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Biomedical subjects

Peter Svensson

Publications and source records attributed to Peter Svensson.

At least 55 records · Page 3Linked to original sources
PubMed2003

Differential modulation of tremor and pulsatile control of human jaw and finger by experimental muscle pain.

Resting tremor is seen in both the limbs and in the trigeminal motor system. These rhythmical perturbations are the result of alternating activation of antagonistic muscles, and these increase in amplitude during slow, voluntary movements. In the present study, we examined the effect of experimental muscle pain on finger and jaw tremor. The tremor in the mandible and in the middle finger was measured on separate occasions, at rest and during two constant-velocity movements. Pain was then induced by the infusion of hypertonic saline into a jaw-closing muscle (masseter) or into a finger extensor muscle (extensor digitorum longus, EDL). During masseter pain, the power at the peak tremor frequency of the mandible decreased significantly both when the jaw was at rest and during voluntary jaw movements at two velocities. In contrast, pain in EDL resulted in a significant increase in the power of finger tremor only during the two speeds of voluntary movement. No change in the peak tremor frequency was seen in either the finger or the jaw during pain. The most likely explanation for these data is that muscle pain tonically modulates the amplitude of the outputs from the central "pulsatile control" generators that drive the alternating activation of antagonistic muscles which produce tremor at rest and during movements. This modulation is in the opposite direction for systems controlling jaw and hand, suggesting a specific interaction of the nociceptive afferents with separate central oscillators.

Adult↗
PubMed2003

Glutamate-evoked pain and mechanical allodynia in the human masseter muscle.

The present study examined the effect of peripheral administration of the excitatory amino acid (EAA) glutamate on the intensity of perceived pain and pressure pain thresholds (PPTs) in healthy young women (n=17) and men (n=18). Two injections separated by 25 min of 0.2 ml, 1.0M glutamate into the masseter muscle produced significantly higher scores of pain on 0-10 cm visual analogue scales (VAS) in women than in men (analysis of variance, ANOVA: P<0.001). There was no significant difference between the VAS scores for the first and the second injections in either men or women. The PPTs determined in the masseter muscle were significantly reduced following the first injection and further significantly reduced after the second injection (ANOVA: P<0.001). Furthermore, the PPTs were reduced to a similar extent in both women and men (maximum 44-56%), suggesting that gender did not influence the process of sensitization. There were no significant difference in VAS scores or PPTs between women taking oral contraceptives (n=9) and those who did not (n=8) (ANOVAs: P=0.709, P=0.153). It is concluded that the VAS scores produced by intramuscular administration of 1.0M glutamate may reflect a gender-dependent activation of nociceptive pathways which, in part, may be mediated through peripheral EAA receptors. The reduction of PPTs in the masseter muscle following administration of glutamate in a concentration of 1.0M may reflect allodynia to mechanical stimuli. This process of sensitization was not gender-dependent. The present results suggest that injection of 1.0M glutamate into the masseter muscle may provide a useful experimental method to test sensitization and efficacy of peripheral EAA receptor antagonists in human subjects.

Adult↗
PubMed2003

Differential recruitment of endogenous pain inhibitory systems in neuropathic pain patients.

Neuronal hyperexcitability is a key finding in patients with neuropathic pain. Contributing to hyperexcitability may be decreased activity in the endogenous pain inhibitory systems. The present study aimed at recruiting descending inhibition, by the use of painful heterotopic stimulation (HTS), in 16 patients with peripheral chronic neuropathic pain and associated brush-evoked allodynia. Two experiments were performed: one examined the effect of HTS on ongoing pain and intensity of brush-evoked allodynia and the other tested the effect of HTS on ongoing pain and area of brush-evoked allodynia. Both experiments consisted of two sessions, one with painful cold HTS (1 degrees C water bath) another with non-painful neutral HTS (32 degrees C water bath). The area of brush-evoked allodynia was significantly reduced (P=0.003) during painful HTS, as compared to non-painful HTS. In contrast, neither the intensity of brush-evoked allodynia nor the ongoing pain was significantly changed. The results indicate that endogenous pain modulating systems can alter some aspects of chronic neuropathic brush-evoked allodynia. The differential effect of painful HTS on ongoing pain and area of brush-evoked allodynia suggest that separate mechanisms are involved.

