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Can Temporomandibular Joint Disorders Be Diagnosed Beforehand by Assessment of Postural Irregularities?

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Aim:In many studies, the relationship between postural status and temporomandibular disorders (TMD) have been investigated, however there is no consensus on this regard. The aim of this study was to investigate the relationship between postural irregularities forward head posture (FHP) and different shoulder levels (DSL) and TMD prevalence in different dentition stages.Materials and Methods:This study, which included children between 4 and 14 years of age attending public schools in Ankara, was planned as a cross-sectional study. Temporomandibular joint (TMJ) was examined intra- and extra-orally. After the examination, the relationship between TMD and body posture (FHP and DSL) was investigated. For statistical analysis, chi-square test and Fisher’s exact test were used with significance level of p
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Ori gi nal Ar tic le
104
J Pediatr Res 2019;6(2):104-9
DO I: 10.4274/jpr.galenos.2018.14890
Can Temporomandibular Joint Disorders Be
Diagnosed Beforehand by Assessment of Postural
Irregularities?
Ad dress for Cor res pon den ce
Akif Demirel MD, Ankara University Faculty of Medicine, Department of Pediatric Dentistry, Ankara, Turkey
Phone: +90 506 287 33 80 E-mail: akifdemirel@ankara.edu.tr ORCID ID: orcid.org/0000-0002-1433-0452
Re cei ved: 31.07.2018 Ac cep ted: 26.09.2018
1Ankara University Faculty of Dentistry, Department of Private Pediatric Dentistry, Ankara, Turkey
2Ankara University Faculty of Medicine, Department of Pediatric Dentistry, Ankara, Turkey
Canan Dağ1, Akif Demirel2, Nurhan Özalp2
Introduction
The temporomandibular joint (TMJ) is an ellipsoid variety
of the synovial joints forming a bicondylar articulation. TMJ
includes a disk, fibrous capsule, synovial membrane and
ligaments (1). TM disorders (D) are defined as neuromuscular
and musculoskeletal problems characterized by TMJ,
masticatory muscles and clinical findings associated with
the related structures (2). TMD are known as functional
irregularities of the general masticatory system, TMD
associated disk displacements and degenerative and
inflammatory diseases of these structures (3,4).
TMD occurs with multiple aetiological factors (5)
and common causes are parafunctional habits such
as macrotrauma, bruxism and clenching, skeletal and
occlusal disorders, psychosocial factors and systemic
factors (6). The prevalence of TMD is highly variable due
to differences in populations studied in children and
adolescents (6). In general, clinical symptoms associated
©Copyright 2019 by Ege University Faculty of Medicine, Department of Pediatrics and Ege Children’s Foundation
The Journal of Pediatric Research, published by Galenos Publishing House.
ABS TRACT
Aim: In many studies, the relationship between postural status and temporomandibular disorders (TMD) have been investigated, however
there is no consensus on this regard. The aim of this study was to investigate the relationship between postural irregularities forward head
posture (FHP) and different shoulder levels (DSL) and TMD prevalence in different dentition stages.
Materials and Methods: This study, which included children between 4 and 14 years of age attending public schools in Ankara, was planned
as a cross-sectional study. Temporomandibular joint (TMJ) was examined intra- and extra-orally. After the examination, the relationship
between TMD and body posture (FHP and DSL) was investigated. For statistical analysis, chi-square test and Fisher’s exact test were used
with significance level of p<0.05.
Results: FHP and DSL were statistically related to TMD (p<0.05). In primary dentition, there was no significant relation between FHP and
TMD, however, DSL were found to be significantly related to TMD (p<0.05). In mixed dentition, both of these parameters were statistically
related to TMD (p<0.05). However, in the permanent dentition, there was no relationship between body posture and TMD.
Conclusion: Since there is a strong correlation between postural irregularities and TMD especially in the mixed dentition stage, TMJ and
postural status of pediatric patients should be examined as early as possible in the stages of the life. In this regard, the awareness of
pediatricians and pediatric dentists to this matter needs to be improved.
