To correlate self-reported bruxism, muscle tenderness, gastrointestinal disturbances, and their relation to the 9 dimensions of the Symptom Checklist-90-Revised (SCL-90-R). Methods: Data from 3 surveys - Bowel Symptom Questionnaire (BSQ), Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) and SCL-90-R were collected between 2005 and 2011 at the Orofacial Pain Clinic at Westmead Centre for Oral Health. BSQ was analyzed using the Rome II criteria to classify the bowel status: no symptoms, functional symptoms and irritable bowel syndrome (IBS). Outcomes of muscle palpation and self-reported bruxism were extracted from the RDC/TMD. SCL-90-R was scored to yield the 9 dimensions: somatization, obsessive-compulsive, interpersonal sensitivity, depression, anxiety, hostility, phobic anxiety, paranoid ideation and psychoticism. Chi-Square was used to compare bruxism and muscle pain; bruxism and bowel status; and bowel status and muscle pain. Multiple logistic regression analysis was performed to identify the predictors of bruxism and IBS. Results: Data for 246 surveys were collected for bruxism, muscle tenderness and bowel status. There is significant correlation between bruxism and muscle pain (p=0.004), IBS and bruxism (p=0.020), and constipation and bruxism (p=0.007). Multiple logistic regression analysis identified "muscle pain" and "constipation" as the predictors of bruxism; and "somatization" as the predictor for IBS. Conclusion: These data establish a relationship between bruxism and gastrointestinal disturbances. Approximately 36% of the Australian population has a functional GI disorder. If bruxism is related to GI disturbances, education regarding higher risk of tooth surface loss and restoration loss is needed for this patient group.
Keywords: bruxism, IBS, SCL-90-R, RDC/TMD
Bruxism is an activity of major concern to dentists because of its consequences of tooth wear, fracture of restorations, tooth hypersensitivity or jaw muscle pain1. In the past, emphasis on teeth and occlusal discrepancies has been considered the main causative factors for bruxism although there was no validated evidence. Currently, the focus has shifted from local environmental to pathophysiological factors2. Psychological factors such as stress and personality disorders are also frequently mentioned in relation to bruxism, and have been reported to be more prevalent in subjects with self-reported bruxism3, 4. Bruxism during sleep has been classified as a sleep-related movement disorder, characterized by rhythmic clenching and grinding. It is secondary to sleep-related micro-arousals, whereby the muscle activity peaks minutes before rapid eye movement. Awake bruxism, on the other hand, is dominated by clenching and is mainly associated with a nervous tic (an involuntary, compulsive, rapid, repetitive movement) or a reaction to stress1. The prevalence of sleep bruxism in the general population is about 8%, whereas awake bruxism is about 20%5.
Adaptation to stress is a priority for all animal species. Stress can be broadly defined as a disruption of homeostasis or an anticipated threat to well-being6. The autonomic nervous system (ANS) provides the most immediate response to stressors (physical or psychogenic) which provoke rapid alterations in physiological state through the innervation of end organs and in particular the heart, blood vessels, the gastrointestinal (GI) tract, and the adrenal medullae. It has been reported that ANS activation may be responsible for the initiation of sleep bruxism, as an increase in cardiac output always precedes bruxism activity, and that further studies are needed to investigate the temporal relationship between cardiac output and sleep bruxism7.
The ANS is recognized as a critical regulator of GI function and evidence suggests that it may also plays an important role in the development of GI symptoms8, 9. GI disturbances, such as irritable bowel syndrome (IBS), have an impact on a person's daily life. The disruption of daily activities due to pain or bloating, which requires frequent or prolonged relieving can be upsetting10. Psychological factors have also been reported to be associated with IBS11-13. However, currently there is minimal data associating bruxism with GI symptoms.
The aim of this investigation was to correlate self-reported bruxism, muscle tenderness, GI disturbances, and their relationship with the 9 dimensions of the Symptom Checklist-90-Revised (SCL-90-R).
Materials and Methods
Subjects and Study Design
Data was collected retrospectively from files including three questionnaires completed by patients referred to the Orofacial Pain Clinic, Westmead Centre for Oral Health over a 5 year period (2007 - 2011). The Orofacial Pain Clinic manages patients presenting with pain in the face and jaw region. Questionnaires have been de-identified as names, contact details and other patient specific information contained within the files are not required.
