Longitudinal course of temporomandibular joint sounds in Japanese children and adolescents.

RESEARCH Open Access
Longitudinal course of temporomandibular joint
sounds in Japanese children and adolescents
Kengo Torii
Abstract
Background: Many epidemiological studies of temporomandibular disorders (TMDs) in children and adolescents
have been performed. However, the results of such studies have varied, and a comprehensive view of the
prevalence and severity of symptoms and signs is difficult to obtain. In the present study, temporomandibular joint
(TMJ) sounds, which are the most common signs and symptoms of TMD, were observed longitudinally, and the
need for treatment was evaluated.
Methods: Seventy individuals in six age groups (5, 6, 7, 8, 9, and 10 years old at the beginning of the observation
period) participated in an epidemiological investigation conducted between 1987 and 1992. During each clinical
examination, the following parameters were examined: maximum unassisted jaw opening, TMJ clicking, and the
coincidence or difference between the midlines of the upper central incisors and the lower central incisors. In
addition, the bilateral bite force was recorded, and the numbers of erupted, decayed, and filled teeth were
recorded.
Results: Eight individuals dropped out because they moved. No TMJ dysfunction requiring treatment was
observed in this series. TMJ clicking was observed in 30 subjects (48%); however, this symptom was temporary in
most of subjects (26 subjects; 42%), and only 3 subjects (5%) had persistent clicking (continuing until the end of
the observation period). The incidences of clicking were not significantly different among the six groups (x2 =
4.265). Clicking was significantly more common among girls (19 subjects) than among boys (11 subjects; P =
0.042). A significantly lower bite force (17 ± 18 kg) was recorded for the subjects with persistent clicking, compared
with that of the other subjects (8- and 9-year-olds; mixed dentition) without persistent clicking (32 ± 17 kg). The
persistent clicking began at an age of 11 or 12 years (permanent dentition).
Conclusion: Most of the clicking observed in the children and adolescents was temporary, and no difference in
the incidence of clicking was observed among the six age groups. Girls had a significantly higher incidence of
clicking than boys.
Background
Since the end of the 1970s, several epidemiological stu-
dies on the signs and symptoms of temporomandibular
disorder (TMD) in children and adolescents have been
performed [1-9]. However, the frequencies of the most
common signs and symptoms varied greatly among
these studies. In addition, whether these signs and
symptoms were persistent was unclear. Therefore, the
present longitudinal study focused on the most common
and greater relevant sign of TMD [2,5,8]: temporoman-
dibular joint (TMJ) sounds. Since
TMJ are reportedly related to the occlusal discrepancy
between the habitual occlusal position and the bite
plate-induced occlusal position [10], the present study
also recorded the bite force [11] and the number of
decayed and filled teeth in each subject as possible cau-
sative factors of the occlusal discrepancy [12].
Materials and methods
The present epidemiological study was performed dur-
ing regular oral health examinations performed in the
spring and autumn of each year at Ikawa kindergarten,
Ikawa elementary school and Ikawa junior high school
in Shizuoka city. The study protocol was approved by
the department of prosthodontics, Nippon Dental
Correspondence: wbs89508@mail.wbs.ne.jp
Department of Prosthodontics, School of Life Dentistry, Nippon Dental
University, 1-9-20 Fujimi, Chiyoda-ku, Tokyo, 102-8159, Japan
Torii Head & Face Medicine 2011, 7:17
http://www.head-face-med.com/content/7/1/17
HEAD & FACE MEDICINE
© 2011 Torii; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.

University, because the university did not have an ethi-
cal committee at that time. The study was also approved
by the local education authority and the parent’s coun-
cil. All the parents of the participants provided their
oral informed consent. The participants were divided
into six groups: the group 1 consisted of 11 subjects
who were 5 years old at the beginning of the study,
group 2 consisted of 13 subjects who were 6 years old,
group 3 consisted of 13 subjects who were 7 years old,
group 4 consisted of 13 subjects who were 8 years old,
group 5 consisted of 8 subjects who were 9 years old,
and group 6 consisted of 10 subjects aged 10 years old.
