The roles of beliefs, catastrophizing, and coping in the functioning of patients with temporomandibular disorders

Pain 92 (2001) 41±51

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The roles of beliefs, catastrophizing, and coping in the functioning of patients with temporomandibular disorders Judith A. Turner a,b,*, Samuel F. Dworkin a,c, Lloyd Mancl d, Kimberly H. Huggins c, Edmond L. Truelove c a

Department of Psychiatry and Behavioral Sciences, University of Washington School of Medicine, Seattle, WA, USA b Department of Rehabilitation Medicine, University of Washington School of Medicine, Seattle, WA, USA c Department of Oral Medicine, University of Washington School of Dentistry, Seattle, WA, USA d Department of Dental Public Health Sciences, University of Washington School of Dentistry, Seattle, WA, USA Received 24 August 2000; received in revised form 7 November 2000; accepted 27 November 2000

Abstract Pain-related beliefs, catastrophizing, and coping have been shown to be associated with measures of physical and psychosocial functioning among patients with chronic musculoskeletal and rheumatologic pain. However, little is known about the relative importance of these process variables in the functioning of patients with temporomandibular disorders (TMD). To address this gap in the literature, self-report measures of pain, beliefs, catastrophizing, coping, pain-related activity interference, jaw activity limitations, and depression, as well as an objective measure of jaw opening impairment, were obtained from 118 patients at a TMD specialty clinic. Controlling for age, gender, and pain intensity, signi®cant associations were found between (1) pain beliefs and activity interference, depression, and non-masticatory jaw activity limitations, (2) catastrophizing and activity interference, depression, and non-masticatory jaw activity limitations, and (3) coping and activity interference and depression. Controlling for age, gender, pain intensity, and the other process variables, signi®cant associations were found between (1) beliefs and activity interference and depression, and (2) catastrophizing and depression. No process variable was associated signi®cantly with the objective measure of jaw impairment. The results suggest that for patients with moderate or high levels of TMD pain and dysfunction, beliefs about pain play an important role in physical and psychosocial functioning. q 2001 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved. Keywords: Chronic pain; Coping; Beliefs; Catastrophizing; Temporomandibular disorders

1. Introduction According to cognitive-behavioral theory, pain-related cognitions and behaviors play important roles in the adjustment of patients with chronic pain. Empirical support for this theory's application to chronic pain comes from several lines of research. First, numerous studies of patients with diverse chronic pain problems have found pain-related beliefs (e.g. perceived control over pain, belief that one is disabled), catastrophizing (expecting or worrying about major negative consequences from a situation, even one of minor importance), and coping strategies (e.g. coping selfstatements) to be associated with pain intensity, psychosocial adjustment, and physical functioning (Jensen et al., * Corresponding author. University of Washington School of Medicine, Department of Psychiatry and Behavioral Sciences, Box 356560, Seattle, WA 98195, USA. Tel.: 11-206-543-3997; fax: 11-206-685-1139. E-mail address: [email protected] (J.A. Turner).

1991; Boothby et al., 1999; Geisser et al., 1999). Second, cognitive-behavioral therapies (CBT), which help patients learn to identify and modify maladaptive beliefs and behaviors and use adaptive cognitive and behavioral coping strategies, have been demonstrated to be ef®cacious for a variety of pain conditions (NIH Technology Assessment Panel on Integration of Behavioral and Relaxation Approaches into the Treatment of Chronic Pain and Insomnia, 1996; Turner, 1996; Compas et al., 1998; Morley et al., 1999). Furthermore, changes in pain-related beliefs and coping strategy use are associated with improvement in pain intensity and physical and psychosocial disability after cognitive-behavioral treatment (Turner and Clancy, 1986; Lorig et al., 1989; Keefe et al., 1990, 1996; Jensen et al., 1994a; Turner et al., 1995). There are compelling reasons for studying the role of cognitive and behavioral factors in temporomandibular disorders (TMD), an interrelated set of clinical syndromes involving signs and symptoms in the masticatory muscles,

0304-3959/01/$20.00 q 2001 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved. PII: S 0304-395 9(00)00469-3

