Remote physical examination for temporomandibular disorders

ABSTRACT

There is a need to further develop telemedicine approaches because of the immediate and perhaps long-term consequences of the coronavirus disease 2019. Thus, a remote protocol for assessment of patients with temporomandibular disorders (TMD) was developed, and the agreement of this protocol was compared with the guidelines of the Diagnostic Criteria for TMD (DC/TMD). A total of 16 individuals were first assessed by a reference standard examination (RSE) and 3 other examinations applied in a random order by 3 examiners: standard physical examination (standard examination), physical examination keeping 2-m distance (physical distanced examination), and examination conducted with the aid of video communication technology (video communication examination). The primary outcomes were the diagnoses of myalgia of the masseter and temporalis muscles and arthralgia. The diagnoses of intra-articular joint disorders were considered secondary outcomes because of a less impact on psychosocial functioning and quality of life when compared with the pain-related diagnoses. The Fleiss kappa coefficient and its 95% confidence interval were computed to determine the level of agreement in diagnoses between each examination protocol and the RSE. There was substantial to almost perfect agreement between the RSE and all the examination protocols for the diagnoses of myalgia (0.86-1.00) and arthralgia (0.74-0.87) (P < 0.001). On the other hand, there was an overall poor agreement (0.30-0.58) between the RSE and all the protocols for the diagnosis of disk displacement with reduction. Remote assessment of patients with pain-related TMD is feasible and presents a high degree of accuracy.

Consensus-based clinical guidelines for ambulatory electromyography and contingent electrical stimulation in sleep bruxism

As yet, there are still no evidence‐based clinical diagnostic and management guidelines for ambulatory single‐channel EMG devices, like the BUTLER^® GrindCare^® (GrindCare), that are used in patients with sleep bruxism. Therefore, a consensus meeting was organised with GrindCare developers, researchers, and academic and non‐academic clinicians experienced with the use of ambulatory EMG devices. The aim of the meeting was to discuss and develop recommendations for clinical guidelines for GrindCare usage, based on the existing clinical and research experience of the consensus meeting's participants. As an important outcome of the consensus meeting, clinical guidelines were proposed in which an initial 2‐week baseline phase with the device in its inactive (non‐stimulus) mode for habituation and assessment of the number of jaw‐muscle activities is followed by a 4‐week active phase with contingent electrical stimuli suppressing the jaw‐muscle activities. As to avoid the commonly reported reduction in sensitivity to the stimuli, a 2‐week inactive phase is subsequently installed, followed by a repetition of active and inactive phases until a lasting reduction in the number of jaw‐muscle activities and/or associated complaints has been achieved. This proposal has the characteristics of a single‐patient clinical trial. From a research point of view, adoption of this approach by large numbers of GrindCare users creates a great opportunity to recruit relatively large numbers of study participants that follow the same protocol.

Sleep Bruxism and Pain

Bruxism is an oral behavior that may lead to repetitive jaw-muscle activity characterized by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible with 2 distinct circadian manifestations: sleep bruxism or awake bruxism. They share common risk factors and lead to similar consequences for the masticatory system but may have different etiology and pathophysiology. This oral behavior has been associated with tooth wear, masticatory muscle tenderness, headaches, and painful temporomandibular disorders. Available scientific evidence does not support the view that bruxism is a direct cause of pain, which should be taken into account when treating/managing patients.

Effects of nerve growth factor experimentally-induced craniofacial muscle sensitization on referred pain frequency and number of headache days: A double-blind, randomized placebo-controlled study

OBJECTIVE

To assess if repeated intramuscular injections of nerve growth factor into the temporalis and masseter muscles increase mechanical sensitivity and entropy scores. Furthermore, to investigate if increased mechanical sensitivity would lead to increased prevalence of referred pain in the studied individuals. Finally, if increased muscle sensitization would lead to an increase in number of headache days during the experimental period.

METHODS

The present double-blind, randomized placebo-controlled study recruited 16 healthy participants who were injected with nerve growth-factor, on 2 days, into the masseter and temporalis muscles and isotonic saline on the contralateral side. Mechanical sensitivity was assessed at seven different time-points (total of 21 days) by application of three different forces to 15 different sites of both muscles. Participants were asked after each force application if they experienced referred pain and were asked to keep a headache diary during the experimental period.

