Clinical and experimental aspects of temporomandibular disorders

Current evidence on atypical odontalgia: diagnosis and clinical management

Patients with atypical odontalgia (AO) complain of medically unexplained toothache. No evidence-based diagnostic criteria or treatment guidelines are yet available. The present paper addresses seven clinical questions about AO based on current knowledge in the literature and discusses diagnostic criteria and guidelines for treatment and management. The questions are (i) What is the prevalence of AO in the community? (ii) What psychological problems are experienced by patients with AO? (iii) Are there any comorbidities of AO? (iv) Is local anesthesia effective for the relief of pain in AO? (v) Are there any characteristic symptoms of AO other than spontaneous pain? (vi) Are antidepressants effective for treatment of AO? (vii) Are anticonvulsants effective for treatment of AO? Our literature search provided answers for these questions; however, there is insufficient evidence-based data to establish guidelines for the diagnosis and treatment of AO. Overall, some diagnostic criteria for neuropathic pain and persistent dentoalveolar pain disorder may be applied to AO patients. The patient's psychogenic background should always be considered in the treatment and/or management of AO. The clinicians may need to treat AO patients using Patient-Oriented Evidence that Matters approach.

A trigeminoreticular pathway: implications in pain

Neurons in the caudalmost ventrolateral medulla (cmVLM) respond to noxious stimulation. We previously have shown most efferent projections from this locus project to areas implicated either in the processing or modulation of pain. Here we show the cmVLM of the rat receives projections from superficial laminae of the medullary dorsal horn (MDH) and has neurons activated with capsaicin injections into the temporalis muscle. Injections of either biotinylated dextran amine (BDA) into the MDH or fluorogold (FG)/fluorescent microbeads into the cmVLM showed projections from lamina I and II of the MDH to the cmVLM. Morphometric analysis showed the retrogradely-labeled neurons were small (area 88.7 µm(2)±3.4) and mostly fusiform in shape. Injections (20-50 µl) of 0.5% capsaicin into the temporalis muscle and subsequent immunohistochemistry for c-Fos showed nuclei labeled in the dorsomedial trigeminocervical complex (TCC), the cmVLM, the lateral medulla, and the internal lateral subnucleus of the parabrachial complex (PBil). Additional labeling with c-Fos was seen in the subnucleus interpolaris of the spinal trigeminal nucleus, the rostral ventrolateral medulla, the superior salivatory nucleus, the rostral ventromedial medulla, and the A1, A5, A7 and subcoeruleus catecholamine areas. Injections of FG into the PBil produced robust label in the lateral medulla and cmVLM while injections of BDA into the lateral medulla showed projections to the PBil. Immunohistochemical experiments to antibodies against substance P, the substance P receptor (NK1), calcitonin gene regulating peptide, leucine enkephalin, VRL1 (TPRV2) receptors and neuropeptide Y showed that these peptides/receptors densely stained the cmVLM. We suggest the MDH- cmVLM projection is important for pain from head and neck areas. We offer a potential new pathway for regulating deep pain via the neurons of the TCC, the cmVLM, the lateral medulla, and the PBil and propose these areas compose a trigeminoreticular pathway, possibly the trigeminal homologue of the spinoreticulothalamic pathway.

A two-year follow-up study of temporomandibular disorders in a female Sami population: validation of cases and controls as predicted by questionnaire

OBJECTIVE

The first aim of this study was to validate persistent, severe symptoms of temporomandibular disorders (TMD) among Sami females, as predicted by questionnaire. The second aim was to establish diagnoses according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) Axis 1 among predicted cases and controls. The third aim was to compare subjects with severe TMD to controls in regard to dental occlusion, general health, and parafunctions.

MATERIAL AND METHODS

The subjects, Sami females living in the Arctic region of northern Sweden, all with long-standing (>or=1 year), intense (>or=5 on NS), and frequent (>or=once a week) symptoms of pain and dysfunction in the jaw-face region, were invited for clinical examination; 22 (63%) agreed to participate. Forty-six subjects with no symptoms in the jaw-face region were matched to these cases in accordance with five age groups. The examiner was blind to subject affiliation.