Keywords: TMJ, TMD, head posture, body posture
105
with TMD are less common in the primary dentition
period than in the mixed and permanent dentition periods
(7).
It is known that TMD is positively related to head
and body posture (8-13). The body posture is a position
associated with muscle activation regulated by the central
nervous system (14). The biomechanical organization of the
body posture is regulated by the functional integration of the
various body structures, and the changes in any biological
subunit result in the differentiation and reorganization of
the postural control systems (11,13).
The stomatognathic system includes structures
which have an important role in postural control such
as the lower and upper jaw, dental arches, neurovascular
soft tissues and muscle groups related to TMJ (14). The
muscular groups of the stomatognathic system belong
to the muscle groups of the neck and all units of the
muscular chain are related to each other. As a matter of
fact, TMJ is a structure which is connected to the neck
region via the muscular and ligamental structures and
this functional unit is called “cranio-cervico-mandibular”
system (14,15). In light of these points, any disorder of the
muscular component leads to a reorganization of other
subunits (11). Therefore, the relationship between body
posture and the incidence of TMD needs to be clearly
defined (11,16) in order to provide the optimal treatment
for TMD patients.
The aim of this study is to investigate the relation
between postural irregularities and TMD prevalence in
different dentition stages. The secondary goal of this
research is to improve the awareness of pediatric dentists
and pediatricians in order to facilitate the early diagnosis
of TMD by additional examinations which include postural
status.
Materials and Methods
Sample Selection and Ethical Approval
This study, which included children between 4-14 years
of age attending public schools in Ankara, was planned as
a cross-sectional study including intra-oral and extra-oral
examinations. The study protocol was approved by the
Ethics Committee of Ankara University (approval number:
150/2). The participants of the study were selected based
on a voluntary basis and the parents of the children who
participated in the study gave informed written and verbal
consent. After detailed information was provided, informed
consent forms were signed by the parents. A power analysis
was performed to determine the sample size by using the
number of children at different dentition groups included in
the study (Table I).
Evaluation of the Postural Status
A total of 6 photographs (3 profile, 3 facade) were
taken for the postural evaluation of the children. After the
participants were positioned on a flat surface, photographs
were taken from a distance of 2 meters. Right and left
shoulder location levels were evaluated in the facade
photographs and the average value of the photographs
were recorded as a result. Similarly, in the photographs
taken in profile, the location of the shoulder and the
ear was evaluated and averages of photographs were
Dağ et al.
Relation Between Posture and Temporomandibular Disorders
Figure 1. Photos taken for posture evaluation and guide lines
Table I. Sample sizes of different dentition groups
Ages n
4-6 (Primary dentition) 298
7-11 (Mixed dentition) 669
12-14 (Permanent dentition) 408
Total 1375
106
recorded. Digital guide lines were used in the evaluation of
photographs (Figure 1). The shoulder levels were examined
based on a horizontal line and in case of inequality in
shoulder location, it was recorded as different shoulder
level (DSL). In the photographs taken from the profile,
the guide line passing over the shoulders was taken as the
criterion and the anterior head position were recorded as
forward head posture (FHP).
Examination of Temporomandibular Joint and
Diagnose of Temporomandibular Disorders
The examination of TMJ and diagnosis of TMD were
performed by observing the bilateral palpation of the skin,
muscles and joints and all movements of the mandible.
Palpation of the joint was carried out intra-orally and
extra-orally. Thus, the presence of tenderness on palpation
and irregularities of lower jaw movements were recorded
as “tenderness of masticatory muscles and TMJ”. The
presence of any findings such as deflection, deviation,
disk displacement and joint sounds (clicking, popping, and
crepitation) in TMJ examination were recorded as TMD.
After this detailed examination, mouth opening capacity,
maximum mouth opening, laterotrusion, retrusion,
protrusion and presence of pain findings were recorded.
Statistical Analysis
The relationship between postural status and TMD in
different dentition stages were analyzed using chi-square
test and Fisher’s exact test with a significance level of
p<0.05.