The examinations were performed twice (in spring and
autumn) each year from 1987 to 1992. In 1987 and
1989, only one examination was performed each year.
Eight participants dropped out of study because they
moved.
Clinical examinations
All the individuals participating in the study were exam-
ined clinically by two experienced dentists according to
the specifications for TMD examinations [13]. The fol-
lowing parameters were recorded:
1. Maximum unassisted jaw opening.
2. Deflection on jaw opening.
3. TMJ clicking or crepitations, TMJ locking, TMJ
luxation and TMJ pain.
4. Coincidence or difference between the midlines of
the upper central incisors and the lower central incisors.
5. Numbers of decayed teeth or filled teeth.
6. Number of erupted teeth.
In addition, another dentist measured the bite force at
the second deciduous molars in the primary dentition
or the first molars in mixed or permanent dentitions
using an occlusal force meter (MPM 3000, NIHON
KOHDEN, Tokyo, Japan). Three measurements were
performed on each side after asking the subject to bite
as strongly as possible, and the mean value for each side
was totaled and regarded as the bilateral bite force [11].
Statistical analysis
A chi-square test was used to analyze the distributions
of the variables in different groups of subjects on a
nominal scale and the Fisher exact test was also used on
a nominal scale. The statistical differences between
mean values were evaluated using a t-test (including the
Cochran-Cox method).
Results
None of the subjects with TMJ dysfunction required
treatment in this series. The distribution of the inci-
dence of TMJ clicking is shown in Table 1. Clicking was
observed in 30 subjects (48%); however, this symptom
was temporary (26 subjects; 42%), and only 3 subjects
Table 1 Incidences of TMJ clicking among six age groups
Group No. 1987 1988 1989 1990 1991 1992
2 □ □
6 □ □ □
G1 7 □ □
10 □ □
12 □ □ □ □ □ □
13 □
18 □ □ □ □ □ □
G2 21 □
23 □ □
24 □
25 □
27 □ □
30 □ □
G3 31 □ □ ■ □ □ □ □
32 □ □
33 □
34 □
37 □
38 □
39 □ □ □
G4 40 □
42 □ □
46 □ □ □ □ □ □ □
47 □ □
G5 49 □
59 □ □ □ □ □ □ □ ■ ■
60 □ □ □ □ □ ■ ■
G6 65 □ □ □ □
67 □
68 □
G1: group of subjects aged 5 years old at beginning of observation; G2: group
of subjects aged 6 years old; G3: group of subjects aged 7 years old; G4:
group of subjects aged 8 years old; G5: group of subjects aged 9byears old
and G6: group of subjects aged 10 years old. The examinations were
performed twice each year except in 1987 and 1989 (only one examination
was performed in each these years). No.: Subject number; □: Clicking; ■:
Crepitation.
Table 2 Contingency table for the number of subjects
with and those without TMJ clicking
Group with clicking without clicking total
G1 5 4 9
G2 6 6 12
G3 3 7 10
G4 6 7 13
G5 4 1 5
G6 8 5 13
X2 = 4.265 < X2(P = 0.5): not significant.
Torii Head & Face Medicine 2011, 7:17
http://www.head-face-med.com/content/7/1/17
Page 2 of 5

(5%) had persistent clicking (continuing until the end of
the observation period). The incidences of clicking were
not significantly different among the six groups (Table
2). Clicking was significantly more common among girls
than among boys (Table 3). The midline difference
between the upper and lower central incisors was not
correlated with clicking (Table 4). Six subjects had click-
ing for more than two years, and the maximum unas-
sisted opening, maximum bite force, and the number of
decayed and filled teeth among these subjects were
compared with these parameters in other subjects
belonging to the same age group. No statistically signifi-
cant differences in the maximum opening were found
between subjects with and those without persistent
clicking (Table 5). Regarding the maximum bite force,
only two subjects (No. 31 and 46) with persistent click-
ing had a significantly lower maximum bite force than
the other subjects during the early period of observation
(their ages were 8 and 9 years old, respectively; mixed
dentition; see Table 6). No significant differences in the
number of decayed, filled, and the total number of
decayed and/or filled teeth were found between subjects
with and those without persistent clicking (Table 7).
