Permanent lingual nerve injury after dental procedures: a retrospective study of 228 patients.

Lingual nerve injury (LNI) is a rare, serious complication and previous studies include limited numbers of cases. The aim of this retrospective study was to report the neurosensory outcomes for a large patient cohort with permanent LNI and correlate the mechanism of injury (surgical vs non-surgical) to neurosensory characteristics. Demographics, procedural parameters, mandibular third molar (M3) position, surgeon type, neurosensory test results, and symptoms were recorded for 228 patients and analysed. The majority were female (67.1%). Overall, 59.6% of LNIs were caused by M3 removal and 36.4% by local anaesthesia. Complete loss occurred more frequently in surgical LNIs (P = 0.013). The presence of pain did not differ significantly, however the burning type of pain was significantly more frequent in non-surgical LNIs (P = 0.008) along with altered gustation (P = 0.025). The most common M3 position related to LNI was distoangular (40.4%), class III (63.2%), level A (58.1%) (Winter/Pell and Gregory classifications). The majority of patients undergoing M3 removal were >24 years. A total of 71.7% showed no sign of recovery and 5.5% reported further impairment in their condition. Overall, nine patients underwent microsurgical repair. This study presents neurosensory characteristics potentially decisive for timely referral of operable LNIs.

How May Placebo Mechanisms Influence Orofacial Neuropathic Pain?

The conceptualization of placebo has changed from inactive pills to a detailed understanding of how patients' perception of receiving a treatment influences pain processing and overall treatment outcome. Large placebo effects were recently demonstrated in chronic neuropathic pain, thereby opening the question of whether placebo effects also apply to orofacial neuropathic pain. In this article, we review the new definitions, magnitude, and social, psychological, neurobiologic, and genetic mechanisms of placebo effects in pain, especially neuropathic pain, to illustrate that placebo effects are not simply response bias but psychoneurobiological phenomena that can be measured at many levels of the neuroaxis. We use this knowledge to carefully illustrate how patients' perceptions of the treatment, the relationship with the health care provider, and the expectations and emotions toward a treatment can influence test and treatment outcome and potentially skew the results if they are not taken into consideration. Orofacial neuropathic pain is a new research area, and we review the status on definition, diagnosis, mechanisms, and pharmacologic treatment of neuropathic pain after trigeminal nerve injury, as this condition may be especially influenced by placebo factors. Finally, we have a detailed discussion of how knowledge of placebo mechanisms may help improve the understanding, diagnosis, and treatment of orofacial neuropathic pain, and we illustrate pitfalls and opportunities of applying this knowledge to the test of dental treatments.

Trigeminal nociceptive function and oral somatosensory functional and structural assessment in patients with diabetic peripheral neuropathy.

This case-control study primarily compared the trigeminal nociceptive function, the intraoral somatosensory profile and possible structural nerve changes between diabetic peripheral neuropathy (DPN, n = 12) patients and healthy participants (n = 12). The nociceptive blink reflex (nBR) was recorded applying an electrical stimulation over the entry zone of the right supraorbital (V1R), infraorbital (V2R) and mental (V3R) and left infraorbital (V2L) nerves. The outcomes were: individual electrical sensory (I0) and pain thresholds (IP); root mean square (RMS), area-under-the-curve (AUC) and onset latencies of R2 component of the nBR. Furthermore, a standardized full battery of quantitative sensory testing (QST) and intraepidermal nerve fibre density (IENFD) or  nerve fibre length density (NFLD) assessment were performed, respectively, on the distal leg and oral mucosa. As expected, all patients had altered somatosensory sensitivity and lower IENFD in the lower limb. DPN patients presented higher I0, IP, RMS and AUC values (p < 0.050), lower warm detection thresholds (WDT) (p = 0.004), higher occurrence of paradoxical heat sensation (PHS) (p = 0.040), and a lower intraoral NFLD (p = 0.048) than the healthy participants. In addition, the presence of any abnormal intraoral somatosensory finding was more frequent in the DPN patients when compared to the reference group (p = 0.013). Early signs of trigeminal nociceptive facilitation, intraoral somatosensory abnormalities and loss of intraoral neuronal tissue can be detected in DPN patients.

