Reduction of sleep bruxism events according to contingent electrical stimulus intensity

BACKGROUND

Although biofeedback with contingent electrical stimulation (CES) has demonstrated the reduction effect on sleep bruxism (SB), the relationship between the actual applied CES intensity and efficacy remains uncertain.

OBJECTIVE

This study aimed to investigate whether the reduction of bruxism events and jaw muscle symptoms could vary according to the intensity of CES and in probable sleep bruxers.

METHODS

Twenty probable sleep bruxers were initially screened for bruxer confirmation based on a 2-week recording of SB events with a portable electromyography recorder (BUTLER®GrindCare®, GC4). A 3-week recording was conducted without CES using a GC4, followed by another 3-week recording with CES. At baseline and before and after the CES (+) session, clinical muscle symptoms were assessed using a 0-10 numerical rating scale (NRS). The relationships between the actual applied CES intensity and the number of SB events/hour, as well as the NRS of clinical muscle symptoms, were analysed.

RESULTS

The actual applied CES intensity was positively correlated with the reduction rate of the number of SB events/hour (R = .643, p = .002), as well as with the reduction rate of NRS for pain, unpleasantness, fatigue, tension and stiffness (R > .500, p < .011).

CONCLUSION

Higher CES elicited a more robust reduction in SB events and clinical muscle symptoms, in probable bruxers. Prior to selecting CES biofeedback as a management option for SB, it would be beneficial to assess the tolerance threshold of CES in each bruxer in order to predict the effectiveness of CES in probable sleep bruxers.

Reliability of an intraoral extension for intraoral palpation and assessment of mechanical sensitivity of the temporal tendon

BACKGROUND

The temporal tendon is a structure often compromised in patients suffering from temporomandibular disorders (TMD), yet its intraoral location makes a standardised assessment difficult.

OBJECTIVES

To evaluate the variability and accuracy to target force of a newly designed intraoral extension for a palpometer device (Palpeter, Sunstar Suisse) when compared to manual palpation, in addition to clinically assessing the mechanical sensitivity and referred sensations of the temporal tendon in healthy individuals.

METHODS

Experiment 1: 12 individuals were asked to target on a scale 0.5, 1 and 2 kg, for 2 and 5 s by using five different methods (Palpeter, Palpeter with three different extension shapes and manual palpation). Experiment 2: 10 healthy participants were recruited for a randomised double-blinded assessment by applying pressure of 0.5, 1 and 2 kg to the right temporal tendon with the three extensions and manual palpation. Participants rated the intensity of their sensation/pain on a 0-50-100 numeric rating scale (NRS), unpleasantness on a 0-100 NRS, and if present, they rated and drew the location of referred sensations. Repeated measures analysis of variance (ANOVA) was used in both experiments to compare differences between palpation methods. Tukey's HSD tests were used for the post hoc comparisons, and p values below .05 were considered significant.

RESULTS

Experiment 1: The extensions showed no significant differences between them regarding reliability and accuracy for all forces and durations (p > .05). The manual method was significantly less reliable and accurate when compared to the other methods (p < .05). Experiment 2: There were no significant differences between the Palpeter extensions regarding pain intensity or unpleasantness NRS scores (p > .05), but all the extensions had significantly increased pain intensity and unpleasantness when compared to manual palpation (p < .05). Similarly, the frequency of referred sensations was similar between extensions but increased when compared to manual palpation.

CONCLUSIONS

The new Palpeter extensions proved to be significantly more accurate and have lower test-retest variability than the manual method in a non-clinical setting. Clinically, they showed no significant differences in NRS scores for pain intensity nor unpleasantness, with no major differences in referred sensations, making any of the extensions suitable for clinical testing of the temporal tendon in future studies.

Comparison of force profiles from two musculoskeletal palpation methods: A methodological study

BACKGROUND

The Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) protocol recommends a 5 s and 1 kg force dynamic palpation around the lateral condylar pole of the temporomandibular joint. However, the accuracy and precision of the generated force are not known.

