March 14, 2016

Can we make mandibles grow? A massive systematic review of cephalometric data!

 Can we make mandibles grow? A massive systematic review of cephalometric data!

This post is on whether functional appliances can alter skeletal growth to meaningful degree. A large amount of research has being carried out over many years to attempt to answer this question.  Many studies have been retrospective and while they have shown some growth changes, these have been moderate and the findings should be considered with caution because of the biases that are inherent in this research method. When randomised trials have been carried out the amount of skeletal change detected has been minor and not clinically significant.  The authors of the paper have carried out a study to provide further cephalometric evidence on this question.

The authors of this paper point out that one problem with this research is that most previous trials have investigated the treatment of pre-pubertal children, for ethical reasons, and that we should investigate the effect of treatment carried out in the pubertal period. They also point out that in the absence of trials, we should evaluate evidence derived from good quality controlled clinical trials or retrospective studies. As a result, the aim of their review was to evaluate the treatment effects of functional appliances in pre-pubertal and pubertal class II patients.

Lateral view of Twin BlockTreatment effects of removable functional appliances in pre-pubertal and pubertal Class II patients: A systematic review and meta-analysis of controlled studies.

Peritetti et al  PLOS ONE 2015. Doi: 10.1371/journal.pone.0141198

This paper was published in a non orthodontic journal which is open access.  It is generally hard to get a paper accepted in this journal.

This was a massively complex systematic review that included a large amount of cephalometric data. I think that this is the largest cephalometric festival that I’ve ever seen. As a result, I found it rather hard to penetrate down to the meaningful findings.

What did they do?

They carried out an extensive systematic review of the functional appliance literature. Their inclusion criteria were the following:

  • Studies investigating class II treatment in health patients
  • Randomised controlled trials or prospective or retrospective controlled clinical trials
  • The study investigated the skeletal and dental effects of treatment
  • There was a method of evaluation of the growth phase of the subject

The primary outcomes were

  • Mandibular length
  • Mandibular ramus height
  • Composite mandibular length (Pancherz analysis)
  • Mandibular base (Pancherz analysis)

Secondary outcomes were: SNA, SNB, ANB, maxillary length, facial divergence and mandibular incisor proclination.

They carried out a good evaluation of bias and quality of the studies. At the end of the filtering process of the literature they identified 11 studies that were included in the meta analysis.

They identified three randomised trials, two were pre-pubertal and one was pubertal. The remaining studies were controlled clinical trials or retrospective investigations.

Overall the studies could be divided into 7 pre-pubertal and 7 pubertal. There was some overlap between the studies and this is why the numbers do not add up, I think.

They provided a large amount of information in the results and I have summarised it here

CategoryInclusion criteria
Partipants characteristicsHumans with Class II malocclusion
InterventionTreatment with fixed functional appliances
ComparisonUntreated patients with Class II malocclusion
Study designRCTs
Prospective controlled clinical trials

This showed that for the 10 outcome measures that they selected, there was a significant difference between the effects of the pre pubertal and pubertal treatments in only three (mandibular length, ramus height and ANB). However, they concluded;

“Functional treatment by removable appliances may be affected in correcting class II malocclusion with relevant skeletal effects if performed during the pubertal growth phase”.

This seems to be based on the selection of the cephalometric measures of mandibular length and ramus height and does not include the data derived from the other measurements.

What did I think?

I found this a very difficult paper to interpret. This was because it was highly detailed and based on cephalometric data. As a result, my conclusions may disagree with those of the authors.

When we consider the findings we need to bear in mind that this data was derived partly from retrospective, poorly controlled, investigations which inevitably include a high level of uncertainty. Nevertheless, my evaluation of the data seems to suggest that there was no real differences between the changes found for pubertal and pre-pubertal treatments.

In this respect, it is worth pointing out that one risk of studying cephalometric data is that there is a tendency to find some “differences” between measurements. These are then concentrated on and yet other variables measuring similar morphology are ignored. I wonder if this is the case in this paper?

