cavity volume after biomimetic oral appliance therapy in adults. Cranio 34(1):6-12, 2016.
Singh GD. On Growth and Treatment: The spatial matrix hypothesis. In: Growth and treatment: A meeting of the minds. McNamara JA Jr (ed.) Vol 41, Craniofacial Growth Series, Ann Arbor, USA, 2004, 197-239.
I have a problem with the concept of “unilateral cross bite with functional shift.” If the distance from the mid-palatal raphé to the mesio-lingual cusp tip of the first permanent molar is equidistant on both sides, then perhaps we have a bilateral cross bite with functional shift. If the occlusion is viewed in Initial Contact, rather than Maximum Intercuspation,” and the upper to lower molars on both sides are buccal cusp tip to buccal cusp tip, but then the mandible shifts to one side to go from Initial Contact to Maximum Intercuspation, isn’t that truly a bilateral cross bite? And if so isn’t a skeletal expansion approach more efficacious than a dental expansion approach?