OBJECTIVE

To assess and compare the force profiles generated from dynamic palpation manually and using a palpometer, based on the forces and time recommendations suggested by the DC/TMD protocol.

METHODS

Nineteen healthy adults applied forces of 0.5 kg, 1.0 kg and 2.0 kg on a calibrated force sensor in a circular motion within target times of 2 s and 5 s. Participants used their right index finger for manual palpation and a calibrated palpometer for device-assisted palpation. Ten repetitions of each target force at both target times were applied. Time taken to complete each application was recorded. Repeated measures analysis of variance was used for analysis of accuracy measured as the relative difference between targeted force and actual force values and precision measured as the coefficient of variation (CV) within the 10 repeated measurements.

RESULTS

Accuracy was significantly lower (better) and precision higher (lower CV) with the palpometer than with manual palpation (p < .001). There were significant differences in accuracy and precision between the different forces but not palpation times. Most participants could not achieve the target times and tended to be faster, irrespective of the palpation method (p > .063).

CONCLUSION

A palpometer is a more accurate and precise palpation method for dynamic force assessment compared to manual palpation; however, it remains difficult to standardize the palpation duration.

Effect of clinical experience and training with visual feedback on standardized palpation outcomes-Potential implications for assessment of jaw muscle sensitivity

BACKGROUND

The evaluation of muscle pain and sensitivity by manual palpation is an important part of the clinical examination in patients with myalgia. However, the effects of clinical experience and visual feedback on palpation of the masticatory muscles with or without a palpometer are not known.

OBJECTIVE

To estimate the effects of clinical experience and visual feedback on the accuracy of palpation in standardized settings.

METHODS

Thirty-two dentists (age 35 ± 11 years) classified as either specialists (n = 16) or generalists (n = 16) participated in this experiment. All dentists were instructed to target force levels of 500- or 1000-gf, as determined on an electronic scale using either standardized palpometers or manual palpation (MP). All dentists participated in four different tests: MP, MP with visual feedback (MPVF), palpometer (PAL) and PAL with visual feedback (PALVF). Actual force values for each type of palpation from 0 to 2, 2 to 5 and 0 to 5 s were analysed by calculating target force level.

RESULTS

The relative differences during 2-5 and 0-5 s with 1000 gf were significantly lower for generalists than for specialists (p < .05). In generalists and specialists, the coefficients of variation and the relative differences during 2-5 s were significantly lower for PAL and PALVF than for MP (p < .05).

CONCLUSIONS

These findings suggest that the use of a palpometer, but not clinical experience with palpation of masticatory muscles, increases the accuracy of palpation, and ≥2 s of palpation with a palpometer is optimal for masticatory muscles.

Referred sensations in the orofacial region are associated with a decreased descending pain inhibition and modulated by remote noxious stimuli and local anesthesia

ABSTRACT

Referred sensation (RS) as a specific clinical phenomenon has been known for a long time, although the underlying mechanisms remain unclear. The aims of this study were to assess if (1) healthy individuals who experienced RS had a less active endogenous pain system when compared with those who did not; (2) activation of descending pain inhibition mechanisms can modulate RS parameters; and finally, (3) a transient decrease in peripheral afferent input because of a local anesthetic (LA) block in the masseter muscle can modulate RS parameters. To assess these, 50 healthy participants were assessed in 3 different sessions. In the first session, conditioned pain modulation (CPM) as well as mechanical sensitivity and RS at the masseter muscle were assessed. In the same session, participants who experienced RS had their mechanical sensitivity and RS assessed again while undergoing a CPM protocol. In the second and third sessions, participants had their mechanical sensitivity and RS assessed before and after receiving an injection of 2 mL of LA and isotonic saline into the masseter muscle. The main findings of this study were (1) participants who experienced RS during standardized palpation exhibited increased mechanical sensitivity ( P < 0.05, Tukey post hoc test) and decreased CPM ( P < 0.05, Tukey post hoc test) when compared with those who did not; RS incidence ( P < 0.05, Cochran Q test), frequency ( P < 0.05; Friedman test), intensity ( P < 0.05, Tukey post hoc test), and area ( P < 0.05, Tukey post hoc test) were all significantly reduced when assessed (2) during a painful conditioning stimulus and (3) after LA block. These novel findings highlight that RS in the orofacial region are strongly modified by both peripheral and central nervous system factors.

