Does sutural expansion really improve the prospects of stability?

Padhraig Fleming writes this excellent post on expansion. There is ongoing debate about the scope of expansion, with increasing discussion about systemic rather than dental benefits. He has decided to avoid that and instead focus on how the mode of expansion influences the prospects of stability.  Read on for his thoughts….

I am a big advocate of sutural expansion. When we require it! Daniele Raviglia, an Italian orthodontist, recently commented on social media that mid-palatal sutural separation is likely our own genuine means of long-term orthopaedic change in orthodontics. And of course, mid-sutural expansion (tooth-borne, bone-borne or hybrid) generates new bone improving space conditions and may limit unwanted vertical opening in certain cases. 

What does research tell us?

Our own research has suggested that the mid-palatal suture is likely to be patent up to at least 13 years in a female and 14 in a male. I use this as a guide to tailor simple (tooth-borne) approaches to achieve very predictable mid-palatal separation in these age groups. And this view is strengthened by an excellent 5-year follow-up by Bjorn Ludwig’s group which failed to highlight a skeletal advantage to bone-borne (hybrid) approaches compared to tooth-borne in juvenile patients (approx. 9 years of age). 

Skeletal vs Dental change

But what is the likely impact of dental versus skeletal change on the relative stability of transverse increase? Two points are important to acknowledge in prefacing this discussion:

1. We may be comparing apples and oranges. In my view, there are clear indications for one approach over the other. I must admit that I am doing more RPE than ever. But one size does not fit all. I have listed some of the considerations below (Full elucidation of these might require a blog post each):

• Age and Mid-Palatal Sutural Maturation
• Magnitude: Bilateral or Unilateral (or Local)
• Skeletal: Transverse Maxillary Constriction
• Buccal bone availability: WALA Ridge and Periodontal Phenotype
• Compensation: Upper or Lower, and
• Lower Arch Form and Extraction Plan

• 2. Expansion is unstable irrespective of the approach. I am biased on this but I will highlight my hierarchy of stability as an argument for tailored approaches to retention and informed conversations regarding planning and consent in this respect (link below). We published this paper in the British Dental Journal a couple of years ago.

The findings from a systematic review

A systematic review evaluating the long-term stability of expansion undertaken at different ages and by different means was published in Orthodontics and Craniofacial Research in 2024. An excellent research group based in Geneva did this review, and it is freely available online: https://doi.org/10.1111/ocr.12690

Like many of our systematic reviews, it is limited by a lack of high-quality prospective comparative studies with prolonged follow-up. As such, the findings do carry some caveats. The authors were able to include a considerable number of primary studies (22). Some of the interesting (and memorable) findings included:

• Basically 1 in 5 (19.5%) of patients had relapse of posterior crossbite at long-term follow-up. 
• Similarly, essentially 20% (19.3%) of the total expansion (including overexpansion) relapsed
• When comparing dental versus skeletal modes of expansion, approx. 15% of expansion was lost when undertaken by sutural separation versus 25% (25.9%) by dental change. 

Messages?

There are some nice messages here. The difference in the relative stability with skeletal versus dental means is interesting. They did find more relapse with dental expansion and this is what I would expect – particularly if the wrong decision was made to expand dentally in a patient with a transverse maxillary constriction – as interaction with the buccal plates is likely problematic both in terms of stability and periodontal support. 

However, let’s take an average patient – one requiring 4mm of maxillary inter-molar increase. Let’s assume we are successful in producing that change. We can expect to lose 20% in the long term (0.8mm). The difference between the methods of expansion is therefore of the order of 0.4mm (1mm versus 0.6mm). I appreciate that this is hypothetical. But that is a small difference. My conclusion is that prospective stability should be low down the list of reasons for choosing between sutural and dental expansion (Some of the considerations above and in the slide below may be more pertinent). 

Over-expansion

A second point relates to over-expansion. This is a bugbear of mine. I understand why we over-expand to accommodate uprighting of the lower posterior dentition and the Curve of Wilson. However, I see clinicians frequently expanding beyond this position and I don’t know why we would do this. There is no evidence comparing the long-term implication of including over-expansion within our protocol. It would also be intuitive to expect potential harm due to periodontal risk and loss of vertical/transverse control. The authors were unable to find a benefit in their review and I note some of their discussion which I think is really useful:

“However, whether overcorrection is necessary remains an unanswered question since it may be interpreted that relapse is a physiological process to counterbalance the overexpansion performed that per se, does not create a stable occlusion …. It is unclear, however, what role the overexpansion and its quantity can have on relapse.”

Finally, the authors were unable to find data linking age of treatment to transverse stability. They also cited recent research showing that up to three-quarters of crossbites in the primary dentition resolve spontaneously. 

Conclusions?

An interesting paper and one that should inform our circular conversations regarding the approach to transverse expansion. The ‘back and forth’ will continue (No pun intended) … but no form of transverse expansion is stable and prospective stability may not give us licence to routinely address the transverse with sutural expansion.