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J.A. Turner et al. / Pain 92 (2001) 41±51

temporomandibular joint (TMJ), and associated hard and soft tissues. First, patients with TMD share characteristics in common with patients with other chronic pain conditions such as headache and back pain, including similar pain intensity levels and associated behavioral and psychological dysfunction (Dworkin, 1995). As is true for many other chronic pain conditions, TMD tends to be persistent and recurrent (Dworkin et al., 1989) and many patients continue to report signi®cant levels of pain and disability despite treatment (Rudy and Turk, 1995). Second, TMD pain is a common condition; for example, the prevalence of TMD was 12.1% in one health maintenance organization (Von Korff et al., 1988) and about 6% of the population seek treatment for pain in the masticatory muscles and/or TMJ (Dworkin et al., 1990a; Lipton et al., 1993). Third, individuals with TMD differ considerably in their levels of physical disability and psychosocial dysfunction (Butterworth and Deardorff, 1987; Rudy et al., 1989; Suvinen et al., 1997a), and physical ®ndings do not appear to explain these differences. Reliably classi®ed subgroups differ significantly on pain level and psychological and pain behavior indices (activity levels and interference, and affective distress), but do not differ on clinical examination ®ndings (maximum interincisal opening, number of TMJ symptoms, and proportion of abnormal TMJ radiographic ®ndings) (Rudy et al., 1989; Dworkin, 1995). Longitudinal studies have demonstrated that there is no clear relationship between changes in physical measures of jaw function and course of pain (Ohrbach and Dworkin, 1998). Taken together, these ®ndings suggest the potential fruitfulness of examining the role of cognitive-behavioral factors in TMD patient functioning. Unlike other chronic pain conditions such as back pain, however, relatively little research has been devoted to the identi®cation of cognitive and behavioral factors associated with pain intensity, pain-related activity interference, and mood among individuals with TMD. The literature to date indicates the need for more studies. In a study of patients with types of TMD involving the TMJ, coping strategies explained 27±58% of the variance in pain and psychological distress measures (Jaspers et al., 1993). In another group of patients with TMD pain, maladaptive coping, as evidenced by an excessive number of negative changes in usual activities, was associated with poor psychological and physical adjustment (Lennon et al., 1990). A study of patients referred for TMD treatment found that when controlling for baseline pain intensity, greater con®dence in the ability to relieve one's pain was associated with less likelihood of pain 1 year later (Massoth et al., 1990). Other TMD studies have found that catastrophizing is more common in women with chronic than with acute pain (LeResche et al., 1992), and is associated with symptom severity (Suvinen et al., 1997a) and treatment failure (Suvinen et al., 1997b). Furthermore, there is evidence that (1) cognitive and behavioral treatments are effective for TMD (Stenn et al., 1979; Gale and Funch, 1984; Stam et al., 1984; Oakley et al.,

1994), (2) treatments that speci®cally target dysfunctional cognitions enhance the positive effects of more generic dental and behavioral treatments (Dworkin et al., 1994; Rudy and Turk, 1995), and (3) changes in beliefs and coping are associated with improvement in pain, jaw functioning, and depression (Turner et al., 1995). This body of research has demonstrated convincingly that beliefs, catastrophizing, and coping play important roles in TMD and other chronic pain patient outcome variables such as functional disability and mood. However, little is known about the relative importance of each of these process variable domains in the psychological adjustment and physical disability of patients with TMD or other chronic pain conditions (Thorn et al., 1999). Identi®cation of beliefs, cognitive responses, and coping strategies strongly and independently associated with activity interference and psychological distress would suggest the value of targeting those variables for modi®cation in treatment. To address this gap in the literature, a previous study (Turner et al., 2000) examined whether measures of pain-related beliefs, catastrophizing, and coping made unique, independent contributions to the explanation of variance in self-reported depression and physical disability among patients with a variety of chronic pain conditions entering a multidisciplinary pain treatment program. Belief measures were signi®cantly and independently associated with both physical disability and depression, after controlling for age, sex, pain intensity, catastrophizing, and coping. Coping measures were signi®cantly and independently associated with physical disability, but not depression. A measure of catastrophizing was independently associated with depression, but not physical disability. The purpose of the present study was to examine the importance of three process variables ± beliefs, catastrophizing, and coping ± for four distinct TMD outcome variables ± pain-related activity interference, depression, jaw activity limitations, and jaw opening impairment. We wished to determine (1) whether each of these three process variable domains was associated signi®cantly with these four outcome variables, (2) whether each process variable domain was associated with each outcome variable after accounting for the effects of the other process variable domains, and (3) the speci®c beliefs and coping strategies most strongly associated with each outcome variable. Based on cognitive-behavioral theory and previous research, we hypothesized that beliefs, coping, and catastrophizing would each be associated signi®cantly with each outcome variable except jaw opening impairment, which is determined primarily by jaw anatomy and physiology and not by psychological variables. We further hypothesized that ®ndings in a sample of patients with diverse chronic pain conditions (Turner et al., 2000) would be replicated in this sample of TMD patients, given the similarities of patients with TMD to those with other chronic pain conditions.