Discussion
Kӧhler et al. reported in their cross-sectional epidemio-
logical study covering two decades that the incidences
of TMJ clicking and crepitation in 10-year-old children
were 14% in 1983, 3% in 1993, and 5% in 2003. Wid-
malm et al. [4] reported that the percentage of TMJ
sounds was 47.8% among 4-6-year-old children. Mag-
nusson et al. [3] reported in their longitudinal epidemio-
logical study that the incidence of TMJ sounds changed
from 5% among 7-year-old subjects to 30% among 11-
year-old subjects. Recently, Tecco et al. reported that
the percentages of TMJ sounds were 1.75% among
subjects aged 5-11 years old and 8.21% among subjects
aged 12-15 years old. In the present study, the overall
incidence of TMJ clicking was 48.3%, but when calcu-
lated on a yearly basis, the incidences were 15% in 1987,
11% in 1988, 13% in 1989, 19% in 1990, 11% in1991 and
11% in 1992. Thus, the incidence fluctuated over time.
In the present study, most of the TMJ clicking was tem-
porary, but persistent clicking was observed in 3 sub-
jects. The persistent clicking began when the subjects
were 11 or 12 years old, and the clicking ultimately
changed to crepitation. Persistent clicking is thought to
be a more important symptom than temporary clicking,
since persistent clicking or crepitation can cause TMJ
locking, resulting in a need for treatment. In the studies
reported by Widmalm et al. [4] and Tecco et al. [6], the
difference in incidence according to sex was not signifi-
cant; in the present study, however, the incidence was
higher among girls than among boys. Magnusson et al.
[7] reported that the incidence of one or more subjec-
tive symptoms of TMJ sounds, jaw fatigue, difficulties in
mouth opening, and pain during chewing was higher
among women than among men (P < 0.05). The higher
incidence among girls in the present study may reflect
the higher tendency of TMD symptoms to appear in
women. Magnusson et al. [7] reported that a positive
correlation was found between subjective TMJ sound
and one or more subjective symptoms of TMD. Kӧnӧ-
nen and Nystrӧm [8] reported that TMJ sounds were
the most frequent findings and increased with age, but
only a few patients consistently reported clicking sounds
or had them recorded in their longitudinal study.
In subjects less than 10 years of age, the dentition is
generally a mixture of deciduous and permanent teeth.
During the mixed dentition stage, numerous occlusal
interferences are present, and the muscles must repeat-
edly learn new patterns of mandibular closure to avoid
interfering or decayed teeth. The pathway of centric
relation (muscular centric position), having only been
established in the central nervous system for a short
time, is not as entrenched as it is in adults. No repeat-
edly used position of occlusal contact that does not
coincide with the centric relation is ever acquired by
chance.
Consequently, a discrepancy between the habitual
occlusal position and the muscular centric position (bite
plate-induced occlusal position) emerges, resulting in
temporary clicking. In the present study, as no relation-
ships were observed between persistent clicking and the
numbers of decayed, filled or total decayed and/or filled
teeth, the avoidance of decayed or filled teeth was not
thought to be a cause of the occlusal discrepancy. These
results suggest that persistent clicking was not caused
by iatrogenic factors. Generally, teeth that erupt in a
malposition that does not coincide with the centric
Table 3 Contingency table for male and female subjects
with or without TMJ clicking
Gender with clicking without clicking total
Male 11 19 32
Female 19 12 30
P = 0.042 (The relationship between girls and clicking was significant when
evaluated using the Fisher exact test).