RESULTS

The positive predictive value of presenting with signs and symptoms of TMD at follow-up was 0.82; the negative value was 0.87. Cases reported impaired general health and awareness of parafunctions significantly more frequently than did controls. Registered dental occlusion factors did not distinguish cases from controls.

CONCLUSIONS

Long-standing, intense, and frequent TMD symptoms remained essentially unchanged over the 2-year follow-up of females in a Sami population. Presence of severe TMD was related to impaired general health and awareness of oral parafunctions.

Cerebral cortical dysfunction in patients with temporomandibular disorders in association with jaw movement observation

Temporomandibular disorders (TMD) represent a group of chronic painful conditions in the masticatory musculature and temporomandibular joint. To examine possible changes in cortical machinery in TMD patients, we compared neuromagnetic signals evoked by cortical neurons between healthy subjects and TMD patients while they were carefully observing the video frames of jaw-opening movements performed by another person. During the movement observation task in the healthy subjects, we found cortical activation in the following sequence with left hemisphere dominance: (1) the occipitotemporal region near the inferior temporal sulcus (human homologue of MT/V5 in monkeys), (2) the inferior parietal cortex (IPC), and (3) the anterior part of the inferior-lateral precentral gyrus (PrCG). In the TMD patients, however, we found deficit or marked attenuation of the neuromagnetic responses in the PrCG and IPC, while the activity of the MT/V5 showed no differences from that in the healthy subjects. In addition, we could not find any differences in cortical magnetic responses between healthy subjects and TMD patients when they were observing palm-opening movements, indicating that cortical dysfunction associated with jaw-movement observation is specific phenomena in the patients of TMD. Thus the present study provides new neuropathological evidence that TMD patients exhibit dysfunction of recognition mechanisms in cerebral cortex during motor observation, and suggests that disturbance of cortical functions regulating visuomotor integration would play a crucial role in development as well as aggravation of TMD.

Assessment of nociceptive trigeminal pathways by laser-evoked potentials and laser silent periods in patients with painful temporomandibular disorders

We assessed the trigeminal nociceptive pathways in patients with painful temporomandibular disorders (TMD) and control subjects using a CO(2)-laser stimulator which provides a predominant activation of the nociceptive system. Fifteen patients with unilateral pain were examined in accordance with the Research Diagnostic Criteria for TMD and 30 gender- and age-matched individuals were included as a control group. Laser-evoked potentials (LEPs) and laser silent periods (LSPs) after stimulation of the perioral region (V2/V3) on the painful and non-painful sides were recorded in all subjects. LEPs were evoked by low-intensity pulses (1.5 x perception threshold (PTh)) and recorded from scalp electrodes at the vertex. LSPs were evoked by high-intensity pulses (4 x PTh) and recorded bilaterally from masseter muscles with surface electromyogram (EMG) electrodes. Subjects also assessed the stimulus intensity on a 0-10 rating scale. LEPs had normal latency but smaller amplitude in TMD patients compared to the control group (P<0.001). Side-to-side comparison within patients showed that LEP amplitude was even more reduced after stimulation on the painful than the non-painful side (P<0.001). TMD patients showed a significant side-asymmetry of the pre-stimulus EMG activity, with a smaller value in the muscle on the painful side (P<0.001). LSPs were completely absent bilaterally in 12 TMD patients and unilaterally in two patients; only one patient had normal and bilateral LSPs. TMD patients perceived the laser stimulus less intense on the painful than the non-painful side (P<0.05). We found suppression of cortical responses and brainstem reflexes elicited by a predominantly nociceptive input in TMD patients. These findings are consistent with recent experimental pain studies and suggest that chronic craniofacial pain in TMD patients may be associated with a dysfunction of the trigeminal nociceptive system.

