November 06, 2017

Which is better a bonded or a vacuum formed retainer?  Here is a new trial.

One of the many controversial areas in orthodontic is our choice of orthodontic retainer. This new study gives us useful information.

I have posted on retention several times. I have concluded that there are disadvantages and advantages of the main types of retainer. However, in general the type of retainer we use depends upon our own and our patients choices. Nevertheless, there is not much information to inform these choices.  I thought that this study goes some way to providing us with clinically useful information. A team based in the North of England did this new trial.

Incidentally, the North of England seems to be a hotbed of clinical trials in orthodontics. This may be a result of the weather.


The EJO published this new study.

Bonded versus vacuum-formed retainers: a randomized controlled trial. outcomes after 12 months

Part I lead author K Forde. doi:10.1093/ejo/cjx058

Part II lead author Madeleine Storey doi:10.1093/ejo/cjx059

As usual, these very useful papers are behind the EJO paywall.  The authors have also published this study in two parts. I have decided to incorporate them into one concise post.  This makes it easier to read and reduces duplication.

The study team set out to answer the following question

“Is there any difference in the effectiveness, patient perception and periodontal outcomes of lower vacuum formed retainers (VFR) and lower bonded retainers (BRs)”.

What did they do?

They did a two arm parallel group RCT with a 1:1 allocation. Their PICO was

Participants: Patients completing fixed appliance therapy

Intervention: Upper and lower VFR worn at night only.

Comparison: Upper and lower BRs

Outcomes: Retainer survival, patient satisfaction measured by questionnaire, relapse measured by Little’s Irregularity Index and periodontal health

They carried out a good sequence generation, concealment and allocation via sealed envelopes.  It was not possible to blind the patient or operator. Importantly, it was not possible to blind the person who was recorded the relapse from the dental models.

They recorded the data at the start of treatment and several time points. I am only going to discuss the data at the start and after 12 months.

I thought that it was great to see that they did an Intention to Treat analysis. This meant that they collected and analysed data for the participants who dropped out or failed to wear their retainers.  They did the relevant statistical analysis.

What did they find?

They enrolled 60 participants. 30 were treated with BRs and 30 received VFRs.  The groups were similar at baseline.

When they looked at stability, they provided a great deal of data.  I have concentrated on the main findings. This table includes the amount of relapse measured by Little’s Index.  They found that the data was not normally distributed so they presented this as the median and inter quartile range.

Number of visits11.45 (10.4-12.6)8.4 (7.7-9.2)3 (1.5–4.5)<0.001
Emergency visits0.7 (0.4–1.0)0.1 (0.03–0.2)0.6 (0.3–0.9)0.6 (0.3–0.9)
Chair time (mins)245 (213–277)167 (149–185)167 (149–185)<0.001
Costs (Euros)1548 (1366–1730)974 (876–1071)574 (385–764)<0.001

They found that there was no difference in survival of the retainers in the maxilla. 63% of the BRs and 73% of the VFRs survived 12 months.  However, in the mandible 50% of the BRs and 80% of the VFRs survived 12 months. This difference was statistically and clinically significant.

The data on patient satisfaction showed that more patients reported difficulty speaking and eating from VFRs and greater discomfort from BRs.

Finally, they showed that the presence of BRs increased levels of plaque, gingival inflammation and calculus when compared to VFRs. However, at 12 months the data suggested that there were no real implications for periodontal health.

The authors conclusions

Their overall conclusions were that when they compared BRs with VFRs:

  • There was no difference in periodontal health
  • No difference in relapse in the maxilla
  • In the mandible the BR is more effective thant VFRs in preventing relapse
  • No difference in the survival rate of the maxillary retainers. However, in the mandible the BRs had a higher failure rate.
  • VR is easier to clean than the BR
  • BR causes less speech and mastication difficulties
What did I think?

In summary, I thought that this was a nicely done study. They used good methodology and the findings were interesting.  However, we need to be a little cautious in our interpretation because the sample size was based upon arch alignment changes. As a result, it may not have been sufficiently powered to detect any differences in the other outcome measures.  This is particularly relevant when “no difference” between the interventions was detected.

Some may criticise the investigators for not measuring compliance with the VFRs.  I feel that this step was not necessary as the intervention was the prescription of the retainer. If the participant did not wear the appliance this reflects the real world situation.

The study provided a lot of useful information.  My feeling is that the BR has some disadvantages, for example, the high failure rate and the plaque and calculus retention.  However, the VFR also has problems, for example, the patients reported that they had mastication and speech difficulties. Nevertheless, as they were asked to wear these at night, I wonder if this is a big issue.  I also was not sure the difference in the relapse was clinically significant.

My favoured retention regime is VFRs at night only and this study reinforces my practice.  But you can interpret this data to inform your retention protocols.

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Have your say!

  1. Useful clinically relevant outcomes.

    Unfortunately, I couldn’t make it to access the full-text version. I was interested to know the wear regimen for the VFR. It may make a contribution to the relapse rate!!
    Although, since they reported the speech issues, I would conclude that it was a full-time wear, not night-time only. Please confirm!