Table 4 Contingency table for number of subjects with
and those without TMJ clicking related to difference or
coincidence between the midlines of the upper central
incisors and the lower central incisors
Midline discrepancy with clicking without clicking total
No discrepancy 16 16 32
Discrepancy 18 12 30
P = 0.149: not significant.
Torii Head & Face Medicine 2011, 7:17
http://www.head-face-med.com/content/7/1/17
Page 3 of 5

relation may have been repositioned into the correct
position coinciding with the centric relation by muscular
force, that is the bite force. Under conditions in which
an occlusal discrepancy exists until the tooth is reposi-
tioned into the correct position, temporary clicking may
be produced. However, if the bite force is small before
the completion of the permanent dentition, the malposi-
tion of the occlusion will be maintained. Once the per-
manent dentition stage has been reached, usually at an
age of 10-12 years, the muscles frequently adopt an
occlusal position that does not coincide with the centric
relation. This new position of occlusal contact usually
begins as an expedient process to avoid interferences,
providing better function than the centric relation pro-
vides at that moment. The continued presence of the
occlusal discrepancy causes the new reflex pattern of
the pathway to be used so repeatedly that the new posi-
tion of the mandible may resemble the centric relation.
This acquired position can be regarded as the usual or
habitual occlusal position [12]. In the present study,
subjects No. 31 and 46 had a significantly smaller bite
force at the ages 8 and 9 years old, respectively (mixed
dentition); thus, the occlusal discrepancy may have
appeared as a result of the small bite force, and this dis-
crepancy may have been maintained once the perma-
nent dentition was achieved, resulting in the persistent
clicking. Although no data on the occlusal force at the
ages of 8 or 9 years were available for subjects No. 59
and 60, the occlusal forces of these two subjects tended
to be smaller than those of the others at later stage (dif-
ference not significant; see Table 6). Therefore, the
Table 5 Unassisted maximum opening (mm) in subjects with and those without persistent TMJ clicking (continuing for
more than two years)
Subjects 1988 1989 1990 1991 1992
No. 12 and 18 41.0 ± 0 41.5 ± 2.1 45.0 ± 4.2 50.0 ± 1.4 45.0 ± 0
Other subjects 42.4 ± 2.8 44.7 ± 4.4 45.6 ± 3.4 45.8 ± 3.2 45.4 ± 3.2
No. 31 and 46 45.5 ± 6.4 48.0 ± 4.2 47.0 ± 1.4 44.5 ± 0.7 47.0 ± 4.2
Other subjects 42.5 ± 4.2 45.5 ± 1.0 46.1 ± 1.0 47.0 ± 3.0 56.9 ± 5.5
No. 59 and 60 49.7 ± 3.2 53.0 ± 5.6 57.5 ± 4.9 60.5 ± 7.8 62.0 ± 5.7
Other subjects 45.0 ± 4.8 47.7 ± 4.0 47.8 ± 3.9 49.5 ± 3.9 50.4 ± 3.5
