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Journal of Dental Research

DOI: 10.1177/154405910708600906 2007; 86; 837 J DENT RES

P.H. Rompré, D. Daigle-Landry, F. Guitard, J.Y. Montplaisir and G.J. Lavigne Identification of a Sleep Bruxism Subgroup with a Higher Risk of Pain

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INTRODUCTION

Sleep bruxism was recently classified as a movement disorder during sleep

(AASM, 2005). In 1996, we proposed sleep bruxism research diagnostic

criteria (SB-RDC) for polygraphic recording of sleep bruxism motor activity

(Lavigne et al., 1996). These criteria were based on a small sample size (18

sleep bruxers and 18 control individuals). They were derived from

electromyographic and audio-video recognition of jaw muscle activity in

relation to: (1) a positive report of tooth grinding during sleep; and (2) the

presence of sleep bruxism in a sleep laboratory. The criteria were: > 4 sleep

bruxism episodes/hr of sleep, > 25 sleep bruxism bursts/hr of sleep, and > 1

sleep bruxism episode with tooth-grinding sounds.

Over the last 15 years, we have made sleep laboratory recordings of 100

individuals with a positive home history of tooth grinding. Interestingly, half

of the persons presented a low frequency of sleep bruxism episodes per hour

of sleep (lower than 4 episodes/hr) and few tooth-grinding episodes, in spite

of their sleep partners' complaints of frequent grinding noise. One

explanation may be that these persons experienced pain, which caused them

to have fewer orofacial activities, in accordance with the pain adaptation

model (Lund, 1995; Lavigne et al., 1997). Therefore, the objectives of this

paper were to validate the 1996 SB-RDC in a large number of control

individuals and sleep bruxers recorded in the sleep laboratory, and to

challenge the hypothesis that pain is associated with lower frequencies of

orofacial activities.

MATERIALS & METHODS

ParticipantsData from 100 sleep bruxers and 43 control individuals, recorded in the sleep

laboratory since 1990, were used for the analysis. Sleep bruxers were chosen

based on: (1) a history of frequent tooth grinding occurring at least 3 nights perweek for the preceding 6 mos, as confirmed by a sleep partner; (2) clinical

presence of tooth wear; (3) masseter muscle hypertrophy; and (4) report of jaw

muscle fatigue or tenderness in the morning (American Sleep Disorders

Association, 1997; AASM, 2005; Lavigne et al., 2005). Control individuals

were selected on the basis of the absence of a history of tooth grinding during

sleep and of other clinical evidence of sleep bruxism (American Sleep Disorders

Association, 1997; AASM, 2005; Lavigne et al., 2005). Exclusion criteria for

both sleep bruxers and control individuals were TMD as a primary complaint, a

medical history of neurological disorders, mental disorders, or sleep disorders

(e.g., apnea, periodic leg movements, insomnia). At the time of recordings, none

of the participants was taking medication, or was under the influence of alcohol,

nicotine, or caffeine. All participants provided informed consent according to the

institutional rules (Hôpital du Sacré-Coeur).

Polygraphic RecordingsIndividuals were studied in the sleep laboratory for two consecutive nights. The

ABSTRACT Sleep bruxism research diagnostic criteria (SB-

RDC) have been applied since 1996. This study

was performed to validate these criteria and to

challenge the hypothesis that pain is associated

with lower frequencies of orofacial activities.

Polygraphic recordings were made of 100

individuals presenting with a clinical diagnosis of

sleep bruxism and 43 control individuals.

TwoStep Cluster analyses (SPSS) were performed

with sleep bruxism variables to reveal groupings

among sleep bruxers and control individuals.

Participants completed questionnaires during

screening, diagnosis, and recording sessions.

Cluster analysis identified three subgroups of

sleep bruxers. Interestingly, 45 of the 46 sleep

bruxers with values below SB-RDC were

classified in the low-frequency cluster. These

individuals were more likely to complain of pain

and fatigue of masticatory muscles than were the

higher-frequency sleep bruxers (odds ratios > 3.9,

p < 0.01). Sleep bruxers were distributed among

three heterogeneous groups. Sleep bruxers with

low frequencies of orofacial activities were more

at risk of reporting pain.

KEY WORDS: sleep bruxism, polygraphy, cluster

analysis, diagnostic criteria, tooth grinding, pain.

