Abstract
This study evaluated differences in pain sensitivities and psychological profiles among different temporomandibular disorder (TMD) pain subtypes. Evaluation was done on 36 normal subjects and 39 TMD patients with high Graded Chronic Pain scale scores. TMD patients were placed in three pain subgroups (myogenous, arthrogenous, mixed) using the Research Diagnostic Criteria for TMD (RDC/TMD) axis I guidelines. RDC/TMD axis II profiles including depression and somatization were analysed. Cold pain threshold (CPT), heat pain threshold (HPT), and heat pain tolerance threshold (HPTT) were measured on three facial regions (anterior temporalis, masseter, TMJ) and a leg region (anterior tibialis). The arthrogenous pain subgroup showed significantly higher CPT and lower HPT and HPTT in the facial region, and lower HPTT in the anterior tibialis region compared with normal and myogenous pain subgroups. The myogenous pain subgroup had significantly higher somatization scores than normal and arthrogenous pain subgroups, and higher depression scores than normal subjects. The results suggest that peripheral and/or central sensitization are present in chronic arthrogenous pain more so than in myogenous pain, and this phenomenon appears to take place regardless of the patient’s psychological profiles. These results may explain the underlying mechanism that aggravates TMD pain.
Some patients with temporomandibular disorder (TMD) develop pain of a persistent and recurring nature in addition to their limitations or alterations of mandibular movement. The presence of chronic pain has the potential to induce long lasting neuroplastic changes of the peripheral and central nervous system. There have been many studies and reports of altered pain perception in patients suffering from generalized chronic pain. For example, patients with fibromyalgia demonstrate clinical evidence of a centrally mediated allodynia and general nociceptive facilitation, which yields higher visual analogue scale (VAS) scores to painful pressure stimuli and lower thermal pain thresholds .
With a more focal pain disorder such as TMD, there is conflicting experimental evidence about whether these patients exhibit enhanced sensory (non-pain) and pain signal facilitation compared with pain-free individuals. One study examined pressure pain thresholds (PPT) and heat pain thresholds on localized myofascial TMD patients before and after giving standardized infusions of pain-inducing hypertonic saline . It reported that while PPT was lower for the pain group no significant group differences were found for heat pain thresholds. Another study showed that pain-free women and women suffering from TMD did not differ in sensitivity to ischemic pain and heat pain tolerance . A study that examined and compared the detection thresholds of two TMD subgroups (temporomandibular joint arthralgia and masticatory myalgia) by examining the heat and electrical detection thresholds of patients suffering from TMD reported that arthralgia patients had a significantly lower electrical detection threshold in the auriculotemporal nerve territory, however pain thresholds and pain tolerance thresholds were not examined nor were other (non-trigeminal) body sites.
Even if there may be a general facilitation of nociceptive signal transduction for fibromyalgia, it cannot be assumed that this is also true for patients with local myofascial pain. While the various quantitative sensory testing studies on TMD described above show inconsistent results and investigational approaches, these data could be explained logically if severe chronic localized inflammatory pain in the temporomandibular joint (TMJ) differed in its effect on pain signal facilitation from localized myofascial pain, which is generally considered as a non-inflammatory disease process. An additional confounder is that pain is a complex sensory experience and chronic TMD pain is frequently accompanied by psychological distress, notably depression and somatization. Psychological factors may be involved in the pain perception process and conversely pain may dramatically affect the personality of patients . Several types of psychophysiological procedures have been developed to measure pain sensitivity in patients showing orofacial pain symptoms. Studies based on quantitative sensory testing in chronic orofacial pain have not consistently included a psychological assessment of their subjects. This study examines whether there is a difference in pain sensitivity between TMD patients and an age- and sex-matched group of normal subjects, and among the well-defined TMD subgroups of myogenous, arthrogenous, and mixed pain. The authors tried to elucidate the relationship between the psychosocial profiles and thermal pain thresholds obtained by quantitative sensory testing.
Materials and methods
39 consecutive patients with primary symptoms of TMD (7 men, 32 women, mean age ± SD = 30.8 ± 11.7 years) were studied. Inclusion criteria were: patients diagnosed with TMD according to the Research Diagnostic Criteria for TMD (RDC/TMD) ; and patients who reported high Graded Chronic Pain (GCP) scale (described later in this report) scores (Grade III or IV). Exclusion criteria were: patients with migraine, neuralgia, other musculoskeletal diseases, recent trauma or general medical diseases that might cause alterations of sensory thresholds; patients with pain in the orofacial region not originating from the TMJ and related structures; and patients younger than 18 years.
