ARTÍCULOS ORIGINALES
Bruxism. Masticatory implications and anxiety
Anne C. Alves1, João C. Alchieri2, Gustavo A. S. Barbosa3
1 Speech Therapist, Federal University of Rio Grande do Norte, Brazil.
2 Psychology Department, Federal University of Rio Grande do Norte, Brazil.
3 Dentistry Department, Federal University of Rio Grande do Norte, Brazil.
CORRESPONDENCE Anne da Costa Alves Rua do Calcario, 100 - apt.203 - Lagoa Nova Natal, RN - Brazil. Postal Code: 59076-240 E-mail: annecalves@hotmail.com
ABSTRACT
In this study we investigate the phenomenon of bruxism, defined as the act of clenching and/or grinding the teeth, a habit that compromises the orofacial region. It is often associated with emotional aspects, such as anxiety and stress, and may result in alterations to orofacial structures, functional modifications and social repercussions. The aim of this study was to determine a possible association between bruxism and anxiety underscoring the primary complaints related to masticatory function. Eighty volunteers participated in the study. They were divided into bruxers (N=40) and non-bruxers (N=40) of both sexes. The diagnosis of bruxism was made by clinical examination. The Trait-State Anxiety Inventory was used to assess anxiety levels and a questionnaire with structured questions related to daily activities, focusing on masticatory function (for the bruxism group), was applied to evaluate psychosocial aspects. The results of the study show a significant difference in state anxiety. Mean and standard deviation of state anxiety in the bruxism and non-bruxism groups was 42.7}9.6 and 38.6}8.2 (p ≤0.04), respectively, while trait anxiety had a mean and standard deviation of 44.5}11.0 and 40.7}9.5 (p ≤0.11). The main complaints of bruxers during mastication were facial pain and headache while chewing as well as the presence of clicking sounds in the jaw joint. Findings demonstrate an association between emotional factors such as anxiety and bruxism, resulting in compromised masticatory function.
Key words: Anxiety; Bruxism; Mastication; Stomatognathic System.
Bruxismo implicações mastigatórias e ansiedade
RESUMO
Neste trabalho procuramos estudar o fenomeno do bruxismo, definido como o ato de apertar e/ou ranger os dentes, um habito prejudicial e destrutivo da regiao orofacial. O bruxismo e frequentemente associado aos aspectos emocionais, entre os mais ressaltados a ansiedade e o estresse, podendo implicar em alteracoes das estruturas orofaciais, modificacoes funcionais e repercussoes sociais. Verificar a associacao entre bruxismo e ansiedade ressaltando as principais queixas referentes a funcao mastigatoria. Participaram oitenta voluntarios, divididos entre grupo com bruxismo (N=40) e sem bruxismo (N=40), do sexo masculino e feminino. O diagnostico do bruxismo foi realizado atraves do exame clinico. Para avaliar os niveis de ansiedade empregou-se o "Inventario de Ansiedade Traco e Estado" e para os aspectos psicossociais um questionario com questoes estruturadas referentes as atividades diarias, focando a funcao mastigatoria (para o grupo com bruxismo). Foram evidenciadas diferencas significativas para a ansiedade estado entre os grupos analisados, verificou-se a media e desvio padrao de ansiedade estado no grupo com bruxismo, 42,7}9,6 e sem bruxismo 38,6}8,2 (p ≤0,04) e de ansiedade traco respectivamente 44,5}11,0 e sem bruxismo 40,7}9,5 (p ≤0,11). O relato dos participantes com bruxismo evidenciou como principais queixas durante a mastigacao a dor na face ao mastigar, cansaco muscular na face, cefaleia ao mastigar e presenca de ruidos articulares. Com base nos resultados evidenciamos uma associacao dos fatores emocionais como a ansiedade e o bruxismo e como resultante os pacientes apontam que a funcao mastigatoria encontrase depreciada.
Palavras-chave: Ansiedade; Bruxismo; Mastigacao; Sistema Estomatognatico.
INTRODUCTION
Bruxism is a nighttime or daytime parafunctional
activity, characterized by clenching or grinding of
the teeth1. It is considered the most harmful and
destructive habit affecting the orofacial region2,3,
due to the non-functional tooth wear that occurs in
situations not involving mastication, swallowing
and phonation4. The mandibular movements with
no functional purpose observed in bruxism impose
an abnormal demand on masticatory muscles,
resulting in hyperfunction, generating painful
symptoms and decreased coordination5 when the
force exerted by the habit exceeds the adaptive
capacity of the stomatognathic system6.