Table 6 Maximum bite force (kg) of subjects with and those without persistent TMJ clicking (continuing for more than
two years)
Subjects 1988 1989 1990 1991 1992
No. 12 and 18 29.5 ± 2.1 39.5 ± 2.1 39.5 ± 12.0 72.0 ± 19.8 50.5 ± 12.0
Other subjects 30.4 ± 12.5 36.8 ± 17.7 47.1 ± 20.6 46.6 ± 20.0 50.7 ± 27.1
No. 31 and 46 17.0 ± 18.4 † 27.0 ± 21.2 25.5 ± 26.2 17.0 ± 14.1 38.0 ± 31.1
Other subjects 31.5 ± 17.0 40.0 ± 23.2 50.0 ± 27.1 44.0 ± 22.5 52.8 ± 17.1
No. 59 and 60 29.7 ± 10.0 50.7 ± 10.0 46.5 ± 13.4 58.0 ± 0 49.0 ± 11.3
Other subjects 43.8 ± 8.6 52.6 ± 17.7 56.6 ± 22.0 62.8 ± 31.4 75.3 ± 31.3
†P < 0.005: significant
Table 7 Number of filled (T1), decayed (T2) and total
number of filled and/or decayed (T1 + T2) of subjects
with or without persistent TMJ clicking (continuing for
more than two years)
Subjects 1988 1989 1990 1991 1992
No. 12 and 18
T1 4.0 ± 0 n.r. 3.5 ± 2.1 8.0 ± 1.4 1.0 ± 1.4
T2 7.5 ± 0.7 n.r. 7.0 ± 2.8 2.5 ± 3.5 1.0 ± 1.4
T1 + T2 11.5 ± 0.7 n.r. 10.5 ± 4.9 10.5 ± 4.9 2.0 ± 0
Other subjects
T1 2.5 ± 2.8 n.r. 5.6 ± 3.5 7.3 ± 4.0 3.0 ± 2.1
T2 3.2 ± 4.1 n.r. 2.6 ± 3.4 1.0 ± 1.0 0.2 ± 0.5
T1 + T2 5.7 ± 5.2 n.r. 8.5 ± 5.2 8.3 ± 4.5 3.3 ± 1.8
No. 31 and 46
T1 3.0 ± 4.2 n.r. 0 7.5 ± 2.1 1.0 ± 1.4
T2 7.5 ± 7.8 n.r. 6.0 ± 8.5 3.5 ± 4.9 3.5 ± 4.9
T1 and T2 10.5 ± 3.5 n.r. 6.0 ± 8.5 11.0 ± 2.8 4.5 ± 3.5
Other subjects
T1 3.6 ± 2.9 n.r. 5.5 ± 3.0 6.6 ± 3.5 2.6 ± 2.1
T2 3.6 ± 3.4 n.r. 1.7 ± 2.3 1.0 ± 1.2 1.2 ± 1.9
T1 + T2 7.4 ± 3.9 n.r. 7.2 ± 3.6 7.7 ± 3.6 3.8 ± 2.7
No. 59 and 60
T1 2.0 ± 0 n.r. 2.5 ± 2.1 3.0 ± 1.4 5.5 ± 0.7
T2 2.0 ± 0 n.r. 1.5 ± 2.1 2.5 ± 2.1 0.5 ± 0.7
T1 + T2 4.0 ± 0 n.r. 4.0 ± 0 5.5 ± 0.7 6.0 ± 0
Other subjects
T1 2.2 ± 1.8 n.r. 3.4 ± 1.9 3.4 ± 1.1 3.8 ± 1.6
T2 2.7 ± 2.8 n.r. 1.1 ± 1.6 1.1 ± 1.4 0.7 ± 0.8
T1 + T2 5.0 ± n.r. 4.5 ± 2.0 5.5 ± 0.7 4.6 ± 1.9
n.r.: not registered
Torii Head & Face Medicine 2011, 7:17
http://www.head-face-med.com/content/7/1/17
Page 4 of 5

persistent clicking in these subjects was thought to have
been caused by an occlusal discrepancy that emerged as
a result of a small bite force during the mixed-dentition
stage. For individuals with persistent clicking, the exami-
ner in charge of routine dental and oral health examina-
tions should tell the subject to visit a dental clinic if
TMJ locking or other TMD symptoms should appear.
Conclusions
Although the population size in the present study was
relatively small, the following conclusions were obtained:
1. Among 5-15-year-old children and adolescents,
most cases of TMJ clicking were temporary, and no dif-
ferences in the incidence of clicking were observed
among the six age groups.
2. Girls had a significantly higher incidence of clicking
than boys.
3. A few subjects had persistent clicking, beginning at
11 or 12 years of age once the permanent dentition had
been achieved.
