Maxillary Overexpansion: Too much of a good thing?
Maxillary expansion is becoming more popular. But what happens when we over-expand? This post by Padhraig Fleming looks at a new study that overexpanded children’s maxillas.
Not for the first time, expansion appears to be the zeitgeist in orthodontics. Orthodontists have spawned a range of novel approaches in recent years. Many of these are invasive, and most are directed at facilitating skeletal expansion in mature individuals. I have concerns that the development of these attractive ‘hammers’ may mean that milder forms of arch constriction are seen as a ‘nail’ with more invasive treatments normalised.
In younger patients with transverse maxillary constriction, we can achieve skeletal expansion readily with non-surgical means. However, the quest for more skeletal change prompted this study to argue that a greater amount of expansion might increase the relative contribution of skeletal change to any transverse increase. A team from Dallas did this study. The Angle Orthodontist published the paper.
Authors: Arun K. Bala; Phillip M. Campbell; Larry P. Tadlock; Emet D. Schneiderman; Peter H. Buschang
Angle Orthod. 2021. doi: 10.2319/032921-243.1
What did they do?
They conducted a pilot randomised controlled trial with 28 participants.
Participants: All participants were aged less than 16 years at the start of the trial. They were in the mixed dentition, required at least 4 mm of palatal expansion to treat transverse deficiencies. Their periodontal health was good.
Interventions: They fitted Rapid maxillary expanders with hyrax screws (10 or 12 mm) to bands on the maxillary first molars. Metal arms extended to the second and first premolars or deciduous molars. The clinicians expanded the conventional group until the palatal cusps of the posterior maxillary teeth were positioned along the lingual incline of the buccal cusps of the posterior mandibular teeth. In the over-expansion group, the participants activated the RME screws activated maximally (10 to 12 mm). Participants turned the expansion screw once (0.25 mm) daily. When the expansion was complete, they measured screw activation intra-orally using digital callipers.
Primary outcome: Skeletal versus dental change.
The investigators used pre-determined randomisation. However, they gave us no information on allocation concealment.
What did they find?
They presented a lot of data. I have tried to pick out the most relevant:
- The screws were activated 1.8 times more in the experimental group (10.1 vs 5.6mm).
- More molar flaring arose in the overexpansion group (2.8-fold)
- Skeletal and dentoalveolar change as a proportion of molar expansion was similar in both groups. Skeletal expansion amounted to 57% and 47% of the change in the overexpansion and conventional expansion groups, respectively
- The amount of skeletal expansion, as a proportion of overall transverse change reduced with increasing skeletal maturity
What did I think?
I thought that this was an innovative and interesting study. It appears that there may be some short term gain from over-expansion; however, the absolute differences were minor. Importantly, these were not statistically significant. It would therefore be intuitive that longer-term gain from over-expansion is unlikely.
From a methodological perspective, the sample size was small. The authors made several statements about possible differences between the approaches; however, statistically, significant differences were rarely observed. This might relate either to the fact that no significant difference exists or may be due to the low sample size, which reduces the statistical power.
Another consideration here is the long term effect of overexpansion. In particular, it does seem that greater expansion does translate into both larger increments of skeletal and dental change. One would have to question whether these more significant transverse increases are associated with a higher relapse potential and the risk of periodontal breakdown. We do know that both of these can take time to manifest. As such, while further research with larger samples may be warranted, it would also be helpful to undertake a more prolonged follow-up.
What can we conclude?
Overexpansion of rapid maxillary expanders may lead to a marginally higher proportion of skeletal relative to a dental change in the short term. Unfortunately, the impact of over-expansion in the longer term is not yet known… We still don’t appear to know how much expansion is enough.
Professor of Orthodontics, Queen Mary University of London, UK