Increased intra-articular concentration of bradykinin in the temporomandibular joint changes the sensitivity of muscle spindles in dorsal neck muscles in the cat

Effects of Thrust Magnitude and Duration on Immediate Postspinal Manipulation Trunk Muscle Spindle Responses

OBJECTIVE

The purpose of this study was to characterize trunk muscle spindle responses immediately after high-velocity, low-amplitude spinal manipulation (HVLA-SM) delivered at various thrust magnitudes and thrust durations.

METHODS

Secondary analysis from multiple studies involving anesthetized adult cats (N = 70; 2.3-6.0 kg) receiving L6 HVLA-SM. Muscle spindle afferent recordings were obtained from L6 dorsal rootlets before, during, and immediately after HVLA-SM. L6 HVLA-SM was delivered posteriorly-to-anteriorly using a feedback motor with peak thrust magnitudes of 25%, 55%, and 85% of cat body weight (BW) and thrust durations of 25, 50, 75, 100, 150, 200, and 250 ms. Time to the first action potential and muscle spindle discharge frequency at 1 and 2 seconds post-HVLA-SM were determined.

RESULTS

A significant association between HVLA-SM thrust magnitude and immediate (≤2 s) muscle spindle response was found (P < .001). For non-control thrust magnitude, pairwise comparisons (25%, 55%, 85% BW), 55% BW thrust magnitude had the most consistent effect on immediate post-HVLA-SM discharge outcomes (false discovery rate < 0.05). No significant association was found between thrust duration and immediate post-HVLA-SM muscle spindle response (P > .05).

CONCLUSION

The present study found that HVLA-SM thrust magnitudes delivered at 55% BW were more likely to affect immediate (≤2 s) post-HVLA-SM muscle spindle response.

The Neurophysiological Impact of Experimentally-Induced Pain on Direct Muscle Spindle Afferent Response: A Scoping Review

Background: Musculoskeletal pain disorders are among the leading causes of years lived with disability worldwide representing a significant burden to society. Studies investigating a “nociceptive-fusimotor” relationship using experimentally-induced pain/noxious stimuli and muscle spindle afferent (MSA) response have been published over several decades. The purpose of this scoping review was to systematically identify and summarize research findings related to the impact of experimentally-induced pain or noxious stimulation on direct MSA discharge/response.

Methods: PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Cochrane and Embase were searched from database inception to August 2020. Eligible studies were: (a) published in English; (b) clinical or pre-clinical studies; (c) original data studies; (d) included the investigation of MSA response to experimentally-induced pain or noxious stimulation; (e) included quantification of at least one direct physiological measure associated with MSA activity/response. Two-phase screening procedures were conducted by a pair of independent reviewers and data extracted from eligible studies.

Results: The literature search resulted in 195 articles of which 23 met inclusion criteria. Six studies (26%) were classified as clinical and 17 (74%) as pre-clinical. Two clinical studies investigated the effects of sacral dermatome pin-pricking on MSA response, while the remaining 4 studies investigated the effects of tonic muscle and/or skin pain induced by injection/infusion of hypertonic saline into the tibialis anterior muscle or subdermal tissues. In pre-clinical studies, muscle pain was induced by injection of noxious substances or the surgical removal of the meniscus at the knee joint.

Conclusion: Clinical studies in awake humans reported that experimentally-induced pain did not affect, or else slightly decreased MSA spontaneous discharge and/or response during weak dorsiflexor muscle contraction, thus failing to support an excitatory nociceptive-fusimotor relationship. However, a majority of pre-clinical studies indicated that ipsilateral and contralateral muscle injection of noxious substances altered MSA resting discharge and/or response to stretch predominately through static fusimotor reflex mechanisms. Methodological differences (use of anesthesia, stretch methodology, etc.) may ultimately be responsible for the discrepancies between clinical and pre-clinical findings. Additional investigative efforts are needed to reconcile these discrepancies and to clearly establish or refute the existence of nociceptive-fusimotor relationship in muscular pain.

