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orthodontic waves 74 (2015) 69–75
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Original article
The relationship between maximum lip closing force and
tongue pressure according to lateral craniofacial morphology
Naosuke Doto DDS, PhD, Kazuhiro Yamada DDS, PhD*
Department of Orthodontics, Matsumoto Dental University, Shiojiri, Nagano, Japan
article info
abstract
Article history:
Purpose: The objectives of this study were to quantitatively evaluate the relationships
Received 29 August 2014
between maximum lip closing force (LCF) or maximum tongue pressure (TP) and lateral
Received in revised form
craniofacial morphology.
20 February 2015
Subjects and methods: The subjects comprised 62 female adult patients with malocclusion
Accepted 24 February 2015
(mean age: 26.4 7.7 years) without a history of orthodontic treatment, who were randomly
Available online 29 March 2015
selected from among the orthodontic patients at our hospital, and 10 adult female volunteers
who exhibited normal occlusion (mean age: 24.4 2.5 years). The patients were divided into
Keywords:
three groups: the skeletal Class I, II, and III groups. Maximum LCF was measured with the LCF
Lip-closing force
measuring device, and maximum TP was measured with the modified LCF measuring device.
Tongue pressure
Results: The maximum LCF of the skeletal Class II patients was significantly weaker than
Lateral craniofacial morphology
those of the skeletal Class III patients and the subjects with normal occlusion. However, no
Lip-closing force and tongue
significant differences in maximum TP or the maximum LCF/maximum TP balance index
pressure balance
were detected among the four groups.
Maximum LCF exhibited significant positive correlations with SNB, FMIA, and the interincisal angle and significant negative correlations with ANB, IMPA, and overjet. The maximum
LCF/maximum TP balance index demonstrated significant positive correlations with SNB and
the interincisal angle and significant negative correlations with ANB and overjet.
Conclusion: These results suggested that LCF is more closely involved than TP in compensatory inclination of the lower anterior teeth due to differences in the anteroposterior
positions of the upper and lower jaws.
# 2015 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved.
1.
Introduction
Since Tomes [1] indicated that soft tissues such as the lips,
cheeks, and tongue affect tooth position and play important
roles in dental arch formation and maintenance, many studies
have examined muscle strength around the oral cavity [2,3], and
the findings of such studies have been applied to treatments
such as myofunctional therapy in routine clinical practice [4].
Lip closing force (LCF) and tongue pressure (TP) have also
been studied extensively, as they are important for preventing
malocclusion and achieving post-orthodontic treatment
* Corresponding author at: Department of Orthodontics, Matsumoto Dental University, 1780 Gobara, Hirooka, Shiojiri, Nagano 399-0781,
Japan. Tel.: +81 263 51 2085; fax: +81 263 51 2085.
E-mail address: [email protected] (K. Yamada).
http://dx.doi.org/10.1016/j.odw.2015.02.004
1344-0241/# 2015 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved.
70
orthodontic waves 74 (2015) 69–75
stability [2,3,5,6]. Previous studies have reported that (1) LCF
affects upper and lower anterior tooth inclination [2,3,7], (2)
the LCF produced by subjects that exhibit Angle Class II
division 1 relationships are weaker than those produced by
subjects that display Angle Class I relationships [3,8], and (3)
TP is not related to craniofacial morphology [8]. However, the
associations between LCF or TP and inclination of the upper or
lower anterior teeth or anteroposterior craniofacial morphology are unclear.
Therefore, the present study aimed to investigate the
possible correlations between lateral craniofacial morphology
or anterior tooth inclination and maximum LCF or TP. This
study examined the hypothesis that maximum LCF and TP are
related to lateral craniofacial morphology.
2.
Subjects and methods
2.1.
Subjects
The subjects comprised 62 adult females with malocclusion
(mean age: 26.4 7.7 years), who were randomly selected from
among the patients at the Department of Orthodontics,
Matsumoto Dental University, and 10 adult female volunteers
with normal occlusion (mean age: 24.4 2.5 years). Normal
occlusion was defined as follows: Class I molar and canine
relationships, a normal overjet and overbite, and the absence
of crowding. The exclusion criteria were as follows: A history
of orthodontic treatment; missing teeth including congenitally
missing teeth (excluding the upper and lower wisdom teeth);
marked mandibular deviation (mandibular menton deviation
of 4 mm or more from the middle of the face on posteroanterior cephalograms); congenital abnormalities present;
bad oral habits that influenced the position of the tongue and
lip sealing, such as tongue thrusting or a low tongue position;
and mouth breathing.
