December 22, 2016

Are Class II elastics as effective as a functional appliance? A trial that may answer this question

Are elastics as effective as a functional appliance?  A trial that may answer this question

Occasionally when I have given a lecture on functional appliances several people have asked whether I think class II elastics have a similar effect to the functional appliance. I have always replied that I am not too sure. This new paper may provide us with a potential answer to this question.

screen-shot-2016-12-21-at-13-14-20Class II subdivision treatment with the Forsus Fatigue Resistant Device vs intermaxillary elastics

Isil Aras; Aylin Pasaoglu

Angle Orthodontist: On line. DOI: 10.2319/070216-518.1


This trial was done by a team from Istanbul, Turkey

The trial was on two methods of  treatment of Angle class II subdivision malocclusion. This is where the molar relationship is Class II on one side and Class I on the other. The authors point out that there are many types of treatment mechanics that are used for this problem. However, there appears to be an increasing trend to use Class II elastics and/or fixed functional appliances.

They carried out a randomised controlled trial to find out the relative effectiveness of class II elastics or fixed functional appliance treatment.

What did they do?

The PICO was;

Participants: 34 patients with angle class II subdivision malocclusion.

Intervention: Forsus Appliance

Comparison: Class II elastics to fixed appliances

Outcome:  Study model analysis and multiple cephalometric measurements!

They randomised the patients by dividing the patients into 17 pairs with similar malocclusions. They then tossed a coin to allocate treatment with either a Forsus appliance or Class II elastics. (I will come back to this later).

They collected data at the start of treatment and 10 to 12 weeks after fixed appliance removal. They measured the molar relationship on study casts and analysed multiple cephalometric measurements many times.

A blinded examiner recorded the data. They carried out a sample size calculation that was based on midline correction.

What did they find?

I was disappointed to see that they removed two patients from the elastic group because of poor cooperation. This means that the study would have become biased.

They provided a large amount of data, particularly cephalometric. I have put what I considered to be the most relevant data in this table.

Attention: The internal data of table “44” is corrupted!

I think that the most important findings were the following:

  • The overall treatment time was significantly shorter with the Forsus
  • They did not find any difference between the interventions when they looked at the multitude of cephalometric measures.
  • The mandibular incisors were proclined in both groups.
  • The Forsus sample showed a significantly greater improvement in overjet but this was only by 0 .9mm. I do not think this is clinically significant.

What did I think?

Firstly, I think we need to consider that they did not investigate the traditional functional appliance treatment for Class II malocclusion. Nevertheless, I wonder if this study does provide an illustration of the comparative effect of a fixed functional appliance and elastics.  In general, I thought that this was a good small trial. The authors should  be congratulated on attempting to answer such a relevant clinical question.

Nevertheless, there are some problems with this study. These are;

  1. The method of randomisation did not conceal the potential group allocation from the investigator. This could lead to bias.
  2. They removed data from patients who could not comply with treatment. This is a fairly basic problem because this means that they only collected data on patients who cooperated. This, of course, leads to selection bias.
  3. The sample size was based upon midline correction. This did not appear to be their primary outcome measure. As a result, the study may have been underpowered for other outcome measures.
  4. The analysis of multiple cephalometric variables that are related to each other could easily result in false findings. I have discussed this before.

While I may have been critical, I still feel that  it was interesting to find that their results do not show any evidence of a difference between these two interventions. This may suggest that the action of the two interventions are similar. When we consider that most research has shown that functional appliances simply tip the teeth, then this result is somewhat logical.

Unfortunately, because of the issues that I’ve highlighted in study design I’m still not able to answer the question that I posed at the start. Which is a shame.

This study only provides us with weak evidence on this interesting problem. But it certainly acts as a model for future research.


Related Posts

Have your say!

  1. Dear Sir.
    About the elastic group, i belive that it could be divided into many groups, depending on the force of the elastics , and depending on the size of wires they started the elastics with, if you consider the (ELSE) which start the elastic in a very early stage , i can see significant difference between this and the traditional protocol for using the Elastics.

  2. Forsus is not a functional appliance. It is just another method of Baker anchorage.

  3. Sir,
    I feel more than the clinical effectiveness of both the techniques. It is the clinical situation that matters. The case selection is of importance. Class 2 elastic s on a.vertical grower has its own side effects. You need to select on a push type or a pull type force.

  4. I am interested in your comment that removal of patients who did not comply leads to selection bias. I think that research on orthodontic treatment that relies on compliance could/should have two sets of data and one of these can show what is possible on average if cooperation is good as this does provide the clinician with useful information because they can say to their patient “if you cooperate/do as we ask this is what is possible” as opposed to clouding the data with both compliers and non-compliers.
    I agree that there should also be data available without this selection bias but I do have another way of looking at it. I would like to know what is possible on average if a child cooperates as well as what is likely to happen on average using the whole data.
    I wonder if anyone has ever looked at the data in your multi centre twin block study and removed the non-compliers? Would that provide some useful information? Everybody knows already that the functional appliance wont work if the child wont wear it. Your 2003 paper has a 16% non-compliance rate and overall 1.9mm of skeletal change with functional appliances but would it be useful to know what the skeletal change would be with this 16% removed? It would tell the clinician what is possible on average if the child wears the appliance.
    I have heard it said from one speaker who took part in your trial that he had no failures in his group which means that somebody must have had A LOT of failures so perhaps this approach of including all the patients in the analysis is not giving us the full story? I believe that both sets of data would be useful and benefit our knowledge (although this does create more work for the researcher!)

    Sorry if I’ve gone off topic. I do have one request I wonder if you might consider looking into and writing a blog on the Carrier appliance. The claim being that it makes the treatment with class 2 elastics more effective.

  5. Your statement, “When we consider that most research has shown that functional appliances simply tip the teeth…”, Underscores a divide among orthodontic researchers. Some want merely to say that treatment A is or is not better than Treatment B; others, however, are as interested in figuring out how A and B do what they do. I am one of the latter and think that cephalometric analysis (e.g., superimposition) is more than a numbers fest. It is simple and dismissive, but incorrect, to say that functionals and Class II elastics merely tip teeth. If one were to descend into the netherworld of cephalometrics, functionals can be shown to produce less than a mm of tooth movement (Herbst a bit more–more lower incisor anchorage loss). The big component is a functional shift that the normal pattern of mandibular excess growth usually makes permanent. (Much like amortizing a mortgage on mandibular position.) Class II elastics also make use of the normal mandibular excess by allowing the usual mandibular excess to take place without maxillary mesial dentoalveolar compensation (plus a mm or so of actual distal upper buccal segment movement, if it is a nonextraction treatment). A curiosity about the underlying mechanism of Class II correction and a little descriptive data make it easier to understand the outcome of an A vs. B trial. Merry Christmas!

Leave a Reply

Your email address will not be published. Required fields are marked *