Craniocervical and Cervical Spine Features of Patients with Temporomandibular Disorders: A Systematic Review and Meta-Analysis of Observational Studies

To assess neck disability with respect to jaw disability, craniocervical position, cervical alignment, and sensorimotor impairments in patients with temporomandibular disorders (TMD), a systematic review and meta-analysis of observational studies trials were conducted. The meta-analysis showed statistically significant differences in the association between neck disability and jaw disability (standardized mean difference (SMD), 0.72 (0.56–0.82)). However, results showed no significant differences for cervical alignment (SMD, 0.02 (−0.31–0.36)) or for the craniocervical position (SMD, −0.09 (−0.27–0.09)). There was moderate evidence for lower pressure pain thresholds (PPT) and for limited cervical range of motion (ROM). There was limited evidence for equal values for maximal strength between the patients with TMD and controls. There was also limited evidence for reduced cervical endurance and conflicting evidence for abnormal electromyographic (EMG) activity and motor control in TMD patients. Results showed a clinically relevant association between cervical and mandibular disability in patients with TMD. Regarding sensory-motor alterations, the most conclusive findings were observed in the reduction of PPT and cervical ROM, with moderate evidence of their presence in the patients with TMD. Lastly, the evidence on impaired motor control and cervical EMG activity in patients with TMD was conflicting.

Jaw-neck motor function in the acute stage after whiplash trauma

BACKGROUND

Jaw-neck motor function is affected in the chronic stage following whiplash trauma. It is not known whether motor function is affected also in the early stage after neck trauma.

OBJECTIVES

To determine how jaw and head movement amplitudes and movement cycle times correlate with jaw and neck pain, and neck disability in the acute stage after whiplash trauma.

METHODS

Jaw and head movements during jaw opening-closing were recorded with an optoelectronic system in 23 cases (4 men, 19 women, 18-66 years) within 1 month after whiplash trauma and compared with 27 controls without neck trauma (15 men, 12 women, 20-66 years). Jaw and head movement amplitudes, head/jaw ratio (quotient of head and jaw movement amplitude) and movement cycle times were evaluated in relation to jaw and neck pain (Numeric Rating Scale) and neck disability (Neck Disability Index). Analyses were performed with Mann-Whitney U test and Spearman's correlation.

RESULTS

Compared with controls, cases showed smaller jaw movement amplitudes (P = .006) but no difference in head movement amplitudes, head/jaw ratios or movement cycle times. There were no significant correlations between movement amplitudes or cycle times and jaw and neck pain, and neck disability. Cases with high neck pain intensity had smaller jaw movement amplitudes compared to cases with low neck pain intensity (P = .024).

CONCLUSION

The results suggest that jaw-neck motor function may be affected in the acute stage after whiplash trauma and more so in cases with higher neck pain intensity.

Jaw-neck movement integration in 6-year-old children differs from that of adults

BACKGROUND

A functional integration between the jaw and neck regions during purposive jaw movements is well described in adults, but there is a lack of knowledge of such integration during jaw function in children.

OBJECTIVES

To determine the movement integration between the jaw and neck during jaw motor tasks in 6-year-olds, whether there is a difference between children and adults.

METHODS

Jaw and neck movements were recorded with an optoelectronic 3D system in 25 healthy 6-year-olds (12 girls, 13 boys) and 24 healthy adults (12 women, 12 men) during paced jaw opening-closing and self-paced gum chewing. Jaw and neck movement amplitudes, intra-individual variation in movement amplitude, ratio between neck-jaw movement amplitudes and movement cycle time were analysed. Differences between children and adults were evaluated with Mann-Whitney U test for independent samples.

RESULTS

Compared to adults, 6-year-old children showed larger neck movement amplitudes (P = .008) during chewing, higher intra-individual variability in amplitudes of jaw (P = .008) and neck (P = .001) movements, higher ratio between neck-jaw movement amplitudes for jaw opening-closing (P = .026) and chewing (P = .003), and longer jaw movement cycle time (P ≤ .0001) during the jaw opening-closing task.

CONCLUSION

Despite integrated jaw-neck movements in 6-year-old children, the movement pattern differs from that of adults and may be interpreted as an immature programming of jaw-neck motor behaviour. The well-integrated movements observed in adults most likely develop over years, perhaps into adolescence, and needs further research including well-controlled longitudinal studies to map this development in order to provide appropriate age-related clinical treatment for functional disorders.