    Typo -the second BRs-;
    “However, in the mandible 50% of the BRs and 80% of the -BRs- survived 12 months. This difference was statistically and clinically significant.”


  2. Kevin. Thank you for this summary. My only observation is that 50% failure of LBR seems extremely high. Having placed thousands in my career I would likely shoot myself or never do another if I saw that sort of failure rate.

  3. “However, in the mandible 50% of the BRs and 80% of the BRs survived 12 months.”
    There is a typo; should read ” 80% of the VFR…”

  4. It seems strange that the BRs had higher failure rate in the mandible. My clinical experience (I bond each patient with upper and lower 3-3 retainer for the last 20 years) does not support it. On contrary, maxillary retainer is more difficult to bond and maintain because of contacts with mandibular incisors and canines. Also 12 months observation time is relatively short, because patients might comply well with VFRs during this time, but they might worse as more time passed since debonding. Also if VFRs were systematically checked during this 12-months period, it could positively affect patients’ compliance.

  5. Thanks Prof for your always interesting posts.

  6. Very useful data. I’m curious if any research has been done attempting to correlate the amount of relapse with various retainers to the pre-treatment alignment and/or amount of tooth movement experienced during treatment. I’m sure I’m not the only orthodontist factoring relapse potential into my retention plan.

  7. Kevin,
    Thanks again for finding and distilling well done research to help your brethren make better clinical decisions.
    That said, I also find the 50% failure rate very high and I would go so far as to say that this level of failure needs further investigation before these results would be clinically useful to me.
    In my practice, I do 99% lower bonded retainers and I find that there are 2 distinct modes of failure and they can be distinguished by when they happen post treatment. (not counting those who are in immediately after the hygienist has pulled it off…..)
    1) One or more off 0-10 days following placement. I attribute this to a bonding failure on our part, and usually the complete pad is off of the tooth with no residual composite on the tooth.
    2) 10 days to 1 year (or longer) after placement. I find that these are usually the result of traumatic occlusion, and usually while the patient is still wearing the removable upper retainer. (FT or just nights) Either growth, tongue thrust, finger nail biting etc, causes a 1 tooth traumatic occlusion and because the lower tooth is held so rigidly by the BR, the stress of this trauma concentrates at the wire/composite interface of the bonded retainer and this eventually causes the composite to fracture with the incisal or gingival half of the pad coming off. I invariably find fremitis on the opposing tooth in the maxillary arch when I place my finger on the tooth and have them tap together lightly. A re-bond and a simple occlusal adjustment solves the problem.
    I would think that the researchers in this study would have noted when the bonded retainers came loose and might be able to shed some light on the very high failure rate by sharing when they came loose. Late bond failures resulting from traumatic occlusion of course opens the door to lots of questions regarding treatment, finishing, settling etc but this 50% failure rate is certainly the most interesting and surprising finding in this study.
    I am sure the study’s authors are reading these comments so I would ask them to possibly mine their data a bit further and seek to answer the questions posed by the 50% failure rate. (“The 50% Failure Rate” strikes me as the possible title of a Sherlock Holmes who dun-it novel or an Agatha Christie mystery, thus very appropriate for a soggy northern England research team……:-)

  8. thanks for such a nice comments and observation. my experience regarding relapse with BR and VFR that VFR work well in cases where aligning done by creation of spaces with extraction or IPR . but when alignment was done by expansion or derotation or proclintion or other means VFR did not maintain the arch length so more relaps occur in VFR than BR .

  9. Thanks for your comments on the paper, as one of the team of authors of the papers, I thought it may be helpful to respond. We thank everyone for responding to Kevin’s excellent blog on the retention RCT papers. We discussed the findings in detail in the papers, including the higher than expected failure rate of the bonded retainers, but we appreciate that not everyone will have access to the whole papers from the European Journal of Orthodontics (they are both worth the read if you get the chance!). So we wanted to clarify this a little further here. In particular, we discuss that “The operators in this study were at the beginning of their orthodontic career and a general reduction in the survival rate has been associated with less experienced operators. This factor may partially explain the higher failure rate in this study.”

    We also discuss the unusual finding that there was a high failure rate in the mandibular retainers than the maxillary retainers. In the paper we discuss that “this differs from many of the published trials,which demonstrate greater failure rates in the maxilla probably due to occlusal stress. The higher mandibular failure rate reported in this study was potentially influenced by the inexperience of the operators. This correlates with Scheibe et al’s retrospective analysis of1062 retainers placed by operators of varying experience where the majority of mandibular failures were associated with less experienced operators.”

    Like all RCTs, the outcomes are always very interesting, but often the trial doesn’t tell us why a particular result is reached. However, in the discussions of both papers we give our personal interpretation about all the findings of the study (both those that were expected and those that may have been more surprising). We hope that readers find that the study goes some way to add some additional information to the very important topic of retention and relapse.

  10. Haven’t read the article but was wondering whether the study looked at contact point displacements in the posterior teeth or just the anteriors.

    I am also quite happy with handing some responsibility to the patient for maintaining their occlusion and recommend VFRs.

  11. Its a great article, Thank you so much dear professor Kevin for your insight

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