J.A. Turner et al. / Pain 92 (2001) 41±51

2. Methods 2.1. Study participants and procedure The study participants were patients seeking care at a TMD specialty clinic and enrolled in a randomized trial comparing usual care in the clinic alone with usual care plus an adjunctive six-session individual CBT program. All data in this report were collected during the study baseline assessment, before participants learned the condition to which they were randomized. Study inclusion criteria were (1) an age of 18±70 years, (2) an ability to complete the study measures, (3) the presence of an RDC/TMD Axis I diagnosis (Dworkin and LeResche, 1992), and (4) painrelated disability, as de®ned by Chronic Pain Grade (Von Korff et al., 1992) of high II, III, or IV, corresponding to low, moderate, or high disability. Patients with these pain grades are typically psychosocially dysfunctional, with greater disability, depression, and frequency of health care visits for pain, as compared with Grades I and low II patients. Study exclusion criteria were the presence of signi®cant oral mucosal lesions or atypical TMD ®ndings requiring further diagnostic evaluation, and major medical or psychiatric conditions that would interfere with the ability to participate in or bene®t from the study (e.g. psychosis, clinical indications for surgical treatment, major medical illness, active suicidal ideation, and current alcohol or other substance abuse). Of the 187 patients identi®ed as eligible during the study period, 118 (63.1%) enrolled in the study. The average age of the study participants was 38.8 years (SD 10.4, range 21± 67 years) and 83.1% were female. Participants had experienced pain for 0.08±40 years (mean 6.23 years, SD 7.43). Information about ethnic/racial groups was given by 113 participants as follows: Caucasian, 82%; African-American, 3%; Asian or Paci®c Islander, 6%; American or Alaskan Native, 1%; and other, 8%. Seventy-four percent were educated beyond high school, 21% had a high school education, and only 5% had less than a high school education. Approximately 6% were receiving disability compensation related to pain, 7.6% were receiving disability compensation unrelated to pain, and 11.9% had an attorney for matters related to their pain problems. All study participants received a standardized RDC/TMD examination (Dworkin and LeResche, 1992) to record clinical ®ndings and to derive an RDC/TMD Axis I diagnosis. The examination was performed by oral medicine dentists and registered dental hygienists trained and calibrated in the examination methods (Dworkin et al., 1990b). Participants also completed the self-report measures described in the following section and a questionnaire that included the items used to determine chronic pain grade classi®cations (Von Korff et al., 1992). Axis I of the RDC/TMD includes three TMD diagnostic categories: (I) myofascial pain disorders, with and without limitation in vertical range of mandibular motion; (II) disc displacement disorders, with

43

and without reduction of the articular disc; and (III) arthralgia, arthritis, and arthrosis. A patient may receive more than one RDC/TMD Axis I diagnosis. Among the sample, 95% met criteria for an RDC Axis I muscle disorder (I) diagnosis (39% for myofascial pain (I.a) and 56% for myofascial pain with limited opening (I.b)). Twenty percent met criteria for disc displacement with reduction (II.a); 6% met criteria for disc displacement without reduction, with limited opening (II.b); and 3% met criteria for disc displacement without reduction, without limited opening (II.c). Fifty-four percent met criteria for arthralgia (III.a) and 10% met criteria for osteoarthritis of the TMJ (III.b). Chronic Pain Grades were high II for 31.4%, III for 27.1%, and IV for 41.5%. The 118 study participant patients were compared with the patients who declined to participate with regard to age, sex, race (Caucasian versus non-Caucasian), marital status (married versus non-married), RDC Axis I diagnosis, pain duration, characteristic pain intensity (as described in Section 2.2), and education. The two groups did not differ signi®cantly on any of these variables. 2.2. Measures 2.2.1. Demographic and descriptive measures Study participants completed a questionnaire assessing sociodemographic variables (including age, ethnicity, gender, employment status, education level, and duration of pain). This questionnaire also assessed whether the participant was receiving disability compensation for pain and whether the participant had retained an attorney for matters related to TMD. 2.2.2. Pain intensity Characteristic pain intensity was calculated by averaging study participant ratings on 0±10 scales of current pain, worst pain in the past month, and average pain in the past month (Dworkin et al., 1990c; Von Korff et al., 1992). Numerical pain intensity scales have been demonstrated to be valid and sensitive to change (Jensen and Karoly, 1992b). Composite pain ratings created by averaging multiple pain ratings have greater stability than do individual pain ratings (Jensen et al., 1999). 2.2.3. Process variables (beliefs, coping, and catastrophizing) 2.2.3.1. The Survey of Pain Attitudes. The Survey of Pain Attitudes (SOPA) (Jensen et al., 1994b) consists of seven scales designed to assess the following beliefs hypothesized to be important in adjustment to chronic pain: (1) Control (belief in one's personal control over pain); (2) Disability (belief that one's pain is disabling); (3) Harm (belief that pain signi®es damage and that activity should be avoided); (4) Emotion (belief that emotions in¯uence pain); (5) Medication (belief that medications are appropriate for chronic