Adult↗
PubMed2003

Injection of nerve growth factor into human masseter muscle evokes long-lasting mechanical allodynia and hyperalgesia.

Nerve growth factor (NGF) is a neurotrophic protein with a pivotal role in development and maintenance of the nervous system on one side and inflammatory and neuropathic pain states on the other. NGF causes clear signs of behavioral hyperalgesia in animal models and following intradermal and systemic administration in humans. The present double-blinded, placebo-controlled study was designed to test quantitatively the effect and duration (1h, 1, 7, 14, 21 and 28 days) of NGF (5 microg in 0.2 ml) injected into the masseter muscle. Pressure pain thresholds (PPT) and pressure tolerance thresholds (PTOL) were used as indices of mechanical allodynia and hyperalgesia in the jaw-closing muscles. In addition, perceived pain intensity was assessed by the subjects on a 0-10 numerical rating scale (NRS) with the jaw at rest and in relation to various oral functions (chewing, yawning, talking, swallowing, drinking and smiling). Repeated measures analysis of variance (ANOVA) was used to test for significant effects. Injection of NGF into the masseter muscle was associated with significantly reduced PPT for 7 days (ANOVA: P<0.001) and PTOL for 1 day (P<0.001). Buffered isotonic saline injections into the masseter muscle also significantly lowered the PPT after 1 day but to a significantly smaller extent than the NGF injections (P<0.001) and isotonic saline had no significant effects on PTOL. In contrast, assessment of PPT and PTOL in the non-injected temporalis muscles demonstrated a significant increase after 14-28 days (P<0.001), which may have reflected an adaptation to the test procedure. NRS scores of chewing and yawning were significantly increased for 7 days following NGF injection (P<0.001). Systemic adverse effects were noted in one subject who reported fever and slight discomfort about 8h after the NGF injection. In conclusion, this is the first study to show that injection of NGF into the human masseter muscle causes local signs of mechanical allodynia and hyperalgesia that persist for at least 7 days as well as pain during strenuous jaw movement. The present pain model is safe and may be used to gain further insight into the neurobiological mechanisms of muscle pain and sensitization.

Adult↗
PubMed2003

Suppression of motor evoked potentials in a hand muscle following prolonged painful stimulation.

Earlier investigations have shown that stimulation of peripheral afferent nerves induces prolonged changes in the excitability of the human motor cortex. The present study compared the effect of experimental pain and non-painful conditioning stimulation on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in the relaxed first dorsal interosseous (FDI) and flexor carpi ulnaris (FCU) muscles. The MEPs were measured in 10 healthy subjects, and stimulus-response curves were generated before and after each of four stimulation paradigms conducted in random order on separate occasions: (a) control; (b) "dual stimulation" consisting of electrical stimulation of the FDI motor point paired with TMS; (c) painful infusion of hypertonic saline in the FDI muscle; and (d) pain combined with dual stimulation. There were no significant changes in FDI MEPs following the control paradigm, and dual stimulation induced an increase in the FDI MEPs only inconsistently. In contrast, the painful stimulation and the combined pain and dual stimulation paradigms were followed by significant suppression of the FDI MEPs at higher stimulus intensities. No changes were observed in the FCU MEPs following the four paradigms. In two additional subjects, the responses evoked in FDI by direct stimulation of the descending corticospinal tracts were significantly depressed following painful stimulation of the FDI, although the ulnar-evoked M-waves remained constant. It is concluded that muscle pain is followed by a period with profound depression of MEPs amplitudes in the resting muscle, but that these changes are at least in part due to a lasting depression of the excitability of the motoneurones in the spinal cord. Hence, painful stimulation differs from non-painful, repetitive stimulation, which facilitates the corticomotor pathway.

Adult↗
PubMed2003

Comparison of the effect of video glasses and nitrous oxide analgesia on the perceived intensity of pain and unpleasantness evoked by dental scaling.