The control group consisted of 36 age- and sex-matched (7 men, 29 women, mean age ± SD = 29.0 ± 7.0 years), pain-free, healthy individuals with no history of any TMD diagnosis and situations pertinent to the exclusion criteria of the patient group. The study was approved by an Institutional Review Board and informed consent was obtained from each subject.
The RDC/TMD axis I guidelines were applied to examining and separating the TMD patients into three pain subgroups. Group 1 included patients with only myogenous pain, who feel pain mainly in the orofacial and/or head musculature during muscle palpation and jaw functioning or resting. Group 2 included patients with only arthrogenous pain, who feel pain mainly in the TMJ area during joint palpation and jaw functioning or resting regardless of the presence of disc displacement and/or degenerative change of the mandibular condyle. Group 3 included patients with both myogenous pain and arthrogenous pain (mixed pain), who feel pain in both the orofacial and/or head musculature and joint area during muscle, joint palpation and jaw functioning or resting. The diagnostic criteria for the three TMD pain subgroups are shown in Table 1 .
| TMD pain subgroup | Diagnosis criteria |
|---|---|
| Myogenous pain ( n = 12) | Pain at facial, TMJ, temporal, preauricular and inner ear areas at rest or during function. |
| Pain during palpation at more than 3 sites among the 20 muscle sites (1 of 3 sites must be on the pain side) | |
| Does not satisfy the criteria of the arthrogenous pain subgroup. | |
| Arthrogenous pain ( n = 12) | Pain during palpation of joint area. |
| Spontaneous pain in TMJ or pain during maximum mouth opening, assisted maximum mouth opening, or lateral movement. | |
| Does not satisfy the criteria of the myogenous pain subgroup. | |
| Mixed pain ( n = 15) | Satisfies all the criteria of both the subgroups. |
RDC/TMD axis II profiles
The Korean version of the RDC/TMD axis II history questionnaire was administered to each subject. The original English version of the RDC/TMD axis II history questionnaire was first translated into Korean. This translation was evaluated and revised by several faculty members in the Department of Oral medicine and Oral Diagnosis, Seoul National University. A native English speaker who was fluent in Korean then translated the draft Korean version back into English. The backward translated English version was compared with the original English version to confirm that the questions had been properly translated. The 1-week interval test–retest reliability of the questionnaire used in this survey was assessed in 154 TMD patients prior to this study, and the result reported good reliability .
Parameters of psychological profiles from the RDC/TMD axis II history questionnaire including depression and somatization were analysed . The method of assessing depression and somatization was derived from the Symptom Checklist-90-Revision (SCL-90-R). Participants responded to a total of 20 items (13 items of depression parameter and 7 items of an additional parameter) from SCL-90-R, and the resultant raw mean score was regarded as the depression scale. The somatization scale was obtained by calculating the raw mean score from the responses to 12 items of non-specific physical symptoms of SCL-90-R. Somatization without pain scale was also calculated by adding the score from responses to 7 items of the non-specific physical symptoms of SCL-90-R and dividing the sum by the number of answered questions. The 5 items excluded from the somatization scale are exclusively concerned with the patient’s pain experiences including headache, chest area pain, muscle pain, lower back pain, and stomach aches.
The severity of chronic pain was assessed with the GCP scale . The GCP scale combines 7 questions reflecting pain intensity, disability days (loss of work days) due to pain, and disability score (interference in daily activities) resulting in a 0–IV score (0, no pain; I, low intensity–low disability; II, high intensity–low disability; III, high disability–moderately limiting; IV, high disability–severely limiting) that reflects the pain intensity and resultant interference with usual functioning at home or work. Patients with Grade I and II are defined as a low disability group, and Grade III and IV are defined as a high disability group. The pain intensity was determined by calculating the average of 0–10 VAS ratings of pain at the time of the interview, usual level of pain, and the worst pain in the past 6 months; this average was multiplied by 10 to yield a 0–100 score. The number of disability days was used to assess the days with pain during the previous 6 months. The disability score was calculated from an average of 0–10 ratings of 3 questions about interference in daily activities multiplied by 10 to yield a 0–100 score.