RESULTS

In summary, a) repeated intramuscular injections of nerve-growth-factor caused an increase in mechanical sensitivity for the masseter but not the temporalis muscle, and an increase in entropy scores when compared to the isotonic saline side. b) Both referred pain frequency and number of headache days were not increased following nerve-growth-factor injections.

CONCLUSIONS

These findings support the idea that mechanical sensitization in the masseter and temporalis muscles differs following injections of nerve growth factor. Furthermore, referred pain and headache frequency do not seem to be related to nerve growth factor sensitization in this model. These findings support the idea that in healthy individuals referred pain may be an epiphenomenon of the muscle in response to noxious input.

Systematic Mapping of Pressure Pain Thresholds of the Masseter and Temporalis Muscles and Assessment of Their Diversity Through the Novel Application of Entropy

AIMS

To assess the diversity of pressure pain thresholds (PPTs) within the masseter and temporalis muscles by using the novel concept of entropy and to assess the differences in PPT scores between different sites of the masseter and temporalis muscles.

METHODS

In this randomized, single-blinded study, the left and right masseter and temporalis muscles of 14 healthy volunteers were divided into 15 sites each, and the PPT was assessed for each of these sites. PPT assessments were performed in two different sessions. Entropy and center of gravity (COG) values were calculated for the PPTs of each muscle. Repeated measures analysis of variance was used to assess differences between muscles, sides, and sites for PPT, entropy, and COG scores.

RESULTS

The main findings were: (1) PPT scores varied significantly between the masseter and temporalis muscles and within each of these muscles; (2) entropy values of PPT scores were not different between the masseter and temporalis muscles; and (3) COG values of PPT scores varied statistically, but these changes do not seem to be clinically relevant.

CONCLUSION

The results of this study suggest that the anatomical layout of the masseter and temporalis muscles has implications for mechanical pain sensitivity and that areas have different sensitivities within these muscles. Furthermore, reference values for the entropy of PPTs in healthy individuals have been estimated, and comparing these values with those of patients with muscle-related pain conditions can provide quantitative information about the spatial heterogeneity of mechanical pain sensitivity, which may be a valuable clinical outcome measure.

Spontaneous jaw muscle activity in patients with acquired brain injuries-Preliminary findings

PATIENTS

High or excessive parafunctional jaw muscle activity is a frequent complication of acquired brain injury (ABI) and may have some similarities to bruxism. Bruxism has been associated with increased tooth wear, masseter hypertrophy and headaches. The aim of this observational study was to identify the levels of jaw muscle activity from fourteen ABI patients having different functional and cognitive levels in their early phase of neurological rehabilitation (according to their Ranchos Los Amigos Scale (RLAS) score). Nine patients were severely cognitive impairement (RLAS score 1-3): with no or little response to any external stimuli due to low arousal and five patients were with RLAS score 4-8: depending on responses to stimuli and confusion level i.e. defining that patients had enough arousal to respond and react and therefore were able to follow the instructions. A single-channel electromyographic (EMG) device was used to assess the jaw muscle EMG activity in ABI patients for two hours continuously at two different days.

DISCUSSION

The mean (±SD) jaw muscle activity observed in patients with ABI was 46.9±6.5 EMG events/h with a wide range between 1-163 EMG events/h but with no significant difference between days (P=0.230).

CONCLUSION

Irrespective of functional and cognitive ability scores patients with ABI had a wide range of EMG activity. The use of ambulatory single-channel EMG devices might open a path for further studies to determine levels of jaw muscle activity associated with potential side effects in ABI patients.

Entropy of Masseter Muscle Pain Sensitivity: A New Technique for Pain Assessment

AIMS

To test whether manipulation of mechanical pain sensitivity (MPS) of the masseter muscle is reflected in quantitative measures of entropy.

METHODS

In a randomized, single-blinded, placebo-controlled design, 20 healthy volunteers had glutamate, lidocaine, and isotonic saline injected into the masseter muscle. Self-assessed pain intensity on a numeric rating scale (NRS) was evaluated up to 10 minutes following the injection, and MPS was evaluated after application (at 5 minutes and 30 minutes) of three different forces (0.5 kg, 1 kg, and 2 kg) to 15 different sites of the masseter muscle. Finally, the entropy and center of gravity (COG) of the pain sensitivity scores were calculated. Analysis of variance was used to test differences in means of tested outcomes and Tukey post hoc tests were used to adjust for multiple comparisons.