Location of mechanically-evoked referred sensations within the trigeminal region are not altered following a heterotopic painful stimulus

To investigate whether the location, area and frequency of referred sensations occurring during palpation of the masseter muscle can be influenced by application of a conditioning painful stimulus to the temporalis muscle. Thirty healthy participants were included in this cross-over study, performed in two sessions with > 48 h in between. At each session, palpation of the masseter muscle was performed before and after 0.2 ml of glutamate (1 mol/L) or isotonic saline (control) were injected into the anterior portion of the temporalis muscle. Palpation of the masseter muscle was done using four different forces (0.5 kg, 1 kg, 2 kg and 4 kg). Participants rated the perceived intensity of the palpation and any referred sensations on a 0-50-100 numeric rating scale, the perceived pain intensity following the injections on an electronic visual analogue scale and drew any referred sensations they experienced. No difference in referred sensations location, area and frequency was shown r during palpation either before or after injections (P > 0.05). A moderate correlation was found between perceived sensation scores and referred sensations intensity for the temporalis muscle following glutamate injection (r = 0.407, P < 0.05). Moreover, significantly more participants reported referred sensations for glutamate injections into the temporalis muscle when compared to isotonic saline (P < 0.05). Finally, a significant decrease in the perceived intensity of palpation of the masseter muscle was seen after glutamate injection in the temporalis muscle (P < 0.05). In the current study, location, area and frequency of referred sensations following mechanical stimulation of the masseter muscle were not altered by the application of a painful stimulus to the temporalis muscle. In addition, there seems to be a positive relationship between painful stimuli and referred sensations frequency and intensity elicited from the temporalis muscle.

Mechanical sensitivity changes in pericranial muscles after local anesthesia and experimentally induced pain in the temporalis tendon: Implications for headache and facial pain

OBJECTIVES

To assess changes in mechanical sensitivity of the pericranial muscles in healthy individuals after a local anesthetic block of the temporalis tendon. In addition, to assess, if experimentally induced temporalis tendon pain, can lead to an increase in mechanical sensitivity of the pericranial muscles and reports of headache.

METHODS

40 healthy participants were recruited for this randomized, double-blinded, controlled experiment, and were randomly injected with mepivacaine and isotonic saline into the dominant-side temporalis tendon in two different sessions, and either nerve growth factor (n = 20) or isotonic saline (n = 20) in a third session. Mechanical sensitivity was assessed in the temporalis, masseter, and trapezius muscles as well as in the temporalis tendon, on the dominant side, before and 10 minutes after each injection, and in a fourth session two days after the third session. Pain drawings and headache diaries were kept for 30 days after the final session to register any developing pain or headache.

RESULTS

Mepivacaine injection into the temporalis tendon caused a significant decrease in mechanical sensitivity in the temporal tendon (-54.5%) and the masseter (-15.4%) muscle (P < 0.05) but not the temporalis (-12.1%) and trapezius muscles (-12.7%) (P > 0.05). Nerve growth factor injection into the temporalis tendon caused a significant increase in mechanical sensitivity in the tendon (+15.4%) and masseter muscle (+14.4%) (P < 0.05) but not the temporalis (+2.8%) or trapezius muscles (+3.1%) (P > 0.05). A significant increase was found for headache frequency in the first seven days (P < 0.05) after nerve growth factor injection compared to after isotonic saline injection, but not intensity (P > 0.05).

