James P. Lund

An assessment of the efficacy of physical therapy and physical modalities for the control of chronic musculoskeletal pain

Abstract An analysis of review articles and controlled clinical trials for temporomandibular disorders and similar chronic musculoskeletal pain disorders was carried out. Although little evidence was found that any specific therapy had long‐term efficacy greater than placebo, we did find strong evidence that symptoms improve during treatment with ost forms of physical therapy, including placebo. When the frequency of significant between‐group differences in trials that used placebo and waiting list control (i.e., no treatment) groups were compared, it was found that treatment was better than placebo in only 7/22 trials, whereas treatment was almost always better than no treatment (15/16). This difference was highly significant (P=0.001). A similar analysis of trials that included more than one treatment group showed that while equal amounts of treatment were usually associated with equal outcome (9/10), unequal treatment regimes led to unequal outcome (10/15; P=0.012). The group that received the most therapy appeared to do best. In conclusion, it seems that patients are helped during the period that they are being treated with most forms of physical therapy. However, most of these therapies have not been shown to be more efficacious than placebo.

Generation of the Central Masticatory Pattern and Its Modification by Sensory Feedback

Mammalian mastication results from the interaction of an intrinsic rhythmical neural pattern and sensory feedback generated by the interaction of the effecter system (muscles, bones, joints, teeth, soft tissues) with food. The main variables that explain variation in the pattern of human mastication are the subjects themselves, their age, the type of food being eaten, and time during a sequence of movements. The intrinsic pattern of mastication is generated by a central pattern generator (CPG) located in the pons and medulla. The output of the CPG is modified by inputs that descend from higher centers of the brain and by feedback from sensory receptors. Intraoral touch receptors, muscle spindles in the jaw-closing muscles, and specialized mechanoreceptors in the periodontal ligament have especially powerful effects on movement parameters.

Brainstem mechanisms underlying feeding behaviors

The essential elements controlling trigeminal motoneurons during feeding lie between the trigeminal and facial motor nuclei. These include populations of neurons in the medial reticular formation and pre-motoneurons in the lateral brainstem that reorganize to generate various patterns. Orofacial sensory feedback, antidromic firing in spindle afferents and intrinsic properties of motoneurons also contribute to the final masticatory motor output.

Identification of brainstem interneurons projecting to the trigeminal motor nucleus and adjacent structures in the rabbit.

Neurons of several nuclei within the medial pontomedullar reticular formation are active during mastication, but their relationship with other elements of the pattern generating circuits have never been clearly defined. In this paper, we have studied the connection of this area with the trigeminal motor nucleus and with pools of last-order interneurons of the lateral brainstem. Retrograde tracing techniques were used in combination with immunohistochemistry to define populations of glutamatergic and GABAergic neurons. Injections of tracer into the Vth motor nucleus marked neurons in several trigeminal nuclei including the ipsilateral mesencephalic nucleus, the contralateral Vth motor nucleus, the dorsal cap of the main sensory nucleus and the rostral divisions of the spinal nucleus bilaterally. Many last-order interneurons formed a bilateral lateral band running caudally from Regio h (the zone surrounding the Vth motor nucleus), through the parvocellular reticular formation and Vth spinal caudal nucleus. Injections of tracer into Regio h, an area rich in last-order interneurons, marked, in addition to the areas listed above, a large number of neurons in the medial reticular formation bilaterally. The major difference between injection sites was that most neurons projecting to the Vth motor nucleus were located laterally, whereas most of those projecting to Regio h were found medially. Both populations contained glutamatergic and GABAergic neurons intermingled. Our results indicate that neurons of the medial reticular formation that are active during mastication influence Vth motoneurons output via relays in Regio h and other adjacent nuclei.

Idiopathic myoclonus in the oromandibular region during sleep: a possible source of confusion in sleep bruxism diagnosis.

