July 08, 2019

The Carriere Appliance does work! A new study

Last week I did a post about a study that suggested that the Carriere appliance was not effective.  Another paper about this treatment was published this week. This suggests it works!  So, I thought that I would have a critical look at it.

One interesting fact about the Carriere appliance is that it has been used for many years. However, until recently there has been no research on this appliance. Just as I published my post last week on the first research paper, the Angle Orthodontist published  this new paper. A team from Michigan did the study.

Treatment effects of the Carriere Motion 3De appliance for the correction of Class II malocclusion in adolescents

Hera Kim-Berman, McNamara JA et al

Angle Orthodontist: On line. DOI: 10.2319/121418-872.1

What did they ask?

They set up this study to answer this simple question

”What are the clinical effects of the Carriere appliance”?

What did they do?

They did a retrospective study. The main study details are:

Participants: 34 patients who had been treated by Dr Luis Carriere with his appliance.

Control: 34 sets of cephalometric records taken from several historic growth studies.

Outcome: Treatment duration and multiple cephalometric measurements.

They obtained a sample of treated cases from the office of Luis Carriere. They asked him to select 30 or more consecutively finished cases. He sent them 44 sets of records. Ten of these were excluded for the following reasons :

  • There was a technical issue with the radiographs.
  • The duration of treatment with the Carriere Motion appliance was greater than 12 months.
  • The post treatment records were made more than 4 months after the end of all treatment.

They “control” group was selected from three large growth studies.

One investigator traced all the radiographs.  They analysed the data at the start of treatment, at the end of the Carriere Motion treatment and at the end of all treatment. They did not report an error analysis.

They then ran simple multivariate statistics across 18 different variables. They decided, from other published work, that a clinically significant difference was a change of greater than 2mm or 2 degrees in any cephalometric variable.

What did they find?

They provided a large amount of data and discussed this in a great deal of detail. Most of this discussion was on cephalometric changes that were not clinically significant (according to the definition that they adopted).   I do not have the space here to cover this amount of data.  However, I thought that the main points were:

  • There was no clinically significant effect of the Carriere on the skeletal pattern.
  • I could not find any data on the amount of upper arch distalisation.
  • The only changes were dental. For example, when they compared the Carriere to the “control” group.  They found that the overjet was reduced by 2.9mm, molar relationship was corrected by 3.1mm and the lower incisors were proclined by 3.8 degrees. We need to consider whether these effect sizes are clinically significant.

I also felt that for most of the variables the standard deviations were large. This indicates a degree of uncertainty in the data.

They looked at the duration of treatment and I calculated the 95% confidence intervals.  They found that mean total treatment time was 18.2 months (95% CI 16.5-19.8) months, the mean duration of treatment with the Carriere was 5.2 months (95% CI=4.2-6.1) months.

They concluded:

“The Carriere appliance is an efficient and effective way of correcting Class II malocclusion”.

What did I think?

I will take the same critical approach with this paper as I did last week with the study that concluded that this appliance was not effective.

This paper was similar to many reports published by the Michigan based group. They retrospectively collect a sample of records and then compare them with historical controls. Unfortunately, this paper suffers from several substantial flaws. These are:

  • This was a retrospective study.
  • The records were all chosen by one clinician, who was the inventor of the appliance. They were also consecutive finishes.
  • The inclusion criteria on the start malocclusion was not clear.
  • They excluded cases that took too long to finish Phase 1. That is they removed the cases that did not “do well”. In effect, they excluded 25% of the records.

If I take all these factors together then there must be considerable selection bias. It is also completely illogical to exclude patients in a study because they did not complete the care in an arbitrary time.

Furthermore, they used an historical control. This method has been previously criticised because of the possibility of secular change.

I could not find any mention of an error analysis. This is important bearing in mind the small effect sizes that they reported.

Finally, they ran univariate statistics across many cephalometric variables. This is not an appropriate way of analysing this type of data because of the risk of false positives.

Final thoughts

My feeling about this paper is similar to the previous paper that I reviewed. I am disappointed to find that this study was significantly flawed in many respects. In fact, when I consider the two papers I am a little surprised that they were published. Perhaps, the journals are very keen to publish something on this appliance?

Where does this leave us with the Carriere Motion? I don’t think that we are much further down the line. As with the previous paper, this report does not help us because it is so flawed.

I think that all we can conclude is that the Carriere appliance may correct the dental component of Class II malocclusion using heavy elastic force. But, we know nothing about its success rate, effectiveness, co-operation rate, harms, effect on skeletal pattern and whether it has an effect on the airway.  We also do not know if it is more or less effective than any other method of Class II correction. In fact, to claim that it is more effective is somewhat unethical.

Several people have commented to me that this is not important. If we consider that the Carriere is a simple method of Class II correction using heavy elastics, then I agree. However, if orthodontists charge an additional fee for the Carriere, based on the manufacturers claims,  then this becomes more relevant and is unethical.

Perhaps, it is time for the manufacturer to run a trial of this appliance? It would cost one just one major KOL annual fee.


Related Posts

Have your say!