Does altered mandibular position and dental occlusion influence upper cervical movement: A cross-sectional study in asymptomatic people

OBJECTIVE

Gross mandibular position and masticatory muscle activity have been shown to influence cervical muscles electromyographic activity. The purpose of this study was to investigate the influence of three different mandible positions including conscious occlusion, tongue tip against the anterior hard palate (Palate tongue position) and natural resting position (Rest), on sagittal plane cervical spine range of motion (ROM) as well as the flexion-rotation test (FRT) in asymptomatic subjects.

MATERIALS AND METHODS

An experienced single blinded examiner evaluated ROM using an Iphone in 22 subjects (7 females; mean age of 29.91years, SD 5.44).

RESULTS

Intra-rater reliability for range recorded was good for the FRT with ICC (intraclass correlation) 0.95 (95% CI: 0.88-0.98) and good for sagittal plane cervical ROM with ICC 0.90 (95% CI: 0.77-0.96). A repeated measures ANOVA determined that mean ROM recorded during the FRT differed significantly between assessment points (F(1.99, 41.83) = 19.88, P < 0.001). Bonferroni Post hoc tests revealed that both conscious Occlusion and Palate tongue position elicited a significant large reduction in ROM recorded during the FRT from baseline (p < 0.01). Despite this, one activation strategy did not influence ROM more than the other. An additional repeated measures ANOVA determined that mean sagittal cervical ROM did not significantly vary between assessment points (F(2, 42) = 8.18, P = 0.08).

CONCLUSION

This current study provided further evidence for the influence of the temporomandibular region on upper cervical ROM. Results suggest that clinicians should focus on the natural mandible rest position when evaluating upper cervical mobility.

Changes in cervical movement impairment and pain following orofacial treatment in patients with chronic arthralgic temporomandibular disorder with pain: A prospective case series

The purpose of this study was to investigate the influence of isolated temporomandibular joint (TMJ) manual therapy on pain and range of motion (ROM) of the TMJ and cervical spine including flexion-rotation test (FRT) in people suffering chronic pain arising from chronic arthralgic temporomandibular disorder (TMD). An experienced clinician managed a case series of 12 patients with TMD (mean duration 28.6 months +/- 26.9). The intervention comprised four-weekly sessions of transverse medial accessory TMJ mobilization and advice. Patients were examined prior to and one-week following the intervention period. Outcome measures included jaw disability (JFLS-20), jaw pain measured by Visual Analogue Scale (VAS), maximal mouth opening ROM, cervical ROM including FRT, and pain during cervical movement. A paired t-test revealed significant improvement following the intervention in disability (p < 0.001), VAS pain score at rest (p < 0.001) and at maximum mouth opening (p < 0.001), jaw opening ROM (p < 0.001), FRT ROM to the left (p = 0.024) and right (p = 0.001). In contrast, no significant change was identified for total cervical ROM (p = 0.905). After the intervention, five patients (41.66%) had no pain at rest or at maximal mouth opening, and all had a negative FRT. The effect sizes indicate a moderate to strong, clinically significant effect for all variables apart from total cervical ROM. While a case series cannot identify a cause and effect relationship, these results provide preliminary evidence for the influence of TMJ manual therapy on measures of TMD including pain, as well as upper but not whole cervical movement and associated pain in patients with a diagnosis of TMJ arthralgia.

Evaluation of Cervical Spine Posture After Functional Therapy with FR-2: A Longitudinal Study

The authors compared postural changes produced in 20 Caucasian female children treated with the Frankel Functional Regulator appliance (FR-2) (Frankel Industries, Morangis Cedex, France) using cephalometric tracings and comparing the tracings to 20 untreated Class II controls from the University of Chieti. Each patient in the study group was treated for exactly two years by the same operator using the FR-2 appliance and a standardized design and clinical technique, including prefunctional orthodontics where indicated. The average starting age was 8.4 yrs. (SD+/-2.1). At the end of the therapy, the average age was 10.3 yrs. (SD+/-2.4). Two teleradiographs were made of each patient: the first one at the beginning of treatment and the second one after six months. The radiographs were taken with the subjects standing in the ortho-position with no ear rods in the cephalostat; mirror position was carried out. In order to detect errors due to landmark identification, duplicate measurements were made using ten radiographs, and the error variance was calculated using Dahlberg's formula. Thirty-seven variables were studied. The cervical lordosis angle (CVT/EVT) was significantly higher in the study group as compared to the control group (p<0.05) at the end of treatment, probably due to a significant backward inclination of the upper segment of the cervical column (OPTNer and CVTNer) in the treated group (p<0.001 and p<0.01) from pre- to posttreatment. There was no significant change in the lower segment of the cervical column inclination (EVT/Ver). The changes resulted in a weak association in the multiple regression model to an increasing of maxillary base length and mandibular protrusion (R2=0.272; p<0.05). Other variables in the multiple regression were not significant.