The questionnaires comprised of:
a) Bowel Symptoms Questionnaire (BSQ)14, an Australian self-report questionnaire provide reliable and valid data on gastrointestinal symptoms used to determine a diagnosis.
b) Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD)15, a 2-part questionnaire consisting of a self-reported history of orofacial pain and dysfunction, and a clinician assessment of range of jaw movement and presence of pain. Integrated questionnaire data indicate a diagnosis of TMD and oral parafunctions including daytime and night-time bruxism.
c) Symptom Checklist-90-Revised (SCL-90-R)16, a self-report questionnaire assesses 9 primary psychological dimensions and three summary scores termed global scores. The psychological profile of a patient is reflected in the derived scores.
BSQ
The BSQ was structured using the Rome-II criteria17 to determine if a patient has: a) no bowel irritations, b) functional symptoms, or c) irritable bowel syndrome. For patients with functional symptoms, the Rome-II criteria also identifies sub-groups of predominantly diarrhea, constipation or bloating (Table 1).
RDC/TMD
The RDC/TMD questionnaire is divided into 2 axes: Axis I on clinical examination and Axis II on self-reported symptoms. Question 8 of Axis I focuses on muscle palpation. As recommended, head and neck muscles are palpated by calibrated clinicians with 2lb pressure. In this study, the jaw muscles of interest were the temporalis and the masseter, which are involved in jaw closure, clenching and bruxism. Question 15 of Axis II focuses on self-reported bruxism. Patients indicate if they are aware of clenching or grinding, whether daytime or night-time, if advised by family or friends, and whether they awoke with jaw clenched and/or jaw pain.
SCL-90-R
The SCL-90-R helps to evaluate a range of commonly presenting psychological charcteristics. The 90 questions are grouped to specifically identify behavioral dimensions of somatization, obsessive-compulsive, interpersonal sensitivity, depression, anxiety, hostility, phobic anxiety, paranoid ideation, and psychotism.
Statistical Analysis
A sample size of 150 was calculated using a 95% confidence level and an 8% confidence interval (calculated on the size of the population reported to have functional GI disturbances, that is, 36% with a 50% possibility that they will also have bruxism).
Statistical analysis will initially be correlation co-efficients to determine the strength and direction of the relationships between the variables (bruxism, bowel status, muscle pain, dimensions of SCL-90-R) using Chi-Square. Mann-Whitney U test will assess the dimension of SCL-90-R against bruxism and GI disturbances with a null hypothesis that all dimensions have an equal distribution. Logistic regression analysis will be applied to variables which reject the null hypothesis. The regression analysis will determine which factors can be predicted by the presence of a positive GI dysfunction diagnosis, and bruxism.
Results
Data collection from 2005-2011included 246 BSQ questionnaires which were completed, of which 191 also completed the SCL-90-R. RDC/TMD examinations were completed for all patients. Using Chi-Square, significant association was identified with muscle pain and bruxism (p=0.004) (Table 2), bowel status and bruxism (p=0.02) (Table 3), and constipation and bruxism (p=0.007) (Table 4). Muscle pain and bowel status (p=0.2) (Table 5), diarrhea and bruxism (p=0.13) (Table 6), and functional bloating and bruxism (p=0.09) (Table 7) were not significantly associated.
The Mann-Whitney U test hypothesis rejected that somatization is the same across all categories of bruxism (p=0.043) (Table 8), and rejected that somatization (p=0.000), obsessive-compulsive (p=0.000), depression (p=0.000), anxiety (p=0.000), hostility (p=0.006), phobic anxiety (p=0.005) and psychotism (p=0.005) are similar across all categories of GI disturbances (Table 9). Variables (SCL-90-R dimensions, bowel status, presence of muscle pain) were entered in the multiple regression model, and the variables remaining were constipation and muscle pain as predictors for bruxism (Table 10), and somatization for GI disturbances (Table 11).
Somatization, the predictor for GI disturbances can also be seen in a box plot where the 75 percentile of the population with GI disturbances scored significantly higher in the SCL-90-R (Fig 1).
Discussion
At present, there are no studies reporting an association between bruxism and GI disturbances. This investigation has examined possible correlations between bruxism, GI disturbances and psychological factors. The findings establish a relationship between bruxism and muscle pain. This has been confirmed by other studies which compared self-reported bruxism and RDC/TMD diagnoses, and reported a higher prevalence for myofasical pain with bruxism18-20. Huang et al16 reported that self-reported bruxism was associated with an odds ratio of 4.8 for myofascial pain in 12468 subjects in Sweden. Michelotti et al18 found a positive report of daytime clenching/grinding which was twice more frequent among TMD patients than controls (66.1% versus 30.6%) and represented a significant risk factor for myofascial pain (OR = 4.9, 95% CI: 3.0-7.8). It was believed that the association between tooth clenching and muscle pain may be attributed to either damage of muscle fibers or to a reduction of blood supply21, 22. Larsson et al21, 22 reported on muscle biopsies studies which showed that mitochondrial damage and a significantly lower number of capillaries per fiber area were present in muscle fibers with myalgia. Nakamura et al23 reported on the measurement of local blood flow in the masseter muscle using hydrogen clearance, and showed perfusion of the muscle is significantly impaired in voluntary isometric contractions.
