Journal of Oral & Facial Pain and Headache, 04/2000

Aims: An animal study of functional biomechanics was undertaken to understand normal loading of the temporomandibular joint (TMJ) and to provide insight into the pathogenesis of TMJ disorders. Methods: Bone strain and ligamentous deformation were measured during mastication in 26 10-month-old minipigs. Half the subjects had undergone a surgical disruption of the left lateral capsular and disc attachments to the condyle 5 to 6 weeks previously. Rosette strain gauges were bonded to the left lateral surfaces of the squamosal bone near the TMJ, the condylar neck, and the mandibular corpus below the molar region. Differential variable reluctance transducers (DVRTs) were placed bilaterally in the lateral capsular tissue of the joints. Bone strains, ligamentous deformations, and the electromyographic activities of the masseters and lateral pterygoids were recorded during natural mastication. Results: In all animals on both working and balancing sides, mastication caused bone strains that were dominated by tension in the squamosal bone site and by compression in the other sites. Measurements from the DVRT revealed elongation of the lateral capsular tissue in the last phase of the power stroke and shortening in the initial phase of opening, which was almost simultaneous with the development of bone strain. Strain in the capsule ranged from 3 to 25%, with the strain of the balancing side exceeding that of the working side. The surgical disruption did not alter chewing side preference or bone strain, but a tendency toward more extensive ligamentous deformation on the intact side was observed. Furthermore, the ratio of masseter to lateral pterygoid activity was smaller on the disrupted side and larger on the intact side, in comparison to control pigs. Conclusion: Both osseous and ligamentous components of the TMJ are strained during mastication, and the latter are more deformed on the balancing side. Disruption of the lateral attachment had little effect on strain in the osseous components but appeared to increase strain in the capsule and to modify the balance of masticatory muscle activity.

Aims: To investigate the effects of a natural emotional stressor on pressure-pain thresholds (PPTs) of the masticatory muscles of symptom-free subjects. Methods: Sixteen healthy dental students were selected before they undertook an academic examination. Sixteen gender-matched students who were not exposed to an examination served as controls. The 2 groups of students were monitored in parallel on 5 separate days over a 1-month period: 2 days before the examination (T1), on the day of the examination (T2), 2 days after (T3), 1 month after (T4), and again after another 2 days (T5). On the day of the examination (T2), the control students were only required to complete a brief, non-demanding questionnaire. On each day, the following parameters were assessed: PPTs of the masseter, the anterior temporalis, and the Achilles tendon; state anxiety; and present stress (measured on a visual analog scale [VAS]). Furthermore, in the students undergoing the examination, venous blood samples for assessment of ß-endorphin levels were obtained at T2 and T5. Results: In the stressed students, the PPTs of the masticatory muscles and the Achilles tendon were significantly lower (analysis of variance [ANOVA], P = 0.02) on the day of the examination (T2) and on the days nearest the exam (T1, T3), and state anxiety and present stress were significantly higher (ANOVA, P = 0.003). No significant change was found in b-endorphin plasma levels (P > 0.05). In the control group, PPTs, state anxiety, and present stress did not change significantly (ANOVA, P > 0.05). Conclusion: The results support a relationship between psychologic stress and pressure-pain sensitivity of the masticatory muscles.

Aims: To estimate the intra- and interrater reliability of current perception threshold (CPT) evaluation, especially within the infraorbital nerve territory (ION) and inferior alveolar nerve territory (IAN) of the orofacial region, and to characterize the CPTs of ION and IAN in the normal population. Methods: Electrical stimulation (at 2,000 Hz, 250 Hz, and 5 Hz) was applied to ION and IAN to allow for CPT evaluation in 200 subjects, all of whom were healthy, had no systemic diseases, and were free from symptoms and history of neuropathic conditions. Twenty-five of the subjects were evaluated 3 times by 2 examiners to test reliability, and the remaining subjects were evaluated once for normative data. Results: The intraclass correlation coefficient of CPTs within examiner and between examiners ranged from 0.46 to 0.95. There were no significant differences between right and left sides in CPT evaluation within the ION and IAN territory. Gender and age did not affect the CPT values for ION and IAN in the normal population. There were significant differences between each of the 3 frequency-dependent (2,000 Hz, 250 Hz, 5 Hz) measures within ION and IAN (P 0.001). Conclusion: Evaluation of CPTs within ION and IAN revealed good intra- and interrater reliability. The study also provided normative data of CPTs of ION, IAN, and the between-site and within-site ratios of CPTs of ION and IAN. This should prove useful in the diagnosis of orofacial neuropathy.