This study was initiated with the prior approval of the
ethics committee of Matsumoto Dental University. The
objective, procedures, methods, benefits, and disadvantages
of the study were explained to each subject in detail, and
informed consent was obtained from each subject prior to
their participation.
tracings separated by two-week intervals [10]. The paired-t
test did not detect significant measurement error (at the
0.05 level). These calculations indicated that the measurement
error ranged from 0 to 1.438 for the angular data and from 0 to
0.11 mm for the linear data. A probability level of less than 5%
( p < 0.05) was considered to be significant.
2.3.
Measurement of maximum LCF and TP
Maximum LCF was measured using the LIP DE CUM1 LDC110R LCF measuring device (Cosmo Instruments Co., Ltd.,
Tokyo, Japan) (Fig. 1). The LIP DE CUM1 displays pressure
values, which it produces by converting the resistance data
collected by its strain gauge. The resultant values are
displayed in newtons (N) as the device measures the force
exerted in the perpendicular direction to its sensor. The LIP DE
CUM1 LDC-110R has a measurement range of 50.0 N and a
measurement error of 0.5% F.S. When measuring maximum
LCF, the subjects were instructed to close their lips with the
strongest force possible without clenching their upper and
lower teeth together (Fig. 2).
A LIP DE CUM1 LDC-110R with a modified sensor was used
to measure maximum TP (Fig. 3); i.e., a stainless steel bracket
was attached to the sensor of the LCF measurement device.
The measurement range and error of the modified device were
the same as those described above. During the maximum TP
measurements, the subjects were instructed to place the
sensor tip in the upper incisive papilla region and press down
on it with their tongue as hard as possible (Fig. 4). We used the
location at which the tongue and maxilla came into contact at
rest as the TP measurement site. For both the maximum LCF
and TP measurements, the subjects practiced the required
movements five times before five measurements were
2.2.
Measurement methods of Lateral cephalometric
radiographs
Lateral cephalograms were obtained whilst the subjects’ teeth
were in the intercuspal position and were traced by one of the
authors. Nine angular measurements and two linear measurements were obtained from the lateral cephalograms (SNA,
SNB, ANB, FMA, the gonial angle, U1 to FH, IMPA, FMIA,
interincisal angle, overbite, and overjet). The female subjects
with malocclusion were classified into the skeletal Class I,
Class II, and Class III groups according to their ANB values as
follows: Skeletal Class I: 18 ANB 48 (19 cases, mean age:
26.4 6.6 years), Skeletal Class II: 48 < ANB (24 cases, mean
age: 28.5 9.1 years) and Skeletal Class III: ANB < 18 (19 cases,
mean age: 24.4 6.0 years) [9].
Measurement error was determined using Dahlberg’s
formula in 10 randomly selected subjects based on pairs of
Fig. 1 – Lip closing force measurement device.
orthodontic waves 74 (2015) 69–75
71
formula is that when the value of this formula is near zero, the
maximum LCF balance with maximum TP. When the value of
this formula is plus, the value of maximum LCF is larger than
that of maximum TP and when the value of this formula is
minus, the value of maximum TP is larger than that of
maximum LCF. The difference of the maximum LCF and TP
divided by the sum of the maximum LCF and TP leads to the
standardization for the value of difference. The reproducibility
of the LCF and TP measurements was assessed using
coefficients of variation.
2.4.
Statistical analysis
The statistical analysis involved comparing maximum LCF,
maximum TP, and the maximum LCF/maximum TP balance
index between the four groups of subjects using the Kruskal
Wallis test and a post hoc test (Games-Howell test). Spearman’s rank correlation coefficient was also used to investigate
the correlations between lateral craniofacial morphology and
maximum LCF, maximum TP, or the maximum LCF/maximum TP balance index in the 62 subjects with malocclusion.
The software SPSS (Ver.14.0, SPSS, IBM Japan, Tokyo, Japan)
was used for all statistical analyses.
3.
Fig. 2 – Measurement of maximum lip closing force.
obtained. The mean values of the five measurements were
then calculated.