Cervical musculoskeletal impairments and temporomandibular disorders

Objectives

The study of cervical muscles and their significance in the development and perpetuation of Temporomandibular Disorders has not been elucidated. Thus this project was designed to investigate the association between cervical musculoskeletal impairments and Temporomandibular Disorders.

Material and Methods

A sample of 154 subjects participated in this study. All subjects underwent a series of physical tests and electromyographic assessment (i.e. head and neck posture, maximal cervical muscle strength, cervical flexor and extensor muscles endurance, and cervical flexor muscle performance) to determine cervical musculoskeletal impairments.

Results

A strong relationship between neck disability and jaw disability was found (r = 0.82). Craniocervical posture was statistically different between patients with myogenous Temporomandibular Disorders (TMD) and healthy subjects. However, the difference was too small (3.3º) to be considered clinically relevant. Maximal cervical flexor muscle strength was not statistically or clinically different between patients with TMD and healthy subjects. No statistically significant differences were found in electromyographic activity of the sternocleidomastoid or the anterior scalene muscles in patients with TMD when compared to healthy subjects while executing the craniocervical flexion test (P = 0.07). However, clinically important effect sizes (0.42 - 0.82) were found. Subjects with TMD presented with reduced cervical flexor as well as extensor muscle endurance while performing the flexor and extensor muscle endurance tests when compared to healthy individuals.

Conclusions

Subjects with Temporomandibular Disorders presented with impairments of the cervical flexors and extensors muscles. These results could help guide clinicians in the assessment and prescription of more effective interventions for individuals with Temporomandibular Disorders.

Experimental masseter muscle pain alters jaw-neck motor strategy

BACKGROUND

A functional integration between the jaw and neck regions has been demonstrated during normal jaw function. The effect of masseter muscle pain on this integrated motor behaviour in man is unknown. The aim of this study was to investigate the effect of induced masseter muscle pain on jaw-neck movements during a continuous jaw opening-closing task.

METHODS

Sixteen healthy men performed continuous jaw opening-closing movements to a target position, defined as 75% of the maximum jaw opening. Each subject performed two trials without pain (controls) and two trials with masseter muscle pain, induced with hypertonic saline as a single injection. Simultaneous movements of the mandible and the head were registered with a wireless optoelectronic three-dimensional recording system. Differences in movement amplitudes between trials were analysed with Friedman's test and corrected Wilcoxon matched pairs test.

RESULTS

The head movement amplitudes were significantly larger during masseter muscle pain trials compared with control. Jaw movement amplitudes did not differ significantly between any of the trials after corrected Wilcoxon tests. The ratio between head and jaw movement amplitudes was significantly larger during the first pain trial compared with control.

CONCLUSIONS

Experimental masseter muscle pain in humans affected integrated jaw-neck movements by increasing the neck component during continuous jaw opening-closing tasks. The findings indicate that pain can alter the strategy for jaw-neck motor control, which further underlines the functional integration between the jaw and neck regions. This altered strategy may have consequences for development of musculoskeletal pain in the jaw and neck regions.

Endurance to physical strain in patients with temporomandibular disorders: a case-control study

OBJECTIVE

The hypothesis tested was whether patients with temporomandibular disorders (TMD) have an impaired endurance to motor tasks, under physical strain.

MATERIAL AND METHODS

The study population included 81 cases with TMD and 75 controls. After giving their informed consent, the participants filled out a questionnaire and performed five endurance trials. Each trial was measured in seconds from start to termination. The tests included: (a) holding the arm in a straight out position with a 2 kg weight in the hand, (b) lifting and lowering the arm with a 2 kg weight in the hand, (c) opening and closing the mandible repeatedly against a resistance of 1.6 kg during the jaw-opening phase, (d) protruding and retracting the mandible repeatedly against a resistance of 1.6 kg during the protruding phase and (e) unilateral chewing of three pieces of chewing gum. Analysis of differences between cases and controls for endurance were evaluated with Mann-Whitney U-test. A p-value < 0.05 was considered statistically significant.

