Journal of Oral & Facial Pain and Headache, 04/2007

Two major theories proposed to explain the effect of pain on muscle activity are the Vicious Cycle Theory and the Pain Adaptation Model. Comprehensive reviews demonstrate conflicting or limited evidence in support of a critical aspect of the Vicious Cycle Theory, namely that pain leads to increased muscle activity. The Pain Adaptation Model proposes that changes in muscle activity limit movement and thereby protect the sensorimotor system from further injury. This model is generally considered the most appropriate explanation of the effect of pain on muscle function. Although there is much literature consistent with the model, there are a number of lines of evidence that appear inconsistent with it. Possible reasons for the lack of consistency between studies include the functional complexity of the sensorimotor system (eg, the possibility of different pain effects at different sites within functionally heterogeneous muscles), and the multidimensional nature of pain. The latter consists of sensory-discriminative, cognitive-evaluative, and motivational-affective components, where factors such as pain location, intensity, and characteristics and other supraspinal/suprabulbar influences may modify the effects of pain on motor activity. The variety of changes in electromyographic (EMG) activity features during pain suggests that pain and motor function are not hardwired. The authors propose that the existing Pain Adaptation Model is a subset of a broader model that could be called the Integrated Pain Adaptation Model. Given the recent view of pain as a homeostatic emotion requiring a behavioral response, this new model states that pain results in a new, optimized recruitment strategy of motor units that represents the individual's integrated motor response to the sensory-discriminative, motivational-affective, and cognitive-evaluative components of pain. This recruitment strategy aims to minimize pain and maintain homeostasis. Keywords: experimental pain, jaw muscle activity, muscle movement, Vicious Cycle Theory, Pain Adaptation Model

Aims: To investigate whether trigeminal manifestations of pain, sensitization, and vasomotor responses following the intradermal injection of capsaicin to the foreheads differ from manifestations following injection of capsaicin in the forearms of healthy humans. Dose dependency and sex-related differences of the evoked responses were also studied. Methods: Twenty-eight healthy volunteers (14 women, 14 men) participated in 2 separate experiments: (1) Features of pain and vasomotor responses following intradermal injection of capsaicin (100 µg/100 µL) to the forehead and forearm were compared. (2) The features after intradermal injection of 2 different doses of capsaicin (50, 100 µg/100 µL) to the forehead were also studied. In both experiments the effect of sex was also investigated. Results: Experiment 1 showed that peak pain intensity (F [1,104] = 24.4, P .001) and duration (F [1,104] = 13.3, P .001) were greater in the forehead. However, the areas of visible flare (F [1,104] = 5.7, P .05) and secondary pinprick hyperalgesia (F [1,104] = 155.1, P .001) were significantly larger in the forearm. Experiment 2 indicated that peak pain intensity in the forehead was not affected by the capsaicin dose (F [1,52] = 1.6, P = .214), but duration of pain (F [1,52] = 6.0, P .05) and perceived pain area (F [1,52] = 13.5, P .001) were greater for the higher dose. The areas of visible flare (F [1,52] = 27.5, P .001) and secondary pinprick hyperalgesia (F [1,52] = 65.6, P .001) were also larger for the higher dose. In both experiments, women showed greater manifestations in several responses. Conclusion: Capsaicin-evoked sensory and vasomotor manifestations were different in the forehead and forearm. The differences are most likely due to the differences in innervation density and neurovascular activity. The capsaicin-induced effects were demonstrated to be dose-dependent and sex-related phenomena. Keywords: capsaicin, forearm, forehead, sex, trigeminal

Aims: To determine the pain characteristics of and medications used for patients seeking emergency care for irreversible acute pulpitis (IAP) or acute apical periodontitis (AAP). Methods: General (age, sex, weight, general health) and specific (pain intensity, localization, tooth mobility, lymphadenopathy, use of medications) information was noted in 209 patients who appeared for emergency care in 2 dental centers of Dakar with either IAP or AAP. Statistical analysis was performed with the Mann-Whitney and chi-square tests. Results: The sample comprised 97 IAP patients (46.4%) and 112 AAP patients (53.6%); there were no significant differences between the 2 groups with respect to age, sex, or weight. Of the involved teeth, 62% were mandibular and 38% were maxillary. IAP patients waited 6.6 ± 5.3 days before seeking an emergency consultation versus 5.0 ± 3.8 days for AAP patients (P .05). Severe pain was reported in 75% of the IAP and 76% of AAP patients (not significant). Percussion and apical palpation were painful only in AAP, in 98% and 40% of patients, respectively. Mobility and adenopathies were noted only in AAP, in 87% and 46% of patients, respectively (P .001). Seventy-five percent of IAP patients and 80% of AAP patients used medications, mainly non-narcotic analgesics, which offered relief in 62% of IAP patients and 46% of AAP patients. Conclusions: Patients with IAP waited longer than those with AAP before seeking treatment. Self-medication offered better relief in cases of IAP than in cases of AAP. Pain to percussion and palpation, lymphadenopathies, and dental mobility were strong indicators for AAP. Keywords: apical periodontitis, emergencies, medication, pain, pulpitis

Aims: To examine differences in temporal summation of mechanically evoked pain between women and men suffering from chronic pain associated with temporomandibular disorders (TMD), as well as between male TMD patients and healthy controls. Methods: Series of 10 repetitive, mildly noxious mechanical stimuli were applied to the fingers of 27 female TMD patients, 16 male TMD patients, and 20 healthy men. The subjects rated the pain intensity caused by the 1st, 5th, and 10th stimulus in the series. Pain ratings were analyzed by 3-way repeated-measures analysis of variance. Results: Pain ratings increased significantly with stimulus repetition for the female TMD patients (P .001). Women with TMD exhibited significantly greater temporal summation of pain than TMD men (P .001). Neither the healthy men nor the male TMD patients exhibited significant increases in pain perception with repetitive stimulation. In the female TMD patient group, perceptual pain magnitudes were higher with an interstimulus interval of 2 seconds rather than 10 seconds (P .005). Conclusion: These findings suggest that central nociceptive processing upregulation is likely to contribute to TMD pain for women but is not a factor for men with TMD. Keywords: chronic pain, gender differences, temporal summation, temporomandibular disorders

Aims: To determine whether Rocabado's 6 x 6 exercise program has an added benefit to self-care alone in reducing myofascial jaw pain and improving forward head posture (FHP) in subjects with myofascial pain and FHP at the end of 4 weeks. Methods: In this double-blinded trial, 45 subjects (43 female and 2 male, mean age 24 years) were randomly assigned to self-care or self-care + 6 x 6 exercises. The primary outcome measure was intensity of jaw pain on a numerical graphic rating scale (NGRS). Secondary outcome measures were jaw pain on a verbal rating scale (VRS), neck pain (NGRS and VRS), and change in head posture. Twenty-one subjects per group resulted in 80% power to detect a difference of 2 in the NGRS for intensity of jaw pain. Alpha was set at .05 for statistical significance. Results: Both groups showed significant statistical (P = .001) and clinical (> 2 on NGRS) improvement in jaw pain intensity. Jaw pain and neck pain improved significantly (P .01) in both groups. There were no differences between groups for any of the measures. A significant change in head posture was not detected in either group. Conclusion: The 6 x 6 exercises were not significantly more beneficial in reducing the intensity of jaw and neck pain than self-care alone. Furthermore, they were not beneficial in improving head posture within the 4-week duration of this study. Keywords: exercises, myofascial pain, posture, randomized clinical trial, self-care, temporomandibular disorders