February 20, 2017

Does childhood obesity increase the rate of tooth movement?

Does childhood obesity increase the rate of tooth movement?

Over the past few years there’s been a lot of interest in factors that may influence the speed of tooth movement. Until now,  I have not considered whether obesity has an influence. However, this new paper suggests that childhood obesity increases the rate of tooth movement.

Impact of Obesity on Orthodontic Tooth Movement in Adolescents:

A Prospective Clinical Cohort Study

H.F. Saloom S.N. Papageorgiou, G.H. Carpenter, and M.T. Cobourne

Journal of Dental Research  https://doi.org/10.1177/002203451668844

When I initially looked at the title of this paper I was not sure what to make of it. Nevertheless, when I read it I thought that it was interesting.  It is certainly different from the usual orthodontic research paper.

A London based team carried out this study.  Interestingly, Martyn Cobourne (lead author) grew up in the same small village as I did in Worcestershire.  But, he is 10 years younger than me. It is strange to think that a country village produced two orthodontic Professors!  I wonder if he remembers playing on these swings behind my house?


Enough reminiscing; now back to the post. They aimed to investigate the effect of obesity on orthodontic tooth movement.

It is well established that childhood  obesity levels have been rising.  This is a major health challenge because of the frequent co-morbidities that are associated with obesity. In the literature review they stated that adipocytes produce proteins that influence metabolic function and inflammatory response. This may influence the rate of orthodontic tooth movement. They investigated this in this prospective cohort study.

What did they do?

They recruited fixed appliance patients aged 12 to 18 years with mandibular arch irregularity of 4 to 12 mm. Importantly, they specifically recruited young people who they classified as being of normal weight or obese.

They collected the following data

  • Tooth alignment from scanned casts using Little’s irregularity index.
  • Unstimulated whole whole mouth salivary flow rate
  • Plaque and gingival indices
  • Analysis of gingival curricular fluid

They placed standardised fixed appliances with initial alignment using a 0.014 inch nickel titanium arch wire. They collected data at multiple time points and saw the patients at six week intervals. Their final data collection was when they fitted 019×025 stainless steel wires.

The primary outcome was the time to achieve tooth alignment in the lower arch. Secondary outcomes were rate of tooth movement and GCF biomarkers.

They calculated a sample size using data from previous investigation and did the relevant univariate and multivariate statistical analysis. The outcome assessor and statistician were blinded to subject classification.

What did they find?

They enrolled 55 patients, (27 male, 28 female) with a mean age of 15.1 years an irregularity index of 7.6 (2.4) millimetres. Mean BMI was 19.4 in the normal weight group and 30.2 in the obese group. At the start of treatment, the obese group had 1.2 mm more mandibular irregularity than the normal weight group.

They pointed out that obese patients needing 23 days less than normal weight patients to reach final alignment. But this was not statistically significant. This means that this finding may have occurred by chance.

The multivariate analysis, which took into account all the possible confounders in this complex study, showed that childhood obesity was associated with increased rates of tooth movement throughout the whole study duration. This difference was 0.017 mm per day. They also showed that there were significant differences in inflammatory biomarkers between the obese and normal weight patients. Finally, they suggested that this may explain the clinical performance differences between the obese and the normal weight patients during orthodontic treatment.

They concluded that obese patients had significantly increased rates of tooth movement during the whole observation period. Although, they did not find any differences in the time taken to achieve alignment. They suggested that this happened because the obese group had greater crowding than the normal weight group at the start of treatment.

What did I think?

I thought that this was an ambitious and detailed study of an interesting orthodontic question.  Strengths of the study were its prospective nature and most patients were included in the final analysis.  While 7 patients missed some of the data collection visits, they did include all the patients at the end of alignment stage of the study.

The authors also outlined a clear rationale for carrying out the study. They also explained the theoretical basis of their findings.

I was interested to see they reported that obese patients needed less time to achieve full alignment, than normal weight patients. However, this was not statistically significant. In effect, this difference may have occurred by chance and we cannot state that there is a “difference”. When the UK Dental Press reported on this study they did not take this into account and several incorrect claims were made. This is a good example of more caution being needed, by the press, in the interpretation of a scientific paper.

However, they did show that the rate of tooth movement was significantly greater in obese children. However, we also need to remember that this is a small effect size.  Interestingly, this is similar to the rate of tooth movement claimed by the manufacturers of various devices that are meant to increase the speed of tooth movement!

Clinical implications?

Finally, I have thought about the clinical implications of these findings. While the findings are interesting, I’m not sure how these translate into clinical practice. We can hardly encourage our patients to become obese in order to speed up their orthodontic treatment. However, it does illustrate to me that there are many variables that may influence the rate of tooth movement. As a result, the use of devices, localised trauma, pills and potions may not have an influence. Greater influences may well be the operator and the patient.

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Have your say!

  1. An observation I have made in my practice and outside my practice is that obese children are often mouth breathers. This changes the physiology and their ability to exercise properly. (We canal remember the ‘fat kid’ at school always being at the back of any PE class/x country etc).
    The fact that they are mouth breathers also means that their tongue sits in the wrong position (low in the mouth) and affects the
    developing growth, first and most importantly in the maxilla which will frequently be long and narrow, and sometimes tied in with other soft tissue functional abnormalities will lead to crowding of the lower incisors.
    Whilst not directly linked to the speed of tooth movement it is relevant to the obese population. Again appreciate my observations are not evidence I would expect that you would observe these findings in your clinical surroundings. In turn this may lead to some meaningful research.

  2. I like the illustration used from the cover art of “In the Court of the Crimson King” by King Crimson – Island Records 1969. Great album too.

  3. Thank you for this interesting post. Another implication came to my mind; to prevent the misuse of these findings, we have to see the BMI data on the future exciting reports about commercial devices that claim to accelerate tooth movement.

  4. I am now thinking about mastication activities in the obese patients, and the genetic agent wich translated as specific protein and the metabolism, and the hormones levels??

  5. Thanks Professor Obrien, this has been very informative. I suggest that orthodontists should begin to document BMI of their patients to identify obese patients, as they may benefit from reduced treatment time and loss of man hours.

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