Effects of different stimulus locations on inhibitory responses in human jaw-closing muscles.

The aim of this study was to examine the inhibitory responses in bilateral masseter and temporalis muscle activity when electrical stimulation with short or long duration was applied to six oro-facial locations. The exteroceptive suppression period (ES2) and inhibitory responses were recorded in the surface electromyogram (EMG) of bilateral masseter and temporalis muscles in 16 healthy subjects. Two stimulus durations (1 ms single pulse and 450 ms pulse train) adjusted to a perceived intensity of 7 (distinct painful) on a 0-10 Numerical Rating Scale (NRS) were applied to the following six oro-facial locations on the right side while the subject was biting at 50% of the maximal voluntary contraction: masseter muscle, temporalis muscle, temporomandibular joint, infraorbital nerve, supraorbital nerve, and mental nerve. The stimulus intensity required to reach an NRS score of 7 was significantly lower for 450 ms train stimuli than for 1 ms single stimuli (P<0·001). There were no significant differences in the magnitude of ES2 suppression among the six different locations (P>0·876) for the 1 ms single stimuli. There were significant decreases in Root-Mean-Square-EMG values in the 400-500 ms post-stimulus epoch compared with the pre-stimulus epoch (P<0·023) for 450 ms train stimuli, but there were no significant differences in the magnitude of inhibition among the six different locations (P<0·893). Short- and long-lasting electrical stimulation of various oro-facial locations induces similar bilateral inhibitory effects in the jaw-closing muscles but with different propensity which may reflect the somatotopic organisation of these responses.

Effect of conditioning electrical stimuli on temporalis electromyographic activity during sleep.

Inhibitory reflexes during voluntary contractions are well described; however, few studies have attempted to use such reflex-mechanisms to modulate electromyographic (EMG) activity in jaw-closing muscles during sleep. The aim was to apply a new intelligent biofeedback device (Grindcare(R)) using electrical pulses to inhibit EMG activity in the temporalis muscle during sleep. Fourteen volunteers participated who were aware of jaw-clenching activity as indicated by complaints from sleep partner, soreness or pain in the jaw-muscle upon awakening and tooth wear facets. The EMG activity was recorded from the temporalis muscle, online analysed and the frequency content determined using a signal recognition algorithm. Based on specific individual parameters for pattern recognition, an electrical square-wave pulse train, which was adjusted to a clear, but non-painful intensity (range 1-7 mA) was applied through the EMG electrodes, if jaw-clenching activity was detected. All volunteers had baseline EMG recordings for five to seven consecutive nights, followed by 3-weeks EMG recordings with the feedback turned on, 2 weeks without the feedback and finally 3 weeks with the biofeedback on. There were no session effects on the average duration of sleep hours (P = 0.626). The number of EMG episodes/hour sleep was significantly reduced during the two sessions with biofeedback (54 +/- 14%; 55 +/- 17%, P < 0.001) compared with baseline EMG activity and the session without biofeedback. The present study suggests that biofeedback with electrical pulses does not cause major disruption in sleep and is associated with pronounced reduction in temporalis EMG activity during sleep.

Relationships between craniofacial pain and bruxism.

A still commonly held view in the literature and clinical practice is that bruxism causes pain because of overloading of the musculoskeletal tissue and craniofacial pain, on the other hand, triggers more bruxism. Furthermore, it is often believed that there is a dose-response gradient so that more bruxism (intensity, duration) leads to more overloading and pain. Provided the existence of efficient techniques to treat bruxism, it would be straightforward in such a simple system to target bruxism as the cause of pain and hence treat the pain. Of course, human biological systems are much more complex and therefore, it is no surprise that the relationship between bruxism and pain is far from being simple or even linear. Indeed, there are unexpected relationships, which complicate the establishment of adequate explanatory models. Part of the reason is the complexity of the bruxism in itself, which presents significant challenges related to operationalized criteria and diagnostic tools and underlying pathophysiology issues, which have been dealt with in other reviews in this issue. However, another important reason is the multifaceted nature of craniofacial pain. This review will address our current understanding of classification issues, epidemiology and neurobiological mechanisms of craniofacial pain. Experimental models of bruxism may help to further the understanding of the relationship between craniofacial pain and bruxism in addition to insights from intervention studies. The review will enable clinicians to understand the reasons why simple cause-effect relationships between bruxism and craniofacial pain are inadequate and the current implications for management of craniofacial pain.

