March 24, 2020

A new trial shows that retention may not be needed?

Retention is one of the areas of orthodontic care that is somewhat controversial.  While we may know the best retention regimes. We do not know what happens if we do not retain our patients. This new trial looks at this question.

Several researchers have carried out good studies on orthodontic retention.  These have looked at different types of retainers and/or the effects of full or part-time wear.  These studies have provided us with evidence that we can share with our patients.  However, the big question about retention is whether we need to retain our treatment? To answer this, we need to carry out studies that look at the effects of not providing retention. I was, therefore, really interested to see this trial that had a control group of patients who did not have any retention.

A team from Malmo, Sweden, did this trial. The EJO published it.

What did they ask?

They asked this simple question;

“Is orthodontic retention needed after orthodontic treatment for impacted maxillary canines and moderate crowding in the maxilla”?

What did they do?

They did a single centre randomised trial with two parallel arms and a 1:1 allocation ratio.  The PICO was:

Participants:

Patients who had at least one impacted or unerupted maxillary canine and moderate irregularity of the maxillary six anterior teeth of 4-6mm (measured by Little’s Index).

Intervention

Upper removable vacuum formed retainer.  They asked the patients to wear this for 22-24 hours per day for the first 4 weeks and then 10-12 hours per day.

Control

No retention.  They removed the archwires and left the brackets in place. Then after 10 weeks if there had been an increase in LI of higher than 3mm, they replaced the wires.  If there had been no relapse, they removed the brackets.

Outcome

The primary outcomes were change in a single contact point displacement and the sum of LI for the six anterior maxillary teeth. Secondary outcomes were changes in arch length, dimensions and rotation of teeth.

They collected data at the end of active treatment (T1) and 12 months later (T2).  Impressions were taken at these points and converted to 3D scans.

They did an explicit sample size calculation, used a pre-prepared randomisation process and concealed the allocation with sealed envelopes.  They did not register the trial before it started.  Blinding of the operator and patient to the treatment allocation was not possible. However, the study casts were anonymised.

What did they find?

The study enrolment started in June 2013 and ended in April 2018. They randomised 32 participants to retention and 31 to no retention. Surgical exposure was carried out for 15 participants in the retention and for 19 in the no retention group.

In the no retention group, one patient had a contact point displacement of >2mm during the 10 weeks “interim” period. They discontinued the observation period and replaced the archwire to align the teeth.

When they looked at the amount of relapse after 12 months. The mean change in Little’s Index for the retention group was 0.4mm (95% CI=0.2-0.6), and for the no retention group, this was 1.3mm (95% CI=0.9-1.7).  This was statistically significant.

They did not find any other significant differences between the groups for the other outcome measures.

Importantly, most of the changes occurred during the first 10 weeks of observation.

Their overall conclusion was;

“The changes in Little’s Index between the retention and no retention groups were statistically but not clinically significant.  Since satisfactory clinical results 1-year post-treatment in the no retention group, retention does not appear to be needed”.

What did I think?

I thought that this was an excellent trial. I was particularly impressed with the way that they introduced and managed a no retention group. The concept of leaving the appliance in place and then replacing the archwires if relapse occurred dealt with the ethical issues that may be associated with no retention.

They did the trial well in terms of randomisation, concealment of allocation and blinding.  Initially, I was a little concerned that the trial was not registered before it started.  However, they started this study in 2013, and trial registration was not widely recognised at this point.  This is important because registering a trial before it starts ensures that the investigators do not change the outcomes as the trial progresses.  This is a definite source of bias.

I thought that the findings were interesting. They were also important because they showed that retention may not be necessary. However, we need to consider that these results may only be relevant to upper incisor/canine relapse.  I am not sure whether we can extrapolate these findings and conclusions to lower incisor crowding.

Final comments

This is an excellent study that certainly provides us with useful clinical information. Its design may also be used to inform future investigations into retention.  I hope that this great team carries on their excellent work, and they continue to provide information that leads to changes in clinical practice.

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Have your say!

  1. Avatar

    If you do not gamble then you may indeed walk past the casino and become a winner.
    I have read the University of Washington’s research on retention over many years and understand that it would neither be ethical, nor wise to withhold retention measures.
    The difference between a trial and long-term evaluation is similar to that between a master and his apprentice. Time.

  2. Avatar

    unfortunately as it is not open source i cannot read the full article. But it appears to be on a selected cohort of mild crowding and impacted canines- not the most common of orthodontic treatments
    My concern is the conclusion seriously “jars” with my clinical experience and previous research that relapse occurs frequently and to the extent that the patient (not always the clinician) is concerned enough to want the teeth realigned. It is very well saying as a clinician the change is minimal and can be accepted… but surely it is the patient who is ‘right’ ??