CONCLUSION

These findings suggest that the therapeutic effect of temporalis tendon anesthetic injections on facial pain and headaches are most likely not only due to a direct effect of the local anesthetic on the temporalis tendon but rather to a more generalized block of the nerves in the area. In addition, the temporal tendon may contribute to the pathophysiological processes of headache.

Evaluation of Pressure Pain Sensitivity in the Forefoot of Healthy Individuals

BACKGROUND

The evaluation of musculoskeletal pain in podiatric medical practice is mainly based on anamnesis and manual examination. However, when manual palpation is performed, the digital pressure necessary to adequately explore the different structures of the foot is unknown. We evaluated the pressure pain threshold in forefoot structures to determine the intensity and duration of the stimulus as clinically relevant and representative.

METHODS

In a transversal analytical study of 15 healthy individuals, 16 forefoot points were explored with a handheld pressure palpometer calibrated to exert maximum pressing force of 1.0 or 2.0 kilogram-force (kgf) applied during 5 or 10 sec. The combinations of the different pressures and intervals were selected randomly. Participants had to self-rate the pressure pain sensitivity of each stimuli on a 100-mm horizontal line (0-100 numeric rating scale), setting the pain threshold to 50 (100 being pain as bad as it could be). Likewise, aftersensation and referred pain patterns were recorded.

RESULTS

All participants indicated painful stimuli at some of the 16 forefoot points studied in the experimental protocol when pressure was applied with the 2.0-kgf palpometer; 53.3% showed evidence of pain at any forefoot point when the 1.0-kgf palpometer was used. The odds of evoking a painful sensation are 9.8 times higher when using a 2.0-kgf palpometer versus a 1.0-kgf palpometer. In addition, referred sensations were observed with a significantly higher frequency when applying the 2.0-kgf palpometer.

CONCLUSIONS

Bone and soft structures show differences in pressure sensitivity, increasing significantly when applying higher pressure force. Soft structures, specifically intermetatarsal spaces, showed the lowest pain pressure thresholds. More research is needed to better understand pressure pain response.

Effect of aging and tooth loss on sensory function of alveolar mucosa

BACKGROUND

Maintain Quality of Life of elderly denture wearers is one of the most crucial tasks for dentists in the super-aged society. Although external mechanical load on removable dentures has been investigated to minimize a risk of soreness caused by dentures, sensory perception of the alveolar mucosa remains obscure.

OBJECTIVES

This study aimed to investigate effect of aging and tooth loss in sensory function on the alveolar mucosa for deep understanding of the characteristics of pain sensitivity in edentulous individuals.

METHODS

Eighteen edentulous participants(ED), as well as 18 age-matched dentate participants(EC) and 18 young dentate participants(YC), participated in this study. Tactile detection threshold(TDT) and pain threshold(PT) were measured with von Frey filaments (0.125-512 mN). Mechanical pain sensitivity(MPS) after a 2-sec application of 1 kg palpation was assessed with a 0-50-100 Numerical Rating Scale(NRS) (0: no pain, 50: slight pain, and 100: the worst pain imaginable). Furthermore, entropy scores of TDT, PT, and NRS on MPS were calculated.

RESULTS

In both maxilla and mandible, EC showed significantly higher TDT and PT, compared to YC, whereas ED showed significantly lower TDT and PT, compared to EC. NRS on MPS in ED was significantly higher than that in EC. The entropy scores of all the outcome parameters showed no significant difference between groups.

CONCLUSION

Both aging and tooth loss can alter tactile and pain perception in the oral mucosa. This suggest that it might be beneficial to assess sensory function of the alveolar mucosa in edentulous patients clinically in prior to denture fabrication.

Painful and non-painful symptoms evoked by experimental bracing and thrusting of the mandible in healthy individuals

BACKGROUND

Bruxism may involve bracing and thrusting of the mandible, in addition to clenching or grinding of the teeth. It is unclear how bracing and thrusting may contribute to potential musculoskeletal symptoms associated with bruxism.