Results
The percentage distribution of the postural irregularities
based on FHP and DSL in different dentition stages is shown
in Table II.
The relationship between postural status and TMD
presence in primary, mixed and permanent dentition is given
Dağ et al.
Relation Between Posture and Temporomandibular Disorders
Table II. Presence of postural irregularities in different dentition
stages
FHP (%) DSL (%)
Primary dentition 5.4 5.4
Mixed dentition 5.8 5.5
Permanent dentition 6.4 6.9
FHP: Forward head posture, DSL: Different shoulder levels
Table III. Relationship between postural irregularities and presence of TMD in different dentition periods
TMD
Chi-square test p valueAbsence Presence Tot al
n % n % n %
Primary dentition
FHP
Absence 267 94.68 15 5.32 282 100
Fisher’s exact test 0.063Presence 13 81.25 3 18.75 16 100
Total 280 93.96 18 6.04 298 100
DSL
Absence 268 95.04 14 4.96 282 100
Fisher’s exact test 0.011*Presence 12 75.00 4 25.00 16 100
Total 280 93.96 18 6.04 298 100
Mixed dentition
FHP
Absence 553 87.78 77 12.22 630 100
27.381 0.000*Presence 22 56.41 17 43.59 39 100
Total 575 85.95 94 14.05 669 100
DSL
Absence 552 87.34 80 12.66 632 100
16.325 0.000*Presence 23 62.16 14 37.84 37 100
Total 575 85.95 94 14.05 669 100
Permanent dentition
FHP
Absence 317 82.98 65 17.02 382 100
Fisher’s exact test 0.107Presence 18 69.23 8 30.77 26 100
Total 335 82.11 73 17.89 408 100
DSL
Absence 316 83.16 64 16.84 380 100
3.180 0.075Presence 19 67.86 9 32.14 28 100
Total 335 82.11 73 17.89 408 100
TMD: Temporomandibular disorders, FHP: Forward head posture, DSL: Different shoulder levels, *Statistically significant difference
107
in Table III. According to the results, there was no relation
between TMD and the FHP in primary dentition, while the
presence of TMD was found to be statistically significant in
DSL (p<0.05). Additionally, the presence of TMD was found
to be statistically significant (p<0.05) in both postural
irregularities in mixed dentition. In permanent dentition,
both postural irregularities were not statistically related to
TMD. Nevertheless, it has been determined that the rate
of TMD was higher in the individuals in whom the postural
irregularities were observed.
The rate of presence of TMD was 34.6% in the
presence of FHP, whereas the rate of TMD in normal head
position was 12.1%. The presence of TMD was statistically
significantly higher in the presence of FHP (p<0.05) (Table
IV). Additionally, the incidence of TMD was 33.3% and 12.2%
in patients with and without DSL, respectively. The presence
of TMD was statistically significantly higher in the presence
of DSL (p<0.05) (Table IV).
Discussion
TMD are common diseases in children and adolescents
being at least as prevalent as for adults (17-20). TMD
develop with multiple etiological factors and occur with
signs and symptoms affecting the joint related muscular
and neuromuscular components (21-23). In the treatment
of TMD, in order to provide preventive procedures, it is
necessary to investigate factors that may lead to this
disease especially during different dentition periods.
Regulation of the postural structure of the body is
possible if the changes in the biological subunit reorganize
the postural control systems (11,13). The neck muscles
that are adjacent to the TMJ region play an important role
in providing the balance of the head and stomatognathic
muscles. It means that any level of differences in these
structures can cause changes throughout the whole
complex. The masticatory muscles can be affected by
alterations in head posture and vice versa. Thus, any
manipulation of the mandibular muscles can lead to
changes in head posture (13,24) and changes in the
cervical spine structure can also play a role in developing
TMD (13).