    I will very much reserve judgment and i will not be changing my retention protocols

  3. Avatar

    The retention debate usually circles around how long and what type so it’s refreshing to see a study looking at the question of “is it really needed?”. Maybe a lot of what we do is not really needed (I’m thinking of headgear here). Anyway I guess the take home message is that not all cases need retainers. Did these cases have a lower brace and lower retainers? If not then hurrah for common sense. If they did then it could be that the lower retention contributed to the upper alignment staying put, just a thought

  4. Avatar

    From the treatment perspective how where the canines exposed in those patients, both groups not undergoing surgical exposure? As someone else mentioned the full article does not seem to be available
    We must consider the fact that the equivalent of a Fiberitomy was applied to more than half the impacted teeth in both groups.
    We know that the fiberitomy procedure will enhance long term stability post completion of orthodontic therapy.
    Also refer to Ferguson et al on enhanced stability following surgical PAOO or SFOT therapy
    Colin Richman/404-784-7272
    Periodontics,Atlanta,Ga
    USA

  5. Avatar

    When my patient pay several thousand dollars and spend a couple of years getting their teeth straight, they want them to stay that way. Everyone’s still getting a retainer in my office.

  6. Avatar

    When my patients pay several thousand dollars and spend a couple of years getting their teeth straight, they want them to stay that way. Everyone’s still getting a retainer in my office.

  7. Avatar

    I appreciate the study BUT I doubt that any orthodontist ,who has any experience,will not need more persuasion than this to abandon retention protocols.
    When folks are “fussy “and /or have paid hard earned dollars for tmnt then my philosophy will remain ~retention is for life or however long you wish to have straight teeth.
    I strongly feel that patients in a semi socialised ,no fee at point of service ,are less particular than total fee for service pts and parents.That has been my experience in the NHS and Canada.
    Either way ,not to retain is asking to do retreats at no cost.
    I strongly advise orthodontists to have the patients/parents sign a debond document that stresses your particular retention philosophy!

  8. Avatar

    This study concerns me significantly. In this instance what is being evaluated as far as I understand is only the upper arch alignment. If that is the case then the conclusions we can draw with respect to retention in general are rather meaningless. We know where the areas of concern are with respect to post-treatment change. There is a plethora of evidence on that.

  9. Avatar

    It says “They removed the archwires and left the brackets in place. Then after 10 weeks if there had been an increase in LI of higher than 3mm, they replaced the wires. If there had been no relapse, they removed the brackets”. This is cherry-picking the data so the results appear to be skewed in favor of non-retention.

  10. Avatar

    Kevin: keep up the great analysis and reporting.

    Very interesting. Your title is at the same time, arresting (peaked my interest) and misleading (obviously,the question referred to a VERY specific situation.)

    Worth mentioning was a paper from the mid- to late ‘60s in the AJO I believe, in which brackets were placed (and bands of course since this was before bonding,) only on 1st premolars….a period went by…and it was determined that the thickness of a bracket alone, caused movement of the bracketed teeth…lingually, so leaving the brackets on for a period on the sample, to me, but not the control, may be a (minor but) confounding and overlooked variable in this study.

  11. Avatar

    This paper is an example of a research design that impresses some yet totally ignores clinical reality. There are a lot of important unanswered questions that if they appear in the full version they should have been included in the summary. (1) There is a huge difference between impacted and unerupted maxillary canines. (2)The location, methods of surgical exposure and group distribution of the impacted canines is not mentioned in the summary. (3) No mention is made of the status of the lower arch regarding anterior crowding, whether there was lower arch treatment, or lower arch retention. (4) Little’s discrepancy index was designed to measure lower anterior crowding. Certainly it can be applied to maxillary anterior crowding but it does not apply to cases with anterior spacing or “butterfly” rotations of the upper incisors where there is clearly crowding but no contact discrepancies.
    In any case lets see a randomized trial on lower arch crowding with no IPR and no fiberotomies. I’ll put my money on the retention group.
    Any takers ?

  12. Avatar

    impacted canine cases (palatal impaction) usually occur in class I uncrowded cases. Prof Adrian Becker in his book regardin the treatment of impacted teeth writes that impactions occur at a higher rate when the laterals are small or peg shaped, and in these cases usually the rest of the dentition is small. So to start with these cases are less prone to having crowding and therefore less relapse.

  13. Avatar

    This theme highlights the classic encounter when the clinic opposes the evidence, and the clinical experience prevails and is decisive in making decisions.
    In the decision-making triad, the evidence is not always the most important, we will not overestimate it over the clinic.

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