OBJECTIVE

To examine the effect of experimental bracing and thrusting of the mandible on the development of musculoskeletal symptoms in healthy volunteers.

METHODS

Thirty healthy volunteers performed six trials of 5 min of repeated bracing and thrusting of the mandible. Bracing involved forcefully maintaining maximum protruded position (5 s with 1 s rest in between), whereas thrusting involved forcefully moving the mandible in a forward direction and back (1 Hz). The participants rated pain, unpleasantness, soreness, fatigue, tension, stiffness, stress and headache on 10-cm visual analogue scales (VAS) before, immediately and 24 h after the tasks. Pain drawings were obtained and maximum voluntary protrusive force (MVPF) was determined before and after the tasks. The outcome parameters for each task were compared between the time points.

RESULTS

There was a significant increase in the VAS scores (2-4/10) of pain, unpleasantness, soreness, fatigue, tension, stiffness and stress immediately following the tasks compared to baseline and 24 h after the tasks (p < .008). Pain was frequently reported in masseter muscles. MVPF values were significantly higher immediately (p < .001) and 24 h after thrusting (p < .001) and bracing (p = .012) tasks compared to the baseline.

CONCLUSIONS

Experimental bracing and thrusting of the mandible evoked transient, mild-to-moderate levels of muscle pain, fatigue, tension and stiffness and increased unpleasantness and stress scores in healthy volunteers.

Sex-related differences in response to masseteric injections of glutamate and nerve growth factor in healthy human participants

The neurophysiological mechanisms underlying NGF-induced masseter muscle sensitization and sex-related differences in its effect are not well understood in humans. Therefore, this longitudinal cohort study aimed to investigate the effect of NGF injection on the density and expression of substance P, NMDA-receptors and NGF by the nerve fibers in the human masseter muscle, to correlate expression with pain characteristics, and to determine any possible sex-related differences in these effects of NGF. The magnitude of NGF-induced mechanical sensitization and pain during oral function was significantly greater in women than in men (P < 0.050). Significant positive correlations were found between nerve fiber expression of NMDA-receptors and peak pain intensity (rs = 0.620, P = 0.048), and expression of NMDA-receptors by putative nociceptors and change in temporal summation pain after glutamate injection (rs = 0.561, P = 0.003). In women, there was a significant inverse relationship between the degree of NGF-induced mechanical sensitization and the change in nerve fiber expression of NMDA-receptors alone (rs = - 0.659, P = 0.013), and in combination with NGF (rs = - 0.764, P = 0.001). In conclusion, women displayed a greater magnitude of NGF-induced mechanical sensitization that also was associated with nerve fibers expression of NMDA-receptors, when compared to men. The present findings suggest that, in women, increased peripheral NMDA-receptor expression could be associated with masseter muscle pain sensitivity.

Drop homotopic effects of masseter-muscle pain on somatosensory sensitivity in healthy participants

Current pain classifications use 1.0-kg palpation of the masseter muscle to distinguish between “pain patients” and “healthy controls” but a thorough understanding of the normal physiological responses to various somatosensory stimuli is lacking. The aim of this study was to investigate somatosensory function of the skin over the masseter muscle in healthy participants that were divided into a masseter pain prone group (MPP) (n = 22) and non-MPP group (n = 22), according to the response to a 1.0-kg palpation. Quantitative sensory testing (QST) was performed at the skin above the right masseter muscle (homotopic). In an additional experiment, 13 individuals each from MPP and non-MPP received application of 60% topical lidocaine tape to the skin over the masseter muscle for 30 min. Immediately after, mechanical pain sensitivity (MPS), dynamic mechanical allodynia, and pressure pain threshold were tested. Homotopic MPS was significantly higher and PPTs significantly lower in MPP than in N-MPP (P < 0.05). Strikingly, no other differences in QST outcomes were observed between the groups (P > 0.05). After lidocaine application, no significant differences in homotopic MPS were observed between groups. The presence or absence of acute provoked pain in masseter muscle is exclusively associated with differences in homotopic MPS which is decreased following topical anesthesia.