Comparison of orofacial thermal sensitivity assessed with simple devices and sophisticated equipment.

BACKGROUND: Simple thermal devices providing reliable data are needed to detect somatosensory disturbances in non-specialized clinical settings. Currently, evidence is lacking about their use. Therefore, the aim was to compare the assessment of perceived thermal sensitivity/pain in healthy humans with a state-of-the-art thermotester and with simple inexpensive customized thermal aluminium devices. METHODS: Twenty healthy volunteers participated in the study. The infraorbital region and the tip of the tongue were tested with the Medoc Pathway thermotester and simple aluminium thermal devices, with temperatures varying between 5-50°C. A numerical rating scale (NRS) from 0-50-100 was used for rating the perceived thermal sensitivity/painfulness. A control experiment was performed with 10 of the participants to test the potential impact of temporal summation of thermal stimuli with the use of temperature ramps (Medoc) compared with static temperature (simple devices). RESULTS: In the original experiment, the scores from the thermotester stimulation were higher than the scores for stimulation with the simple thermal devices with mean NRS differences between devices of 7.2 and 10.2 for the two tested regions. In the control experiment, the mean NRS differences decreased to -0.3 and 2.2, respectively. CONCLUSIONS: Provided that temporal summation of the thermal stimuli was avoided, there were only minor differences in perceived thermal sensitivity/painfulness between the two different assessment methods at both test sites. Therefore, the simple thermal devices can be useful for assessment of thermal sensitivity in clinical settings without access to expensive sophisticated equipment. However, more sophisticated equipment is needed for threshold measurements. SIGNIFICANCE: This study indicates that simple thermal devices to some extent can be used in a comparable way with sophisticated thermal stimulators. Therefore, they can be useful in clinical practice, where access to further equipment is lacking.

Temporomandibular disorders and psychosocial status in osteogenesis imperfecta - a cross-sectional study.

BACKGROUND: Osteogenesis Imperfecta (OI) is characterized by a number of deviations in the orofacial region. The aims of the present study were to investigate the occurrence of temporomandibular disorders, to evaluate the psychosocial status, and to assess the dental occlusion in a population of adult OI patients. METHODS: Participants (n = 75) were classified with mild OI, type I (n = 56), or moderate-severe OI, type III and IV (n = 19). OI patients were examined according to the Research Diagnostic Criteria for Temporomandibular Disorders (axis I and II). RESULTS: Temporomandibular disorders and functional limitations in the orofacial region were rare and did not differ between patients with mild and moderate-severe OI (P > 0.050). No significant differences between Graded Chronic Pain Scale grades 0, 1, and 2 were found in mild OI vs. moderate-severe OI (P > 0.160). Few patients (16%) had signs of depression, but close to half (48%) had signs of somatization. Patients with moderate-severe OI had a lower mean number of teeth compared to patients with mild OI (P <  0.050). In general, malocclusions were prevalent, and mandibular overjet and posterior cross-bite were found more often in moderate-severe OI compared with mild (P <  0.050). CONCLUSIONS: Patients with moderate-severe OI had more malocclusions than patients with mild OI. The psychosocial status of OI patients was remarkably healthy considering the severity of this disabling systemic disorder. The bodily pain complaints frequently reported in OI patients were not largely reflected in the orofacial area as painful temporomandibular disorders.

Multisensory modulation of experimentally evoked perceptual distortion of the face.