Antero-posterior activity changes in the superficial masseter muscle after exposure to experimental pain

The aim of this randomized, controlled, double-blind study was to examine how the activation pattern of the masseter muscle changes during natural function when experimental pain is induced in a discrete anterior area of the muscle. In 20 subjects, three bipolar surface electrodes and three intramuscular fine-wire electrodes (antero-posterior mapping) were simultaneously attached above and in the right masseter muscle to record the electromyographic (EMG) activity during unilateral chewing before and after infusion of a 0.9% isotonic and 5% hypertonic saline bolus in the anterior area of the muscle. The activity of the contralateral masseter muscle was registered by surface electrodes. In addition, the development of pain intensity was quantitatively measured with a numerical rating scale (NRS). While both saline concentrations caused pain, the hypertonic solution evoked stronger pain. The experiments also provided evidence of a significant although differential activity reduction of the ipsilateral masseter muscle in the antero-posterior direction. The activity reduction decreased with increasing distance from the location of the infusion. The results support the idea that the strategy of differential activation protects the injured muscle while simultaneously maintaining optimal function.

Nonpharmacologic approaches to the management of myofascial temporomandibular disorders

The temporomandibular disorders (TMDs) are a heterogeneous group of painful musculoskeletal conditions that include masticatory muscle pain. TMD is a common condition but its etiology is, as yet, poorly understood. Although TMD can be quite disabling, most patients presenting with symptoms improve regardless of treatment type. This article focuses on nonpharmacologic treatments for TMD; recent articles on etiology, assessment, and treatment for this muscle pain condition are reviewed. Psychological approaches include biofeedback, minimal therapist contact interventions, relaxation, and cognitive-behavioral therapy. We suggest that treatments based on the biopsychosocial model of illness should be used concurrently with treatments focusing only on the biomedical aspects of TMD. Psychological treatments need not be viewed as a treatment of last resort, but rather should be delivered concurrent with biomedical treatments. We present data from recent clinical trials showing that treatment-matching approaches tailoring psychological and educational treatments to psychosocial profiles, delivered concurrent with usual dental care, results in greater and more sustained improvement than usual dental care alone. As such, treatment for TMD should be viewed in much the same way as treatment for most other chronic pain conditions, that is, from a multidisciplinary perspective.

Long-term fluctuations of pressure pain thresholds in healthy men, normally menstruating women and oral contraceptive users

The aim of this investigation was to evaluate whether the pressure pain threshold (PPT) in masticatory muscles of symptom-free subjects was influenced by fluctuations of the sex hormones. The PPT was measured with an electronic algometer for at least 10 consecutive menstrual cycles in 10 women using oral contraceptives and 10 women not using oral contraceptives, with a regular menstrual cycle (26-31 days). In addition, 10 men were measured in a regular pattern over a period of 1 year. All subjects were symptom-free with an age range between 18 and 39 years. Measurement sessions were held during three different cycle phases (follicular, luteal, perimenstrual) and each session consisted of four consecutive PPT measurements. By means of a linear mixed model (SAS), the PPTs of the masster, temporalis and thumb muscles were compared between: (1) groups, (2) sex-hormonal phases, (3) the four consecutive measurements of each muscle per session and (4) time. The PPTs of the masseter (p = 0.8419) and temporalis muscles (p = 0.2786) did not change significantly over time. There was no significant difference in variance for the masseter (p = 0.6250), temporalis (p = 0.9705) and thumb (p = 0.7446) between the three groups. The PPTs of all muscles were significantly lower during the perimenstrual phases in the two female groups. The present data showed similar patterns of PPTs for the three muscle groups. Moreover, the results have shown a very good consistency of the PPTs over a long time period, both in males and females.

