Journal of Oral & Facial Pain and Headache, 04/2008

This tribute article to Professor Barry J. Sessle summarizes the 6 presentations delivered at the July 1, 2008 symposium at the University of Toronto. The symposium honored 3 "giants" in orofacial neuroscience, Professors B.J. Sessle, J.P. Lund, and A.G. Hannam. The 6 presentations paying tribute to Sessle spanned the period from the early phase of his career up to some of his most recent studies with colleagues in Asia, Europe, and Australia as well as Canada. The studies have included those providing an improved understanding of the cortical control of sensory inputs in pain perception (presented by R. Dubner) and in the control of mastication and swallowing, as well as brainstem mechanisms of orofacial pain (K. Iwata, G. Murray). His current activities in his laboratory and in Denmark are also highlighted (L. Avivi-Arber, P. Svensson). The potential transfer of basic research discoveries toward drug development in pain control that stem from some of his research is also described (B. Cairns). The final section of the paper includes a commentary from Professor Sessle. Keywords: experimental pain, hypertonic saline, jaw muscles, jaw movement, motor cortex, sensorimotor

This tribute article to Professor James P. Lund stems from 6 of the presentations delivered at the July 1, 2008, symposium that honored 3 "giants" in orofacial neuroscience: B.J. Sessle, A.G. Hannam, and J.P. Lund. It was noted that soon after his training as a dentist in Australia, Jim Lund became interested in research. At the time he decided to do a PhD, there was a lot of discussion about how rhythmic movements were programmed. The early belief, based on Sherrington's studies of motor systems, was that these movements were simply an alternating series of reflexes. In the late 1960s and early 1970s, some still shared this belief, whereas others favored Graham Brown's hypothesis that repetitive movements were centrally programmed and did not depend on reflexes triggered by sensory inputs. There was no strong evidence then for either scenario except for the rhythmic movements of respiration. Lund's pioneering work during his PhD proved the existence of a central pattern generator (CPG) for mastication in the brainstem. Since then he has been interested in understanding how CPGs function and how sensory feedback works to adjust the motor patterns that they produce. Sections in this tribute article to Lund are written by some of his close collaborators and reflect the evolution of his work throughout the years. The first 4 presentations in this article (by K.-G. Westberg, D. McFarland, A. Kolta, and C. Stohler) highlight various aspects of these interests, and the final 2 presentations (by J. Feine and A. Woda) focus especially on clinical aspects of Lund's interests. The last section of this article is a final commentary from Professor Lund. Keywords: mastication, orofacial movements, pain, trigeminal system

This tribute article to Professor Alan G. Hannam is based on 7 presentations for him at the July 1, 2008 symposium honoring 3 "giants" in orofacial neuroscience: Professors B.J. Sessle, J.P. Lund, and A.G. Hannam. This tribute to Hannam's outstanding career draws examples from his 40-year academic career and spans topics from human evolution to complex modeling of the craniomandibular system. The first presentation by W. Hylander provides a plausible answer to the functional and evolutionary significance of canine reduction in hominins. The second presentation, by A. McMillan, describes research activities in the field of healthy aging, including findings that intensity-modulated radiotherapy improves the health condition and quality of life of people with nasopharyngeal carcinoma in comparison to conventional radiotherapy. The developments in dental imaging are summarized in the third paper by E. Lam, and an overview of the bite force magnitude and direction while clenching is described in the fourth paper by M. Watanabe. The last 3 contributions by G. Langenbach, I. Staveness, and C. Peck deal with the topic of bone remodeling as well as masticatory system modeling, which was Hannam's main research interest in recent years. These contributions show the considerable advancements that have been made in the last decade under Hannam's drive, in particular the development of an interactive model comprising, in addition to the masticatory system, also the upper airways. The final section of the article includes a final commentary from Professor Hannam. Keywords: anthropology, biomechanics imaging, bite force, evolution, modeling, occlusal forces

Aims: To compare prevalences of self-reported temporomandibular joint and muscle disorders (TMJMD)-type pain in the 2002 US National Health Interview Survey (NHIS) by age and gender for non-Hispanic whites (Caucasians) and non-Hispanic blacks (African Americans). Methods: Data from the 2002 NHIS included information on gender, age, race, ethnicity, education, and TMJMD-type pain. Rao-Scott survey chi-square and survey logistic regression analyses using sampling weights and accounting for the complex design were used to analyze variables relating to prevalences. Results: A total of 30,978 people, 17,498 females and 13,480 males, 20,389 non-Hispanic whites and 4,179 non-Hispanic blacks, were included. The overall prevalence of TMJMD-type pain was 4.6%, with 6.3% for women and 2.8% for men. However, based on age, a significant but modest racial/ethnic difference emerged after adjusting for socioeconomic status. For non-Hispanic white women up to age 50, the prevalence was ~7% to 8%, but it decreased after age 55. Non-Hispanic black women had much lower prevalence at younger ages (~4% at 25 to 34 years), which increased thereafter up to 55 to 64 years of age. A similar racial pattern seemed to emerge for non-Hispanic black men, with the lowest prevalence at ages 25 to 34 years, while non-Hispanic white men had higher prevalences. Overall, however, age seemed to play more of a role in women than men. Conclusion: This is the first report of findings from a nationally representative US sample for TMJMD-type pain by age and race/ethnicity. TMJMD-type pain differed significantly by race, age, and gender after adjusting for socioeconomic status. Keywords: age, gender, health disparity, prevalence, race/ethnicity, self-report, temporomandibular joint disorders