RESULTS

The main findings were: (1) Compared with both lidocaine and isotonic saline, glutamate injections caused an increase in peak, duration, and area under the NRS pain curve (P < .01); (2) A pressure of 2 kg caused the highest NRS pain scores (P < .03) and entropy values (P < .02); (3) Glutamate injections caused increases in entropy values when assessed with 0.5 kg and 1.0 kg but not with 2.0 kg of pressure; and (4) COG coordinates revealed differences between the x coordinates for time (P < .01) and time and force for the y coordinates (P < .01).

CONCLUSION

These results suggest that manipulation of MPS of the masseter muscle with painful glutamate injections can increase the diversity of MPS, which is reflected in entropy measures. Entropy allows quantification of the diversity of MPS, which may be important in clinical assessment of pain states such as myofascial temporomandibular disorders.

Blood oxygenation of masseter muscle during sustained elevated muscle activity in healthy participants

Myofascial pain associated with temporomandibular disorders has often been linked to pathological muscle hyperactivity. As a result, localised disturbances of intramuscular blood flow could lead to a lower level of oxygen distribution, hypoxia and microcirculatory changes. To assess haemodynamic changes in the masseter muscle during sustained elevated muscle activity (SEMA). Sixteen healthy participants performed thirty 1-min bouts of SEMA with intervals of 1-min 'rest' periods between the bouts on a bite force transducer device. The participants completed three sessions with different percentage of their maximal voluntary occlusal bite force (MVOBF): 0% (no task), 10% or 40% MVOBF tasks. The order of the sessions was randomised with 1- to 2-week intervals. Haemodynamic characteristics of the masseter muscle were estimated with use of a laser blood oxygenation monitor. Tissue blood oxygen saturation (StO₂ ) during SEMA was lower than during rest (P < 0·001). The relative changes in total haemoglobin (Total-Hb) and StO₂ were influenced by condition (SEMA and rest) and with interactions between condition and session (0%, 10% and 40% MVOBF tasks). These results suggest that SEMA may lead to hypoxia in the masseter muscle and that the haemodynamic characteristics and muscle symptoms depend on the magnitude of muscle contractions. Overall, the present findings may help to provide better insights into relationships between jaw muscle activity, haemodynamic changes and symptom developments with implications for clinical conditions such as bruxism characterised by different levels of tooth-grinding and tooth-clenching muscle activity.

Sleep bruxism: an updated review of an old problem

Objective To provide an update on what is known about bruxism and some of the major clinical highlights derived from new insights into this old problem in dentistry. Materials and methods A selective, non-systematic but critical review of the available scientific literature was performed. Results There are two main different types of bruxism, which are related to different circadian periods (sleep and awake bruxism) that may differ in terms of pathophysiology, but they share some common signs and symptoms. Approximately one out of 10 adult individuals may suffer from bruxism, but not all bruxers may need treatment. Bruxism is complicated to diagnose in the clinic and self-report of bruxism may not necessarily reflect the true presence of jaw muscle activity. Better understanding has been acquired of bruxism relationships with sleep stages, arousal responses and autonomic function with the help of polysomnography and controlled sleep studies. Meanwhile, there is still much more to learn about awake bruxism. With the available scientific knowledge it is possible to systematically assess the effects of bruxism and its potential risk factors for oral and general health. Moreover, we can be aware of the realistic possibilities to manage/treat the patient suffering from bruxism. Conclusion Bruxism is a parafunctional activity involving the masticatory muscles and probably it is as old as human mankind. Different ways have been proposed to define, diagnose, assess the impact and consequences, understand the pathophysiology and treat or manage bruxism. Despite the vast research efforts made in this field, there are still significant gaps in our knowledge.

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.