As part of a larger study, polysomnographic and audiovisual data were recorded over 2 nights in 41 subjects with a clinical diagnosis of sleep bruxism (SB). Electromyographic (EMG) events related to SB were scored according to standard criteria (Lavigne et al. J Dent Res 1996;75:546–552). Post hoc analysis revealed that rapid shock‐like contractions with the characteristics of myoclonus in the jaw muscles were observed in four subjects. EMG bursts characterized as myoclonus were significantly shorter in duration than bursts classified as SB. None of the subjects had any history of myoclonus while awake. Myoclonic episodes were more frequent in sleep stages 1 and 2 than in REM. Half of the episodes contained one or two contractions whereas the other half had three or more repetitive contractions. SB and myoclonus coexisted in one subject. To rule out sleep epilepsy, full electroencephalogram montage was done in three subjects and no epileptic spikes were noted. Our results suggest that approximately 10% of subjects clinically diagnosed as SB could present oromandibular myoclonus during sleep.

Differences between the sexes in post-surgical pain.

Abstract It has been shown that women have a lower pain threshold and lower tolerance to some forms of experimental pain then men. However, the evidence that clinical pain is perceived differently by the two sexes is not yet as strong. The placement of intraoral implants is a highly controlled surgical procedure that we have used to investigate this possibility. Forty‐eight edentulous (without teeth) subjects (27 females), aged from 35 to 63 years, received two titanium implants in the anterior mandible under local anesthesia. After the surgery, subjects completed a pain diary three times each day, rating pain intensity and unpleasantness on 100 mm visual analog scales (VAS). Once a day, they chose verbal descriptors from the McGill Pain Questionnaire (MPQ). Age of subjects, duration of surgery, the amount of local anesthetic used and the amount of pain medication taken were not statistically different for the two groups (P≥0.32). Results showed that the senior surgeon produced significantly less pain than a 4th year resident (P=0.04). Although there were no significant differences between sexes for mean daily ratings of intensity or unpleasantness over time (P≥0.10), most women experienced the highest intensity of pain during the day, while most men had higher pain in the evening (P=0.025). Also, the relative unpleasantness (unpleasantness/intensity ratio) increased significantly with time for males, but not for females (P=0.016). Males and females did not differ in the total number of words chosen from the MPQ (P=0.61), or in the averaged Pain Rating Index (PRI) (P=0.53). However, women used significantly more evaluative words than men (P=0.04), suggesting that woman found the overall intensity greater. These results indicate that women find post‐surgical pain more intense than males, but that men are more disturbed than women by low levels of pain that last several days.

Neurons of the trigeminal main sensory nucleus participate in the generation of rhythmic motor patterns

The trigeminal principal sensory nucleus (NVsnpr) contains both trigemino‐thalamic neurons and interneurons projecting to the reticular formation and brainstem motor nuclei. Here we describe the inputs and patterns of firing of NVsnpr neurons during fictive mastication in anaesthetized and paralysed rabbits to determine the role that NVsnpr may play in patterning mastication. Of the 272 neurons recorded in NVsnpr, 107 changed their firing patterns during repetitive stimulation of the left or right sensorimotor cortex to induce fictive mastication. Thirty increased their firing tonically. Seventy‐seven became rhythmically active, but only 31 fired in phase with mastication. The others discharged in bursts at more than twice the frequency of trigeminal motoneurons. Most rhythmic masticatory neurons were concentrated in the dorsal part, and those which fired during the jaw closing phase of the cycle were confined to the anterior pole of the nucleus. Most of these cells had inputs from muscle spindle afferents, whereas most of those firing during jaw opening had inputs from periodontal receptors. Non‐masticatory rhythmical neurons had receptive fields on the lips and face. The majority of rhythmical masticatory units were modulated during fictive mastication evoked by both the left and right cortices and only four changed their phase of firing when switching from one cortex to the other. When coupled with the finding that NVsnpr neurons exhibit spontaneous bursting in vitro[Sandler et al. (1998) Neuroscience, 83, 891], the results described here suggest that neurons of dorsal NVsnpr may form the core of the central pattern generator for mastication.