RESULTS

The cases had statistically significantly (p < 0.0001) lower endurance time than controls for all tests.

CONCLUSIONS

Patients with TMD compared to those without signs and symptoms of TMD have an impaired capacity to endure motor tasks that involve physical demand of the jaw muscles and shoulder girdle muscles.

Patients with temporomandibular disorders have increased fatigability of the cervical extensor muscles

OBJECTIVES

To determine whether patients with myogenous and mixed temporomandibular disorders (TMD) have greater fatigability of the cervical extensor muscles while performing a neck extensor muscle endurance test (NEMET) when compared with healthy controls.

METHODS

A total of 151 individuals participated in this study. Of these 47 were healthy controls, 57 patients had myogenous TMD, and 47 patients had mixed TMD. All patients performed the NEMET. The patients were instructed to maintain a prone lying position with the neck unsupported as long as possible, stopping at signs of fatigue or any discomfort. Electromyographic activity of the cervical extensor muscles during the NEMET and the holding time were collected for all patients and were compared across groups. A 1-way analysis of variance was used to evaluate the differences in holding time between patients with TMD and healthy controls. A mixed model analysis was used to evaluate the differences in normalized median frequency at different times (fatigue index) for the cervical extensor muscles while performing the NEMET between patients with TMD and controls.

RESULTS

There were statistically significant differences (P<0.05) in the slopes of the normalized median frequency between patients with TMD and healthy controls at 10, 30, 40, 50, 60, 70, 80, 90, and 100 seconds of the NEMET. Holding time was significantly reduced in both patients with myogenous TMD and mixed TMD when compared with healthy controls (P<0.05).

DISCUSSION

These results highlight the fact that alterations of endurance capacity of the extensor cervical muscles could be implicated in the neck-shoulder disturbances presented in patients with TMD.

Does a dose-response relation exist between spinal pain and temporomandibular disorders?

BACKGROUND

The aim of this study was to test whether a reciprocal dose-response relation exists between frequency/severity of spinal pain and temporomandibular disorders (TMD).

METHODS

A total of 616 subjects with varying severity of spinal pain or no spinal pain completed a questionnaire focusing on symptoms in the jaw, head and spinal region. A subset of the population (n = 266) were sampled regardless of presence or absence of spinal pain. We used two different designs, one with frequency/severity of spinal pain, and the other, with frequency/severity of TMD symptoms as independent variable. All 616 participants were allocated to four groups, one control group without spinal pain and three spinal pain groups. The subjects in the subset were allocated to one control group without TMD symptoms and three TMD groups. Odds ratios (ORs) were calculated for presence of frequent TMD symptoms in the separate spinal pain groups as well as for frequent spinal pain in the separate TMD groups.

RESULTS

The analysis showed increasing ORs for TMD with increasing frequency/severity of spinal pain. We also found increasing ORs for spinal pain with increasing frequency/severity of TMD symptoms.

CONCLUSION

This study shows a reciprocal dose-response-like relationship between spinal pain and TMD. The results indicate that these two conditions may share common risk factors or that they may influence each other. Studies on the temporal sequence between spinal pain and TMD are warranted.

Electromyographic activity of masticatory, neck and trunk muscles of subjects with different skeletal facial morphology ? a cross-sectional evaluation

The electromyographic pattern activity of masticatory, neck and trunk muscles was assessed using surface electromyography (sEMG) in 60 Caucasian adult females (20 subjects in skeletal class I, 20 subjects in skeletal class II and 20 subjects in skeletal class III), classified on the base of their skeletal class (ANB angle), corrected on the base of maxillary and mandibular rotations. The sEMG activity was recorded at mandibular rest position and during maximal voluntary clenching. At mandibular rest position, the sEMG activities of masseter and anterior temporal muscles were significantly higher in class III subjects than in class I and class II subjects, that showed no significant difference between them. Then, the sEMG activities of posterior cervicals and upper trapezius were significantly higher in skeletal class III subjects than in the other two groups. During maximal voluntary clenching, no significant difference was observed in the sEMG activity of masticatory muscles among the three considered groups. However, the sEMG activities of posterior cervicals and upper trapezius were significantly higher in skeletal class III subjects than in the other two groups, which showed no significant difference between them. In conclusion, the skeletal class seems to affect the sEMG pattern activity of masticatory, neck and trunk muscles.