Diagnostic validity of self-reported measures of sleep bruxism using an ambulatory single-channel EMG device

PURPOSE

Self-reported measures have been widely used to indicate the presence of possible and probable sleep bruxism (SB) in both research and clinical situations. However, few studies have attempted to assess the diagnostic validity of this approach. The aim of this study was to estimate the diagnostic validity of self-reported measures of SB using an ambulatory single-channel electromyographic (EMG) device.

METHODS

A total of 115 participants were enrolled and examined by standardized Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) including two questions related to SB: self-reported SB and morning-jaw symptoms. An ambulatory single-channel EMG device (GrindCare3™, Medotech A/S) was used for measuring jaw-muscle EMG activity during sleep for seven consecutive nights. Cut-off values for different measures of EMG activity (average, maximum and minimum) and the coefficient of variation (CV) were selected to divide participants into two groups, with higher or lower EMG activity or CV values. The sensitivity and specificity for each question and combination of them were calculated.

RESULTS

Self-reported SB had the highest sensitivity (compared with morning-jaw symptoms) for all measures of EMG activity and CV, although the values were low to modest (average: 76.0%, maximum: 76.9%, minimum: 77.3%, CV: 61.0%). The specificity was low for both the questions related to the different measures of EMG activity and CV (35.1-52.4%).

CONCLUSIONS

This study indicated that the diagnostic validity of self-reported measures of SB was low to modest using an ambulatory EMG device assessment as a reference. Using only self-reported measures for the assessment of SB may not have a high validity, which should be taken into consideration in the clinical evaluation of patients.

Intramuscular temperature modulates glutamate-evoked masseter muscle pain intensity in humans

AIMS

To determine whether glutamate-evoked jaw muscle pain is altered by the temperature of the solution injected.

METHODS

Sixteen healthy volunteers participated and received injections of hot (48°C), neutral (36°C), or cold (3°C) solutions (0.5 mL) of glutamate or isotonic saline into the masseter muscle. Pain intensity was assessed with an electronic visual analog scale (eVAS). Numeric rating scale (NRS) scores of unpleasantness and temperature perception, pain-drawing areas, and pressure pain thresholds (PPTs) were also measured. Participants filled out the McGill Pain Questionnaire (MPQ). Two-way or three-way repeated measures ANOVA were used for data analyses.

RESULTS

Injection of hot glutamate and cold glutamate solutions significantly increased and decreased, respectively, the peak pain intensity compared with injection of neutral glutamate solution. The duration of glutamate-evoked pain was significantly longer when hot glutamate was injected than when cold glutamate was injected. No significant effect of temperature on pain intensity was observed when isotonic saline was injected. No effect of solution temperature was detected on unpleasantness, heat perception, cold perception, area of pain drawings, or PPTs. There was a significantly greater use of the "numb" term in the MPQ to describe the injection of cold solutions compared to the injection of both neutral and hot solutions.

CONCLUSION

Glutamate-evoked jaw muscle pain was significantly altered by the temperature of the injection solution. Although temperature perception in the jaw muscle is poor, pain intensity is increased when the muscle tissue temperature is elevated.

Effect of contingent electrical stimulation on jaw muscle activity during sleep: a pilot study with a randomized controlled trial design

OBJECTIVE

To determine the effect of contingent electrical stimulation (CES) on jaw muscle activity during sleep in a double-blinded randomized controlled trial (RCT).

MATERIALS AND METHODS

Eleven patients with myofascial TMD (mean age 37 years) and with a clinical diagnosis of bruxism were included. EMG activity (Grindcare®) was recorded from the anterior temporalis muscle during sleep and analyzed online. Jaw muscle activity related to clenching or grinding triggered an electrical square-wave pulse train (450 ms) adjusted to a clear, but non-painful intensity. TMD patients were randomized into two groups: active treatment with CES or no CES (placebo). Number of EMG episodes/hour sleep was the primary outcome parameter. The following variables were assessed as secondary outcome parameters; number of painful muscles, maximum pain-free jaw opening, characteristic pain intensity, depression scores and Oral Health Impact Profile scores. Numerical Rating Scale scores for self-reported pain and muscle tension were registered for at least 4 nights per week during the experiment.