In addition, the maximum LCF/maximum TP balance index
LCF maximum
TP) 100/(maximum
[(maximum
LCF + maximum TP)] was calculated in order to examine the
balance between maximum LCF and TP. The meaning of this
Results
3.1.
Comparison of cephalometric measurements among
the four groups (Table 1)
Table 1 shows a comparison of the cephalometric measurements of the four groups. SNB, ANB, FMA, IMPA, FMIA, the
interincisal angle, overbite, and overjet all differed significantly among the four groups. The mean IMPA of the
subjects that exhibited skeletal Class I relationships was
significantly smaller than those of the subjects that
displayed normal occlusion. The ANB, FMA, and overjet of
the patients that demonstrated skeletal Class II relationships were significantly larger than those of the subjects
that exhibited normal occlusion. The ANB, IMPA, overbite,
and overjet of the subjects that displayed skeletal Class III
relationships were significantly smaller than those of the
subjects that exhibited normal occlusion, and the mean
FMIA of the former group was significantly larger than that
of the latter group.
3.2.
Comparison of maximum LCF and TP measurements
(Fig. 5)
Fig. 3 – Tongue pressure measuring device.
The CV of LCF and TP ranged from 7.3% to 15.1% (mean:
10.4 2.8%) and from 4.9% to 11.0% (mean: 7.8 1.9),
respectively.
Maximum LCF was 10.0 2.24 N in the subjects who
exhibited normal occlusion, and 7.0 3.69 N, 6.2 2.06 N,
and 8.4 2.49 N in those who displayed skeletal Class I, Class
II, and Class III relationships, respectively. A significant
difference was detected among the four groups, with the
subjects who exhibited normal occlusion or skeletal Class III
relationships exhibiting significantly larger values than those
who displayed skeletal Class II relationships. Maximum TP
72
orthodontic waves 74 (2015) 69–75
Fig. 4 – Measurement of maximum tongue pressure. Sensor position: Incisive papilla region.
was 7.0 3.68 N in the subjects with normal occlusion and
5.6 2.29 N, 5.6 2.09 N, and 6.5 2.61 N in the subjects who
demonstrated skeletal Class I, Class II, and Class III relationships, respectively, and no significant differences were
detected among the groups. The maximum LCF/maximum
TP balance index was 15.0 25.1% in the subjects with normal
occlusion and 9.3 24.9%, 10.8 22.95%, and 19.7 24.8% in
the subjects with skeletal Class I, Class II, and Class III
relationships, respectively, and no significant differences were
detected among the groups.
Table 1 – Comparison of cephalometric measurements among four groups.
Normal
occlusion
SNA
SNB
ANB
FMA
Gonial
angle
U1toFH
IMPA
FMIA
Interincisal
angle
Overbite
Overjet
Skeletal
Class II
Skeletal
Class III
Kruskal–
Wallis
Mean
SD
Mean
SD
Mean
SD
Mean
SD
80.40
77.50
2.90
23.20
117.00
2.989
2.718
0.876
5.224
10.033
82.16
79.21
2.95
28.82
123.55
3.395
3.599
0.667
6.083
7.481
81.42
74.79
6.63
33.00
125.57
3.496
3.987
1.949
6.299
6.388
80.61
81.39
0.79
27.84
125.58
4.115
4.999
2.104
6.338
7.275
NS
111.90
102.00
54.80
123.50
4.812
5.831
6.812
7.517
116.63
92.61
58.58
122.03
7.172
8.882
7.064
12.221
113.50
98.50
48.41
114.80
9.540
5.949
7.957
12.194
117.68
88.63
63.79
125.87
6.214
6.946
7.156
10.109
2.25
2.80
0.858
0.919
1.32
2.95
1.575
2.660
2.93
5.78
2.587
2.842
0.16
0.29
2.173
2.632
NS: not significant.
p < 0.05.
**
p < 0.01.
***
p < 0.001.
*
Skeletal
Class I
Games-Howell
N vs. N vs. N vs. C I vs. C I vs. C II vs.
CI
C II
C III
C II
C III
C III
NS
NS
NS
NS
NS
***
***
**
NS
NS
NS
NS
NS
NS
NS
NS
***
*
***
NS
NS
***
***
**
*
***
***
NS
NS
NS
NS
NS
***
***
***
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
**
***
*
***
NS
NS
NS
NS
NS
NS
NS
*
NS
NS
**
***
***
*
**
***
***
***
***
*
orthodontic waves 74 (2015) 69–75
73
the dentition, maximum LCF displayed significant positive
correlations with FMIA and the interincisal angle and
significant negative correlations with IMPA and overjet.