Received February 14, 2006; Last revision April 18, 2007;

Accepted May 8, 2007

A supplemental appendix to this article is published

electronically only at http://www.dentalresearch.org.

Identification of a Sleep Bruxism Subgroup with a Higher Risk of Pain

P.H. Rompré1, D. Daigle-Landry1, F. Guitard1, J.Y. Montplaisir2, and G.J. Lavigne1,2*1Faculty of Dental Medicine, Université de Montréal, C.P.6128, succ. Centre-Ville, Montréal, Canada, H3C 3J7; and2Centre d'étude du sommeil et des rythmes biologiques,Hôpital du Sacré-Coeur, Canada; *corresponding author,gilles.lavigne@umontreal.ca

J Dent Res 86(9):837-842, 2007

RESEARCH REPORTSClinical

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838 Rompré et al. J Dent Res 86(9) 2007

first night allowed them to adapt to the laboratory setting and

permitted researchers to rule out sleep disorders. On the second

night, sleep bruxism and sleep were analyzed. Polygraphic

recordings, with surface electrodes, included two

electroencephalograms (EEG; C3A

2, O

2A

1), bilateral electro-

oculograms, an electrocardiogram, and electromyograms (EMG)

from chin/suprahyoid, bilateral masseter, temporalis, and tibialis

muscles. Respiration was monitored with a nasal flow sensor. All

signals were amplified and recorded at a sampling rate of 128 Hz

and stored for off-line analysis by Harmonie Software (Stellate

Systems, Montréal, Canada). Audio and video recordings were

carried out simultaneously to distinguish sleep bruxism episodes

from non-specific orofacial activities (Velly-Miguel et al., 1992;

Kato et al., 1999).

Sleep and Sleep Bruxism ScoringSleep was scored according to standard criteria (Rechtschaffen and

Kales, 1968). A micro-arousal was defined as an abrupt EEG

frequency shift (> 3 sec) without complete awakening (American

Sleep Disorders Association, 1991). Sleep bruxism episodes were

scored into phasic (3 EMG bursts or more, each lasting 0.25 to 2.0

sec), tonic (one EMG burst > 2.0 sec), or mixed (both types of

bursts) episodes (Lavigne et al., 1996). Tonic activities were

analyzed for both groups, even though most episodes in control

individuals are phasic or mixed, designated as Rhythmic

Masticatory Muscle Activity (RMMA; Lavigne et al., 2001b).

Scoring was performed blind to participant status.

QuestionnairesParticipants answered questions concerning awareness of sleep

bruxism, sleep habits, anxiety, stress, fatigue, nervousness, current

facial pain intensity, painful jaw upon awakening, and fatigue of

masticatory muscles at different moments. Participants answered a

selection questionnaire during a telephone interview. Then, a

questionnaire was completed during diagnosis, in the dental clinic.

Finally, questionnaires were completed in the sleep laboratory

before bedtime in the evening, and after awakening in the

morning.

Statistical AnalysesSleep and sleep bruxism variables that were not normally

distributed were normalized with a logarithm. For these variables,

groups were compared by two-sample t tests or one-way

ANOVA, followed by Tukey pair-wise mean comparisons (Systat

11). Answers to questionnaires were analyzed by Fisher's exact

test and odds ratio. Answers on a VAS scale were evaluated with

the Mann-Whitney U test. A p < 0.05 was considered statistically

significant. TwoStep Cluster analyses (SPSS 14.0) were

performed with sleep bruxism variables to reveal natural

groupings (or clusters) among sleep bruxers and control

individuals separately. The algorithm tested a range of the number

of clusters. The optimal number of clusters was determined by the

software, with Schwarz's Bayesian Criterion (Norusis, 2006;

SPSS, 2006).

Table 1. Differences in Sleep and Bruxism between Subgroups

Sleep Bruxers/ Sleep Bruxers/ Control Individuals/ Control Individuals/ Contrasts*Included (n = 54) Excluded (n = 46) Included (n = 34) Excluded (n= 9 ) pa < 0.05