  1. This article is excellent, in illustrating how easily a study could be manipulated. Selected patients compared with untreated individuals from half century old growth studies. I thought that studies of this design had been abandoned, perhaps not at Michigan.

    Overjet was reduced (Class II correction), lower incisors proclined and there was a restriction of forward movement at Point A, with an increase in the vertical dimension. Sounds like Class II elastics were worn and anchorage was lost in the lower arch.

    The authors suggested that the treatment was efficient. Perhaps if one compares a treatment group with an untreated control, then it is more efficient at correcting a Class II.

    If the engine providing the force is heavy elastics and everything else is just to provide support, why would a rational clinician expect a change that was different to elastics alone?

  2. The major cost of the Carriere is not its cost.
    It is the fact that you have to spend several appointments to do the treatment with it, then bond braces.
    Even if you were to correct the class II/III relationship faster, would it really worth the extra chair works ?
    The other issue is that you you finish class III the axis of the teeth especially the canine are not correct, so you end up having a longer leveling time.
    I was not surprise by the finding of the first study that found an over all longer treatment time with the device.

    I am not surprise to see this appliance popular with the GP and not so much with the orthodontist. Orthodontist especially in the US are very focus on the overall benefice of the case, GP are a lot more sensitive to the KOL effect.
    I saw GP swearing that the carrier was wonderful when looking at their cases, the cases where 100% doable without the appliance and it was not even obvious what was the claim advantage.
    No obviously none extraction cases treated none extraction
    No faster treatment
    No better finish

  3. Than you Kevin for scientifically prove what I told Luis just out of my experience of 30 years with the Herbst appliance. He didn’t like it , but as I told him and his followers their approach was so much of a marketing one !

  4. Thank you for the clarification. As an aside, I am keen to know as well whether any financial support was declared in the article. It would appear that McNamara serves as a consultant for HSO. I am not aware that this was declared at the AAO

  5. Thank you, I agree with your comments. I would like to add that their conclusions can only be applied to patients with a slight skeletal class II (ANB 5 °, Wits 2.8 mm), a normal vertical skeletal pattern (FH-MandPlane 24 °) and a deepbite (overbite 5.2 mm). Does the treatment of these class II need another appliance instead of class II elastics?

  6. I am in the middle of writing a paper and found this dissection of a academic corpse quite humorous!!! It would be great if we could just ‘exclude data’ if it didn’t behave how we wanted it to!
    And to ask the inventor of an unproven device to send some handpicked cases to use in research to prove his invention works? What could possibly go wrong?

  7. The average molar relationship in the treatment group was about 1.3 mm class II, with a standard deviation of 1.4 mm. These cases hardly fit the criteria for what constitutes a class II, and are arguably very mild at best, if that.

    Just disclusion and mandibular growth would have been more than enough to “correct” the class II. One has to wonder why these patients received the appliance at all. Several of the changes are very small (approaching measurement error, were it assessed) with deviations larger than the mean.

    The other aspect, is one of iatrogenic ramifications of running “heavy” elastics to a canine and molar, unbound by a rigid arch wire. The extrusive effects are likely to be amplified.

    The change in WITs can be explained by molar extrusion, and rotation of the occlusal plane. This may not be desirable from an esthetic or stability perspective, especially if associated with a concomitant down and back rotation of the mandible, thus reducing Pogonion projection.

    This seems to have occurred, with no net forward movement of Pogonion, in the Tx group. With an average SNB of 75.4, anterior movement of Pogonion was likely a desirable change, from an esthetic standpoint. It appears that was not allowed to occur, due to the increase in LFH associated with molar extrusion.

    There appears to be no benefit to this appliance at all and conversely the potential for iatrogenic effects that may not be esthetically desirable.

  8. Nothing corrects Cl II better than a case that starts out being Cl I. The attribute an appliance to it’s success!!! Any wonder there is minimal cephalometirc changes?

  9. We have used the Carriere distalizer for many years in our clinical practice. Probably hundreds of them. We normally use it in conjunction with a full coverage Essex appliance in the lower arch as the anchorage unit. Our results compared to other class two correction appliances we used over the past forty years in clinic practice we’re that it was a quicker, simpler and more patient compliant appliance than any others we’ve used. Needless to say we are big fans. A few years ago I did a cephalometric study of the appliance for my study group (no statistical analysis). I thought I was at least getting a bit of upper arch distalization. Turns out, like most studies have confirmed, most change was dento-alveolar in nature in the lower arch. Nice to know where change comes from but we still use a lot of these appliances for the aforementioned reasons. The takeaway from my rambling… It is unfortunate but axiomatic that advertising claims overstate results. We know that in the consumer arena, perhaps we should get over our outrage while continuing good research to clarify fact from fiction. Kevin, and others please continue your good work, we need you!

  10. Kevin ,you state ,”if we consider that the Carriere is a simple method of class 2 correction using heavy elastics then I agree”.
    I agree totally and anything else claimed by KOL,s is not valid scientifically.
    The term “KOL “is starting to verge on the farcical and derogatory !Just saying !

  11. I’d like to see a meta-analysis on this question and a meta-analysis re the long term mandibular effect.

Leave a Reply

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