Electromyographic Activity of Masticatory, Neck and Trunk Muscles of Subjects with Different Mandibular Divergence

OBJECTIVE

To record and compare the surface electromyographic (sEMG) activity of masticatory, neck, and trunk muscles at different functional requirements of the stomatognathic system in an adult sample classified according to the mandibular divergence angle (SN-GoGn angle).

MATERIALS AND METHODS

60 Caucasian adult subjects were classified on the basis of SN-GoGn angle: 20 subjects with normal mandibular divergence, 20 subjects with lower angles, and 20 subjects with higher angles. Their sEMG activity was recorded at mandibular rest position and during maximal voluntary clenching.

RESULTS

sEMG activity of subjects with a lower angle was significantly higher than that of subjects in the other two groups at mandibular rest position for the masseter, the anterior temporal, the upper trapezius, and the posterior cervical muscles. During maximal voluntary clenching, no significant difference was observed in the sEMG activity of the masticatory muscles among the three groups. However, the sEMG activity of the posterior cervicals and that of the upper trapezius were significantly higher in subjects with a lower angle than in the other two groups.

CONCLUSION

Skeletal class does seem to affect the sEMG pattern activity of the masticatory, neck, and trunk muscles.

Recovery of Joint Position Sense in the Shoulder after Muscle Fatigue

Context:

Fatigue of the shoulder rotator muscles may negatively affect joint position sense (JPS) and ultimately lead to injury.

Objective:

Recovery of shoulder JPS after muscle fatigue.

Design:

A repeated-measures study.

Setting:

Musculoskeletal research laboratory.

Patients:

Thirteen subjects participated in joint position error tests and isokinetic concentric strength assessment in shoulder rotation, before and after rotator muscle fatigue.

Interventions:

Local muscle fatigue was induced using isokinetic concentric contractions of the shoulder rotator muscles.

Main Outcome Measurements:

Shoulder rotator strength and JPS error signals were measured before fatigue, immediately after fatigue, and every ten minutes thereafter for one hour.

Results:

Before shoulder rotation muscle fatigue, the accuracy of shoulder JPS was 2.79 ± 1.67 degrees. After muscle fatigue, the accuracy decreased to 6.39 ± 2.90 degrees. Shoulder JPS was influenced up to 40 minutes after muscle fatigue, but shoulder strength was only affected for 10 minutes after muscle fatigue.

Conclusions:

Proprioceptive recovery was slower than strength following fatigue of the shoulder rotators.

Influence of sympathetic nervous system on sensorimotor function: whiplash associated disorders (WAD) as a model

There is increasing interest about the possible involvement of the sympathetic nervous system (SNS) in initiation and maintenance of chronic muscle pain syndromes of different aetiology. Epidemiological data show that stresses of different nature, e.g. work-related, psychosocial, etc., typically characterised by SNS activation, may be a co-factor in the development of the pain syndrome and/or negatively affect its time course. In spite of their clear traumatic origin, whiplash associated disorders (WAD) appear to share many common features with other chronic pain syndromes affecting the musculo-skeletal system. These features do not only include symptoms, like type of pain or sensory and motor dysfunctions, but possibly also some of the pathophysiological mechanisms that may concur to establish the chronic pain syndrome. This review focuses on WAD, particular emphasis being devoted to sensorimotor symptoms, and on the actions exerted by the sympathetic system at muscle level. Besides its well-known action on muscle blood flow, the SNS is able to affect the contractility of muscle fibres, to modulate the proprioceptive information arising from the muscle spindle receptors and, under certain conditions, to modulate nociceptive information. Furthermore, the activity of the SNS itself is in turn affected by muscle conditions, such as its current state of activity, fatigue and pain signals originating in the muscle. The possible involvement of the SNS in the development of WAD is discussed in light of the several positive feedback loops in which it is implicated.