44

J.A. Turner et al. / Pain 92 (2001) 41±51

pain); (6) Solicitude (belief that others should respond solicitously to pain behaviors); and (7) Medical Cure (belief that a medical cure exists for one's pain). The scales have been demonstrated to have adequate test±retest stability, criterion validity, and internal consistency (Jensen and Karoly, 1992a; Strong et al., 1992; Jensen et al., 1994b). Scores on these scales have been found to be associated signi®cantly with measures of physical and psychosocial dysfunction among patients with chronic pain (Jensen and Karoly, 1992a; Jensen et al., 1994b). 2.2.3.2. The Coping Strategies Questionnaire. The Coping Strategies Questionnaire (CSQ) assesses the frequency of use of different pain coping strategies and includes ratings of belief in one's ability to decrease and control pain (Rosenstiel and Keefe, 1983). Seven scales have been shown to be reliable and valid and were used in this study: Diverting Attention, Reinterpreting Pain Sensations, Ignoring Pain, Praying and Hoping, Coping SelfStatements, Increasing Behavioral Activities, and Catastrophizing. Catastrophizing was considered separately from the other six scales for purposes of this study. The CSQ subscales, including Catastrophizing, have demonstrated excellent internal consistency (Rosenstiel and Keefe, 1983; Keefe et al., 1989) and have been shown to be associated with various measures of functioning among patients with different pain conditions (Keefe et al., 1987, 1989; Jensen and Karoly, 1991; Dozois et al., 1996; Martin et al., 1996). 2.2.4. Self-reported outcome variables (interference, depression, and jaw activity limitations) A variety of outcome measures were chosen because chronic pain can impact multiple domains of functioning and the extent of impact can vary across domains. The self-reported outcome variables were: pain interference with activity, as measured by the Multidimensional Pain Inventory (MPI) Interference Scale (Kerns et al., 1985); depression, as measured by the Beck Depression Inventory (BDI) (Beck and Beamesderfer, 1974; Beck et al., 1979); and jaw activity limitation, as measured by the Mandibular Function Impairment Questionnaire (MFIQ) Masticatory and Nonmasticatory Scales (Stegenga et al., 1993b). 2.2.4.1. MPI Interference Scale. The MPI Interference Scale has been shown to be valid and to have acceptable internal consistency and test±retest stability (Kerns et al., 1985). It assesses patient perceptions of the extent to which pain interferes with social, work, home, and family activities and relationships. 2.2.4.2. Depression. The BDI (Beck and Beamesderfer, 1974; Beck et al., 1979), a 21-item measure of depressive symptom severity, has been shown to have high internal consistency, adequate test±retest reliability, and validity (Beck et al., 1988). It has been demonstrated to be a valid

screening instrument for depression among patients with chronic pain (Turner and Romano, 1984; Love, 1987; Geisser et al., 1997). 2.2.4.3. Jaw activity limitations. The MFIQ (Stegenga et al., 1993b) is a 17-item measure consisting of two subscales (masticatory and non-masticatory jaw disability) demonstrated to be sensitive to change with treatment for TMD (Stegenga et al., 1993a). 2.2.5. Objective outcome variable (jaw opening impairment) The objective outcome, jaw opening impairment, was assessed by measuring maximum assisted jaw opening during the standardized RDC/TMD examination described above. Maximum assisted jaw opening was assessed by applying a moderate amount of pressure to open the study participant's mouth as wide as possible and measuring the distance in millimeters between the edges of the maxillary and mandibular central incisors. This measure is useful in determining whether there is a limitation in opening due to physical causes such as articular fossa shape, arrangement of the mandibular condyle in the fossa, displaced or immovable articular disc, or muscle contraction. 2.3. Data analysis The correlations between pairs of outcome measures supported the use of several measures to assess different outcomes. The only substantial association was between the MFIQ Masticatory and Nonmasticatory Scales (r ˆ 0:69). Other correlations were low to moderate in magnitude, ranging from 0.17 (MFIQ Masticatory and MPI Interference) to 0.49 (MFIQ Nonmasticatory and MPI Interference). Despite their association, we elected to examine separately the Masticatory and Nonmasticatory Scales of the MFIQ because they assess different domains of jaw activities. Each outcome measure was found to be normally distributed. For each outcome measure, regression analyses were performed with the following independent variables: (1) age, gender, and characteristic pain intensity (hereafter referred to as the control variables); (2) control variables and either (a) the SOPA Scales, (b) the CSQ Scales, or (c) the Catastrophizing Scale; (3) all variables (control, CSQ Scales, SOPA Scales, and Catastrophizing Scale) except (a) the SOPA Scales, (b) the CSQ Scales, or (c) the Catastrophizing Scale; and (4) all variables. We examined the change in R 2 between these different models using F-tests to determine (1) whether each of the independent variable domains (beliefs, coping, and catastrophizing) was associated signi®cantly with each outcome measure examined separately after adjusting for the control variables (comparison of models 1 and 2), and (2) whether each of the independent variable domains was associated signi®cantly with each outcome measure after adjusting for the control vari-

