I am writing to comment on the paper entitled: "Effects of
experimental leg length discrepancies on body posture and dental
occlusion" by Maeda, et al. that just appeared in CRANIO (July,
2011). (1) This is a controlled study showing that immediate effects of
experimental leg length inequality exist on both body posture and dental
occlusion. At first glance, the study appears interesting and well
conducted, but after a more accurate reading, one wonders if the
interpretation of the results can be truly considered unbiased, or if
important aspects related to the correlations between the masticatory
system and body posture have been missed.
The investigations on such correlations are both relatively recent
and still controversial. However, a few years ago systematic reviews
(2-4) were published with the aim of pointing out limitations of current
research and suggesting future improvements/directions. In 2009, our
group published one of these systematic reviews (3) that uncovered the
fact that about half of the current publications were negative, and
failed to find any significant correlation. While negative studies carry
the same dignity as positive ones (and should be quoted in any paper as
well), this piece of evidence leaves all questions about the true
existence of such correlations open. Moreover, our analysis (3)
initially uncovered major methodological limitations of published
studies, such as the lack of a method error analysis of the parameters
used to measure aspects of the body posture or dental occlusion. Indeed,
the degree of correlations seen in most of the positive studies,
although statistically significant, are little and there is no proof
that they are beyond the systematic/random errors encountered. In this
view, endeavors to overcome current methodological limitations are
necessary to avoid ambiguous or contrasting results.
Finally, the existence of correlations at a biological level, and
their potential clinical relevance (3,5) need to be considered, along
with how they relate to two distinct aspects that must not be confused.
Therefore, while a correlation may be detected experimentally, this does
not mean that it will have a clinical relevance. Only if the
correlations reach a clinically significant grade would the diagnosis
and the consequent treatment plan have to take such aspects into
account. However, this concept is missed in most of the published
literature (including the above-mentioned study), (1) with a few
Therefore, in consideration that none of the abovementioned reviews
or negative studies have been discussed or cited, the conclusions in the
paper by Maeda, et al. might suffer from bias. Moreover, whether these
correlations are clinically relevant or limited to a biological level is
still far from being clearly demonstrated.
Giuseppe Perinetti, D.D.S., Ph.D.
Luca Contardo, D.D.S., M.S.
Dr. Nozomi Maeda, et al.'s response to Drs. Giuseppe Perinetti
and Luca Contardo.
Our distinguished colleagues are quick to accuse bias in our
interpretation of the data without elaborating on what they see as
biased. Data was presented and the statistics done in a standard,
unbiased way. We would have appreciated some elaboration on the
correlations we have missed. We are still trying to understand what they
are concerned about beside the fact that their names were not included
in our references. This field is still experimental, and, as was
mentioned in our paper, many areas showed no correlation. Our paper was
clear in presenting both positive and negative correlations.
Moreover, it is very obvious that our colleague was quite upset
that we did not quote his group's study in our research. We would
like to point out that their publications came around the same time our
paper was in publication. Our references included both sides of the
argument, and we feel that it is up to the readers to decide what may or
may not be of clinical relevance. It will take a few more research
projects to prove a solid correlation pattern and many more to establish
clinical applications. Our research simply presents a pattern, as
measured by accurate computerized equipment. It is intended to present
data, and to open a discussion regarding its clinical relevance. We look
forward to future research in the area.
Kiwamu Sakaguchi, D.D.S., Ph.D.
Nozomi Maeda, D.D.S., Ph.D.
Atsuro Yokoyama, D.D.S., Ph.D.
Noshir R. Mehta, D.M.D., M.D.S., M.S.
Emad F. Abdallah, D.M.D., M.S.
Albert G. Forgione, B.D.S., M.S.