The purpose of this study was to identify associations between definite sleep bruxism, as defined by the American academy of sleep medicine, and chronic stress and sleep quality.
Sleep bruxism was determined by use of questionnaires, assessment of clinical symptoms, and recording of electromyographic and electrocardiographic data (recorded by the Bruxoff ® device). The study included 67 participants. Of these, 38 were identified as bruxers and 29 as non-bruxers. The 38 bruxers were further classified as 17 moderate and 21 intense bruxers.
Self-reported stress and self-reported sleep quality were determined by use of the validated questionnaires “Trier Inventory for the Assessment of Chronic Stress” (TICS) and the “Pittsburgh Sleep Quality Index” (PSQI).
No statistically significant association was found between sleep bruxism and self-reported stress or sleep quality. However, a significant association between specific items of chronic stress and poor sleep quality was identified.
The results of this study indicate an association between subjective sleep quality and subjective chronic stress, irrespective of the presence or absence of sleep bruxism.
Chronic stress and sleep quality do not seem to be associated with sleep bruxism.
(clinical trial no. NCT03039985)
Bruxism is defined as repetitive jaw-muscle activity characterized by clenching or grinding of the teeth and/or bracing or thrusting of the mandible with circadian manifestations . Because it may have detrimental effects, bruxism is of great interest to a variety of medical disciplines. The effects of bruxism, which include abnormal tooth wear and/or unsuccessful dental restorations, masticatory muscle tenderness and pain, headaches, and disturbed sleep, affect patients’ quality of life and incur dental and medical follow-up costs.
The prevalence of bruxism is between 8 and 31% , depending on the method of diagnosis used. This shows that bruxism is not an uncommon problem and is, thus, worthy of study.
Researchers have, therefore, been working to identify the risk factors for sleep bruxism and its correlation with other dental or medical diseases. Several factors are already associated with sleep bruxism, including gastroesophageal reflux disease , genetic factors , tinnitus , temporomandibular disorders , chronic migraine , and nicotine or alcohol consumption . Poor sleep quality and personality traits, such as stress , have also been associated with sleep bruxism.
Unfortunately, most of these risk factors or correlations have been identified by use of questionnaires for diagnosis of sleep bruxism . According to the criteria for sleep bruxism proposed by Lobezzo et al. , the exclusive use of questionnaires only indicates an association with “probable” sleep bruxism, therefore reducing the usefulness of these studies’ results. Because it is a cost- and time-consuming procedure, very few studies have adhered to the definition of definite sleep bruxism as verified by a polysomnographic recording (PSG). Moreover, this procedure records a patient’s oral behavior in an unusual environment, i.e., during a hospital stay, and not, as would be preferable, in a familiar domestic environment.
By combining electromyographic and electrocardiographic data , use of a portable device (Bruxoff ® ) shows a high correlation and a high agreement to the PSG. This should lead to a reduction in the number of false – positive or false – negative sleep bruxism diagnoses under domestic conditions.
The purpose of this study was to investigate possible associations between definite sleep bruxism (defined by use of questionnaires, assessment of clinical signs, and recording of electromyographic and electrocardiographic data) and chronic stress and sleep quality by use of the validated questionnaires “Trier Inventory for the Assessment of Chronic Stress” and “Pittsburgh Sleep Quality Index”.
The effect of body mass index, profession, and nicotine abuse on sleep bruxism was also studied.
Material and methods
This study was approved by the Ethics Committee of the University of Heidelberg, Protocol No. S-312/2014. All participants were informed about the procedure and possible risks and benefits of the study, and all participants gave informed consent.
The 67 individuals evaluated in this study were pre-selected from a separate clinical study prospectively evaluating molar ceramic single crowns, randomized for patients with and without sleep bruxism (clinical trials no. NCT03039985). All patients included in the study, therefore, needed a natural antagonist molar crown, and were included consecutively in the order in which they qualified for the single crown study.