J.A. Turner et al. / Pain 92 (2001) 41±51

ables, and after adjusting for the other two independent variable domains (comparison of models 3 and 4). The analyses described in the previous paragraph controlled for pain intensity for two reasons: (1) to determine the roles of beliefs, catastrophizing, and coping in the outcome measures beyond any roles played by age, gender, and pain intensity; and (2) to replicate the previous study (Turner et al., 2000). However, such analyses do not shed light on the extent to which process variables may play an indirect role in outcome variables through their in¯uence on pain intensity. For example, catastrophizing may increase pain intensity and this may in turn increase depression and activity limitations, but such effects would not be revealed from models that examine the associations between catastrophizing and these outcome variables only after controlling for pain intensity. Therefore, we also performed the regression analyses without adjusting for pain intensity. Finally, correlation coef®cients were calculated to examine the direct associations between the outcome measures and the pain intensity, belief, catastrophizing, and coping scales. A conservative signi®cance level of 0.01 was used to determine statistical signi®cance in each analysis in this study, given the relatively large number of tests performed.

3. Results 3.1. Process and outcome variable scores Table 1 shows the scores on the study measures. Consistent with the study inclusion criteria, study participants rated their characteristic pain intensity as moderately high on average. The mean MPI Interference Scale score was comparable to that in the MPI development study sample (patients with chronic pain referred to a pain management program) (Kerns et al., 1985). The mean BDI score (15.45) was in the mild to moderate range of depressive symptom severity (Beck et al., 1988). MFIQ Scale scores were higher (indicating greater jaw activity limitation) than those published for a sample of patients with TMD in The Netherlands (Stegenga et al., 1993b). The mean maximum assisted jaw opening in this sample (48 mm) was very similar to that in a previous sample of TMD clinic patients not selected on the basis of level of pain or activity interference (mean 47 mm) and less than that of community controls (mean 52 mm) (Dworkin et al., 1990a). The SOPA Scale scores indicate that, on average, study participants did not hold strong beliefs that: they could control their pain, their pain was disabling, hurt indicated damage, emotions in¯uenced pain, solicitous responses to pain were appropriate, medications were appropriate for chronic pain, or a medical cure existed for their pain. On average, this group of patients `sometimes' catastrophized in response to pain. The most frequently used coping strategies were coping self-statements, increasing activity, and praying/hoping.

45

3.2. Overview of regression analyses Table 2 shows the results of the regression analyses that assessed the associations between each process variable domain (beliefs, coping, and catastrophizing) and each outcome measure. Table 3 shows the results for the comparisons of regression models without each process variable domain versus the model with all independent variables considered. These results enable conclusions to be drawn concerning whether each process variable domain makes an independent contribution to the explanation of variance in each outcome measure, beyond the variance explained by the other process variables and age, gender, and pain intensity. 3.3. Association between beliefs and the outcome measures The belief scales were associated substantially with MPI Interference, after adjusting for the control variables (change in R2 ˆ 0:33, P , 0:0001) (see Table 2) and also after adjusting for all other control and process variables (change in R2 ˆ 0:17, P , 0:0001). The belief measures also made a substantial contribution to the explanation of depression scores after adjusting for the control variables (change in R2 ˆ 0:44, P , 0:0001) (see Table 2) and after controlling for all other variables (change in R2 ˆ 0:14, Table 1 Scores on the measures of pain, outcome variables (interference, jaw activity limitations, depression, and jaw impairment), and process variables (beliefs, catastrophizing, and coping) Measure (possible range) Characteristic pain intensity (0±10) Outcome measures Interference (MPI) (0±6) Depression (BDI) (0±63) Masticatory (MFIQ) (0±1) Non-masticatory (MFIQ) (0±1) Maximum assisted jaw opening (mm) Process measures Beliefs (SOPA) (0±4) Control Disability Harm Emotion Medications Solicitude Medical cure Catastrophizing (CSQ) (0±6) Coping (CSQ) (0±6) Diverting attention Reinterpreting pain Ignoring pain sensations Praying/hoping Coping self-statements Increasing activity

Mean

SD

6.77

1.70

3.33 15.45 0.58 0.30 47.96

1.36 9.85 0.22 0.17 9.35

1.94 1.76 1.88 2.20 2.52 1.48 2.32 2.16

0.70 0.82 0.66 0.82 0.67 0.96 0.64 1.46

2.24 1.15 2.31 2.55 3.66 2.68

1.39 1.18 1.43 1.50 1.12 1.19

46

J.A. Turner et al. / Pain 92 (2001) 41±51

Table 2 R 2 and the change in R 2 in regression models of the association of control variables, beliefs, catastrophizing, and coping with psychological and physical dysfunction Outcome measure