BACKGROUND: Chronic oro-facial pain patients often perceive the painful face area as "swollen" without clinical signs, that is a perceptual distortion (PD). Local anaesthetic (LA) injections in healthy participants are also associated with PD. OBJECTIVE: The aim was to explore whether PD evoked by LA into the infraorbital region could be modulated by adding mechanical stimulation (MS) to the affected area. METHODS: Mechanical stimulation was given with a brush and a 128-mN von Frey filament. Firstly, sixty healthy participants were randomly divided into three groups: (i) LA control, (ii) LA with MS, (iii) isotonic solution (ISO) with MS as an additional control condition. To further examine the role of a multisensory modulation, an additional experiment was conducted. Twenty participants received LA with MS (filament) in addition to visual feedback of their distorted face. The results of the two experiments are presented together. RESULTS: All three LA groups experienced PD; per contra, PD was not reported in the ISO group. MS alone did not change the magnitude of PD: brush (P = .089), filament (P = .203). However, when the filament stimulation was combined with additional visual information of a distorted face, there was observable decrease in PD (P = .002). CONCLUSION: The findings indicate the importance of multisensory integration for PD and represent a significant step forward in the understanding of the factors that may influence this common condition. Future studies are encouraged to investigate further the cortical processing for possible implications for PD in pain management.

Effect of transcranial direct current stimulation on neuroplasticity in corticomotor pathways of the tongue muscles.

The aim of this study is to investigate effects of transcranial direct current stimulation (tDCS) on neuroplasticity in corticomotor pathways related to tongue muscles evoked by a training task using the tongue drive system (TDS). Using a crossover design, 13 healthy participants completed two sessions of tDCS while performing 30 min of TDS training. Sessions were spaced at least 2 weeks apart and participants randomly received anodal and sham tDCS stimulation in the first session and the other condition in the second session. Single and paired pulse transcranial magnetic stimulation was used to elicit motor evoked potentials (MEPs) of the tongue at three time-points: before, immediately after and 30 min after training. Participant-based reports of fun, pain, fatigue and motivation, level of difficulty and effort were evaluated on numerical rating scales. There was no consistent significant effect of anodal and sham stimulation on single or paired pulse stimulation MEP amplitude immediately or 30 min after TDS training. Irrespective of tDCS type, training with TDS induced cortical plasticity in terms of increased MEP amplitudes for higher stimulus intensities after 30 min compared with before and immediately after training. Participant-based reports revealed no significant difference between tDCS conditions for level of fun, fatigue, motivation, difficulty and level of effort but a significant increase in pain in the anodal condition, although pain level was low for both conditions. In conclusion, tongue MEP amplitudes appear to be sensitive to training with the tongue using TDS; however, anodal tDCS does not have an impact on training-evoked neuroplasticity of tongue corticomotor pathways.

Verbal instructions influence pain thresholds assessment: A study using manual and electronic mechanical stimulators.

BACKGROUND: Quantitative sensory testing (QST) relies on psychophysical techniques and instructions to test subjects. This study examined the effect of different verbal instructions for mechanical pain thresholds (MPTs) using two different stimulation techniques; weighted pinprick stimulators and an electronic von Frey device (EvF). The test-retest reliability and within session variability in the MPTs for each verbal instruction were compared in addition. METHODS: Sixteen healthy volunteers participated. The MPTs with two different verbal instructions (pinprick and pain) were evaluated with two different stimulation techniques at three test sites: on the skin of the right cheek (face), on the buccal gingival mucosa of the right upper premolar region (gingiva) and on the tip of the tongue (tongue). The exact same protocol was repeated 1-2 weeks later for test-retest reliability. RESULTS: The MPT values with pain instruction were significantly higher than the values with the pinprick instruction for all sites and both stimulation techniques (p < .001). The absolute values of MPT were affected by instruction differences but it did not seem to have a major impact on reliability, and there were no significant differences in within session variability (p > .079) between the two different verbal instructions (pinprick and pain). CONCLUSIONS: The specific wording of standardized QST instructions resulted in significant differences in MPT values regardless of which of the two stimulation techniques were used; pinprick stimulators or EvF. This emphasizes the importance of careful standardization of QST instructions in addition to standardization of the stimulus application. SIGNIFICANCE: Quantitative sensory testing (QST) is a widely accepted tool for somatosensory testing and the reliability and variability in the QST test battery has been found to be acceptable. Changing minor details in the wording of standardized QST verbal instructions resulted in significant differences in mechanical pain thresholds. This emphasizes the importance of careful standardization of QST instructions in addition to standardization of the stimulus application.