SleepSleep duration (min) 446.5 ± 5.9b 445.6 ± 6.0 450.3 ± 7.2 442.7 ± 9.9 0.94Sleep efficiency (%) 96.6 [85.1-99.3] 96.3 [83.7-99.4] 96.0 [79.2-99.3] 95.6 [84.6-98.2] 0.31Sleep latency 7.0 [0.3-69.3] 7.5 [1.3-42.3] 11.3 [2.3-41.7] 9.7 [2.3-23.3] 0.22Awakenings 24.0 ± 1.7 25.3 ± 1.5 23.3 ± 1.9 29.2 ± 5.6 0.56Micro-arousals/hr 8.4 [0.4-23.5] 6.9 [3.0-16.4] 5.7 [3.1-21.3] 6.0 [1.9-14.0] 0.70Stage 1 (%) 7.7 ± 0.6 8.2 ± 0.6 7.9 ± 0.7 7.3 ± 0.9 0.89 Stage 2 (%) 59.9 ± 1.2 59.4 ± 1.0 58.1 ± 1.5 59.8 ± 1.9 0.76Stage 3+4 (%) 11.0 ± 1.1 10.2 ± 1.0 13.3 ± 1.2 11.2 ± 1.6 0.30Stage REM (%) 21.4 ± 0.7 22.2 ± 0.7 20.8 ± 0.9 21.8 ± 1.3 0.67

Bruxism episodesEpisodes/hr 5.9 [3.7-15.2] 2.1 [0.1-4.5] 1.0 [0.0-4.0] 4.3 [1.3-7.3] < 0.001 1,2,3,4,5,6Phasic episodes/hr 4.0 [0.5-8.5] 0.9 [0.0-3.0] 0.2 [0.0-2.3] 2.7 [1.0-6.3] < 0.001 1,2,4,5,6Mixed episodes/hr 2.6 [0.0-7.8] 0.8 [0.0-2.6] 0.5 [0.0-2.0] 1.1 [0.1-3.9] < 0.001 1,2,3Tonic episodes/hr 0.0 [0.0-1.6] 0.1 [0.0-1.9] 0.1 [0.0-0.8] 0.0 [0.0-0.4] 0.81Episodes with noise 12 [0-84] 1 [0-12] 0 [0-5] 1 [0-39] < 0.001 1,2,3,4,6Episodes with movement 31 [6-92] 11.5 [1-29] 7 [0-23] 24 [10-34] < 0.001 1,2,4,5,6

Bruxism burstsBursts/hr 46.2 [21.0-136.8] 12.6 [0.5-23.4] 4.5 [0.0-33.4] 35.8 [8.2-48.8] < 0.001 1,2,4,5,6Phasic bursts/hr 43.1 [17.1-126.3] 11.1 [0.4-22.0] 3.2 [0.0-31.0] 31.6 [8.1-46.9] < 0.001 1,2,4,5,6Tonic bursts/hr 3.6 [0.0-11.9] 1.1 [0.1-4.7] 0.9 [0.0-8.1] 1.5 [0.1-5.9] < 0.001 1,2Bursts/episode 6.8 [4.2-13.2] 5.4 [3.0-10.7] 4.6 [0.0-19.5] 6.6 [5.4-11.5] < 0.001 1,2,6

* Contrasts: 1 = included bruxers-excluded bruxers, 2 = included bruxers-included control individuals, 3 = included bruxers-excluded controlindividuals, 4 = excluded bruxers-included control individuals, 5 = excluded bruxers-excluded control individuals, 6 = included controlindividuals-excluded control individuals.

a One-way ANOVA, followed by Tukey pairwise mean comparisons.b Mean ± SE or median [min-max] when data were normalized.

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J Dent Res 86(9) 2007 Sleep Bruxism Subgroups Identification 839

RESULTSParticipants were

young, with a mean

age around 25 yrs old

(bruxers, mean ± SE

= 26.5 ± 0.6; control

individuals, 24.5 ±

0.9, p = 0.07). There

was a significantly

higher proportion of

women among

bruxers (60%) and of

men among control

individuals (62.8%, p

= 0.02).

Participants were

included in or

excluded from

further studies based

on an analysis of

results from the

second night in the

sleep laboratory. Bruxers were included when they displayed

values higher than 2 of the 3 previously established cut-offs: 4

sleep bruxism episodes/hr, 25 sleep bruxism bursts/hr, 1

episode with grinding noise. Control individuals were included

when they had values lower than or equal to 2 of the 3 cut-offs.

Based on these EMG criteria, 54 bruxers were included for

further studies, while 46 were excluded. Similarly, 34 control

individuals were included for further studies, while nine were

excluded.