Aims: To investigate chronic orofacial pain experience, psychosocial impact, and help-seeking response in adult Chinese people in Hong Kong. Methods: A cross-sectional population-based telephone interview survey identified 1,352 randomly selected people aged >= 18 years. Standard questions were asked about current or episodic and prior (>= 6 months) experience of 7 orofacial pain symptoms. Pain intensity and psychosocial impact were assessed through the Graded Chronic Pain Scale, and the help-seeking response was assessed using the 4-item Level of Expressed Need (LEN) measure. Results: Current or episodic symptoms of orofacial pain were reported by 57.0% of respondents, and 13.2% of this group reported symptoms that had lasted for >= 6 months (chronic subgroup). In the chronic subgroup, toothache was the most common symptom (42.2%) and oral sores the least common (7.8%). The mean pain intensity in the chronic pain subgroup was 46.6 (SD 21.7) with no age or gender differences (P > .05); 88.2% had low disability levels and 11.8% had high levels. 81.4% had low LEN scores and 18.6% had high scores, with no age/gender differences (P > .05). Conclusion: The prevalence of current/ episodic orofacial pain was relatively high, whereas chronic orofacial pain was much less common. Although the intensity of chronic orofacial pain was significant, associated psychosocial disability was low, as was the level of perceived need for treatment. These findings may be related to more effective pain-coping strategies and greater acceptance of pain in this ethnic group compared to other ethnic groups. Keywords: Chinese, chronic pain, orofacial, prevalence, psychosocial, treatment-seeking

Aims: To test whether extraction of the 2 subscales in the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) affected the subscale score reliability and whether scores from the RDC/TMD subscales are comparable to the same scales when the whole Symptom Check List-90 (SCL-90R) is administered. Methods: The full SCL90-R and a modified version containing only the depression and somatization scales were administered in counterbalanced order to 103 subjects. As another test of context, a subset of participants completed the modified and full versions as part of a larger battery of instruments relevant to facial pain. Statistical analyses included internal reliability for item analysis and intraclass correlation (ICC) and Lin's concordance correlation coefficient (CCC) for total scale score reliability. Results: Internal reliability was approximately 0.95 for depression and 0.87 for somatization, independent of test form. Total scale scores were reliable across test versions, with both ICC and CCC approximately 0.95 for depression and 0.91 for somatization. Permutation tests using the CCC indicated a mild influence on the somatization score but not the depression score due to order effects, but these effects were not significant when considering the 95% CIs based on resampling methods. Conclusion: Whether items from other subscales are present or not does not affect the internal reliability or parallel forms reliability of the total scores from either depression or somatization. Context of administration, via order of forms completion, does not alter total score or reliability of depressive items but may alter total scores for somatization. Keywords: psychometrics, RDC/TMD, reliability, validity

Aim: To replicate and extend previous findings of nerve growth factor (NGF)-induced mechanical sensitization in healthy young men to women and test for associations between mechanical sensitization and oral motor function. Combined these data would indicate if injection of NGF into the masseter muscle is a valid model of muscle pain related to temporomandibular disorders (TMD). Methods: A double-blind, placebo-controlled study was conducted on 14 healthy women. Each subject received an injection of NGF (5 µg in 0.2 mL) into 1 masseter muscle and buffered isotonic saline (control, 0.2 mL) into the other. Pressure pain thresholds (PPT) and pressure pain tolerance (PPTOL) as well as self-assessed pain intensity (numeric rating scale of 1 to 10) with the jaw at rest and in relation to various motor activities (chewing, yawning, talking, swallowing, drinking, and smiling) were recorded prior to and 3 hours, 1 day, 7 days, 14 days, and 21 days postinjection. ANOVAs were used to test data. Results: It was found that NGF significantly reduced PPT and PPTOL 3 hours, 1 and 7 days postinjection (P .001). Numerical rating scale (NRS) scores during chewing and yawning were significantly increased 3 hours and 1 day following NGF injection (P .001). After 3 hours, there were significant correlations between relative changes in PPTs and NRS scores during chewing (r = -0.556; P = .037), between relative changes in PPTOL and NRS scores during yawning (r = -0.607; P = .020), and between relative changes in PPTOL and maximum unassisted jaw-opening capacity (r = 0.868; P .001). Conclusion: This study shows that injection of NGF into the masseter muscle of women causes local signs of mechanical allodynia and hyperalgesia that persist for at least 7 days as well as pain during strenuous jaw movement. Taking the authors' previous results on NGF effects in men into consideration, these findings lend additional support to the suggestion that this model may serve as a proxy of some of the clinical features of TMD-related muscle pain. Keywords: allodynia, jaw motor function, nerve growth factor, pain measurement, TMD pain

Aims: To analyze the nonspecific chronic orofacial pain patient's experience of the pain condition and to gain knowledge on the complexity of the problem. Methods: Fourteen patients (11 female, 3 male) aged 21 to 77 years were selected among those referred to a specialist clinic. All selected patients agreed to participate. Data were obtained through thematic in-depth interviews that exposed the context of the orofacial pain condition. The 2 interviews with each patient were audiotaped and transcribed verbatim. The text material was analyzed using a qualitative research strategy based on phenomenology. Results: The essence of the chronic orofacial pain was expressed by the patients as something that eludes perception and comprehension. The pain was difficult to grasp and to communicate. The consequence of the pain was experienced by the patients as to be stricken by the pain and was expressed as living a life permeated by hopelessness, resignation, and a lack of faith. Conclusion: The patients in this study experienced their chronic orofacial pain to have no limits and to repressively permeate all aspects of their existence: social, practical, and emotional. Keywords: chronic pain, facial pain, pain consequence, patient perspective, qualitative research