Maximum TP did not exhibit significant correlations with
any lateral craniofacial morphological parameter. However,
the maximum LCF/maximum TP balance index demonstrated
significant positive correlations with SNB and the interincisal
angle and significant negative correlations with ANB and
overjet.
4.
Fig. 5 – Comparison of maximum lip closing force (LCF) and
tongue pressure (TP).
3.3.
Relationships between lateral craniofacial
morphology and maximum LCF or TP (Table 2)
With regard to the relationship between maximum LCF and
skeletal pattern, maximum LCF exhibited a significant positive
correlation with SNB and a significant negative correlation
with ANB. As for the relationship between maximum LCF and
Table 2 – Relationship between maximum lip closing
force and maximum tongue pressure with lateral craniofacial morphology (Spearman correlation coefficient).
Maximum
LCF
SNA
SNB
ANB
FMA
Gonial angle
U1 to FH
IMPA
FMIA
Interincisal angle
Overbite
Overjet
**
p < 0.01.
0.136
0.383**
0.359**
0.239
0.107
0.137
0.256**
0.334**
0.399**
0.062
0.386**
Maximum
TP
0.006
0.035
0.050
0.097
0.067
0.0003
0.116
0.049
0.059
0.204
0.114
Maximum
LCF/Maximum
TP
0.114
0.318**
0.305**
0.220
0.105
0.093
0.146
0.238
0.277**
0.177
0.375**
Discussion
Many studies have investigated the relationships between
lateral craniofacial morphology and LCF or TP [2,3,5]. Such
studies have suggested that the position of the dentition is
affected by pressure from the lips, the muscles around the
intraoral area, and the tongue. Specifically, it is considered
that the position of the dentition is determined by the balance
between the forces exerted by the orbicularis oris muscle,
buccinator muscles, and tongue, which is known as the
buccinator mechanism [11], and imbalances in this mechanism can lead to various types of malocclusion. Numerous
studies have investigated the relationships between LCF or TP
and the position of the dentition. Graber considered the
influence of tongue position and tongue size along with the
size of mandible to be important factors in dental arch and
bone formation [12]. As for the relationship between the sizes
of the tongue and mandible, Bandy et al. reported that the
diameter of the dental arch increases with tongue volume [13].
However, Scott who doubted the buccinator mechanism
theory, suggested that the form and position of the dental
arch are determined more by the growth of the alveolar
process itself independently of the pressure exerted by
neighboring soft tissue [14].
In a comparison of maximum LCF and TP according to
skeletal classification, the present study showed that the
maximum LCF values of the patients who exhibited skeletal
Class III relationships or normal occlusion were significantly
greater than that of the subjects who displayed skeletal Class II
relationships. On the other hand, no such differences were
observed during comparisons of maximum TP. Posen [8]
reported that skeletal Class II patients display weak maximum
LCF, which is consistent with the results of the present study.
However, Ueki et al. [15] reported that skeletal Class III patients
exhibited weaker maximum LCF than subjects with normal
occlusion, which disagrees with our results. The subjects who
displayed skeletal Class III relationships in Ueki’s study [15]
required orthognathic surgery. On the other hand, in our
study, the subjects who displayed ANB values of <18 were
considered to have skeletal Class III relationships. Therefore,
the abovementioned discrepancies between our results and
Ueki’s regarding the maximum LCF of individuals that exhibit
skeletal Class III relationships might have been due to
differences in the positions of the subjects’ maxillae and
mandibles. On the other hand, there was no significant
difference in maximum LCF among the subjects that displayed
skeletal Class I or II relationships and those that demonstrated
normal occlusion. FMA differed significantly among the four
groups, and the subjects that displayed skeletal Class II
74
orthodontic waves 74 (2015) 69–75
relationships exhibited larger FMA than those in the other
groups. Therefore, maximum LCF might be affected by vertical
skeletal facial pattern. Further study will be needed to
elucidate the association of vertical skeletal facial pattern to
maximum LCF and TP.