Sleep and sleep bruxism variables for these four subgroups

(included bruxers, excluded bruxers, included control

individuals, and excluded control individuals) are presented in

Table 1. Sleep variables revealed few differences among

subgroups. The number of micro-arousals per hour was

marginally higher in included bruxers than in included control

individuals (47% higher), but this did not reach statistical

significance in these young participants. However, sleep

bruxism variables revealed clear differences among the four

subgroups. All subgroups differed regarding the number of

episodes/hr, since all paired comparisons were statistically

significant. Excluded control individuals showed more

episodes/hr than did excluded bruxers (median 4.3 and 2.1,

respectively, p < 0.05). All paired comparisons involving

phasic episodes/hr, phasic bursts/hr, and bursts/hr were

significant, except the comparison between included bruxers

and excluded control individuals. No significant difference in

the number of episodes with noise was observed between

excluded bruxers and excluded control individuals, while other

comparisons were significant. Paired comparisons among

groups for mixed episodes/hr, tonic bursts/hr, and

bursts/episodes were significant mostly between included

bruxers and excluded bruxers, and included bruxers and

included control individuals. All groups had few tonic

episodes/hr (median near 0, p = 0.81).

TwoStep cluster analysis for bruxers identified three

subgroups of bruxers who differed in sleep bruxism frequency:

low, moderate, and high (Table 2). Box plots for the three

clusters are shown on the Fig. Dotted lines indicate cut-off

values of the SB-RDC. Groups were well-defined, and most

individuals in the low cluster (n = 49) had values lower than

cut-off for episodes/hr (cut-off = 4), bursts/hr (cut-off = 25),

and episodes with noise (cut-off = 1). Interestingly, 45 of the

46 excluded bruxers were classified in this cluster. The

importance of each variable in the three clusters is presented in

the APPENDIX.

Cluster analysis performed in control individuals identified

two clusters (Table 2). Most individuals in the high cluster had

values above cut-off (Fig.). Seven of the nine control

individuals who were excluded were classified in this cluster.

The importance of each variable in the two clusters is given in

the APPENDIX.

Answers to questionnaires (Table 3) revealed that excluded

bruxers were significantly more likely than included bruxers to

complain of clenching, with an odds ratio (OR) and 95%

confidence interval of 4.9 (1.3-18.6). Awareness of tooth

grinding, grinding noise, and tooth wear did not differ between

excluded bruxers and included bruxers. Analyses revealed that

both subgroups differed regarding complaint of pain. Excluded

bruxers were more likely than included bruxers to complain of

painful jaw upon awakening and fatigue of masticatory muscles

(OR over 3.9, Table 3). The level of pain of excluded bruxers

was slightly higher than that of included bruxers (median of

10.0 compared with 0.0 on a 0-100 VAS, p = 0.06). Evaluation

of the psychological state "During the day before recording"

showed no significant difference between subgroups. "Just

before recording", excluded bruxers reported stress and

nervousness in a higher proportion than did included bruxers

(OR 3.5 for stress, Table 3), and stress and fatigue in a higher

proportion than reported by included control individuals (p <

0.04, not shown). No significant difference in psychological

state was observed between included bruxers and control

individuals, either during the day before recording or just

before recording (p > 0.1, not shown).

DISCUSSIONIn a study published in 1996, the selection criteria for sleep

bruxers included having exhibited grinding sounds during sleep

at least 5 nights a wk in the preceding 6 mos (Lavigne et al.,

Table 2. Clusters for Sleep Bruxers (n = 99) and Control Individuals (n = 42)

Cluster 1 Cluster 2 Cluster 3 p

Sleep bruxers low, n = 49 moderate, n = 37 high, n = 13Episodes/hr 2.3 ± 0.2 [0.1-4.5]b 6.2 ± 0.3 [4.3-9.8] 9.6 ± 0.8 [5.9-15.2] < 0.001a

Bursts/hr 13.5 ± 1.0 [0.5-27.7] 41.3 ± 1.9 [21.8-67.3] 83.7 ± 6.1 [56.5-136.8] < 0.001a

Episodes with noise 2.5 ± 0.5 [0-12] 10.5 ± 1.3 [0-26] 39.2 ± 6.0 [10-84]% Participants with > 1 46.9 (n = 23) 89.2 (n = 33) 100.0 (n = 13) < 0.001a

episode with noise

Control individuals low, n = 34 high, n = 8Episodes/hr 1.3 ± 0.2 [0.0-4.0] 5.1 ± 0.5 [3.3-7.3] < 0.001Bursts/hr 6.5 ± 1.0 [0.0-24.7] 38.4 ± 2.7 [29.1-48.8] < 0.001Episodes with noise 0.5 ± 0.2 [0-5] 8.9 ± 4.7 [0-39] 0.06% Participants with > 1 11.8 (n = 4) 50.0 (n = 4)episode with noise

a One-way ANOVA, followed by Tukey's pairwise mean comparisons. Otherwise, two-sample t test was used.b Mean ± SE [min-max].