Agreement between quantitative and qualitative sensory testing of changes in oro-facial somatosensory sensitivity.

Qualitative somatosensory testing (QualST) is a simple chairside test. It can be used to roughly assess the presence or absence of altered somatosensory function. To use QualST clinically, it is important to assess its agreement with quantitative sensory testing (QST). The aims of this study were to assess the agreement between QST and QualST when testing the modulation of facial sensitivity by capsaicin in healthy participants and to explore the agreement between QST and QualST in assessing the intraoral sensory function in clinical atypical odontalgia (AO) patients. Eighteen healthy pain-free adults and data from 27 AO patients were included in the study. Thirteen QST and three QualST parameters were evaluated at each site. Z-scores were computed for healthy participants, and Loss-Gain scores were created. The agreement observed between QST and QualST in participants with no alterations in facial sensation (placebo) was good, that is ranging from 89% to 94%. A poorer agreement was seen after capsaicin application in all test modalities with agreement ranging from 50% to 72%. The commonest misclassification observed was participants classified as normal according to QST, but hyper- or hyposensitive according to QualST after capsaicin application, especially for cold and pinprick. A similar trend was observed in AO patients where patients classified as normal using QST were misclassified as hypersensitive and in few patients as hyposensitive by QualST. In conclusion, the study showed that QualST may be used as a screening tool in the clinical setting, especially to show that subjects have normal sensory function.

Self-management programmes in temporomandibular disorders: results from an international Delphi process.

Self-management (SM) programmes are commonly used for initial treatment of patients with temporomandibular disorders (TMD). The programmes described in the literature, however, vary widely with no consistency in terminology used, components of care or their definitions. The aims of this study were therefore to construct an operationalised definition of self-management appropriate for the treatment of patients with TMD, identify the components of that self-management currently being used and create sufficiently clear and non-overlapping standardised definitions for each of those components. A four-round Delphi process with eleven international experts in the field of TMD was conducted to achieve these aims. In the first round, the participants agreed upon six principal concepts of self-management. In the remaining three rounds, consensus was achieved upon the definition and the six components of self-management. The main components identified and agreed upon by the participants to constitute the core of a SM programme for TMD were as follows: education; jaw exercises; massage; thermal therapy; dietary advice and nutrition; and parafunctional behaviour identification, monitoring and avoidance. This Delphi process has established the principal concepts of self-management, and a standardised definition has been agreed with the following components for use in clinical practice: education; self-exercise; self-massage; thermal therapy; dietary advice and nutrition; and parafunctional behaviour identification, monitoring and avoidance. The consensus-derived concepts, definitions and components of SM offer a starting point for further research to advance the evidence base for, and clinical utility of, TMD SM.

Bilateral sensory deprivation of trigeminal afferent fibres on corticomotor control of human tongue musculature: a preliminary study.

Transcranial magnetic stimulation (TMS) has demonstrated changes in motor evoked potentials (MEPs) in human limb muscles following modulation of sensory afferent inputs. The aim of this study was to determine whether bilateral local anaesthesia (LA) of the lingual nerve affects the excitability of the tongue motor cortex (MI) as measured by TMS. The effect on MEPs after bilateral LA of the lingual nerve was studied, while the first dorsal interosseous (FDI) muscle served as a control in ten healthy participants. MEPs were measured on the right side of the tongue dorsum in four different conditions: (i) immediately prior to anaesthesia (baseline), (ii) during bilateral LA block of the lingual nerve, (iii) after anaesthesia had subjectively subsided (recovery) and (iv) 3 h after bilateral lingual block injection. MEPs were assessed using stimulus-response curves in steps of 10% of motor threshold (T). Eight stimuli were given at each stimulus level. The amplitudes of the tongue MEPs were significantly influenced by the stimulus intensity (P < 0·001) but not by condition (P = 0·186). However, post hoc tests showed that MEPS were statistically significantly higher during bilateral LA block condition compared with baseline at T + 40%, T + 50% and T + 60% (P < 0·028) and also compared with recovery at T + 60% (P = 0·010) as well as at 3 h after injection at T + 50% and T + 60% (P < 0·029). Bilateral LA block of the lingual nerve seems to be associated with a facilitation of the corticomotor pathways related to the tongue musculature.