Thermal pain sensitivity thresholds
The Thermosensory Analyzer II (Medoc, Israel) was used for all thermal threshold measurements. All tests were conducted in the same season (autumn) and room temperature was automatically maintained at 24 °C. To help the patient adjust to the test procedures, there was a practice session in which the thermode was attached to the patient’s forearm and the test was run 1–2 times. The tip of the thermal stimulator consists of a 16 mm × 16 mm contact surface which can be heated or cooled to temperatures between 0 and 53 °C at a rate of 1°/s. Low rates of temperature change (0.5–1/s) minimize reaction time artifact .
To determine the patient’s cold pain threshold (CPT), the thermal stimulator was placed on three facial regions (anterior temporal, masseter and lateral TMJ), and a leg region (anterior tibialis) of the pain side. The temperature was lowered from a baseline of 32 to 0 °C at a rate of 1°/s, until the patient perceived the temperature as painful and stopped the temperature decrease by pressing a button on a computer mouse.
To determine the heat pain threshold (HPT), the thermal stimulator was placed on the same sites tested for CPT. The temperature increase was started from a baseline of 32 °C and increased to a maximum of 53 °C at a rate of 1°/s. Subjects were instructed to press the stop button when the heat started to feel painful. The heat pain tolerance threshold (HPTT) was determined by the same method. This time the patient was instructed to press the button when the pain caused by the temperature was no longer tolerable.
All the measurements were repeated four times and the mean threshold temperature of the four consecutive measurements was calculated as the pain threshold. Measurements were made in the order CPT, HPT and HPTT. The thermal stimulator was placed on the temporal area, moved to the TMJ, then to the masseter area and finally to the anterior tibialis. Every thermal pain threshold (CPT, HPT, HPTT) was determined before the stimulator was moved to a different measurement site.
Statistical analyses
Independent t -test was used to compare thermal pain threshold values and RDC/TMD axis II indices between the control group and the patient group. One-way ANOVA was used to test the difference between thermal pain threshold values and RDC/TMD axis II indices among each TMD subgroup. Post hoc analyses were performed to examine individual mean differences using the Tukey test. Pearson’s correlation analysis was performed to investigate the relationships between psychological profiles and thermal pain thresholds, and between psychological profiles and subjective pain intensity. All analyses were conducted with SPSS version 12.0 software.
Results
Pain intensity and disability
There were no significant differences in pain duration and subjective pain intensity, disability days, and disability score on the GCP scale among the three TMD pain subgroups ( Table 2 ).
| GCP variables | Myogenous | Arthrogenous | Mixed | P -Value |
|---|---|---|---|---|
| Pain duration (month) | 27.72 ± 57.03 | 30.95 ± 35.88 | 31.63 ± 40.42 | 0.980 |
| Pain intensity | 56.60 ± 18.43 | 55.30 ± 24.33 | 61.86 ± 12.89 | 0.626 |
| Disability days | 80.42 ± 62.47 | 74.08 ± 74.26 | 73.67 ± 55.23 | 0.957 |
| Disability score | 47.80 ± 18.18 | 43.57 ± 19.16 | 53.60 ± 21.77 | 0.431 |
| GCP scale | 3.25 ± 0.45 | 3.08 ± 0.29 | 3.40 ± 0.50 | 0.183 |
Psychological profiles of RDC/TMD axis II diagnosis
Every score of the psychological profiles of RDC/TMD axis II (depression, somatization, and somatization without pain) was higher for TMD patients compared with normal subjects. Table 3 shows the comparison of psychological profiles among each TMD pain subgroup. The myogenous pain subgroup had significantly higher depression, somatization, and somatization without pain scores compared with the control group and significantly higher somatization and somatization without pain scores compared with the arthrogenous pain subgroup. The mixed pain subgroup had significantly higher depression, somatization, and somatization without pain scores compared with the control group. The arthrogenous pain subgroup did not show any significant differences in psychological profiles compared with the control group.
| Control (0) | Myogenous (1) | Arthrogenous (2) | Mixed (3) | Multiple comparisons † | |
|---|---|---|---|---|---|
| Depression | 0.36 ± 0.55 | 1.34 ± 0.89 | 0.68 ± 0.59 | 1.22 ± 0.82 | (0,1) ** ,(0,3) ** |
| Somatization | 0.38 ± 0.53 | 1.38 ± 0.97 | 0.60 ± 0.50 | 1.29 ± 0.79 | (0,1) ** ,(0,3) ** ,(1,2) * |
| Somatization without pain | 0.25 ± 0.39 | 1.20 ± 1.05 | 0.51 ± 0.46 | 1.17 ± 0.82 | (0,1) ** ,(0,3) ** ,(1,2) * |
* Significant at 0.05 level, one-way ANOVA.