The aim of this study was to evaluate whether distraction induced by video glasses had an effect on the perceived intensity of pain and unpleasantness during dental scaling compared with the effect of nitrous oxide (N(2)O) analgesia. The pain stimulus was dental scaling (removal of dental calculus) with an ultrasonic scaler. As a standardised, non-dental painful stimulus, Von Frey filaments were used. A total of 26 patients with superficial chronic periodontitis were enrolled in this randomised, controlled clinical study. The effect of video glasses was compared with N(2)O in one session and the effect of video glasses versus a control situation in another. The patients rated the intensity of pain and unpleasantness evoked by dental scaling and Von Frey filament stimulation on 100-mm visual analogue scales (VAS). For dental scaling, there was no effect of video glasses on the perceived pain (p=0.85) or unpleasantness (p=0.73) nor of N(2)O (p=0.69 and p=0.51, respectively) compared with the control situation. Similarly, no significant difference was found between VAS scores in the video glasses and N(2)O session (p=0.48, p=0.58). A significant effect of video glasses and N(2)O(p<0.008) was found on the perceived pain intensity produced by Von Frey filament stimulation compared with the control situation, but no significant difference was seen between these methods (p=0.07). Post-treatment interviews of the patients revealed that 81% of the patients in the video and 65% in the N(2)O session stated that the method had some beneficial effect on their overall experience of the treatment situation. In conclusion, administration of video glasses or N(2)O did not affect the perceived intensity of pain and unpleasantness evoked by dental scaling.

Adult↗
PubMed2003

Prophylactic tolperisone for post-exercise muscle soreness causes reduced isometric force--a double-blind randomized crossover control study.

The role of tolperisone hydrochloride, a centrally acting muscle relaxant in relieving painful muscle spasm is recently being discussed. The present study hypothesizes that the prophylactic use of tolperisone hydrochloride may effectively relieve post-exercise muscle soreness, based on the spasm theory of exercise pain. Twenty male volunteers, aged 25.2 +/- 0.82 years (mean +/- SEM) participated in 10 sessions in which they received oral treatment with placebo or the centrally acting muscle relaxant tolperisone hydrochloride (150 mg) three times daily for 8 days, in randomized crossover double-blind design. Time course assessments were made for pressure pain threshold, Likert's pain score (0-5), pain areas, range of abduction, isometric force, and electromyography (EMG) root mean square (RMS) during maximum voluntary isometric force on day 1 and 6, immediately after an eccentric exercise of first dorsal interosseous muscle, and 24 and 48 h after the exercise. Treatment with placebo or tolperisone hydrochloride was initiated immediately after the assessments on the first day baseline assessments. On the sixth day baseline investigations were repeated and then the subjects performed six bouts of standardized intense eccentric exercise of first dorsal interosseous muscle for provocation of post-exercise muscle soreness (PEMS). Perceived intensity of warmth, tiredness, soreness and pain during the exercise bouts were recorded on a 10 cm visual analogue pain scale. VAS scores and pressure pain thresholds did not differ between tolperisone and placebo treatment. All VAS scores increased during the exercise bouts 2, 3, 4, 5 and 6 as compared to bout 1. Increased pain scores and pain areas were reported immediately after, 24 and 48 h after exercise. Pressure pain thresholds were reduced at 24 and 48 h after the exercise in the exercised hand. Range of abduction of the index finger was reduced immediately after the exercise and was still reduced at 24 h as compared to the non-exercised hand. The EMG RMS amplitude was also reduced immediately after the exercise, but was increased at 24 and 48 h. Isometric force was reduced immediately after the exercise as compared to days 1, 6, and the 24 and 48 h post-exercise assessments with a greater reduction following the tolperisone hydrochloride treatment and the reduction was more in tolperisone group as compared to the placebo group. The results suggest, that the prophylactic intake of tolperisone hydrochloride provides no relief to pain in course of post-exercise muscle soreness but results in reduction in isometric force.

Adult↗
PubMed2003

Effect of muscle relaxants on experimental jaw-muscle pain and jaw-stretch reflexes: a double-blind and placebo-controlled trial.