Increased pain and muscle glutamate concentration after single ingestion of monosodium glutamate by myofascial temporomandibular disorders patients.

BACKGROUND: A randomized, double-blinded, placebo-controlled study was conducted to investigate if single monosodium glutamate (MSG) administration would elevate muscle/serum glutamate concentrations and affect muscle pain sensitivity in myofascial temporomandibular disorders (TMD) patients more than in healthy individuals. METHODS: Twelve myofascial TMD patients and 12 sex- and age-matched healthy controls participated in two sessions. Participants drank MSG (150 mg/kg) or NaCl (24 mg/kg; control) diluted in 400 mL of soda. The concentration of glutamate in the masseter muscle, blood plasma and saliva was determined before and after the ingestion of MSG or control. At baseline and every 15 min after the ingestion, pain intensity was scored on a 0-10 numeric rating scale. Pressure pain threshold, pressure pain tolerance (PPTol) and autonomic parameters were measured. All participants were asked to report adverse effects after the ingestion. RESULTS: In TMD, interstitial glutamate concentration was significantly greater after the MSG ingestion when compared with healthy controls. TMD reported a mean pain intensity of 2.8/10 at baseline, which significantly increased by 40% 30 min post MSG ingestion. At baseline, TMD showed lower PPTols in the masseter and trapezius, and higher diastolic blood pressure and heart rate than healthy controls. The MSG ingestion resulted in reports of headache by half of the TMD and healthy controls, respectively. CONCLUSION: These findings suggest that myofascial TMD patients may be particularly sensitive to the effects of ingested MSG. WHAT DOES THIS STUDY ADD?': Elevation of interstitial glutamate concentration in the masseter muscle caused by monosodium glutamate (MSG) ingestion was significantly greater in myofascial myofascial temporomandibular disorders (TMD) patients than healthy individuals. This elevation of interstitial glutamate concentration in the masseter muscle significantly increased the intensity of spontaneous pain in myofascial TMD patients.

Reports of perceptual distortion of the face are common in patients with different types of chronic oro-facial pain.

Anecdotally, chronic oro-facial pain patients may perceive the painful face area as 'swollen'. Because there are no clinical signs, these self-reported 'illusions' may represent perceptual distortions and can be speculated to contribute to the maintenance of oro-facial pain. This descriptive study investigated whether chronic oro-facial pain patients experience perceptual distortions - a kind of body image disruption. Sixty patients were consecutively recruited to fill in questionnaires regarding i) pain experience, ii) self-reports of perceptual distortion and iii) psychological condition. Perceptual distortions were examined in the total group and in three diagnostic subgroups: i) painful post-traumatic trigeminal neuropathy (PPTN), ii) painful temporomandibular disorder (TMD) or iii) persistent idiopathic facial pain (PIFP). A large proportion of oro-facial pain patients reported perceptual distortions of the face (55·0%). In the diagnostic subgroups, perceptual distortions were most pronounced in PPTN patients (81·5%) but with no significant group differences. In the total group of chronic oro-facial pain patients, the present pain intensity explained 16·9% of the variance in magnitude of the perceptual distortions (R(2) = 16·9, F(31) = 6·3, P = 0·017). This study demonstrates that many chronic oro-facial pain patients may experience perceptual distortions. Future studies may clarify the mechanisms underlying perceptual distortions, which may point towards new complementary strategies for the management of chronic oro-facial pain.

Effect of experimental jaw muscle pain on dynamic bite force during mastication.