** Significant at 0.01 level, one-way ANOVA.
† Post hoc analyses for multiple comparisons were performed using the Tukey test.
Thermal pain sensitivity thresholds
TMD patients were more sensitive to thermal pain, which resulted in a higher CPT, and lower HPT and HPTT values compared with normal subjects. Table 4 shows the descriptive values and statistical results from the comparison of thermal pain thresholds among each TMD pain subgroup. In the arthrogenous pain subgroup, CPT in the temporal area was significantly higher than in the control and other two pain subgroups, significantly higher in the masseter area than in the control group, and significantly higher in the TMJ area than in the control and myogenous pain subgroups. The average CPT value of the three facial regions in the arthrogenous pain subgroup was significantly higher than in the control and myogenous pain subgroups. CPT values of the anterior tibialis area were not significantly different among the three TMD subgroups but the CPT value of the arthrogenous pain subgroup in this area was significantly higher compared with the control group.
| Site | Control (0) | Myogenous (1) | Arthrogenous (2) | Mixed (3) | Multiple comparisons † |
|---|---|---|---|---|---|
| CPT | |||||
| Temporal | 3.36 ± 4.85 | 6.01 ± 9.29 | 17.10 ± 11.45 | 6.75 ± 10.10 | (0,2) ** ,(1,2) ** ,(2,3) ** |
| Masseter | 5.12 ± 8.16 | 7.93 ± 10.44 | 18.02 ± 11.47 | 10.95 ± 11.23 | (0,2) * |
| TMJ | 5.73 ± 8.15 | 6.88 ± 8.39 | 19.92 ± 11.42 | 12.96 ± 11.46 | (0,2) ** ,(1,2) ** |
| Facial region ‡ | 4.74 ± 5.46 | 6.94 ± 8.84 | 18.35 ± 10.65 | 10.22 ± 9.91 | (0,2) ** ,(1,2) ** |
| Anterior tibialis | 4.54 ± 10.09 | 4.87 ± 7.16 | 13.83 ± 10.53 | 7.46 ± 7.64 | (0,2) * |
| HPT | |||||
| Temporal | 47.65 ± 3.05 | 46.72 ± 3.95 | 43.91 ± 4.05 | 46.60 ± 3.10 | (0,2) ** |
| Masseter | 47.11 ± 3.21 | 45.80 ± 3.38 | 41.28 ± 3.76 | 43.65 ± 2.22 | (0,2) ** ,(1,2) ** ,(0,3) ** |
| TMJ | 46.86 ± 3.11 | 47.19 ± 2.67 | 41.47 ± 3.30 | 43.35 ± 3.03 | (0,2) ** ,(1,2) ** ,(0,3) ** ,(1,3) * |
| Facial region | 47.21 ± 2.25 | 46.57 ± 2.75 | 42.22 ± 3.23 | 44.53 ± 1.97 | (0,2) ** ,(1,2) ** ,(0,3) ** |
| Anterior tibialis | 46.28 ± 4.42 | 47.82 ± 1.79 | 44.98 ± 4.27 | 47.34 ± 1.96 | NS |
| HPTT | |||||
| Temporal | 50.22 ± 1.72 | 49.15 ± 2.60 | 46.07 ± 4.02 | 48.59 ± 2.35 | (0,2) ** ,(1,2) ** |
| Masseter | 49.67 ± 1.40 | 48.47 ± 1.80 | 46.18 ± 3.91 | 47.89 ± 2.18 | (0,2) ** ,(0,3) * |
| TMJ | 49.25 ± 1.78 | 48.80 ± 1.77 | 45.08 ± 3.70 | 46.18 ± 3.26 | (0,2) ** ,(1,2) ** ,(0,3) ** ,(1,3) * |
| Facial region | 49.72 ± 1.28 | 48.80 ± 1.76 | 45.77 ± 3.37 | 47.55 ± 1.90 | (0,2) ** ,(1,2) ** ,(0,3) ** |
| Anterior tibialis | 49.69 ± 1.43 | 49.43 ± 0.97 | 46.42 ± 3.39 | 47.83 ± 2.67 | (0,2) ** ,(1,2) ** ,(0,3) * |
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