A randomised, double-blind, placebo-controlled three-way cross-over study was performed to investigate the effect of two muscle relaxants (tolperisone hydrochloride and pridinol mesilate) on experimental jaw-muscle pain and jaw-stretch reflexes. Fifteen healthy men participated in three randomised sessions separated by at least 1 week. In each session 300 mg tolperisone, 8 mg pridinol mesilate or placebo was administered orally as a single dose. One hour after drug administration 0.3 ml hypertonic saline (5.8%) was injected into the right masseter to produce muscle pain. Subjects continuously rated their perceived pain intensity on an electronic 10-cm visual analogue scale (VAS). The pressure pain threshold (PPT) was measured and short-latency reflex responses were evoked in the pre-contracted (15% maximal voluntary contraction) masseter and temporalis muscles by a standardised stretch device (1 mm displacement, 10 ms ramp time) before (baseline), 1 h after medication (post-drug), during ongoing experimental muscle pain (pain-post-drug), and 15 min after pain had vanished (post-pain). Analysis of variance demonstrated significantly lower VAS peak pain scores (5.9 +/- 0.4 cm) after administration of tolperisone hydrochloride compared with pridinol mesilate (6.8 +/- 0.4 cm) and placebo (6.6 +/- 0.4 cm) (P=0.020). Administration of pridinol mesilate was associated with a significant decrease in PPTs compared with tolperisone hydrochloride and placebo (P=0.002) after medication, but not after experimental jaw-muscle pain. The normalised peak-to-peak amplitude of the stretch reflexes were not significantly influenced by the test medication (P=0.762), but were in all sessions significantly facilitated during ongoing experimental jaw-muscle pain (P=0.034). In conclusion, tolperisone hydrochloride provides a small, albeit significant reduction in the perceived intensity of experimental jaw-muscle pain whereas the present dose had no effect on the short-latency jaw-stretch reflex.

Adult↗
PubMed2003

Spread and referral of experimental pain in different jaw muscles.

AIMS: To test the hypothesis that there would be no differences in perceived pain intensity and spread and referral of pain evoked by injection of a similar amount of hypertonic saline into 6 different jaw-muscle sites in healthy female subjects. METHODS: A total of 15 healthy women participated in 3 experimental sessions separated by 1 week. In a randomized sequence, the deep layers of the masseter, superficial layers of the masseter, anterior temporalis, lateral pterygoid, medial pterygoid, and anterior digastric muscles were injected with 5.8% hypertonic saline (0.2 mL). The subjects rated the perceived intensity of pain on an electronic 0- to 10-cm visual analog scale (VAS). The distribution of pain was drawn by the subjects on anatomical maps of the face, and a Danish version of the McGill Pain Questionnaire (MPQ) was filled out. RESULTS: All injections were associated with moderate to strong pain intensity (mean peak value: 5.6 to 6.4 cm) with no significant differences between muscle sites (analysis of variance [ANOVA]: P = .520). Pain rating indices derived from the MPQ did not suggest significant differences between muscle sites (ANOVA: P = .898). However, the area of perceived pain differed significantly between muscle sites (ANOVA: P = .038) with the greatest area following the injection into the anterior temporalis muscle (Tukey: P < .05). On direct inspection, the pain maps appeared quite similar, but a new analysis technique based on a center-of-gravity method revealed significantly different coordinates and length of vectors (ANOVA: P < .001) with longer vectors associated with the pain areas in the anterior temporalis muscle compared with the other muscle sites (Tukey: P < .05). All muscles were frequently associated with referral of pain to intraoral structures (40% to 87%), but only pain in the anterior digastric muscle was referred to the tip of the tongue (53%). CONCLUSION: The data suggest no major differences in pain sensitivity between the examined jaw-muscle sites, but pain in the anterior temporalis muscle spreads to a larger area independent of pain intensity. There are subtle but detectable differences in the location and referral of pain patterns between jaw muscles. This will be helpful in the differential diagnosis of myofascial temporomandibular disorder pain.

Adult↗
PubMed2003

The effect of glutamate-evoked masseter muscle pain on the human jaw-stretch reflex differs in men and women.

