Journal of Oral & Facial Pain and Headache, 04/2010

Dental pain arises from exposed dentin following bacterial, chemical, or mechanical erosion of enamel and/or recession of gingiva. Thus, dentin tissue and more specifically patent dentinal tubules represent the first structure involved in dentin sensitivity. Interestingly, the architecture of dentin could allow for the transfer of information to the underlying dental pulp via odontoblasts (dentin-forming cells), via their apical extension bathed in the dentinal fluid running in the tubules, or via a dense network of trigeminal sensory axons intimately related to odontoblasts. Therefore, external stimuli causing dentinal fluid movements and odontoblasts and/or nerve complex responses may represent a unique mechanosensory system bringing a new role for odontoblasts as sensor cells. How cells sense signals and how the latter are transmitted to axons represent the main questions to be resolved. However, several lines of evidence have demonstrated that odontoblasts express mechano- and/or thermosensitive transient receptor potential ion channels (TRPV1, TRPV2, TRPV3, TRPV4, TRPM3, KCa, TREK-1) that are likely to sense heat and/or cold or movements of dentinal fluid within tubules. Added to this, voltage-gated sodium channels confer excitable properties of odontoblasts in vitro in response to injection of depolarizing currents. In vivo, sodium channels co-localize with nerve terminals at the apical pole of odontoblasts and correlate with the spatial distribution of stretch-activated KCa channels. This highlights the terminal web as the pivotal zone of the pulp/dentin complex for sensing external stimuli. Crosstalk between odontoblasts and axons may take place by the release of mediators in the gap space between odontoblasts and axons in view of evidence for nociception-transducing receptors on trigeminal afferent fibers and expression of putative effectors by odontoblasts. Finally, how axons are guided to the target cells and which kind of signaling molecules are involved is extensively discussed in this review. Keywords: dental pain, mechano/thermosensitivity, nerves, odontoblast, teeth

Aim: To determine if myofascial temporomandibular disorder (TMD) pain patients have elevated interstitial concentrations of glutamate in the masseter muscle. Methods: Thirteen patients (3 men, 10 women) diagnosed with myofascial TMD pain and 10 (2 men, 8 women) age-matched healthy controls participated in a single microdialysis session. Microdialysis was performed in the patients in the most painful point of the masseter muscle, while in the healthy subjects a standardized point in the muscle was chosen. Two microdialysis samples were collected over 40-minute epochs. A blood sample was also taken for analysis of plasma glutamate concentration. Numeric rating scale (NRS) scores of pain intensity and unpleasantness, McGill Pain Questionnaire data, pain drawing areas, pressure pain thresholds, pressure pain tolerances, maximum voluntary bite force, and maximum voluntary mouth opening were collected as secondary measurements. Results: The median concentration of glutamate in the masseter muscle of the myofascial TMD pain patients (7.5 ± 2.6 µM) was significantly higher (P .023, Mann-Whitney test) than the concentration in healthy controls (0.5 ± 0.4 µM). There were, however, no significant correlations between glutamate concentrations in the masseter muscle and NRS pain scores. Plasma concentrations of glutamate were similar in patients and healthy controls. Conclusions: The present study demonstrates a marked increase in interstitial glutamate concentration in the masseter muscle of myofascial TMD pain patients. These novel findings suggest that peripheral glutamate could be involved in the pathophysiology of myofascial TMD pain. Keywords: glutamate, masseter muscle, microdialysis, orofacial pain, temporomandibular disorders

Aims: To determine the prevalence of facial pain and temporomandibular disorders (TMD) in people located in urban and rural areas in a newly industrialized country (Iran). Methods: Two-hundred twenty-three subjects between 18 and 65 years of age (mean: 32.07; SD: 10.83) were randomly selected from an urban area and a rural area. One-hundred nineteen subjects from Mashhad (major city) and 104 subjects from Zoshk (village) were voluntarily recruited from medical health-care centers. Subjects who consulted the health-care center for dental, ear, nose, or throat issues were excluded. The monitoring of public health attendance of all citizens at designated health-care centers is compulsory by local law. All subjects were examined in accordance with the Research Diagnostic Criteria for TMD (RDC/TMD). Facial pain was assessed by using a questionnaire; the prevalence of myofascial pain, disc displacement, and degenerative disorders was determined by clinical examination. Nonparametric tests were used to assess group differences (ie, between village and city). Results: Subjects in urban areas suffered less from facial pain (20.2% versus 46.2%; P .01 [Mann-Whitney U test]) than subjects in rural areas. The frequency of TMD, disc displacement, and degenerative disorders was greater in the rural area. Conclusion: The symptoms under investigation were significantly more widespread in rural than in urban areas. With regard to TMD per se, the place of residence appears to be unimportant. However, the rural population was significantly affected by facial pain. Keywords: degenerative disorders, disc displacement, facial pain, myofascial pain, prevalence