As the TMJ region is directly adjacent to the cervical
and scapular regions, postural changes in the upper neck
and head region correlate with TMD (13). Gonzalez and
Manns (25) stated that FHP was caused by an extension of
the upper cervical spine (C1-C3) and a flexion of the lower
cervical spine (C4-C7) called hyperlordosis. The authors
also emphasized that hyperextension was observed in the
head and upper cervical spinal region in TMD patients.
Alarcón et al. (26) suggested that the position of the
jaw can affect the muscles in the peripheral region and
cause postural adaptations at the spine level. Asymmetric
malocclusions such as unilateral cross bite have been
reported to be a risk factor for unbalanced muscle activity
and postural dysfunction. Similarly, Solow and Sonnesen
(27) stated that there is a strong relationship between the
cervical lordosis grade and vertical craniofacial morphology,
overjet, class 2 and class 3 anomalies. It is thought that
TMD and postural irregularities are related and risk factors
for each other. In this way, it can be stated that there is a
positive relationship between head/body posture and TMD
(8,9,11). In the present study, the aim was to investigate
the relationship between TMD and head/body posture
and this relationship was examined in different dentition
periods. The presence of disk displacement, joint sounds,
muscular irregularities, movement limitations and pain
were accepted as TMD. In postural status evaluation, FHP
and DSL were examined.
In order to determine the postural status, several
techniques (e.g. surface electromyography, kinesiography,
different clinical and instrumental posturographic
approaches) have been used over the years (28). Despite
some studies on the stomatognathic system and its
relationship with posture (29-33), they have restrictive
factors to their clinical application because of the absence
of normative values for age, sex, weight, height and facial
Dağ et al.
Relation Between Posture and Temporomandibular Disorders
Table IV. The relationship between postural irregularities and TMD
TMD Statistical analysis
Absence Presence Tot al
n % n % n % Chi-square p value
FHP
Absence 1137 87.9 157 12.1 1294 100
31.051 0.000*Presence 53 65.4 28 34.6 81 100
Total 1190 86.5 185 13.5 1375 100
DSL
Absence 1136 87.8 158 12.2 1294 100
27.423 0.000*Presence 54 66.7 27 33.3 81 100
Total 1190 86.5 185 13.5 1375 100
TMD: Temporomandibular disorders, FHP: Forward head posture, DSL: Different shoulder levels, *Statistically significant difference
108
morphology. For these reasons, this study was carried
out in an out-of-clinical setting and simple photographic
techniques were used as an evaluation criterion.
In the present study, the presence of TMD was found to
be statistically significant (p<0.05) in those individuals with
FHP and DSL in mixed dentition. In permanent dentition,
an association with both postural parameters and TMD
was not observed as statistically significant. Similar to the
findings of this study, it has been reported that TMD is not
frequently observed during primary dentition, while it is
increasingly observed during mixed dentition (7). Chaves et
al. (34) reported that the alterations in head position were
observed in 56% of cases of moderate to severe TMD in
individuals in the 10-18 years age group. Cortese et al. (35)
stated that FHP was one of the most common postural
anomalies at 10-15 years of age, and this was a risk factor
for TMD. It seems that there is a need for more standardized
studies concerning the relationship between postural
irregularities and TMD in different dentition periods in
children.
Patients in the mixed dentition period should be
carefully assessed for the presence of TMD and postural
irregularities, since TMJ related diseases are expected to
increase especially after the primary dentition period.
It has been reported that TMD stimulate the effects of
masticatory muscles on the compensator mechanism
and this biomechanical adaptation pulls the shoulders
upwards (34). The occurrence of postural disorders is
believed to be due to excessive stresses on the cervical
muscles depending on the increased activity of the
masticatory muscles to compensate for joint disease
in TMD individuals (34). Nicolakis et al. (9) reported
that training for postural correction in those patients
with TMJ disk displacement have had promising results.
Consequently, it is not certain that TMD is caused by
postural changes or postural disorders are caused by TMD
(36). In this respect, both situations should be considered
as a potential risk factor for each other. These patients
should be diagnosed and treated as early as possible by
medical doctors, pediatricians and pediatric dentists using
multidisciplinary approaches.