The study was conducted at the Department of Prosthodontics of the University of Heidelberg, where all participants were recruited.
Patients under the age of 18 or unable to take out a contract were excluded from the study, as were patients who were pregnant or lactating, had acute neuropsychiatric diseases, hemorrhagic diatheses or heart pacemaker, or who had a known allergic reaction to the materials used.
Diagnosis of sleep bruxism
The criteria of the American Academy of Sleep Medicine were used to diagnose sleep bruxism. Definite sleep bruxism was diagnosed: by I) self-reporting of bruxism, II) clinical examination to assess signs of bruxism, and III) by use of the portable EMG and ECG recorder (Bruxoff ® ), as a substitute for PSG.
Two questionnaires were used for self-reporting of bruxism:
The first questionnaire, by Paesani et al. , comprises five items used to assess clenching/grinding while asleep and awake, to be answered “yes”, “no”, or “I don’t know”.
According to Paesani et al., bruxism is present if one of the items is answered “yes”.
The second questionnaire, by Raphael et al. , is a structured interview comprising seven items used to assess sleep clenching/grinding.
According to Raphael et al., bruxism is present if one of the items is answered “yes”.
In this study, self-reported bruxism was recorded as “yes” or “no” if both questionnaires yielded identical results.
Clinical examination to assess four clinical signs of bruxism, answered “yes” or “no”:
Abnormal tooth wear
Impressions of teeth in the buccal region
Impressions of teeth on the tongue
Masseter muscle hypertrophy
The clinical examination was performed by a single examiner, who was unaware of the results of the questionnaires and Bruxoff recordings during the examination.
In this study, clinical signs of bruxism were present if one of the four items was answered “yes”.
Bruxism diagnosis by use of a portable electromyography and electrocardiography device (Bruxoff ® ) for at least five nights and five hours’ sleep per night. Scoring of the Bruxoff recordings was automatically performed by use of specialized software (Bruxmeter ® , OT Biolettonica; Torino, Italy). The software classifies a sleep bruxism episode if the surface EMG burst (bilaterally from the masseter) is greater than 10% of maximum voluntary clenching and if it immediately follows (1–5 s interval) an increase in heart rate of 20% with respect to the baseline .
Sleep bruxism (SB) was diagnosed if more than two SB episodes per hour of sleep could be determined for one or more nights.
The cut-off for moderate sleep bruxism was set at more than two SB episodes per hour of sleep, and the cut-off for intense sleep bruxism was set at more than four SB episodes per hour of sleep .
Patients who answered “yes” to all three items (I–III) were included in the bruxism group, and patients who answered “no” to all three items were included in the non-bruxism group.
Participants with discrepancies between the items were excluded.
All data (I–III) were analyzed by a single examiner, who was unaware of the results of the questionnaires and Bruxoff recordings during the clinical examination. After the clinical examination, the examiner was informed of the results.
Sleep quality was measured by use of the Pittsburgh Sleep Quality Index (PSQI) .
The PSQI assesses sleep quality in the previous month. It comprises 19 items for self-reported sleep quality in the last month and five additional questions to be answered by roommates, if applicable. These five additional questions are not tabulated in the scoring of the PSQI. The 19 items are grouped into seven component scores: sleep quality, sleep latency, sleep duration, efficiency of habitual sleep, sleep disturbance, use of sleep medication, and diurnal dysfunction. These are then added to a global PSQI score. The PSQI score ranges from 0 to 21, with a higher score indicative of poorer sleep quality.
Poor sleep quality is assumed for values above five. This empirically derived cut-off value indicates higher difficulty in at least two components, or moderate difficulty in more than three components.
Chronic stress was measured by use of the Trier Inventory for Assessment of Chronic Stress (TICS) . By use of 57 questions, this standardized questionnaire assesses nine factors: work overload, social overload, pressure to perform, work discontent, excessive demands from work, lack of social recognition, social tensions, social isolation, and chronic worrying. It also provides a screening scale for chronic stress.
