March 13, 2017

Do orthodontic extractions lead to posterior positioning of the condyle?

Do orthodontic extractions lead to posterior positioning of the condyle?

Over the past year I have written several times about the recent research on orthodontic extractions. This new study attempts to find if extractions influence the 3D position of the condyle.

The debate on the effects of orthodontic extractions appears to be never ending.  There are proponents on both sides of the discussion. Interestingly, scientific research does not support most of the claims made by the non-extractionists.   One of these claims is that extractions and retraction of the incisors displace the condyles posteriorly.  A team from Cairo, Yemen and  Saudi Arabia did this study to look at this interesting question.

Three-­dimensional­ assessment­ of ­condylar ­position­ and­ joint­ spaces­ after­ maxillary­ first­ premolar ­extraction­ in­ skeletal­ Class­ II malocclusion.

MS Alhammadi et al

Orthodontics and Craniofacial Research: Advance access DOI: 10.1111/ocr.12141

They pointed out that most of the research into this problem is based upon the analysis of two-dimensional images.  As a result, they wanted to improve the quality of the data by using CBCT to image the condyles.

They set out to:

“Evaluate the effect of premolar extraction and incisor retraction on the TMJ”.

What did they do?

They did a prospective study and the PICO was:

Participants:  32 patients aged 18-25 years with a skeletal Class II malocclusion with a protruded maxilla and “normal’ mandible.

Intervention:  Orthodontic treatment with upper premolar extraction and retraction of the incisors.

Comparison:  This was a “before and after” study.  There was not a control group.

Outcome: Position of the condyle.

They did a sample size calculation based on a change of 30% in the position of the condyle.

They collected CBCT scans and measured TMD status at the start and end of treatment.

What did they find?

They found that there was a statistically significant posterior positioning of the condyle following treatment.  This change in position resulted in an increased anterior joint space and decreased posterior joint space.  However, no participant developed TMD.

I have included the relevant data in this table.

Attention: The internal data of table “48” is corrupted!

You may spot that the 95% CIs overlap. However, this does not always mean the differences are not statistically significant.

What did I think?

I have thought a lot about this study because of their conclusions.  I shall discuss this in terms of the design, analysis and interpretation.

When I looked at the design I thought that it was good to see that this was a prospective study that collected all the data on the participants.  However, the sample size was rather small.  I also had some concerns about the data analysis because this was simplistic.  Ideally, they should have done a regression analysis. This would have taken into account features, such as, starting overjet, gender and amount of retraction.  All these are important variables.

However, my greatest concern is the absence of a control sample.  This could be patients who had been treated without extractions.  In fact, the inclusion of this group would be the only way to answer the study question.

My other concern is about whether the differences that they found were clinically significant.  I cannot help feeling that the differences were rather small with wide confidence intervals.  This means that there is a high level of uncertainty in the data.

What can I conclude?

While is is easy to simply dismiss the results because of the issues I have raised. I think that it is important that they were close to finding interesting information.  This study is not sufficiently powered to change practice.  Nevertheless, they investigated an interesting question that should be researched with larger and more robust studies.

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Have your say!

  1. Avatar

    This was an interesting study that provided some good information. One aspect that was not addressed by the authors was that several patients initially present with differing degrees of a CR-CO slide. Thus, the difference observed pre and post-Tx might to some extent be influenced by the deprogramming/joint seating that tends to occur with treatment. Thus, a control group would have been very important. Also, were the condyles centered within the fossa either before or after treatment? To better delineate the effect of therapy (premolar extraction) vs. deprogramming, a pre-treatment splint phase might have been beneficial. Mechanics-wise, torque control and adequate bite-opening during retraction can prevent several undesirable sequelae. Interesting to see that the changes were restricted to the AP plane and not reflected in the ML and Vertical planes.

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    I may add that interestingly they seem to imply that the RCD/TMD criteria was used to assess TMD but nothing is reported in results regarding changes or not on this index. Due to the relatively small frequency of confirmed TMD a larger sample will certainly be needed.

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    Hi Kevin,

    Interesting… I’m wondering a few things:
    1. Whenever I read a study of treated cases, I always wonder which parameters they use to declare the outcome as a “good result”, especially if they extrapolate conclusion from that particular result.
    2. If an upper extraction case finished with the upper incisors too upright or even slightly retroclined, it may force the mandible back, thus moving the condile back. Not to mention that in such a scenario, you cannot achieve a Key 1 occlusion (perimeter line decreased due to excessively vertical upper incisor), making that outcome not so good.
    3. In my experience, it’s not a good idea to finish any case with lower incisors in full contact with the lingual surface of the upper incisors. In young adolescents, you may experience some residual growth, rebound, etc…, and then you could potentially have a mandible that wants to reposition distally, even if a fraction of a millimeter. Same for adults – more “prone?” to TMJ symptoms???
    4. The outcome of this study reminds me of the 1984/85 TMD lawsuit where GP’s testified that bicuspid extractions caused TMD…
    Like in any medical treatment, we should evaluate outcome with scientific parameters, which, unfortunately, our specialty has not embraced yet. We are living in times (worst than before), where Orthodontics has sided more with art than with science. Sad. Very sad.

