Download Occlusal characteristics in subjects with or without the ability to roll

C. Suárez, G.S. Antonarakis, D. Pham
Department of Orthodontics and Pediatric Dentistry
University of Geneva Dental School, Switzerland
e-mail: [email protected]
Occlusal characteristics
in subjects with
or without the ability
to roll the tongue
abstract
Aim The tongue represents an important intraoral
muscular force which is in direct contact with the dental
arches. The objective of the current study was to compare
occlusal characteristics of patients who have the ability to
roll their tongue (TR+) to those who cannot (TR-).
Materials and methods A hundred consecutive
patients under orthodontic treatment were classified as
TR+ (n=73) or TR- (n=27). Pre-treatment orthodontic
study casts were used to measure intercanine and
intermolar widths, arch lengths, space deficiency, overjet,
overbite, presence or absence of posterior crossbite
and the molar Angle class. For continuous variables,
independent sample t-tests and Mann-Whitney U tests
were used to examine differences between the groups.
For dichotomous variables, chi-square tests were used to
examine differences between groups.
Results TR+ patients showed larger mandibular intermolar widths (1 mm, p<0.05) and less mandibular space
deficiency (1.9 mm, p<0.05) than TR- patients. Mandibular
space deficiency was present in the mandibular arch in
18.5% of TR+ compared to 49.3% in TR- patients (p<0.05).
Conclusions The ability to roll the tongue may lead to
differences in occlusal characteristics, namely an increase
in mandibular intermolar width and a less mandibular
space deficiency.
Keywords Malocclusion; Occlusal characteristics;
Tongue: Tongue rolling.
Introduction
The tongue represents an important muscular force
in the orofacial sphere, and it is said to be the most
European Journal of Paediatric Dentistry vol. 15/2-2014
powerful muscle in direct contact with the dental
arches [Proffit, 1978; Straub, 1962; Volk et al., 2010].
The tongue is central to the equilibrium theory, and
mention of the tongue in this regard can be traced back
to Tomes [1873], who referred to the labiolingual frame
of teeth stating that “the agency of the lips and tongue
is that which determines the position of the teeth”. The
equilibrium theory of tooth position has been since
revisited and it is still widely accepted that the position
of teeth seems to be closely related to the equilibrium
resting pressure created by the tongue, the cheeks
and lips, as well as that created within the periodontal
membrane [Proffit, 1978; Weinstein et al., 1963].
Tongue characteristics such as volume, posture, and
function are important in the aetiology of different
defining occlusal traits [Ghafari et al., 1988; Hanson
and Cohen, 1973; Harvold, 1963; Melsen et al., 1979;
Volk et al., 2010]. It has been argued that tongue
posture and function are the main aetiological factors
in malocclusions [Andrianopoulos and Hanson, 1987;
Proffit, 1978; Straub, 1962]. Proffit [2007] suggests
that tongue posture may be even more important than
tongue function, since the effect of swallowing on the
equilibrium of forces acting on the bones and teeth is
limited due to the short total duration of these forces
daily. Causality as regards tongue posture and function
can be questioned however, with the suggestion that
these characteristics are a consequence of dental and
craniofacial relationships [Cleall, 1965; Subtelny, 1970].
Assessing tongue characteristics clinically is
challenging, due to the anatomic structures surrounding
it as well as the subjective nature of the evaluation [Volk
et al., 2010]. Simple indicators of tongue characteristics
may exist, whereby an ability to perform a certain
tongue movement such as tongue rolling, may possibly
be related to certain occlusal traits.
Tongue rolling is an inherited trait that was first
described by Sturtevant [1940] as the ability to turn
up the lateral edges of the tongue. It is also known
as tongue curling or tongue folding (OMIM 189300).
Prevalence of tongue rolling in the general population
ranges from 65 to 74%, without gender predilection
[Hsu, 1948; Komai, 1951; Liu and Hsu, 1949; Sturtevant,
1940; Urbanowski and Wilson, 1947].
The aim of the present study was to compare occlusal
characteristics of patients who have the ability to roll
the tongue (TR+) to those who cannot (TR-), due to the
importance of the tongue in the orofacial equilibrium.
The null hypothesis was that there are no differences in
terms of the occlusal configuration between TR+ and
TR- children.
Materials and methods
Prevalence estimation
In order to establish the prevalence of tongue
147
Suárez C., Antonarakis G.S. and D. Pham
rolling and its age distribution in our local population,
a prevalence study was conducted among 590 non
orthodontic school children (age range 4-12 years old)
attending an annual check-up at the School of Dentistry
of the University of Geneva. Children were asked
to show the ability to roll the tongue, as shown in a
photo of a patient with this ability (Fig. 1). Differences
in tongue rolling prevalence based on gender and age
were examined using chi-square tests.
Patient sample
The study sample consisted of 100 consecutive
orthodontic patients under treatment at the Department
of Orthodontics of the University of Geneva. Written
informed consent had been obtained from all patients
and their parents in order to use clinical records for
research purposes, and the study was conducted in full
accordance with guidelines put forward by the Helsinki
Declaration, wherever relevant. Inclusion criteria were
the availability of pretreatment diagnostic study casts,
taken at the age of 7 or later.