This study also established a relationship between bowel status and psychological factors, showing that somatization is the main characteristic of patients with GI disturbances11-13. Choung et al11 reported a significant association of IBS status with all subscale scores of the SCL-90-R, with numerically greater mean scores observed in subjects with IBS, except for phobic anxiety. Nicholl et al12 reported scores on each of the baseline psychosocial measures which were higher, reflecting a poorer psychosocial state, in those who reported IBS at follow-up, compared with those who remained symptom free. In a community base study, Koloski et al24 also reported subjects with IBS presented with higher levels of depression, anxiety and neuroticism, compared with subjects free of IBS. Murray et al25 found that acute physical and psychological stress alters the efferent autonomic innervation in the GI; and that patients with IBS showed heightened visceral sensation.
The specific outcome of this study is the correlation between bruxism and GI disturbances. The role of ANS and its response to stressors had been reviewed in past studies26, 27. In Cacioppo's first study24, the author reviewed psychosocial stressors and the ANS. He found that acute psychological stressors activate the sympathetic adrenomedullary system. In their second study27, the authors examined the effects of brief psychological stressors on cardiovascular, neuroendocrine, and cellular immune responses of 22 women. The resulting effects were heightened cardiac sympathetic activation, elevated plasma catecholamine concentrations, which affected the cellular immune response. It has been observed that bi-directional brain-gut interactions play an important role in the regulation of many vital functions in health and disease - in the regulation of digestive processes, modulation of the gut-associated immune system, and in the coordination of the overall physical and emotional state of the organism9. In patients with functional abdominal pain syndromes, conscious perception of interoceptive information from the GI tract can occur in the form of constant or recurrent discomfort or pain. This is often associated with alterations in ANS output and with emotional changes.
Alterations in ANS output have been shown in sleep bruxism in the form of elevated sympathetic cardiac activity1. Sleep bruxism is an extreme manifestation of rhythmic masticatory muscle activity (RMMA) occurring during sleep. RMMA during sleep is characterized by co-activation of both jaw-opening and jaw-closing muscles instead of the alternating jaw-opening and jaw-closing muscle activity pattern typical of chewing. This activity is 3 times more frequent and higher in amplitude in sleep bruxism patients28. During light sleep, most sleep bruxism episodes are observed in relation to brief cardiac and brain reactivations (3-15s) termed "micro-arousals". RMMA are secondary to a sequence of events in relation to sleep micro-arousals: the heart (increase in autonomic sympathetic activity) and brain are activated in the minutes and seconds, respectively, before the onset of activity in suprahyoid muscles and finally by RMMA in jaw closing master or temporalis muscles. This suggest that the onset of RMMA and sleep bruxism episodes are under the influences of brief and transient activity of the brainstem arousal-reticular ascending system contributing to the increase of activity in autonomic-cardiac and motor modulatory networks29. Cardiac autonomic modulation monitoring using spectral analysis of heart rate variability showed higher activity in bruxism patients than controls, which suggests increased stress30. Manabe et al8 reported abnormal fingertip blood flow responses, using continuous-wave Doppler sonography, which suggested the presence of high levels of sympathetic activity. The authors noted that increased sympathetic nervous system activity and decreased parasympathetic nervous system activity have been the most frequently noted differences when IBS patients were compared with healthy controls.
While the present study has established a relationship between bruxism and GI disturbances, it is recognized that the methodology is based on questionnaires answered by patients who attended the Orofacial Pain Clinic at Westemad Hospital. Of the 3 questionnaires, only the RDC/TMD is available in languages other than English, where as BSQ and SCL-90-R are English-only questionnaires. The results obtained were not broken down based on race, age or gender as the sub-sample would not generate enough power to provide a significant analysis.
Conclusion
Subjects were from those attending the Orofacial Pain Clinic, and were able to understand and complete the 3 questionnaires. The RDC/TMD is available in other languages, but the BSQ and SCL-90-R is only available in English. The limitation of this study is that the data reflect the association between bruxism and GI disturbances within this group of patients, which may or may not reflect an association in the general population.
These data nevertheless establish a relationship between bruxism and GI disturbances. Epidemiological data reports that 36% of the Australian population have a functional GI disorder, and 13% have a diagnosis of IBS31. Our data indicates that bruxism is related to GI disturbances, and requires patient education regarding the higher risk of tooth wear and restoration loss for this patient group.
