May 09, 2022

How long should patients wear their retainers?

It is great to see an increasing amount of research into retention. This new study looked at the effect of different wear times of retainers on the amount of relapse. It reinforces clinical opinion and provides us with practical, clinically relevant information.

We know that part-time wear is as effective as full-time retainer wear. But we do not accurately know how long our patients wear their retainers. Therefore, the investigators used thermal timing devices to answer this question in this study.

A team from Denizil, Turkey, did this interesting study. The Angle Orthodontist published the paper, and it is open access!

Evaluation of relapse with thermoplastic retainers equipped with microsensors

Sait Ishakoglu and Serpil Cokakoglu

Angle Orthodontist 2022;92:340–346. DOI: 10.2319/072221-578.1

What did they ask?

They did the study to

“Find out whether long or short wear times of removable retainers are effective for the maintenance of stability”.

What did they do?

The team did a prospective cohort study by enrolling 47 patients aged between 15 and 25 years.

The inclusion criteria for the participants were:

  • They completed fixed appliance treatment with four premolar extractions.
  • The final occlusion was good.

All the patients received upper and lower vacuum-formed retainers. In addition, they fitted a Theramon timer into the lower retainer.

The operator asked all the patients to wear their retainers for 20-22 hours per day. The patients attended the clinic every 8 weeks, and the team collected data from the Theramon sensors.

They calculated the mean daily wear time at the end of the study period.

Finally, the investigators collected Irregularity Index data, arch widths, arch length, overjet and overbite from 3D models. This data was collected before treatment (T0), at debonding (T1), 6 months later (T2), and 12 months after debonding (T3).

What did they find?

The mean daily wear time was only 9.24hrs/day for all the patients. They then divided the patients into two groups according to their wear time. The short wear time group wore their retainer less than 9 hours per day, and the long wear time group (>9hours wear per day).

Five patients dropped out of the study. The reasons were 2 requested leaving, 2 lost their retainers, and 1 had no data. This left 20 in the SWT and 22 in the LWT groups.

Stability

There were no statistically or significant differences between the groups. However, they found a more significant irregularity in the SWT (LII = 2.37) than the LWT (LII= 1.0) group in the mandible. However, the effect size was only 1, which may not be clinically significant.

Their overall conclusions were:

“There were no significant differences between the wear time groups for maxillary irregularity, transvers measurement, overjet, overbite and arch length after 1 year of retention”.

“There were differences in mandibular irregularity between the groups. However, the effect size was small”.

What did I think?

This cohort study revealed some interesting and clinically relevant findings. Firstly, I was surprised to see that the patient’s co-operation was very poor. This was far below the hours that the operators recommended. Other investigators have found similar problems with the wear time of Twin Block appliances. This does make me wonder whether any of our patients comply with our instructions? It also raises issues about the effectiveness of part-time wear of appliances.

When I looked at the relapse data, I wondered about the wear time of the retainers. This was that even part-time wear of vacuum-formed retainers seemed to be effective. This is reinforced by studies that have looked at night-only retention and shown that this is effective. So perhaps we are concluding that retainer wear of only 9-10 hours at night is sufficient to retain in the short term. This is certainly supported by the results of some randomised trials.

We do need to consider the shortcomings of this study. The sample size was small, the retention period was short at 12 months, and I would have liked to see a regression analysis that treated wear time as a continuous variable.

Nevertheless, I feel that this study does add to our knowledge about the wear time needed for retainers. It is up to you to decide if this influences your recommendations to your patients.

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Have your say!

  1. Hi Prof, even if a study shows that part time wear of retainers is as effective as full time wear, we should continue to encourage patients to wear their retainers full time in the first 6 months as they are seldom compliant with our instructions. In this study, patients were instructed to wear their retainers for 20-22 hours but they only wore it for 9 hours. Imagine if we ask them to wear for 10-12 hours then they’ll only wear the retainers for 4-5 hours? Haha.

    • The long-lasting unanswered question!!

    • Hi Jason,

      I’m not sure it works like that. 20-22 hours/day is a big ask for patients, I feel, and then they lose them at school / at lunch etc + they wear down more quickly. The nine hours these patients wore their retainers in the study was most likely at night time as they google’d the evidence 🙂
      Night time is doable – they put the retainer next to their toothbrush and (presuming they clean their teeth every night!) in it goes.
      It’s not a % of the total time requested of them that patients wear their retainers – it’s not wearing them during the day.
      Daytime is too much for most folks, burnt out from years of appliances and they just want their life back.
      My patients are 20hours/day for 2 weeks for zero evidence based reasons other than to get across how important retainers are – then just at night time. In 20 years it works as well as any other regime I’ve tried. Just my tuppence worth anyway 🙂 Cheers

  2. Thank you verry much for this interesting study. I agree completely with your opinion. Pr Lahcen Ousehal. Department of orthodontics.

  3. we get patients to wear VFR retainers 24hrs full time then night only without problems, and no obvious changes
    i know of one hospital audit that had a failure rate of 70%+ within 9 months of debond and still kept doing the same thing (meeting Einstein’s definition of stupidly)

    maybe it is how we communicate with patients has the greater effect – we constantly talk about importance of retention with patients, with bespoke information leaflets given at start and end of treatment (not the BOS ones!

    • The inclusion of only extraction patients in the study is a creative way of solving one retention timing dilemma yet leaves another type of retention timing dilema unanswered.