Functional Change in Experimental Allodynia After Glutamate-Induced Pain in the Human Masseter Muscle

Background: Glutamate, as well as nerve growth factor (NGF), is involved in nociception from peripheral tissues, such as muscles. However, the potential interaction between glutamate and NGF still remains unclear. This study investigated the interaction between glutamate-induced masseter muscle pain and NGF-induced allodynia on pain perception and jaw function in healthy individuals, and any possible sex differences in the response.

Materials and Methods: Thirty pain-free adult participants (15 men and 15 women, mean age ± SD: 24 ± 4 years) participated in this study consisting of three sessions (Day 0, Day 3, and Day 4). NGF (5 μg/mL, 1.0 mL) was injected into the masseter muscle on Day 0 to induce muscle allodynia. On Day 3, glutamate (1M, 0.2 mL) was injected into the same masseter muscle. Before and after injections on Day 0 and 3, and post-injection (Day 4), spontaneous pain, temporal summation pain, as well as functional pain and fatigue in response to chewing were assessed with validated scales, and the pressure pain threshold (PPT) was recorded.

Results: Spontaneous pain intensity was significantly higher after glutamate than NGF (P < 0.001). PPTs, temporal summation pain and functional measures were all reduced 3 days after NGF injection (P's < 0.001). Injection of glutamate on Day 3 did not further affect PPTs or temporal summation pain and there were no sex differences in the effects (P > 0.189). Chewing pain (P = 0.022) and fatigue increased after glutamate injection to a higher degree in the women than men (P = 0.037).

Conclusion: Taken together, while glutamate injected into the NGF-sensitized muscle was painful, it did not alter muscle tenderness in women vs. men. However, pain and fatigue evoked by jaw function were higher in women after glutamate injection. This suggest that sex differences reported for masseter myalgia, mimicked by glutamate and NGF mediated pain in this study, may be greater for measures of perceived jaw function, which should be considered in a clinical evaluation.

Quantitative sensory testing of periauricular skin in healthy adults

The aim of this study was to investigate the test-retest reliability of quantitative sensory testing (QST) and mechanical sensitivity mapping of the periauricular skin. Twenty volunteers (10 men, 10 women) participated in two sessions at intervals of one week. Cold and warm detection threshold (CDT&WDT), cold and heat pain threshold (CPT&HPT), mechanical detection and pain threshold (MDT&MPT), pressure pain threshold (PPT) and two-point discrimination (2PD) were measured at five sites: bilateral subauricular and postauricular sites (LA, RA, LB, RB) and the dorsum of left hand (control). Pressure stimulation was applied at each of the four periauricular test sites. The test-retest reliability of the QST data implied fair to excellent agreement as evaluated by the intra-class correlation coefficients (ICC; all >0.4) for different days. There was no difference between each side in the QST parameters and mechanical sensitivity mapping (P ≥ 0.057). Significant differences between subauricular and postauricular sites were shown for WDT and PPT (P ≤ 0.028). NRS scores of mechanical sensitivity mapping showed significant effects of gender, site and point (P ≤ 0.040). QST and mechanical sensitivity mapping can be considered to be a reliable technique to assess somatosensory function of the periauricular skin.

Comparison of masseter muscle referred sensations after mechanical and glutamate stimulation: a randomized, double-blind, controlled, cross-over study