Aims: To examine temporomandibular disorder (TMD) patients' illness beliefs and self-efficacy in relation to bruxism, and to examine whether these beliefs are related to the severity of patients' self-perceived bruxing behavior. Methods: A total of 504 TMD patients (75% women; mean age ± SD: 40.7 ± 14.6 years), referred to the TMD Clinic of the Academic Centre for Dentistry Amsterdam, completed a battery of questionnaires, of which one inquired about the frequency of oral parafunctional behaviors, including bruxism (clenching and grinding). Patients' illness beliefs were assessed with a question about the perceived causal relationship between bruxism and TMD pain; patients' self-efficacy was assessed with questions about the general possibility of reducing oral parafunctional behaviors and patients' own appraisal of their capability to accomplish this. Results: Sleep bruxism or awake bruxism was attributed by 66.7% and 53.8% of the patients, respectively, as a cause of TMD pain; 89.9% believed that oral parafunctions could be reduced, and 92.5% believed themselves capable of doing so. The higher a patient's bruxism frequency, the more bruxism was believed to be the cause of TMD pain (Spearman's rho 0.77 and 0.71, P .001) and the more pessimistic the self-efficacy beliefs were about the reducibility of oral parafunctions (Kruskal-Wallis χ2 = 19.91, df = 2, P .001; and Kruskal-Wallis χ2 = 7.15, df = 2, P = .028). Conclusion: Most TMD patients believe in the harmfulness of bruxism and the possibility of reducing this behavior. Bruxism frequency is associated with illness beliefs and self-efficacy. Keywords: bruxism, illness beliefs, oral parafunctions, self-efficacy, temporomandibular disorders

Aims: To test if the disappearance of clicking associated with anterior disc displacement with reduction (ADDR) is related to a gradual loss of reducing capacity of the disc in the temporomandibular joint. Materials: Twenty-five ADDR subjects without and 30 ADDR subjects with intermittent locking participated in this 2-year follow-up study. Clinical examinations and mandibular movement recordings were performed at baseline and after 1 and 2 years. If mandibular movement recordings no longer showed signs of an ADDR, magnetic resonance imaging (MRI) of the disc was carried out. Results: Mandibular movement recordings showed the moment of disc reduction (MDR) to be stable over the observation period in the subjects without intermittent locking (P = .95). In the subjects with intermittent locking, MDR had shifted to a later mouth opening (P = .000). In seven of these subjects, clicking had totally disappeared, usually without symptoms of permanent locking. On the MRI scans of these subjects, the disc displacement was still present, but with no, or only a partial, reduction. Conclusion: Intermittent locking may be indicative of the development of a disc displacement without reduction. This loss is only rarely accompanied by symptoms of permanent locking. Keywords: human, intermittent locking, mandibular movement recordings, MRI, temporomandibular joint

Aims: To use functional magnetic resonance imaging (fMRI) to determine whether orofacial cutaneous or muscle pain is associated with changes in primary motor cortex (M1) activity that outlast the duration of perceived pain, and whether these M1 changes are different during cutaneous pain compared with muscle pain. Methods: fMRI was used in healthy subjects experiencing orofacial muscle (n = 17) or cutaneous (n = 15) pain induced by bolus injections of hypertonic saline (4.5%) into the belly of the masseter muscle (0.5 ml) or subcutaneously (0.2 ml) into the overlying skin, respectively. To determine the effects of the injection volume, isotonic saline (n = 4) was injected into the masseter muscle. Results: Similar pain scores were observed following subcutaneous (mean [± SEM]; 4.73 ± 0.51) or intramuscular injections (4.35 ± 0.56). Orofacial muscle but not cutaneous pain was associated with a transient increase in signal intensity in the contralateral M1. Cutaneous and muscle orofacial pains were associated with similar signal intensity decreases within the contralateral M1 that continued to decrease for the entire scanning period. Isotonic saline did not evoke pain or changes in M1 signal intensity. Conclusion: The transient contralateral M1 signal intensity increase during orofacial muscle pain may underlie escape-like motor patterns. However, once the initial threat has subsided, longer-term reductions in M1 activity and/or excitability may occur to aid in minimizing movement of the affected part, an effect consistent with the general proposals of the Pain Adaptation Model. Keywords: face, jaw muscle, magnetic resonance imaging (MRI), pain, skin, trigeminal