AIMS: To compare jaw-stretch reflex responses in male and female subjects and to determine whether injection of glutamate into the masseter muscle facilitates these responses in both sexes. METHODS: Jaw-stretch reflex responses were evoked with a muscle stretcher, and pain intensity was scored by 11 men and 13 women before and after the injection of glutamate (1.0 mol/L, 0.2 ml) into the masseter muscle. The subjects rated glutamate-evoked pain intensity on a visual analog scale. RESULTS: Baseline jaw-stretch reflex responses were larger and glutamate injections into the masseter muscle were significantly more painful in women than in men, however, glutamate significantly facilitated jaw-stretch reflex responses in men but not in women. CONCLUSION: These results suggest that there is a significant sex-related difference in human jaw-stretch reflex responses and their modulation by painful stimuli. Since one possible function of facilitated jaw-stretch reflex responses during jaw muscle pain may be to reduce jaw mobility and thus protect against further exacerbation of an existing injury, the finding of a sex-related difference in modulation of jaw-stretch reflex responses may prove to be important in clarifying why the prevalence of temporomandibular disorders is greater in women than in men.

Adult↗
PubMed2003

A human model of intraoral pain and heat hyperalgesia.

AIM: To examine, in a double-blind and placebo-controlled crossover manner, the effect of topical application of capsaicin on the alveolar mucosa with a battery of intraoral quantitative sensory testings (QST) in 16 healthy volunteers. METHODS: Thirty microL of 5 mg/mL capsaicin or vehicle (control) was applied to a 3 x 3-mm paper disk and applied to the alveolar mucosa under an oral bandage. The subjects rated the perceived pain intensity on a 0 to 10 electronic visual analog scale (VAS) for 15 minutes. Quantitative sensory testings were performed before and immediately after the 15-minute application and consisted of assessments of cold detection threshold, warmth detection threshold (WDT), cold pain threshold, beat pain threshold (HPT), mechanical sensitivity to single and repeated punctate mechanical stimulation with von Frey filaments and to single and repeated brush stimulation with a cotton swab, and detection and pain thresholds to electrical stimulation of the alveolar mucosa and maxillary first premolar tooth. Analysis of variance was used to test the data. RESULTS: Application of capsaicin caused moderate levels of pain (VASpeak scores 5.0 +/- 1.9) whereas the vehicle was practically painless (VASpeak 0.9 +/- 2.4). No significant effects of vehicle on QST could be detected (P > .143). In contrast, capsaicin application was associated with significant decreases in WDT and HPT (P < .001). No other significant changes in QST were observed for capsaicin application. CONCLUSION: The intraoral capsaicin pain model is associated with signs of heat hyperalgesia, but not mechanical hyperalgesia. Since the somatosensory sensitivity is not well characterized in most orofacial pain conditions, mainly due to lack of tradition and techniques, intraoral QST may provide a better description of the somatosensory sensitivity and underlying mechanisms in orofacial pain conditions.

Administration, Topical↗
PubMed2002

Opioid-insensitive hypoalgesia to mechanical stimuli at sites ipsilateral and contralateral to experimental muscle pain in human volunteers.

Musculoskeletal pains are often characterised by referred pain and hyperalgesia. The aim of the present study was to examine the sensitivity to pressure and pinprick at sites ipsi- and contralateral to capsaicin-induced pain in the tibialis anterior (TA) muscle. Visual analogue scale (VAS) scores of the sensation to sub- and supra-pain threshold stimuli by pressure and pinprick were recorded before, during and after experimental muscle pain. It was found that pressure stimulation (120% of baseline pain threshold) delivered over the ipsilateral deep peroneal nerve between the 1st and 2nd metatarsal bones showed a significant increase in VAS scores during muscle pain. The referred pain did not overlap this hyperalgesic site. Ipsilateral test sites at the TA muscle, great toe and between the 3rd and 4th metatarsal bones did not show any changes in response to pressure stimulation during pain. In contrast, test sites at the ipsilateral ankle showed hypoalgesia to pressure during muscle pain. In the contralateral leg hypoalgesia to pressure was found at all sites during pain. The decreased sensitivity to pressure was confirmed with both sub- and supra-pressure pain-threshold stimuli. VAS scores to pinprick were either decreased or unchanged during pain compared to before pain. Naloxone administrated in a placebo-controlled manner had no effect on hypoalgesia to pressure or pinprick during muscle pain. Thus, the generalised decreased sensitivity may reflect activation of non-opioid endogenous pain inhibitory systems. The lack of change in sensitivity at some sites could indicate a competitive balance between excitatory and inhibitory mechanisms. The deep peroneal nerve specifically innervates both the TA muscle and the only site of hyperalgesia indicating spatial summation of afferent activity from these structures.