Conclusion
TMD is not only a problem affecting adults but can also
be seen in pediatric patients. However, when considering
the relationship between postural status and changes and
presence of TMD, it is unclear which one is the etiological
factor for the other. The disorders mentioned should be
diagnosed at the youngest possible age. This approach
will be beneficial in terms of the elimination of both TMD
and postural irregularities. Therefore, it is recommended
that pediatric dentists and pediatricians should evaluate
the findings that may raise suspicions about the diagnosis
of TMD and postural irregularities in a multidisciplinary
manner.
Ethics
Ethics Committee Approval: The study protocol was
approved by the Ethics Committee of Ankara University
(approval number: 150/2).
Informed Consent: Informed consent was obtained by
the parents.
Peer-review: External and internal peer-reviewed.
Authorship Contributions
Surgical and Medical Practices: C.D., N.Ö., Concept:
C.D., A.D., N.Ö., Design: C.D., A.D., N.Ö., Data Collecting or
Processing: C.D., N.Ö., Analysis or Interpretation: C.D., A.D.,
N.Ö., Literature Search: C.D., A.D., N.Ö., Writing: A.D., N.Ö.
Conflict of Interest: No conflict of interest was declared
by the authors.
Financial Disclosure: The authors declared that this
study received no financial support.
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Relation Between Posture and Temporomandibular Disorders
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Neuromuscular dentistry has been a controversial topic in the field of dentistry and still remains debatable. The issue of good occlusion and sound health has been repeatedly discussed. Sometimes we get complains of sensitive teeth and sometimes of tired facial muscles on getting up in the morning. Owing to the intimate relation of masticatory apparatus with the cranium and cervico-scapular muscular system, the disorders in any system, draw attention from concerned clinicians involved in management, to develop an integrated treatment protocol for the suffering patients. There may be patients reporting to the dental clinics after an occlusal restoration or extraction, having pain in or around the temporomandibular joint, headache or neck pain. Although their esthetic demands must not be undermined during the course of treatment plan, whenever dental treatment of any sort is planned, occlusion/bite should be given prime importance. Very few dentist are able to diagnose the occlusal disease and of those who diagnose many people resort to aggressive treatment modalities. This paper aims to report the signs of occlusal disease, and discuss their association with TMDs and posture.
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These were to 1) estimate the prevalence of subjective symptoms and clinical signs of temporomandibular disorders (TMD) in children and adolescents in the city of Jönköping, Sweden, 2) follow possible variations in TMD signs and symptoms over a 20-year period, and 3) study possible associations between TMD symptoms and signs and factors of interest. About 100 individuals in the age groups of 3, 5, 10 and 15 years participated in cross-sectional stratified epidemiological investigations in 1983, 1993 and 2003. All participants were asked to fill in a questionnaire including questions on general and oral health, dental care habits and some socio-demographic issues. More specific questions recorded the presence or absence of subjective symptoms: tiredness in the jaws on awakening or during chewing; clicking sounds or crepitations from the temporomandibular joints (TMJs); locking/ catching of the mandible; luxation of the mandible; reduced jaw movement capacity; pain during jaw movements; other pain conditions in the jaws or in the TMJ regions. Subjects were examined clinically at each time period for; jaw mobility (maximum jaw opening including vertical overbite, maximum laterotrusion to the right and to the left, maximum protrusion); TMJ function (normal function, deflection on jaw opening of >2 mm, TMJ clicking or crepitations, TMJ locking, TMJ luxation); pain on jaw movement (no pain on movements, pain on one movement, pain on more than one movement); muscle pain (no muscle pain, pain on palpation in 1-3 sites, pain on palpation in >3 sites); TMJ pain (no joint pain, pain on lateral palpation of one or both joints, pain on posterior palpation of one or both joints). No functional examination of the masticatory system was performed in children aged 3 and 5 years. TMD-related symptoms were very rare in 3- and 5-year-olds. In the age groups of 10- and 15-year olds, 5-9% of the participants reported more severe symptoms, up to 50% showed one or more TMD signs, while it was estimated that 1-2% were in need of TMD treatment. Several symptoms and signs increased with age. No gender differences, with the exception of recurrent headache, were noted. Oral parafunctions were reported by 11-47%. Apart from a few variables, no statistically significant changes in the prevalence of TMD symptoms and signs were observed over the 20-year period. Clenching/grinding of teeth and general health factors were found to be associated with TMD symptoms and signs. The prevalence of more severe TMD symptoms and signs in children and adolescents was generally low in all three examinations and did not change significantly during the 20-year period. Increasing age, general health factors and oral parafunctions were associated with TMD symptoms and signs in 10- and 15-year-olds.