Raw values were converted into weighted (T-) values according to the age of the participants.
A T-value higher than 50 indicates higher stress in the respective factor. The same applies to the stress screening scale.
Nicotine abuse, body mass index, and work status
Participants were also asked about their nicotine consumption, i.e., whether they were a non-smoker, smoker, or ex-smoker. Participants’ body mass index (BMI) and work status were obtained from the PSQI questionnaire.
Data were evaluated by use of statistical software (SPSS 24; IBM Corp., New York, United States and SAS version 9.4; SAS Institute Inc., Cary, United States) with the participant as the statistical unit. Statistical evaluation included chi-squared tests for categorical data and Kruskal–Wallis tests for ordinal data. Statistical significance was set at α = 0.05. For BMI, the Receiver Operating Characteristic curve (ROC curve) was also plotted and the Youden Index optimal cut-point was calculated to discriminate between bruxers and non-bruxers. The Youden Index used as a performance index to assess the accuracy of diagnostic tests assigns equal weight to sensitivity (i.e. the probability of correctly identifying the presence of sleep bruxism on the basis of BMI value) and specificity (i.e. the probability of correctly identifying the absence of sleep bruxism on the basis of BMI value) in the formula Youden Index = sensitivity + specificity – 1. Selecting an optimal cut-off on the basis of the Youden Index ensures the used cut-off used is both highly sensitive and specific.
The study group comprised 67 participants ( Table 1 ). For one participant, no PSQI data and, therefore, no BMI data were available. Because another two participants (one male, one female) did not provide information about their weight, their BMI could not be calculated.
|n (%) male||10 (34.5)||16 (42.1)||26 (38.8)|
|n (%) female||19 (65.5)||22 (57.9)||41 (61.2)|
|Mean (SD)||59.7 (13.1)||49.7 (10.5)||54 (12.6)|
Of the 67participants, 38 were identified as bruxers (SB episodes >2) and 29 as non-bruxers. The 38 bruxers were further categorized into 17 moderate bruxers (SB episodes >2 and ≤4) and 21 intense bruxers (SB episodes >4).
Table 2 shows the results of the statistical analysis comparing sleep quality between the different categories of sleep bruxism. No differences were found between bruxers and non-bruxers when compared for sleep quality ( p ≥ 0.118).
|Variable||Non-Bruxer n = 29||Moderate Bruxer n = 17||Intense Bruxer n = 21||Total n = 67||p -value|
|≤5||18 (64.3%)||10 (58.8%)||12 (57.1%)||40 (60.6%)|
|>5||10 (35.7%)||7 (41.2%)||9 (42.9%)||26 (39.4%)|
|Mean ± SD||5.50 ± 2.89||6.12 ± 4.48||5.67 ± 4.05||5.71 ± 3.68|
|Mean ± SD||1.04 ± 0.51||0.94 ± 0.83||1.10 ± 0.83||1.03 ± 0.70|
|Mean ± SD||1.21 ± 0.74||1.00 ± 1.00||1.14 ± 0.96||1.14 ± 0.88|
|Mean ± SD||0.54 ± 0.64||1.18 ± 1.07||0.86 ± 0.91||0.80 ± 0.88|
|Efficiency of habitual sleep||0.559|
|Mean ± SD||0.71 ± 0.90||0.76 ± 1.15||0.52 ± 1.08||0.67 ± 1.01|
|Mean ± SD||1.07 ± 0.47||1.29 ± 0.59||1.10 ± 0.62||1.14 ± 0.55|
|Mean ± SD||0.14 ± 0.45||0.00 ± 0.00||0.19 ± 0.51||0.12 ± 0.41|
|Mean ± SD||0.75 ± 0.59||0.94 ± 0.83||0.76 ± 0.89||0.80 ± 0.75|