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READERS’ FORUM
Letters to the editor*
Class II subdivision malocclusion
We appreciate the efforts of Dr Janson and his colleagues
for their research on Class II subdivision malocclusion; it has
enriched the orthodontic literature. We followed with great
interest their article, “Cephalometric evaluation of symmetric
and asymmetric extraction treatment for patients with Class II
subdivision malocclusions” (Janson G, Carvalho PEG,
Cançado RH, de Freitas MR, Henriques JFC. Am J Orthod
Dentofacial Orthop 2007;132:28-35).
The results of the study were commendable with the
exception of the upper lip retraction after incisor retraction
when the groups were compared. The authors concluded from
their results that upper lip retraction was significantly greater
in group 2 compared with group 1, even though the maxillary
incisor retraction amounts (angulation and linear) were not
significantly different.
That finding needs to be clarified by the authors, because
previous studies have reported direct relationships between
incisor retraction and upper lip changes associated with it.1,2
Because the amounts of linear upper lip retraction were
similar in the groups (–2.11 mm in group 1 and –2.33 mm in
group 2), the upper lip should have shown similar changes in
both groups in contrast to the results of their study.
Apart from hard-tissue changes, lip response also depends on lip morphology and its tonus. Oliver3 showed a high
correlation between incisor retraction and lip movement in
subjects with thin lips compared with subjects with thick lips.
These factors should have been considered when evaluating upper lip response to incisor retraction in the asymmetric and symmetric extraction groups.
Suruchi Jain
Ashima Valiathan
Manipal, India
Am J Orthod Dentofacial Orthop 2008;133:4
0889-5406/$34.00
Copyright © 2008 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2007.11.009
REFERENCES
1. Rudee DA. Proportional profile changes concurrent with orthodontic therapy. Am J Orthod 1964;50:421-33.
2. Roos N. Soft tissue profile changes in Class II treatment. Am J
Orthod 1977;72:165-75.
3. Oliver BM. The influence of lip thickness and strain on upper lip
response to incisor retraction. Am J Orthod 1982;82:141-9.
metric and asymmetric extraction treatment for patients with
Class II subdivision malocclusions.” Yes, we agree that a
significant maxillary incisor retraction would be expected to
be somehow associated with the significant upper lip retraction that we found. However, because it did not occur, we
speculated that it could have resulted from the large standard
deviations in the amount of maxillary incisor retraction.
When extrapolating the correlation found between maxillary
incisor retraction and upper lip retraction in the mentioned
studies,1,2 one must notice that they were obtained between
linear variables and therefore differently from our study.
Additionally, the correlation coefficients obtained were
0.72652 and 0.421; these are not considered statistically
high,3-7 and there were also large individual variations in the
response of the soft tissues to changes in the underlying
skeletal structures.1 Lip thickness and strain, as mentioned,
also play roles.8 Therefore, under these circumstances, it is
likely that the results we obtained are possible. Perhaps this
explanation could have been added to the discussion. In the
article, we did not further explore this topic because it was not
our primary objective. However, it surely is an interesting
issue to be investigated and clarified in the future.
Guilherme Janson
Rodrigo Hermont Cançado
Bauru, SP, Brazil
Am J Orthod Dentofacial Orthop 2008;133:4
0889-5406/$34.00
Copyright © 2008 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2007.11.010
REFERENCES
1. Roos N. Soft-tissue profile changes in Class II treatment. Am J
Orthod 1977;72:165-75.
2. Rudee DA. Proportional profile changes concurrent with orthodontic therapy. Am J Orthod 1964;50:421-33.
3. Le CT. Fundamentals of biostatistical inference. New York:
Dekker; 1992.
4. Looney SW. Biostatistical methods. Totowa, NJ: Humana Press;
2002.
5. Selvin S. Practical biostatistical methods. Belmont, Calif: Duxbury Press; 1995.
6. Zar JH. Biostatistical analysis. 4th ed. Upper Saddle River, NJ:
Prentice Hall; 1999.
7. Altman DG. Statistics in medical journals. Stat Med 1982;1:
59-71.
8. Oliver BM. The influence of lip thickness and strain on upper lip
response to incisor retraction. Am J Orthod 1982;82:141-9.
Authors’ response
We thank Drs Jain and Valiathan for their constructive
comments on our article, “Cephalometric evaluation of sym*The viewpoints expressed are solely those of the author(s) and do not reflect
those of the editor(s), publisher(s), or Association.
4
Self-ligating brackets
With great curiosity, I began reading the August issue of
the AJO-DO. Had the orthodontic community actually taken
an interest in research about self-ligation? I could hardly