Effects of chemical stimulation of masseter muscle nociceptors on trigeminal motoneuron and interneuron activities during fictive mastication in the rabbit

&NA; An electrophysiological study was carried out in sixteen decerebrate and paralyzed New Zealand rabbits to determine how a bolus injection of a nociceptor stimulant (hypertonic saline, 5%) into the masseter muscle influences the activity of the trigeminal motor circuitry during fictive jaw movements. Hypodermic needles connected to a syringe held in a computer‐ controlled infusion pump were inserted into the anterior deep layer of either the right or the left masseter. Twenty‐three infusions of 50, 70 or 80 &mgr;l saline were made in fourteen animals at constant rates over 1 min. Eight control infusions of normal saline (0.9%) were made in a subpopulation of five animals in an identical manner. Fictive jaw movements were evoked before and after the infusions by repetitive electrical stimulation of the cortico‐bulbar tract. Effects were assessed by extracellular microelectrode recordings made from the digastric motoneuron pool and from putative last‐order interneurons in the oral subnucleus of the spinal trigeminal tract and adjacent structures. In comparison with pre‐infusion control cycles, nociceptor stimulation caused significant slowing of the rhythm and a reduction of the area of the digastric motoneuron bursts in the majority of the animals (12/14). The decrease in cycle frequency was due almost entirely to a lengthening of the time between the digastric bursts. Changes usually began 1–2 min after the infusion and returned to pre‐infusion values within 10–15 min. No significant effects were seen when isotonic saline was applied. Recordings were obtained from nine interneurons, eight of which had low threshold mechanosensitive receptive fields. One neuron was, in addition, excited by pinch. Eight were not active in the absence of motor activity and this did not change when hypertonic saline was applied. However, once fictive movements began, all started to fire rhythmic bursts of spikes. In five cases, there was a significant post‐infusion increase in spike frequency, and three showed decreases. Seven showed significant post‐infusion changes in mean phase and/or concentration of their firing within the movement cycle. Changes in the preferred phase of interneuronal firing were significantly correlated to changes in the phase of offset of the digastric burst. The present results provide evidence that the stimulation of nociceptors in a muscle slows the frequency of rhythmical movements in the absence of sensory feedback. They confirm that infusions into one muscle affect the output of its antagonist. The results also suggest that neurons in the oral subnucleus of the spinal trigeminal tract and adjacent reticular formation appear to participate in programming these changes in motor output.

Physical therapy: A critique

Some forms of physical therapy are used relatively frequently in the treatment of chronic musculoskeletal pain conditions, including the temporomandibular disorders. We found evidence that cold seems to be a useful treatment for postsurgical pain and swelling and that most patients being treated for most chronic musculoskeletal pain seem to do better with most forms of therapy. However, we agree with the authors of previous reviews that there is little evidence that these methods of management cause long-lasting reductions in signs and symptoms. Findings of recent clinical trials tend to support this conclusion, although evidence is beginning to accumulate that exercise programs designed to improve physical fitness have beneficial effects on chronic pain and disability of the musculoskeletal system.

Researching the impact of oral health on diet and nutritional status: Methodological issues

OBJECTIVES Assessment of the impact of dental function on diet and nutritional status requires robust methodologies and a standardised approach to increase accuracy of results and to facilitate cross study comparisons. The objectives of this paper are: to report the outcomes of a consensus workshop that critically reviewed publications reporting on dietary methodologies in relation to the impact of oral health on nutrition; to highlight future directions for research and; to make recommendations for appropriate use of methodologies for future research. DATA Data relevant to nutrition and dental status published from 1980 to 2005 in English were presented at the consensus workshop for discussion and appraisal. SOURCES Relevant papers were retrieved through PubMed. Relevant texts were obtained from the library at Newcastle University, UK. STUDY SELECTION A purposive sample of original articles that illustrated the application of a range of nutritional methodologies to the study of oral health impacts was identified. Original flagship texts on nutritional methodologies were reviewed. CONCLUSIONS Numerous studies have shown an association between loss of teeth and inferior diet. Further research is required to elucidate the impact of novel approaches to prosthetic rehabilitation and the impact of contemporaneous dietary and dental intervention on diet, nutritional status, disease progression and quality of life. The recommendation of the consensus workshop was that future studies should adopt a comprehensive approach to the assessment of nutrition that encompasses measurement of diet, body composition, biochemical indices of intake and levels of nutrients, and functional biomarkers of disease.