Adult↗
PubMed2002

Naturally occurring mutations in the thrombomodulin gene leading to impaired expression and function.

Sporadic mutations in the thrombomodulin (TM) gene occur in patients with both arterial and venous thrombosis, but the effects of these mutations on expression and function are largely unexplored. Full-length wild-type TM complementary DNA (cDNA) was incorporated into vector pcDNA6 for transfection into COS-7 cells for transient expression. Mutagenesis was performed to create 7 TM mutants with natural mutations either previously identified (Ala25Thr, Gly61Ala, Asp468Tyr, Pro477Ser, Pro483Leu) or reported here (an 11-base pair [bp] deletion, del791-801, leading to STOP306, and a missense mutation, Arg385Ser). Four mutations were found to detrimentally affect the level of expression of the TM protein. Of the missense mutations, 3 had reduced expression compared to wild-type TM (100%), Arg385Ser (50.2% +/- 5%, P <.001), Pro477Ser (76.8% +/- 1%, P <.001), Pro483Leu (82.1% +/- 8%, P <.007). No TM protein expression could be detected on the cell surface for mutation del791-801. The cofactor activity of TM in protein C activation was also evaluated. The Michaelis constant (K(m)) for wild-type thrombin-TM complex was 634 +/- 6 nmol/L. Two mutants, with Arg385Ser and Pro477Ser, had increased (P <.0001) K(m), 2967 +/- 283 nM, and 2342 +/- 219 nM, respectively, demonstrating impaired function of the thrombin-TM complex. This work presents biochemical evidence that certain (but not all) natural mutations in the TM gene reduce expression and impair function of the protein on the cell surface, and helps clarify the suggested contribution that these mutations might make to the risk of thromboembolic disease.

Adult↗
PubMed2002

Effects of experimental muscle pain on electromyographic activity of masticatory muscles in the rat.

The aim of the present study was to investigate the effects of noxious chemical stimulation of a jaw muscle on postural electromyographic (EMG) activity from several masticatory muscles in lightly anesthetized rats. Unilateral injection of a substance known to induce acute muscle pain (5% NaCl) or longer duration of pain with inflammation (mustard oil) was made into the masseter muscle. The changes in EMG activity following the injection were recorded from the injected and contralateral masseter muscles and the ipsilateral digastric muscle. The algesic chemicals produced a significant but transient increase in EMG activity in all three muscles. The data from the present study and similar observations from clinical and experimental human studies suggest that increased activity from muscle nociceptors is not sufficient to produce a prolonged increase in postural EMG activity. Therefore, the development and maintenance of chronic jaw muscle pain does not appear to result from a feedback cycle mechanism.

Action Potentials↗
PubMed2002

Modulation of trigeminal laser evoked potentials and laser silent periods by homotopical experimental pain.

Cutaneous laser stimulation activates predominantly the A-delta and C mechano-heat nociceptors. Applied to the perioral region, low intensity CO(2)-laser pulses evoke reproducible trigeminal cortical evoked potentials (LEPs). High intensity CO(2)-laser stimuli induce a reflex response in the contracted jaw-closing muscle, the so-called laser silent period (LSP). Both LEPs and LSP provide a useful tool to study the physiology of the trigeminal nociceptive system. In ten healthy subjects we recorded the subjective ratings of the perioral laser stimulation and the trigeminal LEPs and LSP before, during and after homotopic experimental tonic muscle (infusion of hypertonic saline into the masseter muscle) and tonic skin pain (topical application of capsaicin to the cheek). LEPs were recorded from the vertex at two stimulus intensities: low (1.1 x pain threshold, PTh) and high (1.5 x PTh). LSP from masseter and temporalis muscles were recorded bilaterally through surface electromyographic (EMG) electrodes. CO(2)-laser pulses were applied to the perioral region (V2/V3) on the painful and non-painful side. The amplitude of LEPs increased with higher stimulus intensities (P<0.0001), but were suppressed by 42.3+/-5.3% during experimental muscle pain (P<0.0001) and by 41.6+/-3.2% during skin pain (P<0.0001). No pain-related effects were observed for the N and P latency of the LEPs (P> 0.20). The LSP in the masseter and temporalis muscles had similar onset-latency (80+/-5 ms), offset-latency (111+/-5 ms) and duration (31+/-4 ms). Experimental pain had no effect on the onset- and offset-latency (P>0.05). Experimental pain, whether from muscle or from skin, reduced the degree of suppression (P<0.01) and the area under the EMG curve (P< 0.005) of the LSP. The LSP was still suppressed during the post-pain recordings when the skin pain had disappeared (P<0.05). In all experiments experimental tonic pain decreased the subjective ratings of the perioral laser stimulation (P< 0.001). Experimental tonic pain, either from muscle or from skin, induced bilateral inhibitory effects on the trigeminal laser evoked potentials and brainstem reflex responses and on the subjective ratings of the laser pulses. These effects could be mediated through the activation of segmental and suprasegmental inhibitory systems that may function interdependently.