Control variables (R 2) a

Beliefs (change in R 2)

Catastrophizing (change in R 2)

Coping (change in R 2)

Interference (MPI) Depression (BDI) Masticatory jaw activities (MFIQ) Non-masticatory jaw activities (MFIQ) Maximum assisted jaw opening

0.12** b 0.04 0.12**

0.33**** 0.44**** 0.05

0.14**** 0.33**** 0.01

0.13** 0.12* 0.03

0.18****

0.15**

0.08***

0.06

0.12**

0.06

0.01

0.02

a

Age, gender, and characteristic pain intensity. *P , 0:05, **P , 0:01, ***P , 0:001, ****P , 0:0001 for the F-test for the change in R 2 as compared to the model with control variables only or for R 2 in the model with the control variables. b

P , 0:001) (see Table 3). The belief scales made a signi®cant additional contribution to the control variables in the explanation of variance in non-masticatory jaw activity limitations (change in R2 ˆ 0:15, P , 0:01) (see Table 2), but the amount of additional variance explained after the other process variables were also in the model was not statistically signi®cant (see Table 3). Beliefs were not signi®cantly associated with masticatory jaw activities or maximum assisted jaw opening after controlling for age, gender, and pain intensity (see Tables 2 and 3).

other process and control variables (change in R2 ˆ 0:05, P , 0:001) (Table 3). Catastrophizing was signi®cantly associated with non-masticatory jaw activity limitations (change in R2 ˆ 0:08, P , 0:001), but not masticatory jaw activity limitations or maximum assisted jaw opening after adjusting for the control variables (Table 2). In models with all other process and control variables, catastrophizing did not explain a statistically signi®cant amount of additional variance in any outcome measure except depression (Table 3).

3.4. Association between catastrophizing and the outcome measures

3.5. Association between coping and the outcome measures

The Catastrophizing Scale was associated signi®cantly with MPI Interference, after adjusting for the control variables (change in R2 ˆ 0:14, P , 0:0001) (Table 2). After also adjusting for the other process variables, however, catastrophizing explained only a very small amount of variance in MPI Interference Scale scores, and this association was not statistically signi®cant at the level set for this study (change in R2 ˆ 0:02, P , 0:05) (Table 3). Catastrophizing explained an additional 33% of the variance (P , 0:0001) in depression symptom severity scores after adjusting for the control variables (Table 2). Catastrophizing made a statistically signi®cant, but small, contribution to the explanation of variance in depression after controlling for all

The coping scales were associated signi®cantly with MPI Interference (change in R2 ˆ 0:13, P , 0:01), and there was a trend toward a statistically signi®cant association between the coping scales and depression scores, after adjusting for the control variables (change in R2 ˆ 0:12, P , 0:05) (Table 2). Coping was not associated signi®cantly with Masticatory or Nonmasticatory Scale scores or maximum assisted jaw opening after controlling for age, gender, and pain intensity (see Table 2), or with any outcome measure after also adjusting for the other process variables (Table 3). 3.6. Regression models not controlling for pain intensity To examine whether the process variables could be asso-

Table 3 Difference in R 2 between the model with all control and process variables and models without each process variable Outcome measure

All variables but beliefs (change in R 2)

All variables but catastrophizing (change in R 2)

All variables but coping (change in R 2)

All variables (R 2) a

Interference (MPI) Depression (BDI) Masticatory (MFIQ) Non-masticatory (MFIQ) Maximum assisted jaw opening

0.17**** b 0.14*** 0.06 0.08 0.08

0.02* 0.05*** 0.00 0.01 0.02

0.01 0.01 0.06 0.03 0.04

0.49**** 0.53**** 0.23* 0.38**** 0.23

a

Age, gender, characteristic pain intensity, beliefs, catastrophizing, and coping. *P , 0:05, **P , 0:01, ***P , 0:001, ****P , 0:0001 for F-test for the change in R 2 as compared to the model with all variables or for R 2 in the model with all variables. b

J.A. Turner et al. / Pain 92 (2001) 41±51

47

Table 4 Correlations between the outcome measures and measures of pain intensity, beliefs, catastrophizing, and coping Measures of pain, beliefs, catastrophizing, and coping Characteristic pain Beliefs (SOPA) Control Disability Harm Emotion Medication Solicitude Medical cure Catastrophizing (CSQ) Coping (CSQ) Diverting attention Reinterpreting Ignoring Pray/hope Coping statements Increase behavioral activities a