Tooth grinding involves a sliding movement of
occlusal surfaces in eccentric contact, favoring
tooth wear. During tooth clenching, the increased
tension in centric occlusion, through the isometric
contraction of jaw elevator muscles, may cause
pain, fatigue and masticatory muscle hypertrophy.
The neuromuscular system becomes compromised
as a consequence of atypical functional demand
imposed on the muscles involved, also affecting
mastication7.
Although bruxism is a frequent habit in adults6, 8, 9,
its causal factors are complex and still not fully
understood2, 10. Until a few years ago peripheral factors,
such as occlusal disorders and anatomical
alterations, were the most commonly implicated.
However, current research has questioned the action
of occlusion on the origin of bruxism, promoting
conceptual change that suggests the influence of
central and psychogenic factors2, 4, 11, 12. Thus, it is
believed that the multifactorial theory may be the
most plausible hypothesis2, 10, 12-14.
The influence of emotional factors, such as anxiety,
has been widely emphasized, for both triggering
and perpetuating bruxism, resulting in an increase
in muscle tension caused by emotional stress during
moments of anxiety15, manifesting itself somatically,
i.e., a form of body language that cannot be
understood by the subject16. Anxiety is an emotional
state triggered by the body, which includes both
psychological and physiological components,
becoming pathological when exaggerated or disproportional
in relation to the trigger. This leads to
disruption and failure to perform its role as a psychobiological
alarm, with the potential to develop
into a pathology when exceeding the individual's
adaptive capacity17, 18. Based on this evidence and
the non-conclusive data contained in the literature
regarding the influence of emotional factors on
bruxism, the aim of this study was to determine the
association between bruxism and anxiety, underscoring
the primary complaints related to masticatory
function.
MATERIALS AND METHODS
This is a comparative cross-sectional descriptive
study, approved by the Research Ethics Committee
at the Federal University of Rio Grande do
Norte, Brazil, under protocol No. 065/09. All participants
provided informed written consent, after
being informed of the objectives and methods to
be used. Data were collected among all patients
with bruxism who sought treatment at the Integrated
Care Center for Patients with Stomatognathic
Apparatus Dysfunction (CIADE) between April
2009 and April 2011, as part of an extension project
for the Occlusion course in the Dentistry
Department of the Federal University of Rio
Grande do Norte.
The non-probabilistic sample was composed of
80 subjects of both sexes, divided into Group 1 -
bruxism and Group 2 - non-bruxism. The inclusion
criterion was that only adults would be considered
for both groups. Exclusion criteria were
individuals with neurological disorders and
patients who had undergone orthognathic or disccondyle
complex surgery. For the group with bruxism,
individuals who reported clenching/ grinding
their teeth, indicating the need for an occlusal
splint and pain in the orofacial region, were
included. The bruxism group was composed of 40
patients, (37 women and 3 men), mean age 33.4 }
11.5 years.
The non-bruxism group contained
40 individuals, (36 women and 4 men), mean age
36.3 } 10.1 years.
In addition to clinical examination, bruxism was
also evaluated through a self-report instrument,
based on a previous study19, 20. The survey asked
the following questions: Do you wake up in the
morning or during the night clenching or grinding
your teeth? (yes/no); Do you feel fatigue or
masticatory muscle pain on awakening? (yes/no);
Do you wake up in the morning or during the
night with your jaws locked? (yes/no); Do you
have recent history of chronic dislocation of permanent
or temporary restorations? (yes/no); Do
you have recent history of noises associated with
nocturnal teeth grinding as reported by a third
person? (yes/no).
Clinical examination revealed signs and symptoms
of bruxism, as reported in the literature21, based on
the patient's primary complaints. The evaluation
was performed by dental students, previously
trained and supervised by professors, recording the
following: presence of tooth wear (yes/no); dental
fractures (yes/no); periodontal trauma (yes/no);
masseter and temporal muscle pain (yes/no); muscle
hypertrophy (yes/no); restricted mandibular
movement (yes/no); sensitivity in head and neck
muscles (yes/no) and joint noise (clicking and/or
popping) (yes/no).