Exclusion criteria were patients with sucking
or interposition habits, short lingual frenulum or
ankyloglossia, cleft lip and palate patients, syndromic
patients, patients with missing permanent teeth and
patients who had already undergone an orthodontic
treatment. Patients were asked to participate in the study
in a consecutive manner during regular orthodontic
appointments. Patients accepting to participate were
asked to show the ability to roll the tongue as shown
in a photo of a patient with this ability, and classified as
either TR+ or TR-.
Occlusal measurements
Pre-treatment study casts were used to measure the
following occlusal characteristics for each of the included
patients: intercanine and intermolar widths, presence
of posterior crossbite, maxillary and mandibular arch
lengths, presence and amount of space deficiency in
the maxilla and mandible, molar Angle classification,
overjet and overbite. Measurements were performed
using digital calipers.
Statistical methods
All statistical analyses were carried out with a statistical
software package (SPSS for Apple, version 17.0, SPSS
Inc, Chicago, Ill, USA). All measured continuous variables
were tested for normality with the Kolmogorov-Smirnov
test. Independent sample t-tests were used to determine
statistically significant differences between groups for
the variables which were normally distributed. MannWhitney U tests were used when assessing differences
in those variables which were not normally distributed.
For the measured dichotomous variables, chi-square
tests were used to determine statistically significant
differences between groups. Statistical significance was
set at the p<0.05 level.
148
fig. 1 The photograph shown: an individual with the ability to
roll the tongue.
Method error
Repeated measurement of study casts were performed
by the same examiner on 20 randomly selected patients,
on two separate occasions one month apart. The error
of the method was calculated using Dahlberg’s formula
[Dahlberg, 1940], which is defined by √Σd2/2n (n=
number of patients undergoing repeated measurements;
d = difference in measurements). The error was found
to not exceed 0.8 mm except for space deficiency
measurements where it was found to be 1.4 mm.
Results
Prevalence estimation
The results of the prevalence study are shown in
Figure 2. The prevalence of TR+ was 66.4% for the
whole sample (n=392/590). No statistically significant
differences were found between male and female
patients. It was observed that TR+ prevalence was higher
in children aged 7 years and older, when compared to
those below the age of 7 (p<0.05).
Tongue rolling and occlusal characteristics
The study sample consisted of 51 males (mean age:
14.6 years) and 49 females (mean age: 13.6 years). In
this sample TR+ was present in 73/100 patients (37/51
males and 36/49 females).
Descriptive statistics and statistical comparisons of
measurements performed on dental casts are shown
in Table 1. No statistically significant differences were
found concerning Angle molar classification. Mandibular
intermolar distance showed to be statistically different
between the two groups, being 1 mm larger in the TR+
group than in the TR- group (p<0.05). Mandibular space
deficiency was 1.9 mm less in the TR+ than the TR- group,
this difference being statistically significant (p<0.05).
When recording mandibular space deficiency as a
dichotomous variable (present or absent), this was
present in 49.3% of TR- patients as compared to 18.5%
of TR+ patients (Fig. 3). A chi-square test showed this
difference to be statistically significant (p<0.05).
European Journal of Paediatric Dentistry vol. 15/2-2014
Tongue rolling and arch measures
100
100
90
90
80
80
70
60
Patients %
Prevalence (%)
70
50
40
30
60
Yes
50
No
40
30
20
20
10
10
0
4
5
6
7
8
9
10
11
12
0
Age (years)
TR+
fig. 2 Prevalence of tongue rolling in schoolchildren aged 4 to
12 years.
Dental cast measurements (mm)
TR+
TR-
mean ± SD
mean ± SD
Maxillary intercanine width
32.5 ± 3.1
32.9 ± 2.5
0,4
Mandibular intercanine width
26.5 ± 2.7
25.9 ± 2.9
0,6
Maxillary intermolar width
45.4 ± 3
45.3 ± 3.5
0,1
Mandibular intermolar width
41.3 ± 2.8
40.3 ± 2.8
1.0 *
Overjet
4.4 ± 2.4
4.3 ± 1.6
0,1
Overbite
3.2 ± 2
2.8 ± 1.7
0,4
Maxillary space deficiency
-1.7± 4.1
-2.0 ± 4.1
-0,3
Mandibular space deficiency
-1.1± 4.2
-3.0 ± 4.6
-1.9 *
Maxillary arch length
70.4 ± 5.1
70.2 ± 4.6
0,2
Mandibular arch length
MD
62.0 ± 5.2
59.9 ± 4.4
2,1
Measurements were performed to the nearest 0.1 mm. SD= standard deviation, MD= mean
difference.
p-values <0.05 were considered statistically significant and are marked with an asterisk.
Twelve TR+ patients (16.4%) presented with a
posterior crossbite compared to five TR- patients
(18.5%). A Pearson’s chi-square test failed to show a
statistically significant difference between the groups
regarding the existence of posterior crossbite.