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    Dear Kevin, I’ve followed your blog for quite a while now and often refrained from posting any comments or questions (afraid of language barrier). However, I feel that all these papers completely disregard occlusion and function. We are 3D beings (some will say 4D) and TMJ as well as occlusion is dynamic, not static; wouldn’t it be best to evaluate patients in a dynamic way instead all of these static methods (CBCT, MRI, X-rays, etc)? Shouldn’t we take into consideration that since occlusion dictates positioning of the mandible and the TMJ is highly adaptable, how these patients occluded before and after treatment? If they performed group function of canine protection before and how they were after treatment? Interferences and evasion patterns in mediotrusion before and after? Orthodontic outcome depends on the professional’s knowledge and ability, as well as patient compliance. It’s hard!!! I believe we should map out true hinge axis, as well as mandibular function (it can all be measured very accurately with a digital condylography, all movements, X-rays, split-casts mounted in fully adjustable articulators, night time brux checkers,) and only them would we have all variables to assess condyle positioning after treatment?

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    And it could be interesting too to analyze condilar changes in non extraction but molar distalization, in similar patients

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    Kevin:

    I forgot to mention the most important thing, in “my book”: CR-CO problems and all diagnoses done in CR!!! We see so many cases diagnosed in CO (where there is a big slide), and even worse, many cases finished because they look completed while asking the patient to “bite”. I check CR-CO discrepancies every appointment… There is no well treated and finished case without proper funcional analysis and correction. And again, most studies where they study finished cases do not provide any evidence of how they were finished.

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      Let’s hope there isn’t going to be a return to good old ‘collapsodontics’ accompanied by steepened anterior guidance.
      Then,what would I know being a retired general dentist.

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    I suspect there is a very important mistype of the figure for the posterior joint space post treatment!

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    Does posterior repositioning of the condyle imply a reduction in airway space??

    • Avatar

      Sweet Jesus!

    • Avatar

      Does posterior positioning of the condyles imply a reduction in airway space? The science probably says ‘no’, but common sense and anatomical knowledge tell us that if the mandible is retruded (as in posterior condyles) then there must be a reduction in oral and pharyngeal volume. So I would say ‘yes’, but the effects are matter of degree and individual response.

      More significant for me is the relationship between retruded condyles and TMD; my experience tells me there are many people with retruded condyles who show none of the symptoms of TMD. However, very few patients with TMD symptoms (and a history of extractions) do not have retruded condyles.

      I would suggest the study should be done the other way round; we should select a large group TMD patients with retruded condyles, and establish how many of them have had extraction-based orthodontic treatment.

  9. Avatar

    So let me raise some questions that this paper raises for me?
    1) Is there really such a thing as a Class II case with a protrusive maxilla with a normal mandible? I was taught there was in school but when I look at the face, most often I see a retrusive maxilla with an even more retrusive mandible.
    2) if the mandible is retrusive to begin with, what is the condition of the TMJ BEFORE starting treatment? Whether the condyle is centered in the fossa or not, don’t you think there would already be some sort of distortion in the joint morphology or function? Since bone has a way of remodeling in the presence of dysfunction, isn’t it possible that the pre-operative position of the condyle is the result of adaptation of both the condyle AND the fossa, including the positioning of the temporal bone in space? So, what about the joints in this study can be considered healthy to begin with?
    3) Whether healthy or pathologic, isn’t it possible that ANYTHING – be it traumatic, chronic, or therapeutic – can create a retrusive vector on the mandible pushing the condyle into the fossa? Why does it have to be limited to extractions (as was clearly demonstrated here). Any dysfunction or intervention that limits forward growth of either jaw has the potential to “distalize the mandible”. This includes headgear, Class II elastics, functional appliances that have a “headgear” effect, tongue-thrust swallows with a reciprocal distal vector of the mandible , forward head postures to keep the airway open, etc, etc.- and all this no matter whether there are extraction or no extractions applied.

    The problem with extrapolating this “evidence” to practice is that even if it does indict extraction therapy, it does not tell you WHICH ONE of your extraction (or headgear or retraction) cases will actually distalize and show joint position changes (as shown in this paper). So the question is not CAN it distalize, but WILL THIS PATIENT in front of me distalize. And since you can never tell, then…
    4) Isn’t it prudent to avoid ANY therapy that has the potential to put undue stress on the TM complex? And isn’t it advisable to do anything that will alleviate any current stressors on the TM complex that already exists by helping one or both of the jaws grow forward? In fact, shouldn’t it be medically necessary to help relieve the dysfunction first?

    I wish we (our profession) would stop playing this charade of “We do no harm” (to the joints, to the face, to the airway) and start playing “Let’s do some GOOD” (for the joints, for the face, and for the airway).

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