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840 Rompré et al. J Dent Res 86(9) 2007

1996). Moderate to severe sleep bruxers were recruited, as

shown by their number of sleep bruxism episodes/hr (mean ±

SE, 5.4 ± 0.6) and number of bursts/hr (40.7 ± 6.7). These

values are comparable with those of sleep bruxers included for

further studies and with those of the moderate cluster. Over the

years, to have access to a larger pool

of potential participants, investigators

have reduced the criterion for reported

grinding sounds during sleep from 5 to

3 nights a wk. Based on this criterion,

46 sleep bruxers recorded in the sleep

laboratory were excluded from further

studies, according to the SB-RDC.

Consequently, the sensitivity and

specificity of the SB-RDC established

in 1996 would be lower if re-evaluated

based on the total sample of sleep

bruxers (n = 100) and control

individuals (n = 46), due to the low

sleep bruxers and control individuals

with high frequencies of activities. For

example, the cut-off of 4 episodes/hr

would lead to lower sensitivity (55%

instead of 72%) and specificity (84%

instead of 94%). Lower values of cut-

off (2.5 episodes/hr instead of 4.0)

would be required to have sensitivity

and specificity around 70%. However,

the classification established by the

SB-RDC closely matches that of the

cluster analyses. Sleep bruxers in the

low cluster and control individuals in

the high cluster are those excluded by

the SB-RDC. These persons displayed

frequencies of activities different from

those typical of their clinical group.

Their inclusion in sleep laboratory

studies is therefore not suitable.

Close to 50% of persons with a

clinical history of tooth grinding

presented low frequencies of jaw

muscle contractions (episodes/hr,

bursts/hr) and tooth-grinding events

in the sleep laboratory. A high

proportion of these participants

reported painful jaw and fatigue of

masticatory muscles, although they

did not complain of or present TMD

(temporomandibular muscle or joint

pain or dysfunction). Other studies

have reported that sleep bruxers

frequently present with low pain

intensity in jaw and neck muscles, or

temporal headaches upon waking

(Bader et al., 1997; Lavigne et al.,1997; Camparis et al., 2006; Huynh

et al., 2006). The possibility that this

episodic pain and headache occurred

in relation to the recording in the

sleep laboratory may have con -

tributed to a reduction in the motor

activity, as suggested by the Pain Adaptation Model (Lund,

1995). Another explanation could be the natural variability in

the occurrence of sleep bruxism over time. We noted that the

variability in the number of episodes/hr of sleep was 25%,

while the variability in the number of episodes with grinding

Figure. Subgroups identified by cluster analysis based on sleep bruxism frequency. (a) Sleep bruxerswere divided into three clusters: low (n = 49), moderate (n = 37), and high (n = 13). (b) Controlindividuals were divided into two clusters: low (n = 34) and high (n = 8). Box plots combined withsymmetrical dot densities are shown. Dotted lines indicate cut-off values of the SB-RDC.

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J Dent Res 86(9) 2007 Sleep Bruxism Subgroups Identification 841

sound was over 50% (Lavigne et al., 2001a).

Conversely, approximately 20% (8/42) of control

individuals displayed a high frequency of orofacial activities

and were classified in the 'high control' cluster. Seven of these

control individuals had more than 4 episodes/hr of sleep, eight

reported more than 25 bursts/hr of sleep, and four presented at

least 2 episodes with grinding sounds. This last finding may be

surprising, but can be explained by the fact that some control

individuals, who are young (mean age = 25 yrs old), may grind

their teeth very rarely. Persons may also sleep alone or with a

sleep partner who is not disturbed by their grinding sounds,

thus providing an unreliable report of absence of tooth grinding

at home.