Interference (MPI) 0.34*** a

Depression (BDI) 0.16

Masticatory jaw activities (MFIQ) 0.32***

Nonmasticatory jaw activities (MFIQ) 0.39****

Maximum assisted jaw opening 20.33***

20.10 0.60**** 0.22* 0.08 0.16 0.22* 0.05 0.45****

20.34**** 0.52**** 0.20* 0.24** 0.22* 0.41**** 0.07 0.60****

20.18 0.16 0.25** 20.05 0.02 0.12 0.11 0.20*

20.17 0.40**** 0.29** 20.01 0.10 0.25** 0.08 0.37****

0.15 20.05 20.17 0.04 20.16 20.08 20.02 20.03

0.22* 0.12 20.12 0.30*** 20.18 0.06

0.06 20.07 20.18 0.16 20.29** 20.05

0.10 20.03 20.12 0.18* 0.03 0.09

0.14 0.04 20.14 0.25** 20.06 0.10

20.09 0.00 0.08 20.12 20.02 20.05

*P , 0:05, **P , 0:01, ***P , 0:001, ****P , 0:0001.

ciated indirectly with the outcome variables through their association with pain intensity, the regression analyses were repeated without pain intensity as a control variable. Overall, the results were similar to those controlling for pain intensity. As would be expected, the control variables as a group accounted for less of the variance in the outcome measures when pain intensity was not included. However, the additional variance in the outcome measures explained by the process variables was only slightly greater when pain was not controlled. The increase in variance explained was less than 5% in all cases except for the explanation of variance in MPI Interference by beliefs (6%), catastrophizing (7%), and coping (6%). Similarly, the values shown in Table 3 changed only slightly in the analyses without pain intensity. The difference in the change in R 2 was #0.04 in all cases. For all outcome measures except depression (which remained unchanged), the R 2 for models with all variables was somewhat less (difference of 0.03±0.06) when pain was not included. In no case did a non-signi®cant value become statistically signi®cant at the 0.01 level when pain was not controlled.

The SOPA Disability Scale accounted for most of the variance in interference, depression, and jaw activity limitations explained by the belief variables. Among all the process variable measures, the SOPA Disability Scale and the Catastrophizing Scale show consistently signi®cant associations with the self-reported outcome measures (although the association between the Disability Scale and one self-reported outcome measure, the MFIQ Nonmasticatory Scale, was not statistically signi®cant). There was a signi®cant association or trend toward a signi®cant association between depression and all belief and catastrophizing measures except the Medical Cure Scale. In general, the correlations between the speci®c coping strategies and the outcome measures were not strong and were not consistent across outcome measures. However, the CSQ Praying and Hoping Scale was correlated 0.30 with the Interference Scale and 0.25 with the Nonmasticatory Scale. Greater self-reported use of praying or hoping things would get better was associated with greater dysfunction. Interestingly, not a single process measure was associated signi®cantly with the objective measure of jaw impairment.

3.7. Correlations between outcome measures and measures of beliefs, catastrophizing, and coping

4. Discussion

For descriptive purposes, Table 4 shows the correlations between the outcome measures (interference, depression, jaw activity limitations, and jaw impairment) and the measures of pain intensity, beliefs, catastrophizing, and coping. Pain intensity was associated signi®cantly with each outcome measure except depression, but the correlations were not high. The SOPA Disability Scale and Catastrophizing were more strongly associated than was pain intensity with the MPI Interference Scale and the BDI.

As hypothesized, pain-related beliefs, measured by the SOPA Scales, explained statistically signi®cant and substantial proportions of the variance in activity interference (33%), non-masticatory jaw activity limitations (15%), and depression (44%), after adjusting for the control variables (age, gender, and pain intensity). The Disability Scale, re¯ecting the extent to which patients believed that their pain was disabling, accounted for most of the variance in these outcome measures explained by the SOPA Scales.

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J.A. Turner et al. / Pain 92 (2001) 41±51

