What do we know about orthodontic retention? A new Cochrane Review tells us something?
Can a new Cochrane review help us with deciding on the best orthodontic retention?
One of the most challenging areas of orthodontic care is deciding on how we are going to retain the great treatment that we have done. I also find that most of my patients ask many questions on retention. Can the answer to our problems be found in this new Cochrane Review on orthodontic retention?
Littlewood S, Millet D, Doubleday B, Bearn D, Worthington H
Cochrane Database for Systematic Reviews. DOI: 10.1002/14651858.CD002283.pub4
I have discussed retention before on this blog and in my last posting I asked whether Simon Littlewood would stop going round the world lecturing and get round to updating his systematic review. I am pleased to see that he and the rest of the team, based in the North of England and Scotland, have found some time and updated their Cochrane review, which was originally published 8 years ago in 2006. This is a picture of the North of England, it is bleak up North!
What did they do?
They carried out this review to evaluate the effects of different retention strategies used to retain orthodontic treatment. As with all Cochrane reviews they only included randomised trials. The other inclusion criteria were
Participants: Adults and Children
Intervention: Any orthodontic retainer at the end of all orthodontic treatment
Outcome measures: Any measure of tooth irregularity
They carried out an extensive search of the literature using standard Cochrane methods.
Two authors selected the papers, data was extracted onto a customised data form and assessment of bias was carried out with the Cochrane risk of bias tool.
What did they find?
They initially found 441 articles. They then filtered them for relevance and quality to leave a final sample of 13 papers. They provided a lot of data on each trial. These studies compared different types of retainers including vacuum formed, bonded and Hawley retainers.
They decided that the most important outcome to report was Little’s Irregulariy Index.
When they looked at risk of bias they found that four studies were at low risk and ten had a high risk of bias.
This was a complex review with many comparisons and interventions being included and I have concentrated on those that I think are most important to me.
Lower fixed retainers vs lower thermoplastic.
They found an overall 4% failure rate and there was some evidence that bonded retainers were slightly better at reducing relapse than thermoplastic retainers. There was also some evidence that patients were more satisfied with bonded than thermoplastic retainers.
Thermoplastic v Hawley retainers
There was limited evidence to suggest that thermoplastic retainers were better than Hawley retainers and patients were happier with thermoplastic retainers.
Full vs Part-time wear
There was some evidence that part-time wear was as effective as full-time wear.
What did I think?
This is a Cochrane review and the findings are of high quality. One of their conclusions was that most of the studies they included were of high risk of bias. However, one of the concerns that I have with the Cochrane risk of bias assessment is that it is very unforgiving and when I looked at the reason for the classification of some of the studies, I felt that this was rather harsh. As a result, it is important to evaluate the risk of bias tables in these reviews and come to your own decisions on whether findings are going to influence your practice.
So, how does this review influence my practice. In previous postings I have emphasised that when we evaluate a study we need to look closely at the treatment effect. I have looked closely at the differences that they calculated for this review and all these are very small. As a result, I cannot help feeling that when we look at the effectiveness of the different regimes they all seem to “work”. It is also important to point out that the most important factor in retention is patient co-operation and I presume that the trials included this as an outcome, but I could not find any detailed information.
My next step was to look at patient preferences and acceptability The analysis showed that patients tended to prefer bonded retainers. So at this point I am beginning to think that bonded retainers are the best? But I really do not like them because of hassle with failures. I was, therefore, surprised to see that they reported low failure rates.
I was in a dilemma and I wondered how I could practice evidence based orthodontic retention. But I got round this by considering that evidence based care is built around a combination of scientific evidence, clinical experience and patient opinion. If we factor this in, I can conclude the following:
- The research evidence shows that it all works.
- My clinical experience of bonded retainers is not good, I get too many debonds.
- Patients like thermoplastic retainers and they can be worn part time.
As a result, I am going to stick with thermoplastic retainers which are worn at night only. Or…have I dodged the issue?
Emeritus Professor of Orthodontics, University of Manchester, UK.