An occasionally irregular blog about orthodontics

What are the adverse effects of lingual orthodontic appliances? A new systematic review

What are the adverse effects of lingual orthodontic appliances? A new systematic review

A systematic review on the adverse effects of lingual orthodontic appliances.

One of the most important developments in orthodontics has been the introduction of lingual orthodontic appliances. There is no doubt that these have significant aesthetic advantages over labial appliances.  But are their adverse effects such as pain and discomfort the same?  This question was investigated by a team from Oviedo and Valencia in Spain and is the subject of this weeks post.

incognito1Adverse effects of lingual and buccal orthodontic techniques: A systematic review and meta-analysis

Fadi Ata-Ali et al  AJO-DDO 2016: 149: 820-829.

DOI: 10.1016/j.ajodo.2015.11.031



This was a systematic review in which they attempted to answer the following question:

“ Are lingual fixed orthodontic appliances associated with greater or fewer adverse effects than Buccal fixed appliances”?

They carried out a standard systematic review and included randomised controlled trials and controlled clinical trials that involved comparisons between lingual and labial fixed appliances.

What did they find?

They identified eight studies these were divided into 5 CCTs and 3 RCTs.  They assessed the risk of bias for the randomised controlled trials by using the Cochrane Risk of Bias Tool and for the controlled clinical trials they used to Newcastle – Ottawa scale.  They extracted the relevant data on:

  • Pain (from five studies)
  • Caries  (two studies)
  • Eating difficulties (five studies)
  • Speech difficulties
  • Deficient or hygiene (three  studies).

The Risk of Bias Tool revealed that one study was at high risk, one was moderate and one was at low risk of bias. The Newcastle – Ottawa assessment showed that 4 studies were high-quality and 1 was of low quality.

They presented their data as odds ratios and confidence intervals. I have extracted this into this table:

VariableOdds ratio95% Confidence limitP
Pain in tongue28.38.6-93.280.0001
Pain in cheek0.0870.036-0.2130.001
Pain in lips0.130.04-0.390.001
Caries risk1.150.77-76.90.8
Oral Hygiene3.491.02-11.950.048
Eating difficulty3.740.86-16.250.079
Speech difficulty9.393.78-23.30.001

This data was interesting. But I think that I should explain odds ratios because this can be a difficult area to understand. I have also covered this in more depth in a previous blog post.

  • The odds ratio measures the ratio of the odds that an event or a result will occur with a treatment (or no treatment).
  • For example, if we look at the data from this study in the table above, you will see that the odds ratio they reported for pain in the tongue was 28.3.  This means that the odds of pain in the tongue for the lingual appliance was 28.3 times greater than for the labial appliance.
  • If the odds ratio is less than one. The interpretation is more tricky, but in simple terms, this means that the first group (lingual) was less likely to experience an event. Therefore, if we look at data from pain in the cheek this is less likely with lingual appliances than for labial appliances.
  • If the confidence interval of the odds ratio includes one then there is no difference between the two groups.

They also presented a large number of Forest plots which were interesting and illustrated many of the findings.   They concluded that the patients who had lingual appliances experienced greater pain in the tongue,  greater speech difficulties and problems in maintaining oral hygiene than those who were treated with labial appliances.

What did I think?

This study was interesting and provided us with useful information. I put a slightly different interpretation on the data.   I felt that, when pain was considered, those patients who had lingual appliances reported more pain in their tongue. However, patients who had labial appliances reported more pain in their lips and cheeks. That is both groups reported pain and discomfort from different sites and I was not sure whether one appliance was “worse than the other”.

When I looked at the oral hygiene data I was more cautious than the authors, because the confidence intervals almost included 1.  This was, therefore, a rather uncertain conclusion.

I also had a look at the original papers and I found that these studies tended to report the outcomes over only a short period. Importantly, most of the differences had washed out after a few months. As a result, the findings of this review are only relevant to the patient’s initial experience.

Finally, I would like to draw attention to the studies that they included.  They included controlled clinical trials which are at a greater risk of bias than randomised controlled trials, even though these were mostly rated as good. Consequently, we have to consider that the strength of evidence from this review may be rather low. Nevertheless, this paper does give us information to give to our patients. Some operators maybe very critical and suggest that the findings are obvious, but at least they are now supported by evidence that we can give to our patients.

Next week I am going to start a series of post on sleep disordered breathing and orthodontic treatment…I am ready for the discussions!

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  1. Geoffrey Wexler says:

    It’s important that “obvious” things are tested to be correct – or not.
    Thanks for your insightful anaylsis


    Interesting paper to read, correct me if I’m wrong but I think the confidence interval for eating difficulty crosses the line-of-no-effect, therefore there’s no difference in terms of eating difficulty between lingual and labial appliance.

    “They concluded that the patients who had lingual appliances experience greater pain in the tongue, greater speech and eating difficulties and problems in maintaining oral hygiene than those who were treated with labial appliances”

  3. Hello Kevin,

    Thanks as always for your insights! I would like to point out a few relevant details that I think are important to the study of lingual appliances with respect to comfort and speech.

    The studies used in the meta-study above incorporate lingual appliances with two very different approaches to tooth movement; each with a different impact on patient comfort and speech. The basic difference in the two approaches is due to some manufacturer’s antiquated concept of how to balance patient comfort with ease of use for the operator. In reality, there is no reason for use of the “Straight-wire” approach any longer in lingual technique. Wire manufacturing using CAD/CAM allows a robot to place bends in the wire for us and obviates the need for the straight wire approach.

    In the studies incorporated in the meta study that used either Stb (Ormco), Kurz 7th generation (Ormco) or Stealth (American) lingual brackets the straight-wire approach was used. The rationale for using this approach is to reduce the number of bends necessary to be placed by the operator into the lingual archwires used. In theory, using a straight-wire approach negates wire bending and makes wire insertion easier. As mentioned, prior to the advent of CAD/CAM and wire-bending robots, this was true and made sense because bending lingual archwires is considerably more difficult than bending labial archwires. But today, one must question why a manufacturer would continue to use a straight-wire approach for manufacturing lingual appliances because it has such a profound effect in worsening patient comfort and speech.

    Consider, for instance, the faciolingual thickness of the mandibular incisors which are very thin to the mandibular canines which are relatively thick. In order to have a relatively straight wire with few in/out bends fall into the lingual bracket slots of these teeth with varied thickness, the slots of the mandibular incisor brackets must be brought out to the lingual somehow to allow the wire to fall into their slots. In systems using a straight-wire approach this is done by adding thickness to the bracket pads of thinner teeth-in this case the mandibular incisors.

    The problem in making the mandibular incisor brackets thicker for use in these straight-wire systems is obvious. By making the brackets thicker the bracket body; hooks, tie-wings and all, are now occupying more of the tongue’s space and adding to tongue irritation.

    In the studies that used Incognito (3M Unitek) the archwires are bent much more because 1st and 2nd order bends are incorporated into the archwires. The use of such a wire means it is bent in and out to match the lingual surfaces of the teeth and so brackets are made to be very thin in the faciolingual dimension and are much more flat against the lingual surfaces of the teeth. This, of course, improves comfort for the patient as the appliance is kept out of the tongue’s space more than with the above mentioned lingual appliances.

    I am not aware of any studies that have compared the comfort of straight-wire lingual appliances to customized lingual appliances such as Incognito or WIN but I do hope this occurs someday. In the meta study above both types of lingual appliances were lumped together without any mention of the enormous impact the two different approaches have on patient comfort and speech. This should not have been ignored.

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