Is There a Relation between Tension-Type Headache, Temporomandibular Disorders and Sleep?

Introduction. Tension-Type Headache (TTH) is the most prevalent headache often associated with impaired function and quality of life. Temporomandibular Disorders (TMD) and TTH frequently coexist; characterized by pericranial tenderness and impact on daily life. We aim to apply a standardized questionnaire for TMD to characterize and analyse an eventual relation between sleep and oral health in TTH in a controlled design. Material and Methods. 58 consecutive TTH patients and 58 healthy controls were included. The Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) questionnaire, Oral Health Impact profile (OHIP) and questionnaires for sleep were applied. Results. TTH-patients had significantly higher pain scores (P < 0.001), decreased quality of life (P < 0.001), and higher total sleep scores (P < 0.001) compared to controls. Conclusion. For the first time we have identified a clear relation between TTH and TMD symptoms, depression, anxiety, poor sleep, and impairments of oral function in carefully classified patients. These findings indicate a close, but incomplete, overlap between TTH and TMD. Their underlying pathophysiological mechanisms need further research.

Effect of stimulus parameters and contraction level on inhibitory responses in human jaw-closing muscles: Implications for contingent stimulation.

OBJECTIVE: Examine the effect of stimulus duration, intensity and level of muscle contraction on the inhibitory responses evoked by electrical stimuli in human jaw-closing muscles applied to the right mental nerve. DESIGN: The inhibitory jaw-reflexes, short-latency (ES1) and long-latency (ES2), were recorded in the surface electromyogram (EMG) of masseter and temporalis muscles in 16 healthy subjects. Three stimulus durations (1ms single square-wave pulse, 10 and 450ms square-wave pulse train), two stimulus intensities adjusted to perceived intensity of 3 (non-painful) and 7 (distinct painful) on a 0-10 verbal rating scale were applied to the right mental nerve while the subject was biting at 25% and 50% of the maximal voluntary contraction (MVC). RESULTS: The magnitude of suppression in the ES2 evoked by 1 and 10ms stimuli was dependent on stimulus intensity (P<0.002 and P<0.001, respectively) but not contraction level. However, ES1 could not be observed in most of the recordings. There were significant decreases evoked by the 450ms stimuli in RMS-EMG values in the 400-500ms compared with the pre-stimulus interval (P<0.001) which was dependent on contraction level (P<0.01) but not on stimulus intensity (P=0.486). CONCLUSIONS: The present results suggest that the ES2 reflex response is associated with the duration of the electrical stimuli, the intensity level but not the contraction level. In contrast, the inhibitory effects of ultra-long stimuli (450ms) are not specifically related to the intensity level suggesting that this is a non-nociceptive response.

Effect of a nociceptive trigeminal inhibitory splint on electromyographic activity in jaw closing muscles during sleep.

The nociceptive trigeminal inhibitory (NTI) splint has been claimed to decrease the electromyographic (EMG) activity of jaw-closing muscles and relieve symptoms of various types of temporomandibular disorders (TMD) and bruxism. The present study was designed to address the question about EMG-changes during sleep. Ten patients (age: 23-39 years) with a self-report of tooth-grinding during sleep were recruited. Patients were examined at baseline and after each treatment period with the use of the Research Diagnostic Criteria for TMD. A portable EMG-device was used to record EMG-activity from the masseter muscle during sleep. The patients received two 2-week splint treatments in a randomized cross-over fashion; an NTI splint and a standard flat occlusal splint (OS). EMG data were analysed according to published criteria. Using a 10% of maximum clenching EMG-activity cut-off threshold to determine the number of EMG-events h(-1) of sleep, the NTI splint was associated with a significant reduction (9.2 +/- 3.2 events h(-1)) compared with baseline EMG (19.3 +/- 4.0; anova: P = 0.004, Tukey post hoc: P = 0.006), whereas there were no differences between the OS (16.2 +/- 4.7) and baseline EMG (19.2 +/- 4.1; P = 0.716). There were no effects of either NTI or OS on clinical outcome measures (anovas: P > 0.194). This short-term study indicated a strong inhibitory effect on EMG-activity in jaw closing muscles during sleep of the NTI, but not the OS. However, the EMG-activity was not directly related to clinical outcome. Further studies will be needed to determine long-term effects and possible side effects of the NTI splint.