Discussion and conclusion
The present study suggests that the ability to roll the
tongue may lead to differences in occlusal characteristics,
namely an increase in mandibular intermolar width
and less mandibular incisor space deficiency. The
null hypothesis can therefore be rejected. Orofacial
function and resting tongue position are reported to
play a significant role in the development of posterior
crossbite [Proffit, 2007; Thilander and Lennartsson,
2002]. Given that tongue rolling action is expressed in
the transverse dimension it could be hypothesized that
occlusal transverse differences might be found between
TR+ and TR- patients. No differences in the prevalence
of posterior crossbite were found between groups
however. Mandibular intermolar width, nevertheless,
European Journal of Paediatric Dentistry vol. 15/2-2014
TR-
fig. 3 Mandibular space deficiency in TR+ and TR- patients.
Yes = present; No = absent. Chi square=7.728, p-value<0.05.
tabLE 1 Maxillary
and mandibular dental
measurements used.
showed a larger width in TR+ patients. Despite statistical
significance, the 1 mm decrease in mandibular intermolar
distance in TR- patients may not be clinically significant
or important enough to create posterior crossbites.
Patients that were TR+ showed less mandibular space
deficiency than TR- patients. Although a statistically
significant difference was found, the error of the method
was rather large (1.4 mm) compared to the difference
of 1.9 mm found between groups. The clinical relevance
of this finding is thus questionable. When looking at
mandibular space deficiency as a dichotomous variable
(present or absent) however, a significant difference
was again found between groups. Tongue rolling could
thus offer a partial explanation for differences observed
in mandibular space deficiency. From the anatomical
and functional point of view, tongue rolling would seem
more closely related to mandibular space deficiency than
other associations that have already been established
for lower arch dental crowding, such as head posture
[Pachì et al., 2009]. One possible hypothesis is that the
ability to roll the tongue may be associated with a small
increase in the transverse dimension of the mandibular
arch and thus a larger arch perimeter would lead to less
149
Suárez C., Antonarakis G.S. and D. Pham
space deficiency.
It has been previously suggested that there may exist
a period in which tongue rolling is learned or developed.
Komai [1951] found that the prevalence of TR+ changes
with age and that only around 50% of children are TR+
before 7 years of age and that prevalence of TR+ stabilizes
to normal values at 12 years old. In our prevalence study
performed in 590 school children from 4-12 years of
age, similar results were obtained. At 7 years of age,
the prevalence of TR falls within the same values as
described by other authors [Hsu, 1948; Liu and Hsu,
1949; Urbanowski and Wilson, 1947]. Our study sample
therefore consisted of patients older than 7 years of age.
The prevalence study showed an increase in prevalence
that stabilises after the age of 7 years old. Rather than
developing the ability to roll their tongue, children below
7 years of age may sometimes be unaware of this ability
or are ashamed to show it during clinical examination
as we could corroborate. Prevalence of the trait is more
reliable when older children are taken into account as
was the case with our study sample.
The tongue may be important as regards differences
in occlusal characteristics, in aspects such as tongue
volume, resting posture, lateral forces, muscular
activity and function. The ability to roll the tongue, as
is shown in the present investigation, seems to give
some but limited insight into differences in occlusal
traits. The present study did not attempt to address
why occlusal differences exist from a functional
viewpoint, or the possible link between the genes
responsible for tongue rolling and those controlling
specific occlusal characteristics. Given the difficulties
in measuring characteristics of the tongue such as size,
tongue rolling might be used as a simple indicator of
tongue characteristics. Tongue movements require
synchronized actions of intrinsic and extrinsic tongue
muscles, and exactly which muscles are required to roll
the tongue is as yet unknown. Research looking into
the anatomical muscle variations between TR+ and TRpatients may be needed in order to better understand
tongue rolling and its significance in tongue posture and
function, as well as the development of malocclusion.
The understanding of muscular activity leading to
tongue rolling may help in grasping the complexity of
tongue movements and muscular control. Whether
this inherited trait is related to muscle tone, swallowing
patterns, or functional aberrations of the tongue, such
as tongue thrusting, requires further research.
Future studies using tongue rolling as a possible
simple clinical indicator of tongue characteristics, may
examine aspects such as post-orthodontic stability,
or late mandibular arch dental crowding. Differences
in stability regarding arch form, arch width, and
mandibular arch crowding between TR+ and TRindividuals may provide further insight into tongue
function and posture in these two groups of patients.
It has been proposed that myofunctional therapy can
150
be useful as an adjuvant to orthodontics in patients
with myofunctional dysfunction involving the tongue
[Saccomanno et al., 2012a; 2012b].
In conclusion, the present study suggests that the
ability to roll the tongue may partly lead to differences
in occlusal characteristics, namely an increase in
mandibular intermolar width and less mandibular space
deficiency. Many other factors however also play a role
in the development of occlusal characteristics.
Acknowledgements
The authors acknowledge the help of undergraduate
and postgraduate colleagues in the collection of the
patient sample. We equally acknowledge Dr. Marie
Cornelis for critically reviewing our manuscript.
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