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The purpose of this study was to determine the prevalence of temporomandibular disorder (TMD) signs and tooth wear levels in a group of hospitalised patients with mental retardation (MR). A total of 118 patients with MR and 104 mentally healthy individuals (control) were included in this study. The groups consisted of equal numbers of male and female patients. TMD signs were evaluated according to the Research Diagnostic Criteria to assess the limitation in maximum mouth opening, the alterations in the mouth opening pathway and temporomandibular joint sounds. In addition, tooth wear was recorded. The frequency of at least one sign of TMD observed in patients with MR (79·7%) was significantly higher than in controls (69·2%) (P=0.03). In addition, 43.2% of the patients with MR had more than one sign of TMD compared with 28.8% of the control group (P = 0·02). Prevalence of each sign exhibited in the MR and control groups was as follows: limitation in mouth opening, 24·6% vs. 13·5% (P=0·02); deviation, 18·6% vs. 26·9% (P=0·001); deflection, 29·7% vs. 10·6% (P=0·001); TMJ sounds, 46·6% vs. 41·1% (P=0·43); bilateral joint sounds 28·8% vs. 16·3% (P=0·05) respectively. Prevalences of TMD signs were not different between genders in both groups (P>0·05). Severe tooth wear was evident in 43·2% of the patients with MR compared with 20·6% of the controls (P=0·001). In conclusion, patients with MR seem to be more prone to having TMD signs compared with the control population.
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In recent years, many researchers have investigated the various factors that can influence body posture: mood states, anxiety, head and neck positions, oral functions (respiration, swallowing), oculomotor and visual systems, and the inner ear. Recent studies indicate a role for trigeminal afferents on body posture, but this has not yet been demonstrated conclusively. The present study aims to review the papers that have shown a relationship between the stomatognathic system and body posture. These studies suggest that tension in the stomatognathic system can contribute to impaired neural control of posture. Numerous anatomical connections between the stomatognathic system's proprioceptive inputs and nervous structures are implicated in posture (cerebellum, vestibular and oculomotor nuclei, superior colliculus). If the proprioceptive information of the stomatognathic system is inaccurate, then head control and body position may be affected. In addition, the present review discusses the role the myofascial system plays in posture. If confirmed by further research, these considerations can improve our understanding and treatment of muscular-skeletal disorders that are associated with temporomandibular joint disorders, occlusal changes, and tooth loss.
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Aim: To evaluate the effect to the degree of temporomandibular dysfunctions (TMD) in adolescents and occlusal classes in the cervical posture. Methods: A cross-section, observational study was carried out, in which 296 adolescents took part. For the evaluation, the patients were divided into groups according to the presence and severity of the TMD, using the Helkimo questionnaire and occlusal Angle classification. The posture analysis was carried out using photogrammetry and the software Alcimage®to measure the predefined angle based on the protuberances of the Spinous Process of the 7 th cervical vertebra (C7), manubrium of the sternum and mentum vertex. Results: 48% (n= 142) of the 296 adolescents evaluated presented no dysfunction, while 52% (n= 154) presented some degree of TMD. Of the different degrees of TMD, the highest average cervical angulation observed in the group with moderate dysfunction was 97.59°±7.40, followed by a mild degree, of 96.32°± 9.36, and the lowest average was 93.01°±10.08 in the patients with a severe degree in the different occlusal classes. In relation to occlusal class, higher values for this angulation were observed in class II (96.77°± 8.79), compared with class I (90.64°±8.80) and class III (94.67°± 10.70), a difference which was statistically significant. Conclusions: The subjects with TMD presented a greater alteration in head posture, compared with those without TMD. In particular, the Class II Angle was correlated with TMD and alterations in cervical posture.