A translated and validated Portuguese version22 of the State-Trait Anxiety Inventory (STAI), an
instrument developed by Spielberg, Gorsuch and
Lusheneem (1964), was used to identify and
characterize the anxiety level of participants. It
consists of two self-report questionnaires: 1) Stateanxiety
and 2) Trait-anxiety. The survey, which
assesses state-anxiety, consists of 20 statements in
which patients indicate how they feel at a particular
point in time. The trait-anxiety questionnaire
contains 20 items and is designed to determine
patient personality characteristics throughout their
lives. It is important to point out that this instrument
was used in both groups. Moreover, the
State-Trait Anxiety Inventory was employed after
application of the self-report instrument and
assessment of clinical indicators of bruxism, prior
to the dental procedure. Thus, intergroup differences
in relation to state anxiety may result from
administration of the State-Trait Anxiety Inventory
after dental consultation.
A structured questionnaire developed by the
researchers was also applied. It contained closed
questions related to the masticatory functions in
daily activities (only for the bruxism group in
order to investigate its implications and face pain
symptoms), enquiring about type of teeth clenching
and/or grinding and when it occurs (daytime,
nighttime or both). Next, subjects were asked how
bruxism-related face pain interferes in activities
of daily living, (emphasizing masticatory function)
such as sleep; appetite /eating; swallowing;
speech; restricted mandibular movements and
mastication - When chewing, do you experience
facial pain, tired facial muscles, headache and
joint noise?
Data were transcribed onto a standard patient
record and inserted into a data bank for statistical
analysis using SPSS 16.0 software. In the descriptive
analysis, quantitative variables are presented
as mean and standard deviation (sd), while categorical
data are depicted in tabular form, as
absolute and relative frequency. Student's t-test
for independent samples was applied to compare
the means of continuous independent variables in
relation to the groups. Pearson's chi-square test
(X2) was used to compare differences in the proportion
of independent variables to dependent
variables with respect to the groups. A p-value of
0.05 and confidence interval of 95% were adopted
for all tests.
RESULTS
Analysis of sociodemographic aspects of the bruxism
group demonstrated higher prevalence of
women (37 = 92.5%) than men (3 = 7.5%), with
mean age and standard deviation of 33.4}11.5, and
prevalence of single individuals (18 = 45.0%). The
non-bruxism group was composed of 36 (90.0%)
women and 4 (10.0%) men, mean age 36.3} 10.1,
the majority of whom are married (26=65.0%).
State-trait anxiety data for both groups are shown in Table 1. In relation to the characterization of bruxism
with respect to the habit of clenching and/or
grinding the teeth and the point in time at which it
occurred can be seen in Table 2. Data from clinical
examinations of bruxism related to daily functions
and activities, (Table 3) showed a significant assocation in the following: tooth wear with impaired
mastication (≤0.001); dental fractures with impaired
mastication (≤0.002); restricted mandibular movements,
influencing appetite/eating (≤0.01) and hindering
speech (≤0.03); sensitivity in head and neck
muscles, showing associations with appetite/eating
(≤0.01), swallowing difficulties (≤0.01), speech
difficulties (≤0.01) and headache while chewing
(≤0.01).
Based on the accounts of patients with bruxism and
the main complaints observed during mastication,
significant associations were found for appetite/
diet (≤0.004), facial pain when chewing (≤0.007),
facial muscle fatigue(≤0.004), headaches (≤0.02)
and joint noise (≤0.001).
Table 1: Distribution of means and standard deviations
of anxiety in the bruxism and non-bruxism
groups.
*≤0.05%
Table 2: Characterization of the bruxism group regarding
the habit of clenching and grinding their teeth
and when the habit occurs.
Table 3: A significant association between the clinical
examination of bruxism and the variables
related to daily functions activities.
DISCUSSION
Several recent studies have sought to determine the
relationship between bruxism and emotional
aspects, highlighting anxiety13, 23, 24 as one of the
psychological factors that play an important role in
triggering and perpetuating the parafunction. The
greater prevalence of women with bruxism can be
explained by different theories, including physiological
and biological differences among molecular
factors related to gender, somewhat associated to
"facilitation" of pathologies involving the temporomandibular
joint, such as cases of morphological,
rheumatic and psychosocial diseases25; as to cognitive
level, pain threshold may be lower in women
than in men; with regard to social differences, different
upbringing between girls and boys may make
it more acceptable for women to externalize pain
than men26. Moreover, women are more aware of
the need to seek treatment25.