RESULTS

The number of EMG episodes/hour sleep was significantly reduced (52 ± 12%) in the CES group during the sessions with CES (ANOVA: p = 0.021) compared to baseline. There were no significant differences in the secondary outcome parameters (ANOVA: p > 0.513) or pain or muscle tension scores between groups (p = 0.645). The average duration of sleep hours during the nights with and without CES was not significantly different (p = 0.646).

CONCLUSIONS

These results demonstrate a significant inhibitory effect of CES on jaw muscle EMG activity during sleep in a RCT, but with no effects on self-reported pain.

Acidic saline-induced pain as a model for experimental masseter myalgia in healthy subjects

BACKGROUND

Repeated injection of acidic saline into skeletal muscles of the leg in rodents induces a prolonged bilateral mechanical hyperalgesia that persists for up to 30 days and may be useful to model widespread muscle pain conditions. In this study, repeated injection of acidic (pH 3.3) saline solution into the masseter muscle of healthy human subjects was undertaken to determine if these injections are painful and whether they would induce a prolonged period of muscle sensitization to artificial and/or natural mechanical stimulation of the masseter and temporalis muscles.

METHODS

Eighteen subjects (10 male, 8 female) participated in the study. Subjects received two injections of 0.5 mL acidic or regular isotonic saline 2 days apart, in a randomized, double blind, crossover design.

RESULTS

There was no significant difference in pain intensity ratings when acidic saline injections were compared with regular saline injections. Pain area drawings were, however, significantly larger in response to the first injection of acidic saline than to the second injection of acidic saline or to either the first or second injection of regular saline. Repeated injection of acidic saline did not significantly alter pressure pain thresholds from the masseter or temporalis muscles on either the injected side or the opposite side over the 10-day post injection monitoring period. There was also no effect of injections on chewing.

CONCLUSION

These findings indicate that, unlike in some rodent models, repeated injection of low pH solutions into jaw muscles of humans fails to induce a period of prolonged muscle hyperalgesia.

Experimental myalgia induced by repeated infusion of acidic saline into the human masseter muscle does not cause the release of algesic substances

BACKGROUND

Animal studies have shown that two repeated intramuscular injections of acidic saline induce mechanical allodynia that lasts for 4 weeks with spread to the contralateral side. In this study, we tested the hypothesis that two repeated intramuscular infusions of acidic saline into the human masseter muscle is associated with pain, mechanical allodynia and release of algesic substances. Eighteen healthy volunteers participated. On day 1, 2.5 mL of acidic saline (pH 3.3) was infused into one of the masseter muscles and isotonic saline (pH 6.0) into the other (randomized and single-blind). Two days later, intramuscular microdialysis was performed to sample serotonin, glutamate, pyruvate, lactate and glucose, during which the saline infusions were repeated. Pain and pressure pain thresholds (PPTs) were recorded before and after infusions on both days.

RESULTS

Pain intensity induced by the infusions was higher after acidic than that after isotonic saline (p < 0.05). PPTs were decreased on both sides after microdialysis compared with baseline day 1 (p's < 0.05), but there were no differences in PPTs between sides at any time point. The levels of serotonin, glutamate, pyruvate, lactate or glucose did not change significantly during microdialysis.

CONCLUSION

Infusion of acidic saline caused low levels of muscle pain, but no mechanical allodynia and no increased release of algesic substances. The value of this model appears modest, but future studies could be performed with larger sample size and higher flow rate before definite conclusions about the validity of the model for craniofacial myalgia can be drawn.

Comparison of glutamate-evoked pain between the temporalis and masseter muscles in men and women

Pain in myofascial temporomandibular disorder (TMD) can affect both the masseter and temporalis muscles. Glutamate injection into the masseter muscle evokes pain that is greater in men than in women and this pain is attenuated by co-injection of the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine (10 mmol/L) in men. Animal studies suggested that pain induced by peripheral NMDA receptor activation could differ between the temporalis and masseter muscles and between men and women. The study aims were to investigate differences in glutamate-evoked pain between these muscles and the effectiveness of ketamine to attenuate glutamate-evoked pain in both genders. Pain and mechanical sensitivity were induced in 2 sessions of an experiment in 14 women and 16 men by repeated injections of glutamate (0.5 mol/L) with and without ketamine (20 mmol/L) into the masseter and temporalis muscles. Two injections were applied into the same masseter muscle and 2 injections into the same anterior temporalis muscle at each session. Visual analogue scale (VAS) pain intensities and pain drawing areas were assessed. Glutamate-evoked pain and pain drawing area were significantly greater from the temporalis muscle than from the masseter muscle (P<.02) in both genders. Women reported significantly greater glutamate-evoked masseter muscle pain than men (P<.03). Co-injection of ketamine, at higher dose than previously used, was equally effective in attenuating glutamate-evoked pain from both muscles in both genders (P<.01). The current findings indicate that the characteristics of pain generated by intramuscular injection of glutamate vary for different masticatory muscles and may be partially generated through activation of peripheral NMDA receptors.