Author details
Visiting professor, School of Life Dentistry, Nippon
Dental University, Tokyo, 1-9-20 Fujimi, Chiyoda-ku,
Tokyo, 102-8159 Japan
Acknowledgements
The author is grateful to the teaching staff at Ikawa kindergarten, Ikawa
elementary school and Ikawa junior high school for their cooperation.
Authors’ contributions
KT conceived the study, participated in the study’s design, and performed
clinical examination and statistical analysis.
Competing interests
The author declares that they have no competing interests.
Received: 4 March 2011 Accepted: 27 October 2011
Published: 27 October 2011
References
1. Vanderas AP: Prevalence of craniomandibular dysfunction in children
and adolescents: a review. Pediatr Dent 1987, 9:312-316.
2. Nydell A, Helkimo M, Koch G: Craniomandibular disorders in children-A
critical review of the literature. Swed Dent J 1994, 18:191-205.
3. Magnusson T, Egermark-Eriksson I, Carlsson GE: Four-year longitudinal
study of mandibular dysfunction in children. Community Dent Oral
Epidemiol 1985, 13:117-120.
4. Widmalm SE, Christiansen RL, Gunn SM, Hawley LM: Prevalence of signs
and symptoms of craniomandibular disorders and orofacial parafunction
in 4-6-year-old African-American and Caucasian children. J Oral Rehabil
1995, 22:87-93.
5. Kӧhler AA, Helkimo AN, Magnusson T, Hugoson A: Prevalence of
symptoms and signs indicative of temporomandibular disorders in
children and adolescents. A cross-sectional epidemiological investigation
covering two decades. Eur Arch Paedrt Dent 2009, 10(Suppl. 1):16-25.
6. Tecco S, Crincoli V, Di Bisceglie B, Saccucci M, Macri M, Polimeni A, Festa F:
Signs and symptoms of temporomandibular joint disorders in Caucasian
children and adolescents. Cranio 2011, 29:71-79.
7. Magnusson T, Egermark I, Carlsson GE: A longitudinal epidemiological
study of signs and symptoms of temporomandibular disorders from 15
to 35 years of age. J Orofac Pain 2000, 14:310-319.
8. Kӧnӧnen M, Nystrӧm M: A longitudinal study of craniomandibular
disorders in Finnish adolescents. J Orofac Pain 1993, 7:329-335.
9. De Boever JA, Van den Berghe L: Longitudinal study of functional
conditions in the masticatory system in Flemish children. Community
Dent Oral Epidemiol 1987, 15:100-103.
10. Torii K, Chiwata I: Relationship between habitual occlusal position and
flat bite pane induced occlusal position in volunteers with and without
temporomandibular joint sounds. Cranio 2005, 23:16-21.
11. Hagberg C: Assessments of bite force: A review. J Craniomandib Disord
Facial Oral Pain 1987, 1:162-169.
12. Moyers RE: Some considerations of centric and other jaw relations. J
Prosthet Dent 1956, 6:183-194.
13. Dworkin SF, LeResche L: Research diagnostic criteria for
temporomandibular disorders. Review, criteria, examinations and
specifications, critique. J Craniomandib Disord Fascial Oral Pain 1992,
6:301-355.
doi:10.1186/1746-160X-7-17
Cite this article as: Torii: Longitudinal course of temporomandibular
joint sounds in Japanese children and adolescents. Head & Face Medicine
2011 7:17.
Submit your next manuscript to BioMed Central
and take full advantage of:
• Convenient online submission
• Thorough peer review
• No space constraints or color figure charges
• Immediate publication on acceptance
• Inclusion in PubMed, CAS, Scopus and Google Scholar
• Research which is freely available for redistribution
Submit your manuscript at
www.biomedcentral.com/submit
Torii Head & Face Medicine 2011, 7:17
http://www.head-face-med.com/content/7/1/17
Page 5 of 5