Referred sensations (RS) are commonly found in various musculoskeletal pain conditions. Experimental studies have shown that RS can be elicited through glutamate injection and mechanical stimulation. Despite this, differences and similarities between these modalities in RS outcomes remain unclear. The aim of this study was to assess differences between mechanical-induced and glutamate injection-induced RS in the trigeminal region. The present randomized, double-blind, controlled, cross-over study recruited 60 healthy participants who were assessed in 2 different sessions. In both sessions, pressure was applied to the masseter muscle with 4 different forces (0.5, 1, 2, and 4 kg), and glutamate (1 mol/L or 0.25 mol/L) was injected into the same area. Participants rated their perceived masseter sensations and rated and drew any RS they experienced. No difference was found in number of participants reporting RS after glutamate injection compared with mechanical stimulation. More participants reported RS when the stimulus was painful compared with a nonpainful stimulus. Furthermore, it was shown that the more intense the stimulus, the higher the frequency of RS. Finally, RS centre-of-gravity location was similar between the 2 sessions. In summary, RS was elicited in healthy individuals through both modalities, and no differences in frequency of RS were observed in the orofacial region. Hence, RS does not seem to be modality-dependent, and only the painfulness of the stimulus caused an increase in frequency of RS. Finally, RS location for each participant was similar in both sessions possibly indicating a preferred location of referral. These findings may have implications for our understanding of RS in craniofacial pain conditions.

Is quality of life affected by temporomandibular disorders?

OBJECTIVE

To determine the impact of temporomandibular disorders in quality of life.

METHODS

A total of 102 volunteer patients (68 female) aged 19 to 86 years, who sought medical care in health clinics of the university and were evaluated in the period from September to December 2013. The subjects were examined according to the Research Diagnostic Criteria for Temporomandibular Disorders, using a mechanical algometer (Palpeter®) with standardized pressure of 0.5 and 1.0kg, and Medical Outcomes Study 36-Item Short Form Health Survey (SF-36) questionnaire, to assess quality of life. The data were tabulated for statistical analysis and the variables were correlated with the clinical findings of the temporomandibular disorders and quality of life.

RESULTS

Fifty percent of patients were positive for temporomandibular disorders and 39.2% classified as myofascial pain group. The temporomandibular disorder group was significantly associated with uncomfortable bite (p=0.0000), temporomandibular joint clicking (p=0.0001) and tooth clenching (p=0.0001). The Mann Whitney test used to analyze the SF-36 revealed that the domains of pain (mean score of 47.80%; p<0.0001) and mental health (62.67%; p<0.05) were strongly associated with temporomandibular disorders.

CONCLUSION

The quality of life of individuals with temporomandibular disorders was negatively affected by the presence of pain and mental health disorders.

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.

Concurrent validation of a pressure pain threshold scale for individuals with myofascial pain syndrome and fibromyalgia

Background

Manual pressure palpation is an examination technique used in the classification of myofascial pain syndrome (MPS) and fibromyalgia (FM). Currently, there are no validated systems for classifying results. A valid and reliable pressure pain threshold scale (PPTS) may provide a means for clinicians to grade, document, and report findings. The purpose of this investigation was to validate a PPTS in individuals diagnosed with MPS and FM. Intra-rater reliability, concurrent validity, minimum cut-off value, and patient responses were evaluated.

Methods

Eighty-four participants who met the inclusion criteria were placed into three groups of 28 (N = 84): MPS, FM, and asymptomatic controls. All participants underwent a two-part testing session using the American College of Rheumatology criteria for classifying FM. Part-1 consisted of manual palpation with a digital pressure sensor for pressure consistency and part 2 consisted of algometry. For each tender point (18 total), participants graded tenderness using the visual analog scale (VAS) while the examiner concurrently graded response using a five-point PPTS.

Results

The PPTS had good intra-rater reliability (ICC ≥ .88). A moderate to excellent relationship was found between the PPTS and VAS for all groups with the digital pressure sensor and algometer (ρ ≥ .61). A minimum cut-off value of 2 on the PPTS differentiated participants with MPS and FM from asymptomatic controls.

Discussion

The results provide preliminary evidence validating the PPTS for individuals with MPS and FM. Future research should further study the clinimetric properties of the PPTS with other chronic pain and orthopedic conditions.

Levels of Evidence

2c.

Clinical Trial Registration

ClinicalTrials.gov registration No. NCT02802202.

Can palpation-induced muscle pain pattern contribute to the differential diagnosis among temporomandibular disorders, primary headaches phenotypes and possible bruxism?

