February 12, 2024

Are Bonded retainers better than vacuum-formed retainers, a new RCT?

In the last decade, researchers have done several clinical trials and systematic reviews to understand the short-term effectiveness of different retention regimes. One of the significant questions that they are trying to answer is the comparative efficacy of bonded and vacuum-formed retainers. A recent study has investigated this issue in detail.

I have written several blog posts about retainer research, and after reviewing various papers, it appears that there are not many significant differences between the two main types of retainers. Therefore, when deciding on a retention regime, it is important to take into account the patient’s preferences. A new paper supports this conclusion.

A team from Brazil and Michigan, USA, did this study. Orthodontics and Craniofacial Research published the paper.


Treatment stability with bonded versus vacuum-formed retainers after 12 months in adolescents and young adults: A randomized clinical trial

Silvio Augusto Bellini-Pereira et al

Orthodontic and Craniofacial Research: Advanced access. DOI: 10.1111/ocr.12753

What did they ask?

The aim of this study was to

“Compare the clinical effectiveness of V Bend bonded retainers versus Vacuum formed retainers (VFRs) regarding their capacity to maintain treatment stability and survival rates after 12 months”.

What did they do?

They did a single centre 2-arm parallel-group RCT with a 1:1 allocation ratio.  The PICO was


Completed orthodontic patients with a satisfactory occlusion at the conclusion of their treatment.  They had treated the patients with any form of orthodontic treatment.


V Bend Bonded retainers to the maxillary and mandibular teeth.


Maxillary and mandibular vacuum formed retainers.  They asked the patients to wear the retainers at night only.


The study’s primary outcome was the change in Littles Irregularity Index. Other outcomes included changes in arch dimensions, overjet, overbite, and participant interviews about removable retainer wearing time.

The team collected data from scans of the teeth at the time of fixed appliance removal (T0),  and after 3 months (T1), 6 months (T2) and 12 months (T3).

Before beginning the study, they conducted a sample size calculation that indicated a need for 17 patients in each group. To compensate for potential dropouts, they increased the sample size to 25 patients for each group..

Importantly, the study was conducted well, using a pre-prepared block randomization method and opaque envelopes to conceal the treatment allocation. An independent operator was responsible for opening the envelopes immediately before allocating retainers. All stages of the randomisation and allocation process were carried out by this operator.

Their statistical analysis was relevant to the study design and the data.

What did they find?

The team enrolled 50 patients into the study. No patients dropped out and they were all analysed.

At the start of the retention, there were no differences between the groups of patients.

There were no differences in any outcomes up to 6 months after placing the retainers.

At 12 months, the only significant differences were in the Little’s Index scores for the upper and lower arches.

ArchBonded retainerVacuum formed retainer
Lower0.27 (0.26)0.54 (0.56)
Upper0.34 (0.36)0.68 (0.52)
Little’s Index scores after 12 months

There were no differences in the retainer’s survival rates after 12 months.

They pointed out that even though the VFs were less effective, no patient had a LII greater than 2mm after 12 months. As a result, both retainer regimes were effective.

Their final conclusions were;

“Bonded retainers were more effective in maintaining the alignment of the incisors compared to vacuum formed retainers after 12 months”.

What did I think?

The study’s results were consistent with other research, showing that although there were variations in relapse, they had no significant clinical impact..

The study also revealed that only 40% of the participants wore their VFRs for the recommended duration. This could account for the differences in relapse observed after the 12-month period.

Importantly, the authors of this study stated that they will track these patients for another five years, providing valuable insights into long-term maintenance.

Final comments

It seems that this paper supports the widely accepted belief that there are only slight variations in the effectiveness of different retention methods. Therefore, I think we can use this knowledge to involve our patients in selecting their own retention treatment. This would be an excellent example of implementing evidence-based healthcare practices.

Have your say!

  1. a rather pointless study as length of study is far too short
    -need 5 /10/15 year plus studies to make an informed decision

  2. Instead of asking either-or, one must consider that possibly that fixed plus removables are really necessary if long term stability is the goal.

  3. An interesting study but we need to see results over a longer time frame, say 5 years. Do orthodontists discontinue retention after only 12 months with VFR’s? I didn’t.

  4. “The study also revealed that only 40% of the participants wore their VFRs for the recommended duration.” Compliance will only get worse. As stated above, results from 5+ years would be much more meaningful and possibly much different.

  5. Thanks. This study was very helpful (to me).
    Richard Riedel, Bob Little and others at the UW would have probably questioned whether a goal of universal long term stability is realistic. Perhaps informed consent is more important.
    Here is a paraphrase from Ralph Waldo Emerson. ..As to methods, there are a million and then some. But principles are few. The person who grasps principles may successfully select their own methods. The person who tries methods, ignoring principles, is more likely to have trouble….
    So perhaps we should not be advocating our responsibility to really understand and communicate the principles, selecting a “best” method in our hands and experience, rather than leaving it up to the patient?

  6. Compliance of the patient is an important factor to be included in the study as much as the time factor as my colleague suggested.
    I still prefer the fixed retainer plus scaling more often according to the patient situation.

    Thank You

  7. The great danger in bonded retainers is the habit that many patients end up acquiring of keeping their tongue on the floor of their mouth. They feel a foreign object and their tongue searches for it all day long. A low tongue is a path to snoring and sleep apnea.

  8. These studies look at dental stability and lose sight of the toxicity and plaque accumulation that these retainers can offer. greetings

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