      Including only extraction patients would appear to have two big advantages. The first is that it would seem to make for a more consistent pre-treatment group, patients whose crowding was severe enough to require extraction treatment. So a somewhat homogeneous group was tested as per the two criteria.

      Studying only extraction patients would also eliminate patients treated non-extraction, perhapse not ideally, with excessive proclinatuon or expansion. This latter group would be expected to be more prone to relapse. So the study does seem to tell us if part time retainer wear is sufficient to prevent relapse for well treated crowding cases.

      However, by including only extraction patients, patients who started with spacing would be elinated from the study. Patients who start with spacing would not be expected to receive extractions. So the study does not tell us if part time is sufficient to prevent relapse of spacing.

      I read this with interest as my own personal protocol and bias, for years now, has been that sleep only retention is sufficient to prevent relapse of crowding. However, again this is bias, my personal observation is that part time can be insufficient to prevent relapse of spacing. As a result, patients who started with dpacing are put on full time wear for 6 months, before going to part time wear.

      That so many patients in the study only wore their retainers part time, despite full time instructions, is of course disturbing. Now I question if my spacing patients who are placed on full time wear are really doing it. Yet one more thing to consider. Thanks for the great article.

  4. Advising patients to wear their new retainers FTW (full-time wear) will only lead to lost retainers, as kids all-too-often forget them in the school lunchroom or elsewhere outside the home. More reasonable is to say 12 hours daily. That, combined with fixed lingual wires, does the job in probably >95% of cases. Then there’s the question, “So, doc, how long do I need to wear them?” The honest and best answer is to answer them with this question, “Well, how long do you want straight teeth?”

    • Similar to my admonition and qualification

      If you want to be 85 and in a nursing home with straight teeth, you better still be wearing your retainer.

  5. Interesting study. Did the patient knew there was a Theramon timer in the retainer? I wonder if this could change the wear time?
    However, it would be more realistic if they were not aware they were timed. Even if some studies say it doesn’t change anything.
    Also funny to see that 2 patients, who participated in a study on retainer wear time, lost their retainers. I guess it says a lot about their chance of relapsing 🙂

  6. I initially instructed my patients 3 months full time wear then 6 months Night time, then alternate nights. Other colleagues in the practice went to NT retention straight from debond for 6 months then alternate nights. We found there was no difference in outcome so I adopted the NT only retention regime for 6 months then alternate nights for as long as the patients wanted to maintain straight teeth, any losses or breakages to be paid for by the patient.

  7. Retention, the bane of every Orthodontist. It is quite easy to assess whether a patient would wear retainers regularly or not, I more or less figure that out during treatment based on their elastic wear. If they are good elastic wearers then there is some hope. My retention protocol involves lower lingual bonded 3-3 and upper Essix ( First 6 weeks full time and then night time only for a year, following which alternate nights). In cases where there is a midline diaestema, openbites, the bite allows me to and the patient I know would not wear a retainer, I place a upper lingual bonded 2-2 and essix retainer for night time wear ( am increasingly doing this). Most importantly I tell the parent and patient that teeth are set in bone not stone and if they want it to stay that way they need to wear retainers. I ask them to come and see me every year till they are 18 and even after that if they would like to on a yearly basis. At the yearly appointment I do update photos and this gives me a lot of data on retention. I have to agree with Gavin that full time retainer wear is a recipe for disaster, the patients would just get burnt out.

  8. When I was a dental student in the 1970s, our head of department was fond of quoting Edward Angle who apparently said “if there is one who could tell me how long to keep a patient in retention, I would gladly give him half my fee”

    When I was an orthodontic postgraduate in the 1980s, our head of department, Professor JRE Mills emphasised the importance of treating patients to achieve arch stability and avoid the temptation of for example, proclination of the lower incisors to reduce overjet and achieve alignment.

    During my career as an orthodontist, I noticed how the easy availability of vacuum formed retainers and the relatively straight forward provision of bonded retainers often encouraged practitioners to embark on non-extraction treatment using the retainers to maintain teeth in what were in fact ,in unstable positions, certainly so according to the Mills doctrine.

    I note the comments from colleagues still in practice, that long retention periods are a very big ask for patients who would like their life back and I propose that orthodontic treatment should not be a life sentence without parole!

    Now a retired practitioner and blessed with the opportunity for reflection, (which of course is not more powerful than careful randomised controlled trials) but nevertheless my feeling is that it is always wise to put teeth in positions of stability vis-a-vis the lip and tongue pressures and only have the retainers in place until the final effects of treatment have worked out.

    And I think there is one more dimension to consider. I cannot think of any other medical specialty which offers or thinks it should offer patients lifetime guarantees of the ability of result. Thus, patients may need more than one course of orthodontic treatment in their lifetimes to remain in ideal alignment. People change throughout life as I observe when I look in the mirror and as our teeth do not wear interproximally as they might have done when we ate a ‘caveman diet’, there is no active mechanism to provide extra space and give opportunity for natural realignment as the years pass.

    In a nutshell, treat teeth to positions of stability, use retainers to maintain alignment (or longer in special circumstances such as significant rotations) whilst the final effects of treatment take place and be prepared to see the patient again if further alignment is needed in the future.

  9. Dear professor O’Brien, thank you for the excellent review of this article. You mention that ‘the effect size was only 1, which may not be clinically significant’, but isn’t Cohen’s d of 1 in fact rather high? I learned that any value above 0.8 of Cohen’s d is qualified as a large effect size, but maybe I’m wrong?

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