Aims: To investigate the stability of temporomandibular joint (TMJ) clicking over a 10-day period and the effect of different open/close velocities on sound amplitude and power spectra in a group of subjects with subjectively stable unilateral clicking during the 3 months preceding the recordings. Methods: Ten volunteers were recorded with a self-developed microcomputer-based system used in a previous study on asymptomatic subjects. The recordings were performed during 4 different sessions at 3 different open/close rates in each session. The subjective sound intensity was measured with a 100-mm visual analog scale (VAS). The VAS scores, the maximum amplitudes, and the power spectra of the signals were tested for statistical differences among the different open/close rates and over the sessions. The reliability of measurements was also calculated. Results: The maximum amplitude and the power spectra of the TMJ clicking varied between subjects in a broad range that differed from those reported for asymptomatic subjects. No statistically significant differences were found within subjects for the subjective VAS scores for the maximum signal amplitudes or for the power spectrum parameters among the open/close rates and over the 4 sessions. For all 3 open/close rates and for the 4 sessions, a good to excellent reliability of measurements was determined, the values of r being mostly over 0.75. Conclusion: Within the limits of the experiment, TMJ clicking was subjectively and objectively stable over a period of 10 days. Therefore, the constant subjective perception of sound intensity was supported by the objective measurements.

Aims: To determine potential differences in predictive models of acute temporomandibular disorder (TMD) patients divided into groups based on the physiologic characteristics of their TMD. Methods: One hundred seventy-seven acute TMD patients were evaluated with an extensive battery that included biologic and psychosocial measures. Subjects were separated into 3 groups based on a physical exam using the Research Diagnostic Criteria for TMD (RDC): those with a myofascial pain diagnosis, those with either a disc displacement or other joint condition, and those who reported pain but did not receive an RDC Axis I diagnosis. Six months later, it was determined whether patients had sought additional treatment for relief of their symptoms. Treatment-seeking and non-treatment-seeking groups were compared for significant differences, and predictive models were generated to determine the array of variables that best predicted treatment-seeking behavior among each of the 3 classifications of TMD patients used in this study. Results: Among patients with a diagnosis of myofascial pain, gender, Multidimensional Pain Inventory (MPI) interference score, and MPI affective distress score accurately predicted treatment-seeking behavior in 76.1% of the sample. For patients with a diagnosis of disc displacement, arthralgia, arthritis, or arthrosis, the following variables predicted treatment utilization behavior in 93.6% of the sample: race, RDC graded chronic pain, and the introversion scale of the Minnesota Multiphasic Personality Inventory-2. For patients with no RDC Axis I disorder, 80.5% of the sample was accurately classified with regard to treatment-seeking behavior through the use of only the characteristic pain intensity score (ie, mean of visual analog scale scores for pain right now, worst pain, and average pain). Conclusion: The factors that predict which acute TMD patients are most likely to seek additional treatment vary depending on the physiologic basis of their TMD. This suggests that acute TMD patients may benefit from different modalities of treatment, depending on the type of TMD with which they present.

Aim: To study the development over 20 years of signs and symptoms of temporomandibular disorders (TMD) in an epidemiologic sample and to analyze possible correlations between tbese signs and symptoms and some other variables. Methods: Tbe original group comprised 135 randomly selected 15-year-old subjects who were examined clinically and by means of a questionnaire for signs and symptoms of TMD. The examination was repeated after S, 10, and 20 years by the same metbods. After 20 years, when tbe original group bad reached tbe age of 35 years, 124 individuals (92%) could he traced, and they were sent a questionnaire and invited for a clinical examination. Tbe response rate was bigh: 114 subjects (92%) completed and returned the questionnaire, and 100 subjects (81%) attended the clinical examination. Results: There was a substantial fluctuation of both reported symptoms and clinically recorded signs over the 20-year period, but progression to severe pain and dysfunction of the masticatory system was rare. In botb the 15-year-old and 35-year-old subjects, 13% reported 1 or more frequent TMD symptoms. At age 35, only 3 subjects (3%) were classified as having severe or moderate clinical signs of dysfunction according to the Helkimo Index, fewer than in previous investigations. Women reported TMD symptoms and headacbe and had muscle tenderness and joint sounds more often than men. Correlations between tbe studied variables were mainly weak. Among the highest correlations found (r¡ = 0.4) were those between reported clenching and hruxing habits and TMJ sounds and jaw fatigue. Conclusion: In tbis epidemiologic sample followed from age 15 to 35 years, a substantial fluctuation of TMD signs and symptoms was found over time. Progression to severe pain and dysfunction was extremely rare. J OROFAC PAIN 2000;14;310-319 Keywords: bruxism, epidemiology, headache, orofacia! pain, temporomandibular joint