BACKGROUND

The evaluation of possible differences in the distribution or characteristics of palpation-induced pain in the masticatory muscles could be valuable in terms of diagnostic assessment. The aim of this study was to evaluate the impact of different combinations of anterior temporalis (AT) and masseter palpation-induced pain in the diagnostic of temporomandibular disorder (TMD), primary headaches and bruxism.

MATERIAL AND METHODS

A total of 1200 dental records of orofacial pain adult patients were analyzed. The outcomes were dichotomously classified (presence/absence) as following: a) AT and/or masseter palpation-induced pain; b) myogenous TMD; c) temporomandibular joint (TMJ) arthralgia (arthrogenous TMD); d) migraine; e) tension-type headache (TTH); f) self-reported bruxism. Binomial logistic regression model (α = 5%) was applied to the data considering the palpation-induced muscle pain as the dependent variable.

RESULTS

Mean age (SD) were 35.7 years (13.4) for 635 included dental records (83% females). Myogenous and arthrogenous TMD, migraine, TTH and bruxism were mainly associated with, respectively, masseter palpation-induced pain (p<0.001 - OR=5.77, 95%CI 3.86-8.62), AT or masseter palpation-induced pain (p<0.001 - OR=2.39, 95%CI 1.57-3.63), bilateral AT palpation-induced pain (p<0.001 - OR=2.67, 95%CI 1.64-4.32), masseter and AT palpation-induced pain (p=0.009 - OR=1.62, 95%CI 1.12-2.33) and bilateral masseter palpation-induced pain (p=0.01 - OR=1.74, 95%CI 1.13-2.69).

CONCLUSIONS

Palpation-induced pain in the masticatory muscles may play a role in the differential diagnosis among painful TMD, primary headaches and bruxism.

Test-retest studies in quantitative sensory testing: a critical review

Quantitative sensory testing (QST) investigates the graded psychophysical response to controlled thermal, mechanical, electrical or chemical stimuli, allowing quantification of clinically relevant perception and pain thresholds. The methods are ubiquitously used in experimental and clinical pain research, and therefore, the need for uniform assessment procedures has been emphasised. However, varying consistency and transparency in the statistical methodology seem to occur in the QST literature. Sixteen publications, evaluating aspects of QST variability, from 2010 to 2012, were critically reviewed in detail. A considerable heterogeneity in the statistical evaluations of test-retest data was demonstrated. The authors, using a secondary analysis of published data for didactic purposes, propose and present minimal requirements for reporting of test-retest QST data.

Gender differences in low and high pain palpation thresholds in the TMJ and neck areas

The null hypothesis was that pain pressure thresholds are the same for young healthy males and females and do not differ between the temporomandibular joint (TMJ) and muscle sites. The aim of the current study was to compare pain pressure threshold levels using an algometer with a convex-formed contact piece and pressure increase rates similar to those in conventional finger palpation, making the conditions more like clinical examination of painful spots with commonly used physiotherapeutic methods. Healthy subjects, 12 male, mean age 22.5 +/- 1.62 (SD), and 12 female, 22.4 +/- 2.19 (SD), were enrolled. A transducer with a calibrated load range, 0 to 25 pounds, was used to measure pressure threshold levels for low (T1), VAS to approximately 2, and high (T2), VAS to approximately 8, pain levels bilaterally in the occipital (OC), sternocleidomastoid (SCM), upper trapezius (TU), transverse process of first vertebra (C1), and lateral temporomandibular joint (TMJ) areas. The null hypothesis was rejected. Levels T1 and T2 were significantly lower in the females in all tested areas. The range of the mean for T1 levels was 4.9-8.0 pounds for males and 3.2-5.1 pounds for females. For T2 levels, the range was 8.9-15.6 pounds for males and 6.2-10.3 pounds for females. Significant differences were found between muscle sites. These results support the use of different threshold levels: a) for males and females; and b) for different muscle areas.

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.