The effect of experimental muscle pain on the amplitude and velocity sensitivity of jaw closing muscle spindle afferents

The effect of experimental muscle pain on the amplitude and velocity sensitivity of muscle spindle primary afferent neurons in the trigeminal mesencephalic nucleus (Vmes) was examined. Extracellular recordings were made from 45 neurons designated as spindle primary- or secondary-like on the basis of their response to ramp-and-hold jaw movements. Velocity sensitivity was assessed in spindle primary-like afferents by calculating the mean dynamic index of each unit in response to three different velocities of jaw opening before and after intramuscular injection with hypertonic saline (HS, 5%, 100 microl). The amplitude sensitivity of all jaw muscle spindle afferents was assessed by calculating the mean firing rate of each unit in response to three different amplitudes of jaw openings during both the open and hold phases of the movement and with best-fit lines obtained, using linear regression analysis, before and after HS injection. The variance of the two regression lines obtained for each unit before and after the injection was compared using the coincidence test, and changes in intercept and slope were determined. Seventy-five percent of the primary-like units and 80% of the secondary-like units presented with changes in static behavior after HS injection. Thirty-six percent of the primary-like units showed changes in dynamic behavior. Injection of isotonic saline (control) did not alter the responses of the spindle afferent to jaw opening. Thus, our results demonstrate that the predominant effect of noxious stimulation was a shift in the amplitude sensitivity of both spindle primary-like and secondary-like afferents and, to a lesser extent, the velocity sensitivity of the spindle primary-like unit. In accordance with earlier studies in the cat hindlimb and neck muscles, these results suggest that the activation of masseter muscle nociceptor alters spindle afferent responses to stretch acting primarily through static gamma motor neurons.

Evaluation of cervical posture of children in skeletal class I, II, and III

Previous studies on the relationship between morphological structure of the face and cervical posture have predominantly focused on vertical dimensions of the face. The aim of this study was to investigate whether there are significant differences in cervical posture in subjects with a different sagittal morphology of the face, i.e., a different skeletal class. One hundred twenty (120) children (60 males and 60 females, average age 9.5 yrs., SD+/-0.5) were admitted for orthodontic treatment. Selection criteria was: European ethnic origin, date of birth, considerable skeletal growth potential remaining and an absence of temporomandibular joint dysfunction (TMD). Lateral skull radiographs were taken in mirror position. Subjects were divided into three groups based on their skeletal class. The cephalometric tracings included postural variables. The most interesting findings were: 1. children in skeletal class III showed a significantly lower cervical lordosis angle (p<0.001) than the children in skeletal class I and skeletal class II; 2. children in skeletal class II showed a significantly higher extension of the head upon the spinal column compared to children in skeletal class I and skeletal class III (p<0.001 and p<0.01, respectively). This is probably because the lower part of their spinal column was straighter than those of subjects in skeletal class I and II (p<0.01 and p<0.001, respectively). Significant differences among the three groups were also observed in the inclination of maxillary and mandibular bases to the spinal column. The posture of the neck seems to be strongly associated with the sagittal as well as the vertical structure of the face.

Molecular correlates of temporomandibular joint disease

OBJECTIVE

The relation between disease severity and the known mediators of pain, inflammation, and tissue damage-prostaglandin E 2 (PGE 2 ), leukotriene B 4 (LTB 4 ), malondialdehyde (MDA), nitric oxide (NO), and myeloperoxidase (MPO)-was examined in the synovial fluid of patients with internal derangement (ID) of the temporomandibular joint (TMJ).

STUDY DESIGN

Thirty-two patients with ID were classified according to Wilkes by clinical and radiological examinations, and TMJ synovial fluid samples were obtained by arthrocentesis. PGE 2 and LTB 4 levels were measured by ELISA kits, MDA levels were determined by a fluorometric method, myeloperoxidase activity was determined by an end-point method, and NO levels were measured by Griess reaction.

RESULTS

The earliest significant increase was observed in NO levels (stage II) and this elevation persisted in the subsequent stages. The first significant elevation in PGE 2 and LTB 4 levels and MPO activity were observed in stage III. Both PGE 2 and LTB 4 levels were increased in stage III and were correlated with each at this stage and in the subsequent stage. Significant increases in MDA levels were observed only in stage IV. At stage IV there was correlation between MDA and PGE 2 , MDA and LTB 4 , and MDA and MPO. The relation between PGE 2 and MDA was the most powerful one.

CONCLUSION

Results of this cross-sectional study point out the relation between disease severity and levels of some molecular mediators in synovial fluid of TMJ. Longitudinal studies are needed to explore the role of these molecular mediators in the progression of ID.