August 15, 2022

How long do bonded retainers last?

Retention is one of the most essential phases of orthodontic treatment. We have done several posts on this over the past few years. While these studies have been good, we have pointed out that it would be good to see long-term retention investigations. This new paper looked at retention after 5 years. Its results are clinically relevant and important.

Over the years, I have used most methods of retention. While bonded retainers were my favourite for many years. I gradually moved towards vacuum-formed retainers because of their ease of use. However, I knew that I was taking a gamble on patient co-operation. I missed the “permanence” of fixed retainers, but I was also concerned with my retainer failure rate (20%), so I stuck with VFRs. This new paper looked at long-term retention with bonded retainers. It may suggest that bonded retainer failure rates are high.

What did they ask?

They did this study to find:

“The number of failures of direct and indirect bonded retainers at 5 years follow up and investigate the stability of tooth positions”.

What did they do?

They did a single centre 2 arm parallel randomised controlled trial with a 1:1 allocation.

The PICO was

Participants

Orthodontic patients with a fixed retainer bonded directly or indirectly between September 2012 and June 2013.

Interventions:

Fixed mandibular retainers made from 0.0215 multistrand wire bonded directly.

Control:

Identical retainer bonded indirectly.

Outcome:

The primary outcome was 5-year survival of the retainers. Secondary outcomes were inter-canine and inter-premolar distances.

This was a follow-up study to a previously reported trial. The authors had reported details of this study before. However, they outlined that they used pre-prepared randomisation and did allocation concealment by contacting a trial coordinator. They could not blind the operator or patient, but they collected the data blind.

They used Kaplan-Meier survival analysis to look at the retainer’s survival. Then they used a relevant multivariate analysis for the other data.

What did they find?

In any long-term study, it is essential to look closely at the dropout rate. This is because a high dropout rate can indicate potential bias, lead to loss of statistical power, and reduce the generality of the results. At the start of the study, 64 patients were randomised to have their retainers bonded directly or indirectly. At the end of the study, 52 participants remained (26 in each group). This meant that there was a dropout rate of 18.7%. I will come back to this later.

The most important finding was that 14 participants in each group had a bonding failure. This was a very high 54%. There were no differences between the groups. The five-year survival rate was 46%.

Interestingly, 83% of the failures occurred in the first year and 86% in the first two years. From then on, the failure rate dropped significantly.

They then looked at the dental relapse for the 24 failure-free patients. Again, there were no differences between the groups. Unfortunately, they did not report the deterioration of the patients whose retainers had failed.

The authors reported also reported on unexpected changes.  Interestingly, at T2 they found that 5 participants showed an increased lingual crown torque of the mandibular left canine.  However, in only one of these was the change felt to be severe.

Their overall conclusions were:

  • The 5-year survival rate for the retainers was 46%
  • Most failures occurred in the first year (83%).
  • There was no marked change in intercanine and inter-premolar distances.
  • There was no difference between the direct and indirectly bonded retainers.
What did I think?

This was a well carried out and nicely reported trial. The authors should be congratulated for completing this study with a long follow-up time. This was an outstanding achievement. While some may consider that the dropout rate was high, I feel this is good for a long-term orthodontic study, and it would be hard to do this any better. As a result, we should accept the results.

The results were both interesting and disappointing. While there were no differences in the failure rate between the techniques. The failure rate was very high. While we may all feel that our retainer success rate is higher than this. We need to remember that in this study, all the patients were accounted for, and we tend to be optimistic when we evaluate our own performance. There are no other comparable studies over this period. As a result, we should accept their findings.

However, while the number of failures may be concerning. We must consider that this trial was done in a post-graduate orthodontic clinic. As a result, we cannot ignore the effect of proficiency bias. It would be reasonable to suggest that a highly experienced operator should have a higher success rate.

Final thoughts

This trial provides helpful information on bonded retainers’ failure rates. Notably, most retainers fail in the first two years, which suggests that once a patient has worn a retainer for two years, we may not need to review them on a 12-month basis. Perhaps, we should also warn our patients that failure rates are high.

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Have your say!

  1. Years ago, at the start of my career, retainers were not worn forever. This was probably due to patients not bothering too much if the teeth moved coupled with the treatment of more severe crowding etc. Over the years milder problems have been treated and patients are more demanding. This has necessitated the rise of the indefinite bonded retainer. I can’t help feeling that gluing teeth together is not “a good thing” on the whole and patients should leave their mild problems alone and also accept the horror (the horror) of teeth moving a bit as they inevitably age. This is probably not going to happen so we are as we are, mending glued wires until something more important comes along.