Bruxism is defined as "an anxiety response to environmental
stress". Emotional factors such as anxiety,
fear, frustration and emotional stress are related
to muscle hyperactivity3, 27. Strengthening this
hypothesis, Manfredini et al. determined that psychological
traits such as anxiety, depression and
maniacal symptoms, as well as stress sensitivity,
show significant differences in individuals with
bruxism, whereas occlusal factors showed no significant
difference12, 28.
This study demonstrated a relationship between
anxiety and bruxism, showing significant state anxiety
differences in individuals with bruxism when
compared to the control group. State anxiety is
characterized as a transitory emotional reaction to
everyday stressful events2. It consists of an
unpleasant feeling of anxiety and stress activated
by the autonomous central nervous system29 that
can vary in time and intensity30. Increased stateanxiety
in individuals with bruxism occurs when
nociceptive stimuli reach the central nervous system,
and are directed not only to the cerebral cortex,
but also to the limbic structures, which assess
and influence the painful experience on an emotional
level. In other words, pain is caused by complex
interactions in the higher centers. It is
important to underscore that the face, an essential
human structure, is the primary means of eating
and communicating, allowing interaction with others
to display our emotions, objectives and opinions,
as well as providing sources of both physical
and emotional gratification and satisfaction.
Changes to the orofacial segments associated with
pain symptoms may increase insecurity and threaten
individual wellbeing. They result in altered body
image and can be influenced by psychological
aspects, including anxiety31. Thus, it is believed
that high state-anxiety levels may be related to the
presence of pain symptoms. No difference was
found for trait anxiety, in contrast to findings in the
literature - Da Silva et al.32 - which report greater
propensity to trait anxiety in bruxers.
Researchers such as Gungormus and Erciyas
observed that people who grind their teeth have
higher levels of anxiety and depression13. Along
these lines, Kampe et al. found that individuals
with bruxism had different personalities from the normal population, displaying greater tendency
towards anxiety, increased vulnerability to psychosomatic
disorders and difficulty in social relationships27.
However, a study conducted by Manfredini
et al. showed no association between bruxism
and psychopathological anxiety23. Rompre et al.
report that levels of anxiety and stress do not differ
between control and experimental groups33.
Clinical diagnosis of bruxism has provided a
detailed description of psychosocial problems in
individuals with bruxism, underscoring psychological
issues, stress, anxiety, mood disorders,
temperamental and emotional traits, as well as
social matters such as work and personal relationships,
all of which could have a negative effect on
health2.
In addition to personality traits, the relationship
between living conditions and bruxism has also
been explored. It regularly manifests itself in individuals
affected by stress, which determines the
frequency, duration and severity of the condition3.
The literature reports that individuals with sleep
bruxism experience greater stress in their daily
lives and at work, compromising their physical
status and causing them to deal with stressful
situations in a negative manner10. This opinion is
also common among patients, who often report
increased teeth grinding during sleep and at
stressful moments in their life2, reacting with negative
emotions. Although the relationship between
bruxism and stress is still inconclusive, it is suggested
that elevated levels of daily stressful
events may be a risk factor23. However, Pierce et
al. found no significant relationship between electromyographic
measurements recorded over 15
consecutive nights and self-reports of stress in
individuals with bruxism, demonstrating significance
only for eight of the one hundred subjects
evaluated34.
Diagnosis of bruxism is complex due to the various
assessment criteria, such as self-reports, clinical
evaluation, electromyography and polysomnography,
with questionnaires being the most widely
used method21. In this study, self-reports and clinical
assessments were adopted as diagnostic criteria.
Questionnaires to determine bruxism are
generally used in epidemiological studies and
clinical situations21 owing to their low cost and
rapid diagnosis. However, this method does not
distinguish between clenching and grinding teeth
during sleep or during the day23. Polysomnography
is the gold standard for diagnosing sleep
bruxism, but the method is limited by its high
cost. Diagnostic criteria do not clearly distinguish
between sleep and daytime bruxism or
its severity23. A recent literature review suggests
that self-reports of bruxism may be adequate
for detecting conscious teeth clenching during
wakefulness, which may be associated with masticatory
muscle sensitivity or fatigue, whereas
analysis of tooth wear or sleep laboratory recordings
are more appropriate for detecting teeth
grinding, whose implications may be different
from clenching35.