A correlation of sleep bruxism with stress and anxiety from

situational or psychological sources has been suggested (Rugh

and Harlan, 1988; Hicks et al., 1990; AASM, 2005). However,

this association remains controversial (Harness and Peltier,

1992; Pierce et al., 1995; Watanabe et al., 2003). The present

sleep study does not support this association, since the levels of

stress and anxiety did not differ between included sleep bruxers

and control individuals.

The observation of 3 clusters in sleep bruxers and of 2 in

control individuals further supports the suggestion that jaw

muscle contractions during sleep are a natural activity, with a

wide spectrum of frequency (number of episodes/hr). In a

previous study, control individuals presented from 0.1 to 12.6

episodes/hr of jaw muscle contraction during sleep, while sleep

bruxers presented from 1.2 to 15.2 episodes/hr (Lavigne et al.,2001b). It was also observed that the probability of jaw muscle

contraction during sleep is related to intrinsic physiological

cardiac and brain-related arousals called 'micro-arousals'

(Macaluso et al., 1998; Kato et al., 2001, 2003). From the

above observations, we suggested that these contractions are

probably distributed over a continuum, from a low-frequency

range to intermediate and high ranges, with coincidental tooth

grinding (Lavigne et al., 2003).

This study provides confirmation that the SB-RDC

developed ten years ago facil i tates a high level of

discrimination between sleep bruxers and control individuals.

The SB-RDC distinguishes low sleep bruxers and high

control individuals from the other individuals within their

group. Furthermore, pain is frequently reported among sleep

bruxers who display low frequencies of jaw muscle

contractions.

ACKNOWLEDGMENTSThis study was supported by the Canadian CIHR and the Québec

FRSQ. The authors thank Mrs. Christiane Manzini and Nelly

Table 3. Differences in Answers* to Questionnaires between Included and Excluded Sleep Bruxers

OR (95% CI)Sleep Bruxers/ Sleep Bruxers/ Sleep Bruxers Excluded/ Control Individuals/Included (n = 54) Excluded (n = 46) pa Sleep Bruxers Included Included (n = 34)

Complaint of sleep bruxismClenching 74.0 (37/50) 93.3 (42/45) 0.014 4.9 (1.3-18.6) 32.3 (10/31)Tooth grinding 81.3 (39/48) 67.5 (27/40) 0.15 0 (0/23)Grinding noise 97.7 (42/43) 100.0 (37/37) 1.00 0 (0/22)Tooth wear 74.4 (32/43) 88.2 (30/34) 0.16 13.6 (3/22)

Complaint of painPainful jaw upon awakening 48.9 (22/45) 78.9 (30/38) 0.006 3.9 (1.5-10.4) 0 (0/22)Fatigue of masticatory muscles 31.3 (15/48) 70.0 (28/40) 0.001 5.1 (2.1-12.8) 9.1 (2/22)Restless legs 29.5 (13/44) 58.3 (21/36) 0.013 3.3 (1.3-8.4) 6.3 (1/16)Current facial pain intensity(0-100 VAS)b 0.0 (0.0-80.0) 10.0 (0.0-70.0) 0.06c 0.0 (0.0-0.0)

Psychological stateDuring the day before recording

Anxiety 48.1 (13/27) 50.0 (14/28) 1.00 25.0 (2/8)Stress 55.6 (15/27) 64.3 (18/28) 0.59 37.5 (3/8)Fatigue 63.0 (17/27) 71.4 (20/28) 0.57 37.5 (3/8)Nervousness 33.3 ( 9/27) 50.0 (14/28) 0.28 37.5 (3/8)

Just before recordingAnxiety 18.5 ( 5/27) 35.7 (10/28) 0.23 12.5 (1/8)Stress 22.2 ( 6/27) 50.0 (14/28) 0.05 3.5 (1.1-11.3) 0 (0/8)Fatigue 59.3 (16/27) 71.4 (20/28) 0.40 25.0 (2/8)Nervousness 14.8 ( 4/27) 39.3 (11/28) 0.07 0 (0/8)

* Proportions of participants who answered yes, followed by their number, are shown. Values of included control individuals are listed for contrast.a p values for comparison between included and excluded sleep bruxers.b Median (min-max); otherwise, % of participants is shown.c Mann-Whitney U test; otherwise, Fisher's Exact Test was used.

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842 Rompré et al. J Dent Res 86(9) 2007

Huynh for their help in recruiting participants. We appreciate Dr.

Alice Petersen's contribution to editing of this paper.

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