Aims: To evaluate both cosmetic and functional effects of temporalis muscle atrophy, by means of clinical examination, magnetic resonance imaging (MRI), and electromyographic (EMG) activity in patients who underwent craniotomy in order to treat refractory mesial temporal lobe epilepsy (MTLE). Methods: A total of 18 controls and 18 patients who underwent surgery for MTLE were investigated. The temporalis muscle volume of the patients was assessed by a 3D reconstruction. The image analysis software (ITK-SNAP) was used for the 3D reconstruction. In addition, the amplitude of the EMG signal during a maximum voluntary clench was recorded from both temporalis muscles by surface electrodes. The presence of temporomandibular disorder (TMD) signs was assessed by clinical examination that was performed only after surgery. Data were analyzed statistically by means of the Mann-Whitney U test, paired t-test, Pearson χ2 and linear regression. Results: The volume of the temporalis muscle of the operated side was significantly reduced (P = .004). The EMG results confirmed the presence of muscle atrophy, the amplitude of the EMG signal being significantly decreased on the operated side (P .05). Also the patients' maximum mouth opening after surgery was significantly reduced compared to that of the controls (P .0001). Patients presented facial asymmetry, signs of TMD (pain, disc displacement, and joint sounds), and masticatory abnormalities. Conclusion: These preliminary results showed that, despite the good control of seizures, some patients may experience cosmetic and functional abnormalities of temporalis muscle secondary to atrophy and fibrosis. Keywords: craniotomy, electromyography, epilepsy surgery, magnetic resonance imaging, temporal muscle atrophy, volumetry

Aims: To investigate the effect of a low dose of intramuscular (im) ketorolac compared with lidocaine (LA) in a double-blinded, randomized, and controlled trial. Methods: Twelve healthy women participated in three sessions and received two injections into their right masseter muscle per session. The first injections contained hypertonic saline (HS, 5% in 0.2 mL) to induce muscle pain. The second injections were given 30 minutes later and contained, together with HS, either ketorolac (3 mg in 0.2 mL), LA (2% lidocaine in 0.2 ml), or HS alone (control). HS-evoked pain intensity was scored on a 0 to 10 electronic visual analog scale (VAS) measuring peak, duration, and area under the curve (AUC). Pressure pain thresholds (PPT), pressure pain tolerance levels (PPTOL), and pain on palpation (POP) were determined bilaterally on the masseter muscle before and 5, 15, and 25 minutes after the injections. Maximum jaw opening (MJO) was measured at baseline and every 10 minutes after. McGill Pain Questionnaire (MPQ) scores and the extent of the HS-evoked pain (pain drawings) were recorded at baseline, 2 minutes after the first and second injections, and every 10 minutes during the entire experimental session. Results: There were no differences between the three sessions in HS-evoked pain measures from the first injection (P > .05). During the second injection, HS + LA demonstrated significantly lower VAS peak, duration, and AUC scores than control and HS + ketorolac (P .001). In the HS + ketorolac session, the VAS AUC was significantly lower than in the control session (P .005). The sessions had no main effect on PPT, PPTOL, POP, MJO, or pain drawings (P > .05). Conclusion: A low dose of im ketorolac has a significant and immediate analgesic effect on HS-evoked jaw muscle pain but significantly less than LA. A local anesthetic-like effect may be the underlying mechanism. Keywords: experimental muscle pain, ketorolac, local anesthetics, NSAIDs, trigeminal nociception

Headache and facial pain are both very high in the general population. Headache has been identified as one of the associated conditions in patients with chronic orofacial pain. The interrelation between the two has not been explored in the literature. Patients with facial pain often initially seek the care of a dentist. Misdiagnosis and multiple failed treatments (including invasive procedures) are very common in this population. This case report describes four patients whose condition fulfilled the International Headache Society's criteria for hemicrania continua but whose teeth were extracted because their pain was suspected to be of odontogenic origin. Each patient's records and the literature were reviewed for possible reasons for the unnecessary extractions. The findings suggest that initial treatment with drugs specific for primary headache disorders should be instituted before subjecting patients to invasive procedures. Keywords: facial pain, headache, hemicrania continua, indomethacin, indomethacin responsive headaches

This case report describes a male patient with trismus and generalized muscle weakness as the presenting symptom of disseminated malignancy. Trismus was caused by the presence of multiple small nests of undifferentiated tumor cells between muscle fibers of the masseter muscles as well as of other skeletal muscles. The diagnosis was suggested by increased uptake of 18-fluoro-deoxyglucose on positron emission tomography and subsequent ultrasound exami-nation. The primary tumor was not found on autopsy. The patient was at increased risk for malignancy due to his renal transplantation 16 years before. Keywords: malignancy, positron emission tomography, transplantation, trismus, weakness