Fatigue and pain in human jaw muscles during a sustained, low-intensity clenching task

Fatigue, pain and changes in the electromyographic (EMG) activity of the jaw-closing muscles are well documented during short, high-intensity tooth-clenching tasks but less so during sustained, low-intensity tasks. In this study, 11 healthy men clenched on a bite-force meter for 60 min at 10% of the maximal voluntary contraction (MVC) and scored the intensity of fatigue and pain on separate 10 cm visual analogue scales (VAS). Surface EMG activity from the masseter and anterior temporalis muscles was recorded in 10 s epochs every 5 min throughout the task. Pressure-pain thresholds (PPTs) in the jaw-closing muscles, unassisted maximum jaw opening and MVC were determined before and after the task. All participants reported an increasing sensation of fatigue in the jaw-closing muscles during the task (mean+/-SD: peak VAS=7.5+/-2.0 cm) but all were able to maintain the required force. Most (7/11) also reported a painful sensation (peak VAS=2.7+/-2.8 cm). The jaw-opening capacity (59.5+/-7.4 vs. 58.3+/-6.5 mm, P=0.031) and the MVC (777+/-73 vs. 652+/-115 N,P=0.002) were slightly, but significantly, decreased immediately after the task whereas the PPTs remained unchanged (ANOVA: P=0.612). The mean frequency of the EMG activity decreased in all muscles during the task (95.7 vs. 46.6 Hz;P<0.001), and the root mean squares increased (53.2 vs. 154 microV, P<0.001). The changes in EMG activity were more strongly correlated with the sensation of fatigue than pain. These findings demonstrate that a sustained, low-intensity clenching task can induce subjective and electrophysiological indications of fatigue.

Analysis of stimulus-evoked pain in patients with myofascial temporomandibular pain disorders

The pathophysiological mechanisms of myofascial temporomandibular disorders (TMD) are still under investigation. The hypothesis that TMD pain is caused by a generalized sensitization of higher order neurons in the nociceptive pathways combined with a decreased efficacy of endogenous inhibitory systems has recently gained support in the literature. This study was designed to further investigate the somatosensory sensibility within and outside the craniofacial region. Twenty-two patients fulfilled the research diagnostic criteria for TMD for myofascial pain (Dworkin and LeResche, J Craniomandib Disord Facial Oral Pain 6 (1992) 301) and 21 age- and sex-matched subjects served as a control group. The somatosensory sensibility to a deep tonic input was tested by standardized infusions of hypertonic saline into the masseter and anterior tibialis muscle. Furthermore, pressure pain thresholds (PPTs) and heat pain thresholds (HPTs) were assessed with phasic stimuli at the same sites before and following the infusions. Myofascial TMD patients reported infusion of hypertonic saline to be more painful on 10 cm visual analogue scales (peak pain 8.8 +/- 0.4 cm) than control subjects (6.8 +/- 0.5 cm, t-test: P = 0.003) in the masseter but not in the anterior tibialis (7.4 +/- 0.5 vs. 6.6 +/- 0.5 cm, P=0.181). The perceived area of experimental masseter pain measured on drawings was marginally larger in TMD patients (2.6+/-0.5 arbitrary units (a.u.)) than in control subjects (1.4 +/- 0.2 a.u., Mann-Whitney: P = 0.048) but no differences were observed for the anterior tibialis (P = 0.771). The PPTs were lower in the myofascial TMD patients compared to the control group, both in the masseter (analysis of variance (ANOVA): P = 0.002) and in the anterior tibialis (P = 0.005), whereas there were no significant differences in HPT (ANOVAs: P = 0.357, P = 0.101). There were no significant correlations between measures of somatosensory sensibility and measures of clinical pain intensity, pain duration, graded chronic pain scores or somatization or depression scores (Pearson: R < 0.304, P > 0.172). The present study in a well-defined group of myofascial TMD patients found that the responsiveness to both tonic and phasic deep stimuli, but not to phasic superficial inputs at the pain threshold level, in the craniofacial region was higher compared with a control group. These findings suggest that myofascial TMD pain is associated with a facilitation of stimulus-evoked pain primarily, but not exclusively related to the painful region.