Orthodontic retention, we have a new trial!
In this post I am going to return to the subject of orthodontic retention and review a new study on retention methods. This is an update on a previous post. With the addition of this paper I think that we are beginning to build on our knowledge of retention. Maybe it is, also, time for Simon Littlewood to stop jetting around the world and get his team to update their Cochrane review on retention?
This paper is published in the EJO and the full text is denied to most people because it is not an open access journal.
Gudrun Tynelius and Harvigland Stubbarp
What did they do?
In this paper they presented the results of a long-term study of retention and I think that this new publication goes some way to address the criticism that most other studies have been concerned with short term outcomes.
This was a single centre RCT carried out by one team. The sample of patients were essentially Class I crowding cases requiring four pre molar extractions and straight wire fixed appliance treatment. This could be described as straightforward traditional orthodontic treatment based on sound mechanics and philosophy!
When the treatment was completed the patients were randomly allocated to one of three retention regimes, these were
- Upper vacuum formed retainer (VFR) and a lower canine to canine bonded retainer
- Upper VFR and stripping of lower incisors with no retainer
- A positioner.
The removable retainers were worn mostly at nights in the first year and then every alternate night for the remaining 12 months of a two year retention regime.
Dental casts were measured at the start of treatment, at debond, at the end of retention at two years and then five or more years out of retention.
They measured several dental variables but I am only going to mention the findings for Little’s Irregularity Index.
Randomisation was done by a ballot system; there was good blinding of data recording and analysis. They carried out a sample size calculation.
75 patients were randomised and it was important to find that 26 failed to complete the study.
What did they find?
They found that there were no significant differences in Little’s Index at the start, debond or at the end of retention. After five years out of retention there was some relapse but this was not marked (1.8-2.6mm). There were no differences between the groups at any point of data collection.
What did I think?
I felt that this was a good, well carried out and reported study that adds to knowledge. However, as with most studies we do need to interpret the results carefully. I think that there are two important factors that we need to consider.
Firstly, there was a significant “drop out” rate. The authors acknowledge this, but state that this did not result in a lack of statistical power. While this is a good point, the high number of patients who did not complete the study does introduce some bias. We could argue that this is a fact of life for all long-term orthodontic studies, as many of our patients move away from our clinics. Nevertheless, it does introduce a degree of uncertainty because we know nothing about the patients who did not return for final records.
The other important factor that we need to consider is that the patients were Class I crowding cases treated to a high standard with extractions. Consequently, the findings may only be relevant to this type of case and treatment. I am not sure that we can extrapolate this to current trend in non-extraction treatment based around arch expansion, proclination of lower incisors, short-term orthodontics, “super fast” and other compromise treatment …
Overall, I thought that this was a good well-conducted study that will reinforce the practice of many operators. It provides further evidence that VFRs are effective. I am less convinced about carrying out stripping, it may be a form of preventing relapse, but to me it is bit invasive. I am not sure why, I just don’t like it!
I will continue with my current VFR night only retention for my patients and this study supports my practice. But what do I do about the expansions and proclinations that are resulting from the current non-extraction phase of my treatment provision?
Edman Tynelius, G., Petren, S., Bondemark, L., & Lilja-Karlander, E. (2014). Five-year postretention outcomes of three retention methods–a randomized controlled trial The European Journal of Orthodontics DOI: 10.1093/ejo/cju063