It is important to underscore that anxiety may manifest
itself physiologically in different ways, including
bruxism, caused by the increase in muscle
tension, evidenced by hyperactive masticatory muscles,
especially the masseter24. Bruxism is the most
harmful and destructive habit to affect the orofacial
region, due to the fact that mandibular movements
with no functional purpose2, 12, 35 cause masticatory
dysfunction8.
A large proportion of complaints from individuals
with bruxism are related to the masticatory function,
since the association between clinical data
and psychosocial aspects of daily activities shows
a significant correlation with chewing disorders.
It is important to note that mastication occurs via
interaction between morphological aspects of orofacial
structures, muscle and joint functional
capacity, as well as food characteristics36. The
bilateral pattern of chewing favors the health of
orofacial structures25. This indicates that constant
bruxism generates alterations in the normal physiological
process of masticatory muscles4. It is a
parafunctional habit that threatens the integrity of
oral structures, since the force exerted exceeds the
adaptive capacity of the masticatory system and
the functional equilibrium of the stomatognathic
system may be altered, causing a series of signs
and symptoms6, highlighting alterations in dental
structures, joint noise and facial pain. The altered
mastication observed implies that persistent
bruxism prolongs the excitability of afferent nociceptors
of the masticatory and facial muscles,
resulting in sensitization. This increases the
painful stimulus, particularly in areas close to the
oral cavity and those related to chewing. As such,
it is believed that bruxism can be detrimental to
the masticatory function8. It is also a risk factor
for temporomandibular dysfunctions (TMD) 12, 23,
35. Some authors have analyzed the association
between bruxism, symptoms of temporomandibular
dysfunction and pain, hypothesizing that bruxism
may be one of the causes8, and a contributing
factor for TMD4. A recent systematic literature
review on the relationship between bruxism and
temporomandibular dysfunction showed a positive
association between them, based on clinical
diagnostic or self-report methods, whereas quantitative
methods for bruxism diagnosis - polysomnography
and electromyography - demonstrate low
association for TMD symptoms35.
Implications that patients report during mastication
corroborate the findings of Sutin et al. who
found that individuals with bruxism complained
of joint noise and chewing difficulties37. In order
to investigate the relationship between bruxism
and craniofacial pain and masticatory symptomatology,
Ciancaglini et al. demonstrated a complex
association among the variables analyzed, underscoring
difficulty with opening the mouth, joint
noise, sensitivity or mandibular muscle fatigue
and pain during mandibular movements8. Pizolato
et al. analyzed maximum bite force in patients
with temporomandibular dysfunction and bruxism,
reporting that the presence of pain in the
facial region is related to marked functional compromise4.
It is believed that distribution of muscle
strength in the teeth and temporomandibular joints
of individuals with bruxism may result in tooth
wear as well as hyperactivity and masseter muscle
hypertrophy4.
Modification in orofacial muscles and the stomatognathic
functions of chewing, swallowing and
speaking characterize an orofacial myofunctional
disorder. This may be associated with causal
factors of the dysfunctions, provoking an imbalance
in the functioning of the temporomandibular
joint. It may also be the result of nociceptive
stimulation caused by occlusion and/or the temporomandibular
joint, which may provoke compensatory
muscle behavior that can aggravate or
perpetuate the problem25. Alterations in mastication
and other orofacial behavior may provoke a
significant change in mechanical load of one
temporomandibular joint (TMJ) or the other.
TMDs involve changes in stomagtognathic functions
as well as in lip and tongue position owing
to the presence of nociceptive stimuli, triggered
by occlusion and/or TMJ. These modifications
are considered a compensatory or adaptive
response, aimed at facilitating masticatory function
and preserving structures in order to minimize
pain and avoid discomfort. Unilateral
mastication in individuals with TMD causes
irregular movement, such as slowness, altered
direction of movement and increased pain when
chewing, where individuals opt for the side with
greater masticatory efficiency25. It is important
to note that unilateral mastication in patients
with TMD involves considerable risk of pain and
increased signs and symptoms of dysfunction.
Furthermore, compromised mastication occurs
if functional adaptation exceeds structural and
functional tolerance of TMJ, which may trigger
dysfunction38.