Administration, Topical↗
PubMed2002

Topical review: modulation of trigeminal sensory input in humans: mechanisms and clinical implications.

In this review, the modulatory effects of tooth and implant loading, orofacial pain, and psychological factors on somatosensory and jaw-motor function in humans are assessed. Experimental studies on the control of jaw actions have revealed that patients with prostheses supported by osseointegrated implants show an impairment of fine motor control of the mandible. One possibility is that this may be related to the loss of afferent information from periodontal ligament mechanoreceptors, which results in considerably higher and more variable forces to hold and manipulate food between the teeth. However, psychophysical investigations have shown that patients still perceive mechanical stimuli exerted on osseointegrated implants in the jawbone. The use of somatosensory evoked potentials may revealed what specific receptor groups are responsible for this so-called osseoperception phenomenon. Orofacial pain is another modulator of trigeminal system functioning. Experimental jaw muscle pain has several effects on the somatosensory and motor function of the masticatory system, all of them serving to warn the individual about the ongoing damaging of tissues. Finally, the influence of mental state on the sensory and motor functions of the trigeminal system will be addressed. While some animal studies suggest that psychological stress can reduce acute pain, less speculative are the findings in human subjects that the anticipation of receiving a painful stimulus or undertaking difficult mental tasks can modulate jaw reflexes, including those evoked by mechanical stimuli applied to the teeth. Since such stimuli occur regularly during normal oral activities, the study of the resulting motor effects may yield clinically meaningful results in the context of other variables that modulate mandibular function.

Afferent Pathways↗
PubMed2002

Temporomandibular disorders after whiplash injury: a controlled, prospective study.

AIMS: Whiplash injury to the neck is often considered a significant risk factor for development of temporomandibular disorders (TMD), and has been proposed to produce internal derangements of the temporomandibular joint (TMJ). Few studies, however, have examined TMD-related pain in acute whiplash patients compared with a matched control group. The aim of the present study was to assess pain and sensorimotor function in the craniofacial region in an unselected group of patients sustaining a motor vehicle accident involving a rear collision. METHODS: Prospectively, 19 acute whiplash patients exposed to a motor vehicle accident involving a rear collision participated in a study of TMD. The control group consisted of 20 age- and gender-matched ankle-injury patients. Participants were seen within 4 weeks and again at 6 months post-injury. The masticatory system was examined in accordance with the research diagnostic criteria. Participants underwent structured interviews, filled out the McGill Pain Questionnaire (MPQ), and had their masticatory system examined by a trained dentist, blinded to their diagnosis. Pain detection threshold (PDT) to pressure stimuli, and maximal voluntary occlusal force (MVOF) were obtained at each visit. RESULTS: One whiplash patient and 1 ankle-injury patient had jaw pain at the first visit. Palpation scores of the TMJ and the summated palpation scores only tended to be higher in patients sustaining a whiplash injury than in ankle-injury controls at the first visit. However, MPQ, TMD symptoms and signs, MVOF and PDT were not significantly different in whiplash-injury and ankle-injury patients after 4 weeks and 6 months. CONCLUSION: TMD pain after whiplash injury and ankle injury is rare, suggesting that whiplash injury is not a major risk factor for the development of TMD problems. Further studies are needed to identify which other factors may contribute to TMD pain.

Adult↗