In short my interpretation of this paper is that;

  • There is no difference between the pre-and post-pubertal treatment effects of functional appliances.
  • Any skeletal changes are small and not clinically significant.

Finally, I have posted about the limitations of cephalometric research before. In the past cephalometrics has been central to our understanding of orthodontic treatment. However, times have now changed and an emphasis should be placed upon outcomes that are more relevant to our patients. For example, their perceptions of appliances, discomfort during treatment, and treatment duration. I am not sure that I will gain much from another cephalometric investigation into functional appliances. I am fairly certain that we know the answers to these questions.  It is time to move on….

This is my last blog for a few weeks. I will post again in early April.  If you need a blog fix during this time, why not have a look at some of the older posts etc?

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Have your say!

  1. Well said Dr. O’Brien. Thank you for your critical eye once again.

  2. Lysle Johnston put this to rest decades ago. We keep beating a dead horse.

  3. So I understand we can not make the mandible grow.

  4. Hello Kevin

    I cannot agree more with you than cephalometric measurements are not the best way to evaluate the effect of any appliance or technique when the treatment is established to correct a malocclusion. An orthodontic treatment with a Myofunctional Technique is generally delivered for about two years. Such a time is not enough to produce enough bone apposition to be significant when measurement in an x-ray. To understand that, we need to enter deeply in the biology of the bone tissues.
    The Bone Remodelling Period (BRP) refers to the lifespan of the bone´s basic multicellular unit to produce bone turnover. In other words, it is the time required for the osteoclasts to remove a piece of bone and the osteoblasts to apposition bone on that specific site. It has been determined that in humans, the BRP lasts for approximately 17 weeks to produce bone turnover in an area of approximately 200 µm radius (a fifth of a mm).
    Let´s say we are intending to stimulate bone apposition on the surface of either the maxilla or the mandible. If the BRP lasts 17 weeks to add approximately 200 µm, it means that in about 52 weeks, a year, approximately 600 µm may be added on the surface of those bones. In that context, about 1.2 mm of new bone would be added in a period of 2 years. I do not consider that that amount of bone potentially added on the surface of the mandible or the maxilla can produce significant differences when measuring distances on a cephalic x-ray. To demonstrate bone growth in the maxilla or mandible based on linear measurements on an x-ray after a myofunctional treatment, we would need to follow up the studied patients for 5 years or more.
    Having said that, we should be measuring changes in the muscular activity (frequency of contractions and force delivered). Our studies have demonstrated that the Myobrace System produces statistical significant changes in both, the frequency of contractions in the facial and masticatory muscles (Yagci, 2010 World J Orthod, Uysal, 2011 Eur J Orthod), and in the force delivered by the masticatory muscles (Satygo, 2014, J Clin Ped Dent). And remember, bone apposition does not occur if the loading on the bone is not altered !!! And, that loading on the bone is produced by the muscles !!!
    Therefore, we dentists treating malocclusions should understand better the bone biology, as well as the relationship between muscles and bone growth. We should be measuring muscular activity with electromyography and stop wasting our time discussing if a Myofunctional technique is able to produce maxillary or mandibular growth. Bone growth needs years and, it does not occur if the muscles do not load that bone harder !!!

    • First, thank you Kevin for this blog. You address great topics. Thank you German for reminding us if this. During a time our profession is looking at the most time efficient method, it is easy to forgot some basic biology. Additionally, it seems those that do not favor Phase I do so because of lack of profitability. However, if our profession wants to influence bone growth, time and development are required.

  5. Important work. Thank you. Would you comment on the effectiveness of the fixed functional appliances in growing mandibles to correct skeletal mamdibular deficiency, Herbst, Forsus for example.
    Thank you.

  6. Chirurgical Repozition of the muscles. !!!!! ? ???

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