As for the relationships between maximum LCF or TP and
craniofacial morphological parameters, the maximum LCF
was found to exhibit weak positive associations with SNB
(r = 0.383), FMIA (r = 0.334), and the interincisal angle (r = 0.399)
and weak negative associations with ANB (r = 0.359), IMPA
(r = 0.256), and overjet (r = 0.386). These results indicate
that higher maximum LCF values result in the mandible being
positioned anterior to the maxilla, reducing overjet, with the
lower anterior teeth inclined lingually to compensate. Our
findings were consistent with those of a previous study that
examined lingual inclination of the lower incisors [7] and
another study in which subjects with Angle Class II division 1
relationships exhibited weaker LCF than those with Angle
Class I relationships [3].
The detection of correlations between the maximum
LCF/maximum TP balance index and lateral craniofacial
morphological parameters indicated that when the maximum
LCF was stronger than the maximum TP, ANB and overjet were
small and SNB and the interincisal angle were large. On the
other hand, when the maximum LCF was weaker than the
maximum TP, ANB and overjet were large and SNB and the
interincisal angle were small. These results were consistent
with those of a previous study by Maeda [7], who found that
strong LCF were associated with upper and lower incisor
inclination. Our findings also agreed with those of the studies
by Posen [8] and Lambrechts [3] on the difference in LCF
between subjects with Angle Class I and Class II relationships.
However, it has not been elucidated how the balance between
LCF and TP is affected by craniofacial morphology. The present
study suggested that the maximum LCF/maximum TP balance is
related to the anteroposterior positions of the maxilla and
mandible and the inclination of the upper and lower anterior
teeth. However, the present study also found that the associations between the craniofacial morphology parameters and LCF
or TP exhibited low correlation coefficients of 0.4. The
inclination of the upper and lower incisors can be affected by
skeletal pattern. However, incisor inclination can also be affected
by arch dimensions, especially intercanine width and depth. The
weak correlations detected between the craniofacial morphology
parameters and LCF or TP in the present study suggest that the
other factors, such as intercanine width and depth, might
influence lateral craniofacial morphology. In future, detailed
studies will be needed to elucidate the associations between
craniofacial morphology and LCF, TP, or other factors.
However, while our comparisons of maximum LCF and TP
among the different skeletal classification groups indicated
that the maximum LCF of the skeletal Class III patients was
significantly greater than that of the skeletal Class II patients,
no such significant difference in maximum TP was observed
between these two groups. Moreover, maximum TP did not
exhibit a significant correlation with any of the examined
lateral cephalogram measurements. This suggests that LCF
plays a greater role than TP in the compensatory lingual
inclination of the lower anterior teeth induced in response to
differences in the anteroposterior positions of the maxilla and
mandible. According to Frederick [16,17], the buccinator strap,
which controls the form of the alveolar process and the
dentition, is heavily involved in determining the position of
the dentition based on the effects of the forces produced by the
lips, cheeks, and tongue. This is also true of the lower labial
orbicularis oris muscle, which particularly affects the anteroposterior positioning of the anterior teeth and the volume of
the associated gingiva. As for the relationship between
maximum TP and the dentition there was no difference
among the 4 groups, which was consistent with the findings of
a previous study [3,8]. Patients with functional abnormalities
of the tongue or lips such as a habit of tongue thrusting or lip
closure dysfunction were excluded from the present study.
Further studies involving such patients are required in order to
investigate the correlations between lateral cephalogram
measurements and LCF or TP.
Problems with adapting to a new soft tissue environment
can cause relapses after orthodontic treatment. It has been
reported that dental stability cannot be achieved if an
imbalance between the pressure from the inner side of the
dentition produced by the tongue and that from the outer side
of the dentition produced by the lips develops after orthodontic treatment [18–21]. Functional therapy is considered to be
effective at preventing such relapses. As lip closing movements are mainly performed by the orbicularis oris, buccinator, and mentalis muscles, functional therapy is important for
improving the balance between these muscles and TP. The
present study suggested that in subjects with normal lip and
tongue function LCF plays a more important role than TP in
compensatory inclination of the lower anterior teeth due to
differences in the anteroposterior positions of the upper and
lower jaws. In the future, further studies investigating the
correlations between imbalances in LCF and TP and the
relapse of dental problems after orthodontic treatment will
need to be performed.
Conflict of interest
The authors declare that there is no conflict of interest.
Acknowledgements
This study was supported by a Grant-in-Aid for Scientific
Research (25463205) from the Ministry of Education, Culture,
Sports, Science, and Technology, Japan. The authors declare
that no competing interests exist.
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