Bruxism causes changes in stomatognathic functions
and structures, negatively affecting wellbeing
when painful symptoms are present. As stated in
research by Macfarlane et al. on orofacial impact,
the most prominent effects resulted in consulting a
dentist or doctor, taking medication, sleep disturbances
and changes in eating habits. In addition to
more severe behavioral impacts, we also highlight
the inability to work, need for bed rest and reduced
social contact, where patients reported a less satisfactory
life26, negatively affecting their emotional
health.
In conclusion, individuals with bruxism displayed
significant differences in state anxiety, in contrast
to the non-bruxism group, showing an association
between emotional factors and bruxism. The masticatory
function in patients with bruxism was
reduced, which may be the result of hyperactivity
of the masticatory muscles caused by increased
muscle tension. Due to the sample size and type of
study employed, and considering the results
observed, a limitation of this study was that its findings
cannot be generalized. It is suggested that
future investigations on masticatory function and
orofacial myofunctional disorders should strive for
better diagnostic and therapeutic methods, as well
as employ interdisciplinary teams in a biopsychosocial
context.
ACKNOWLEDGMENTS
The authors are grateful to the Department of Dentistry for its support and encouragement of research and development.
1. Lavigne GJ, Khoury S, Abe S, Yamaguchi T, Raphael K. Bruxism physiology and pathology: an overview for clinicians. J Oral Rehabil 2008;35:476-494.
2. Manfredini D, Lobbezoo F. Role of psychosocial factors in the etiology of bruxism. J Orofac Pain 2009;23: 153-166.
3. Katayoun E, Sima F, Naser V, Anahita D. Study of the relationship of psychosocial disorders to bruxism in adolescents. J Indian Soc Pedod Prev Dent 2008; 26 Suppl 3:S91-97.
4. Pizolato RA, Gaviao MB, Berretin-Felix G, Sampaio AC, Trindade Junior AS. Maximal bite force in young adults with temporomandibular disorders and bruxism. Braz Oral Res 2007;21:278-283.
5. Blini CC, Morisso MF, Bolzan GP, Silva AMT. Relacao entre bruxismo e o grau de sintomatologia de disfuncao temporomandibular. Rev CEFAC 2010;12:427-433.
6. de la Hoz-Aizpurua JL, Diaz-Alonso E, Latouche- Arbizu R, Mesa-Jimenez J. Sleep bruxism. Conceptual review and update. Med Oral Patol Oral Cir Bucal 2011; 1:231-238.
7. Almeida FL, Silva AMT, Correa ECR, Busanello AR. Relacao entre dor e atividade eletrica na presenca de bruxismo. Rev CEFAC 2011;13:399-406.
8. Ciancaglini R, Gherlone EF, Radaelli G. The relationship of bruxism with craniofacial pain and symptoms from the masticatory system in the adult population. J Oral Rehabil 2001;28:842-848.
9. Castelo PM, Barbosa TS, Gaviao MB. Quality of life evaluation of children with sleep bruxism. BMC Oral Health 2010;10:16.
10. Giraki M, Schneider C, Schafer R, Singh P, Franz M, Raab WH, Ommerborn MA. Correlation between stress, stresscoping and current sleep bruxism. Head Face Med 2010;6:2.
11. Winocur E, Uziel N, Lisha T, Goldsmith C, Eli I. Selfreported bruxism - associations with perceived stress, motivation for control, dental anxiety and gagging. J Oral Rehabil 2011;38:3-11.
12. Bayar GR, Tutuncu R, Acikel C. Psychopathological profile of patients with different forms of bruxism. Clin Oral Investig 2012;16:305-311.
13. Gungormus Z, Erciyas K. Evaluation of the relationship between anxiety and depression and bruxism. J Int Med Res 2009;37:547-550.
14. Restrepo CC, Vasquez LM, Alvarez M, Valencia I. Personality traits and temporomandibular disorders in a group of children with bruxing behaviour. J Oral Rehabil 2008; 35:585-593.
15. Fissmer JFW, Garanhani RR, Sakae TM, Traebert JL, Filho EJS. Relacao entre ansiedade e bruxismo em academicos de odontologia. ACM Arq Catarin Med 2008;37:25-29.
16. Molina OF, Sobreira MA, Tavares PG, Dib JE, Aquilino RN. Anxiety in craniomandibular disorders and bruxing behaviour patients: the role of pain in single and multiple sites and severity of bruxing behaviour. Part I: inclusion of the extreme behaviour group and report of preliminary psychological data on anxiety. Rev Neurocienc 2006; 14:23-30.