Interstitial glutamate concentration is elevated in the masseter muscle of myofascial temporomandibular disorder patients

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.

Effect of peripheral NMDA receptor blockade with ketamine on chronic myofascial pain in temporomandibular disorder patients: a randomized, double-blinded, placebo-controlled trial

AIMS

To investigate the effects of local intramuscular injection of the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine on chronic myofascial pain and mandibular function in temporomandibular disorder patients.

METHODS

Fourteen myofascial temporomandibular disorder pain patients (10 women and 4 men) were recruited. The subjects completed 2 sessions in a double-blinded randomized and placebo-controlled trial. They received a single injection of 0.2 mL ketamine or placebo (buffered isotonic saline [NaCl], 155 mmol/L) into the most painful part of the masseter muscle. The primary outcome parameters were spontaneous pain assessed on an electronic visual analog scale and numeric rating scale. In addition, numeric rating scale of unpleasantness, numeric rating scale of pain relief, pressure pain threshold, pressure pain tolerance, completion of a McGill Pain Questionnaire and pain drawing areas, maximum voluntary bite force and maximum voluntary jaw opening were obtained. Paired t tests and analysis of variance were performed to compare the data.

RESULTS

There were no main effects of the treatment on the outcome parameters except for a significant effect of time for maximum voluntary bite force (analysis of variance; P = .030) and effects of treatment, time, and interactions between treatment and time for maximum voluntary jaw opening (analysis of variance; P < .047).

CONCLUSION

These results suggest that peripheral NMDA receptors do not play a major role in the pathophysiology of chronic myofascial temporomandibular disorder pain. Although there was a minor effect of ketamine on maximum voluntary jaw opening, local administration may not be promising treatment for these patients.

Effect of a peripheral NMDA receptor antagonist on glutamate-evoked masseter muscle pain and mechanical sensitization in women

AIMS

To test the hypothesis that local injection of the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine would significantly attenuate glutamate-evoked masseter mechanical sensitization and muscle pain in healthy young women either taking oral contraceptives (W+OC) or not taking oral contraceptives (W-OC).

METHODS

Experimental pain was evoked in 47 healthy female subjects (W+OC, n=25; W-OC, n=22) by 2 injections of glutamate (0.2 mL, 1 mol/L) into the masseter muscle. A first injection of glutamate alone was followed by a second injection, 35 minutes later, of glutamate combined with ketamine (0, 1, or 10 mmol/L). Evoked pain intensity was scored on a 10-cm electronic visual analog scale (VAS). Distribution of perceived pain was drawn on a lateral view of the face (pain drawing). Masseter muscle pressure pain thresholds (PPT) and pressure-pain tolerances (PPTOL) were determined bilaterally before and at regular time intervals after injections. Analyses of variance (ANOVA) were used to test the data.

RESULTS

There were no main effects of ketamine on any of the VAS pain parameters or on the pain drawing (ANOVAs: P > .055). Furthermore, there were no differences in PPT, PPTOL, VAS peak pain, duration, overall VAS pain, or pain drawing when W-OC were compared with W+OC (ANOVAs: P > .087). Repeated injection of glutamate alone significantly decreased PPT and PPTOL (ANOVAs: P < .001); however, this effect was not significantly attenuated by ketamine.

CONCLUSIONS

Peripherally administered ketamine had no effect on glutamate-evoked masseter muscle pain and sensitization in healthy young women, which contrasts with recent observations in healthy young men. Further studies will be needed to reveal the mechanisms that underlie this apparent sex-related difference in ketamine-mediated analgesia.