  2. Thanks for a great original article and great review, in the Blog
    It is really valuable topic and and a really well done study,
    I am wondering if the method of tooth preparation before the bonding, as described, may have been a cause of such a high early failure rate.

    The tooth preparation was described in reference (7), as
    “Lingual surfaces were pumiced and etched with
    35% phosphoric acid for 30 seconds”
    (AJODO December 2014 Vol 146 Issue 6, pp 702)

    In my experience this pumicing method of tooth cleaning leads to high early failure rates because it does not remove the calculus and the bonding to dental enamel is interfered with. Pumicing is not a sufficient way to remove all the coatings on the lingual of lower anterior teeth. We stopped using this method about 10 years ago.
    In my experience, one needs to use either sand blasting or a TC fluted bur in the shape of an Australian Football.
    If the tooth-cleaning technique in future trials were changed to a more aggressive cleaning process that removes powdery calculus, then possible failures simply due to an insufficient tooth cleainng technique I believe the retainers would survive better and we may see other results.

    • You’re exactly right! I use a microetcher to clean first but it’s always important to inspect the etched area well to detect areas that were still obscured by plaque/calculus. I have found that a diamond bur works well for cleaning this up as it leaves a rougher surface than a carbide bur. My fixed retainers often last over 10 years. A diamond bur shaped like an American football is best of course.

  3. I’ve often wondered who the client is in the orthodontic relationship. Is it the dentist? The parent? The patient? Of course it is all three and I think the parent is far happier with a fixed lower retainer rather than a removable lower retainer. The VFR (actually Pressure Formed Retainer) may be cheaper, easier for the orthodontist but I wonder how effective it is for long term retention. It is also unforgiving g. If you don’t wear it consistently, it very soon stops fitting. On there other hand, a fixed lower serves to retain the entire system once the upper teeth have settled against the lower teeth. Of course, when I say fixed lower, I mean a bar attached just to the cuspids. I don’t have the numbers in front of me but I believe Dr. Zachrisson has published much more favorable success numbers for that kind of retainer. Far better than 46% long term.

  4. Between inadvertent tooth movement due to distortion/activation, relapse due to partial debonds, oral hygiene challenges and the poor long-term survival rate, bonded retainers are way more trouble than they are worth. I have not used fixed retainers in about 7 years and couldn’t be happier. Early correction and stabilization of rotations, minimally altering the IC width and arch form, leveling the COS, controlling lower incisor position & inclination and full correcting the torque of lingually-displaced upper and lower lateral incisors etc. can go a long way in improving the stability of a treated case. While nothing is a 100%, adhering to time-tested and proven principles during active treatment can certainly simplify the retention needs after debond.

  5. An excellent article. I much preferred Essix (VFR) retainers as the onus and responsibility was then on the patient and not the operator. I agree that failure rate for bonded retainers was high as single pad detachment was often not noticed by the patient until it was too late and a tooth had moved. I got to the stage where if I fitted a bonded retainer, I also gave the patient a VFR backup to use at night..

  6. We abrade the enamel before 30sec etch (Hadad, Hobson & MacCabe Dent materaisl 2006) which increases laboratory bond strength by >60% and this has massivly reduced clinical debonds
    we found in a 2 year follow up of pts bonded in our clinic by experienced orthodontists and therapists to be
    16% in first 3 months
    7% in next 9 months
    2% in year 2

    hence we review bonded retainers at 3, 12 and 24 months as then you pick up the early fails.
    we have reviewd VFDM ‘failure’ and found it to be slightly higher – mainly due to non wear

    so I would propse that idealy we need ‘dual retention’ – BOTH bonded and VFM. This is what i recommend to patients as the best regime for retention

  7. Thanks for this excellent and important article and your review.
    I always found it very frustrating to have failure rates of about 10% although we use the double retention strategy (VFRs + bonded retainers). It is also frustrating not to know whether 10% is below or above average. At least this study tells practitioners how our individual figures compare.
    However, we have to emphasize to our patients the importance of an excellent (interdental) oral hygiene to avoid calculus where the retainer is bonded to improve longevity.

  8. It may sound harsh, but bonding failures are result of poor technique. equally important to cleaning the enamel by air-abrasion/diamond is absolute dryness before the bonding. Where we mostly fail is the exhaled air from the patient, that condenses on the invariably cooler etched enamel just before we place the resin. This happens in just a “breath” and to prevent it you cannot ask the patient not to breath! We can however, place a high-volume suction in the mouth so that any exhaled moist air can be sucked out and replaced by dryer room air.

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