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Temporomandibular disorders (TMD) are a heterogeneous group of musculoskeletal and neuromuscular conditions involving the temporomandibular joint complex, and surrounding musculature and osseous components. TMD affects up to 15% of adults, with a peak incidence at 20 to 40 years of age. TMD is classified as intra-articular or extra-articular. Common symptoms include jaw pain or dysfunction, earache, headache, and facial pain. The etiology of TMD is multifactorial and includes biologic, environmental, social, emotional, and cognitive triggers. Diagnosis is most often based on history and physical examination. Diagnostic imaging may be beneficial when malocclusion or intra-articular abnormalities are suspected. Most patients improve with a combination of noninvasive therapies, including patient education, self-care, cognitive behavior therapy, pharmacotherapy, physical therapy, and occlusal devices. Nonsteroidal anti-inflammatory drugs and muscle relaxants are recommended initially, and benzodiazepines or antidepressants may be added for chronic cases. Referral to an oral and maxillofacial surgeon is indicated for refractory cases.
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The aim of this investigation was to perform a review of the literature dealing with the issue of relationships between dental occlusion, body posture and temporomandibular disorders (TMD). A search of the available literature was performed to determine what the current evidence is regarding: (i) The physiology of the dental occlusion-body posture relationship, (ii) The relationship of these two topics with TMD and (iii) The validity of the available clinical and instrumental devices (surface electromyography, kinesiography and postural platforms) to measure the dental occlusion-body posture-TMD relationship. The available posturographic techniques and devices have not consistently found any association between body posture and dental occlusion. This outcome is most likely due to the many compensation mechanisms occurring within the neuromuscular system regulating body balance. Furthermore, the literature shows that TMD are not often related to specific occlusal conditions, and they also do not have any detectable relationships with head and body posture. The use of clinical and instrumental approaches for assessing body posture is not supported by the wide majority of the literature, mainly because of wide variations in the measurable variables of posture. In conclusion, there is no evidence for the existence of a predictable relationship between occlusal and postural features, and it is clear that the presence of TMD pain is not related with the existence of measurable occluso-postural abnormalities. Therefore, the use instruments and techniques aiming to measure purported occlusal, electromyographic, kinesiographic or posturographic abnormalities cannot be justified in the evidence-based TMD practice.
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Electromyographic (EMG) assessment has been used as a non-invasive tool to objectively assess muscle function, although with controversial research and clinical potential. The aim of this study was to assess within-, inter-subject and between-day repeatability of serial EMG recordings. The study sample included 10 asymptomatic subjects with no history of temporomandibular disorders or muscle parafunctions. Bilateral masseter and anterior temporalis muscle EMG parameters were assessed in two standardized serial recordings (day 1 to day 2) using a portable EMG equipment (ME 6000 recorder, Mega Electronics, Kuopio, Finland). The functional tasks included postural/resting activities as pre- and post-recording series of 30 s each and jaw opening/closing, intercuspal and maximal voluntary clenching activities of 5 s, repeated three times. The assessed EMG parameters included the mean amplitude, s.d. and error. In addition, the power spectrum EMG parameter assessment included the median power frequencies and the averaged EMG spectrum data values. The results of the intraclass correlation coefficient analysis indicated reliability for nearly all of the intercuspal and all clenching EMG amplitude and power spectrum parameters. This was complemented by the repeated measures anova and post hoc analyses that indicated non-significant differences between day 1 and 2 in task- and muscle-related analyses. Most variability was noted in postural and some in opening/closing tasks. In conclusion this study assessed the reliability, repeatability and limitations of postural and various dynamic masseter and temporalis EMG recordings for serial assessment.