Knowledge about how Temporomandibular Disorder (TMD) pain patients regulate masticatory function is still unclear. To investigate the effect of experimental jaw muscle pain as well as texture and size of food on mastication, twelve healthy participants (30.6±7.5 years old) participated in this study. Experimental pain was induced by an infusion of 0.5 M monosodium glutamate (MSG) with isotonic saline (IS) serving as a control. After the infusions, the Jaw Functional Limitation Scale (JFLS) and Pain Catastrophizing Scale (PCS) were filled out. Electromyographic (EMG) activity in the masseter and temporalis muscles, jaw movements and bite force, which was measured by a customized intra-oral device, were recorded simultaneously during mastication of three different types of food. Pain was scored continuously on a visual analog scale. The results demonstrated a trend towards a decrease in the impulse of the bite force, as well as a significant decrease in EMG activity of the masseter muscle during the first five masticatory cycles, in the MSG session. Also, MSG induced increased JFLS and PCS scores compared with IS. On the other hand, the results suggested that the applied levels of pain may not change habitual masticatory movements. This study has revealed that a clinically relevant level of pain in the masseter muscle has only minor impact on the performance of mastication, probably due to a lack of exacerbation of pain during function. In future studies of jaw muscle function during painful conditions, it is important to include patient-based reports of functional limitation and emotional distress.

Reliability of intra-oral quantitative sensory testing (QST) in patients with atypical odontalgia and healthy controls - a multicentre study.

The reliability of comprehensive intra-oral quantitative sensory testing (QST) protocol has not been examined systematically in patients with chronic oro-facial pain. The aim of the present multicentre study was to examine test-retest and interexaminer reliability of intra-oral QST measures in terms of absolute values and z-scores as well as within-session coefficients of variation (CV) values in patients with atypical odontalgia (AO) and healthy pain-free controls. Forty-five patients with AO and 68 healthy controls were subjected to bilateral intra-oral gingival QST and unilateral extratrigeminal QST (thenar) on three occasions (twice on 1 day by two different examiners and once approximately 1 week later by one of the examiners). Intra-class correlation coefficients and kappa values for interexaminer and test-retest reliability were computed. Most of the standardised intra-oral QST measures showed fair to excellent interexaminer (9-12 of 13 measures) and test-retest (7-11 of 13 measures) reliability. Furthermore, no robust differences in reliability measures or within-session variability (CV) were detected between patients with AO and the healthy reference group. These reliability results in chronic orofacial pain patients support earlier suggestions based on data from healthy subjects that intra-oral QST is sufficiently reliable for use as a part of a comprehensive evaluation of patients with somatosensory disturbances or neuropathic pain in the trigeminal region.

An update on pathophysiological mechanisms related to idiopathic oro-facial pain conditions with implications for management.

Chronic oro-facial pain conditions such as persistent idiopathic facial pain (PIFP), atypical odontalgia (AO) and burning mouth syndrome (BMS), usually grouped together under the concept of idiopathic oro-facial pain, remain a diagnostic and therapeutic challenge. Lack of understanding of the underlying pathophysiological mechanisms of these pain conditions is one of the important reasons behind the problems in diagnostic and management. During the last two decades, neurophysiological, psychophysical, brain imaging and neuropathological methods have been systematically applied to study the trigeminal system in idiopathic oro-facial pain. The findings in these studies have provided evidence for neuropathic involvement in the pathophysiology of PIFP, AO and BMS. The present qualitative review is a joint effort of a group of oro-facial pain specialists and researchers to appraise the literature on idiopathic oro-facial pain with special focus on the currently available studies on their pathophysiological mechanisms. The implications of the findings of these studies for the clinical diagnosis and treatment of idiopathic oro-facial pain conditions are discussed.

Neurosensory assessment in patients with total reconstruction of the temporomandibular joint.