17. Andrade LHSG, Gorenstein C. Aspectos gerais das escalas de avaliacao de ansiedade. Rev Psiquiatr Ciln 1998;25: 285-290.
18. Duarte D, Hubner MMC. Ansiedade, bruxismo e aprendizagem: uma analise comparativa em alunos da 7a serie do ensino fundamental. Psicol Teor Prat 1999;1:43-52.
19. Calderon Pdos S, Kogawa EM, Lauris JR, Conti PC. The influence of gender and bruxism on the human maximum bite force. J Appl Oral Sci 2006;14:448-453.
20. Molina OF, dos Santos Junior, Nelson SJ, Nowlin T. A clinical study of specific signs and symptoms of CMD in bruxers classified by the degree of severity. Cranio 1999; 17:268-279.
21. Koyano K, Tsukiyama Y, Ichiki R, Kuwata T. Assessment of bruxism in the clinic. J Oral Rehabil 2008;35: 495-508.
22. Gorenstein C, Andrade LH. Validation of a Portuguese version of the Beck Depression Inventory and the State-Trait Anxiety Inventory in Brazilian subjects. Braz J Med Biol Res 1996;29:453-457.
23. Manfredini D, Landi N, Fantoni F, Segu M, Bosco M. Anxiety symptoms in clinically diagnosed bruxers. J Oral Rehabil 2005;32:584-588.
24. Basson RA, Mwaba K, Rossouw RJ, Geerts GAVM, Kotze TJV, Stuhlinger ME. The significance of sub-threshold symptoms of anxiety in the aetiology of bruxism. S Afr J Psychol 2010;40:119-124.
25. Ferreira CL, Da Silva MA, de Felicio CM. Orofacial myofunctional disorder in subjects with temporomandibular disorder. Cranio 2009;27:268-274.
26. Macfarlane TV, Blinkhorn AS, Davies RM, Kincey J, Worthington HV. Oro-facial pain in the community: prevalence and associated impact. Community Dent Oral Epidemiol 2002;30:52-60.
27. Kampe T, Edman G, Bader G, Tagdae T, Karlsson S. Personality traits in a group of subjects with long-standing bruxing behaviour. J Oral Rehabil 1997; 24:588-593.
28. Manfredini D, Landi N, Romagnoli M, Bosco M. Psychic and occlusal factors in bruxers. Aust Dent J 2004;49: 84-89.
29. Bellini M, Marini I, Checchi V, Pelliccioni GA, Gatto MR. Self-assessed bruxism and phobic symptomatology. Minerva Stomatol 2011;60:93-103.
30. Guillen-Riquelme A, Buela-Casal G. Psychometric revision and differential item functioning in the State Trait Anxiety Inventory (STAI). Psicothema 2011;23: 510-515.
31. Okeson JP. A psicologia da dor. In: Okeson JP, editor. Dores Bucofaciais de Bell. Sao Paulo: Quintessence, 1998;93-102.
32. da Silva AM, Oakley DA, Hemmings KW, Newman HN, Watkins S. Psychosocial factors and tooth wear with a significant component of attrition. Eur J Prosthodont Restor Dent 1997;5:51-55.
33. Rompre PH, Daigle-Landry D, Guitard F, Montplaisir JY, Lavigne GJ. Identification of a sleep bruxism subgroup with a higher risk of pain. J Dent Res 2007;86:837-842.
34. Pierce CJ, Chrisman K, Bennett ME, Close JM. Stress, anticipatory stress, and psychologic measures related to sleep bruxism. J Orofac Pain 1995;9:51-56.
35. Manfredini D, Lobbezoo F. Relationship between bruxism and temporomandibular disorders: a systematic review of literature from 1998 to 2008. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:26-50.
36. Berretin-Felix G, Genaro KF, Trindade IEK, Trindade Junior AS. Masticatory function in temporomandibular dysfunction patients: electromyographic evaluation. J Appl Oral Sci 2005;13:360-365.
37. Sutin AR, Terracciano A, Ferrucci L, Costa PT. Teeth Grinding: Is Emotional Stability related to Bruxism? J Res Pers 2010;44:402-405.
38. de Felicio CM, de Oliveira MM, da Silva MA. Effects of orofacial myofunctional therapy on temporomandibular disorders. Cranio 2010;28:249-259.