Somatosensory sensitivity and postoperative endogenous pain modulation have not been investigated in temporomandibular joint (TMJ) prosthesis patients. The objectives of this study were to assess somatosensory function at the TMJ and examine possible differences in conditioned pain modulation (CPM) between patients with total TMJ prostheses (n=7) and a reference group of healthy controls (n=20). Somatosensory abnormalities were assessed using quantitative sensory testing (QST), which encompasses thermal and mechanical testing procedures. CPM was tested by comparing pressure pain thresholds (PPT) before (baseline), during, and after the application of painful and non-painful cold stimuli. PPTs were measured at the TMJ and thenar eminence (control). The effect of CPM on PPT values was tested with analysis of variance. Three patients exhibited mixed somatosensory loss (i.e., decreased thermal and mechanical detection) with mixed hyperalgesia (i.e., increased sensitivity to thermal and mechanical pain) and two patients exhibited mixed loss with only mechanical hyperalgesia. There was a significant decrease in pressure pain sensitivity at both sites during painful cold application in healthy controls (P<0.001) but not in patients (P=0.476). In conclusion, QST measures demonstrated somatosensory abnormalities in patients with total TMJ prostheses. Noxious conditioning cold stimuli evoked CPM-like effects in healthy subjects but not in patients with TMJ reconstruction.

Analysis of brain and muscle activity during low-level tooth clenching--a feasibility study with a novel biting device.

In electromyographic (EMG) and functional magnetic resonance imaging (fMRI) studies, muscle and brain activity was compared during low levels of tooth clenching using a novel biting device to control bite force. A total of 21 healthy subjects performed motor tasks, comprising tooth clenching at 5, 10 and 20 N. During all measurements, subjects kept the novel bite device between the anterior teeth during tooth clenching. The EMG study (n = 15) characterised jaw muscle activity for the three motor tasks and demonstrated significant differences in root mean square (RMS) EMG amplitude between 5-, 10- and 20-N tooth clenching (F = 46.21, P < 0.001). There were no differences in variability of muscle activity between the three tooth-clenching levels. In an fMRI pilot study (n = 6), statistical comparisons were used to identify brain regions with significant activation in the subtraction of baseline from 5- or 20-N tooth-clenching activity. 5- and 20-N tooth clenching significantly and bilaterally activated the sensorimotor cortex, supplementary motor area, cerebellum and basal ganglia (P < 0.05, corrected for multiple comparisons). However, activation of each brain region did not differ significantly between two tooth-clenching tasks. Based on these preliminary findings, we propose that the novel biting device may be useful in further fMRI studies on controlled jaw muscle activation patterns in different craniofacial pain conditions. In addition, our fMRI result suggests that there are no significant differences in brain activity within low levels of tooth clenching with controlled force.

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.

Ethnic differences in oro-facial somatosensory profiles-quantitative sensory testing in Chinese and Danes.

Ethnic differences in pain experiences have been widely assessed in various pathological and experimental conditions. However, limited sensory modalities have been described in previous research, and the affective-motivational factors have so far been estimated to be the main mediator for the ethnic differences. This study aimed to detect the ethnic differences of oro-facial somatosensory profiles related to the sensory-discriminative dimension in healthy volunteers. The standardised quantitative sensory testing battery developed by the German Research Network on Neuropathic Pain was performed bilaterally in the infraorbital and mental regions on age- and gender-matched healthy Chinese and Danes, 29 participants each group. The influences of ethnicity, gender and test site on the somatosensory profile were evaluated by three-way anova. The ethnic disparities were also presented by Z-scores. Compared to Danes, Chinese were more sensitive to thermal detection, thermal pain, mechanical deep pain and mechanical pain rating parameters (P < 0·002) related to small fibre functions. However, the inverse results were observed for mechanical tactile modality related to large fibre function (P < 0·001) and wind-up ratio (P = 0·006). Women presented higher sensitivity compared to men. The mean Z-scores of all the parameters from Chinese group were in the normal zone created by Danish Caucasians' means and SDs. The ethnic disparities in somatosensory profile illustrated the necessity of establishing the reference data for different ethnic groups and possibly individual pain management strategies for the different ethnic groups.