Also as hypothesized, Catastrophizing explained signi®cant proportions of the variance in activity interference (14%), non-masticatory jaw activity limitations (18%), and depression (33%), after adjusting for the control variables. We hypothesized that the coping scales would also be associated signi®cantly with each outcome variable except jaw opening impairment. Coping explained a signi®cant amount of the variance in activity interference (13%), but there was only a trend (P , 0:05) toward a signi®cant association with depression and the association with jaw activities was not signi®cant, after controlling for age, gender, and pain intensity. Our hypothesis that ®ndings in a sample of patients with diverse chronic pain conditions would be replicated in this sample of patients with TMD was generally supported. Beliefs made substantial unique contributions to the explanation of variance in activity interference (17% of the variance) and depression (14% of the variance), replicating the previous ®nding (Turner et al., 2000) that beliefs were signi®cantly and independently associated with selfreported physical disability and depression, after controlling for age, sex, pain intensity, catastrophizing, and coping. That beliefs were substantially and independently associated with different measures of disability and depression in studies with different patient populations supports the argument (Haythornthwaite and Heinberg, 1999; Thorn et al., 1999) that beliefs are conceptually distinct from coping and catastrophizing, and their importance in the physical and psychosocial functioning of patients with chronic pain, regardless of site. Also replicating the previous study (Turner et al., 2000), coping did not make an independent contribution to the explanation of variance in depression. It appears likely that speci®c pain coping strategies, at least the ones measured by the CSQ, do not play a unique role in depressive symptom severity apart from their association with pain-related beliefs and catastrophizing. This suggests that in the treatment of depression associated with chronic pain, helping patients learn to identify and modify maladaptive cognitions may be more ef®cacious than teaching pain coping strategies. Unlike the previous study, which found that coping was signi®cantly and independently associated with selfreported physical disability, coping was not independently associated with activity interference or jaw activity limitations in the present study. It is unknown whether this discrepancy in ®ndings is due to differences in the coping measures, the outcome measure, the patient sample, or other factors. The previous study included another measure of coping in addition to the CSQ and used the Roland Scale (Roland and Morris, 1983) rather than the MPI Interference Scale. Unlike the Roland Scale, which primarily assesses physical disability, the Interference Scale assesses patient perceptions of pain interference with social, work, home, and family activities and relationships. Relations between speci®c pain coping strategies and outcome variables have

varied in strength across other studies (Boothby et al., 1999). Further research is needed to answer the question of what coping strategies are associated with particular disability variables in various patient populations, and to identify moderators of coping strategy effectiveness. Catastrophizing was independently associated with depression but not jaw activity limitations, and its association with activity interference was very small and not clinically signi®cant. This replicates the ®ndings of the previous study that catastrophizing was independently associated with depression but not physical disability (Turner et al., 2000). However, after controlling for all other variables, the association between catastrophizing and depression, although statistically signi®cant, was small (5% of the variance). In the previous study, catastrophizing independently explained a much larger proportion of the variance in depression (19%). This discrepancy may be due to differences in depression measures, patient populations, or other factors. Beliefs and catastrophizing explained signi®cant portions of the variance in non-masticatory jaw activity (e.g. laughing and yawning) limitations, but none of the process variables were associated with masticatory jaw activity (e.g. eating an apple) limitations, after adjusting for the control variables. This suggests that the pain-related cognitions assessed in this study play important roles in mood and general activities, but not in speci®c jaw activities associated with eating. Neither masticatory nor non-masticatory jaw dysfunction was signi®cantly associated with beliefs, catastrophizing, or coping, after adjusting for the other process and control variables. When the regression analyses were repeated without controlling for pain intensity, results were similar and in no case did a non-signi®cant association between a process variable and an outcome variable become statistically signi®cant at the 0.01 level. Correlations between pain intensity and the outcome measures were statistically significant, but not high. For example, the correlation between pain intensity and the MPI Interference Scale was 0.34. Similarly, we previously (Turner et al., 2000) found that pain intensity explained only 8% of the variance in the Roland measure of physical disability. These ®ndings indicate that across different chronic pain conditions, factors other than pain intensity play a role in how disabled a patient is by his or her pain. As shown in these and other studies, such factors may include beliefs, catastrophizing, and coping. Other important factors may include depression and social and environmental contingencies associated with pain and disability behaviors. It should be emphasized that the study participants were selected based on moderate to high pain intensity and disability levels from among patients seen in a TMD clinic. A limitation of this study is that only 63% of eligible patients agreed to participate. However, comparisons between the study participant patients and the patients who were eligible but declined to participate revealed no

J.A. Turner et al. / Pain 92 (2001) 41±51

signi®cant differences in age, sex, race, marital status, RDC Axis I diagnosis, pain duration, characteristic pain intensity, or education. This supports the generalizability of the study ®ndings to other groups of patients seeking treatment in a specialty clinic for TMD associated with moderate or greater pain and disability. A second limitation of the study is that beliefs, catastrophizing, coping strategies, interference, and depression were all assessed by self-report measures. Shared method variance may explain a portion of the associations among these measures. A particularly important issue to consider is whether the SOPA Disability Scale, the MPI Interference Scale, and the MFIQ Nonmasticatory Jaw Activities Scale all, to some extent, re¯ect a similar construct, one's beliefs about how disabled one is by pain. The SOPA Disability Scale includes items such as, `My pain problem does not need to interfere with my activity level' (reverse scored), `I consider myself to be disabled', and `I can do nearly everything as well as I could before I had a pain problem' (reverse scored). Some similar items are on the MPI Interference Scale; for example, `How much does your pain interfere with your day to day activities?' and `How much has your pain changed your ability to take part in recreational and other social activities?' On the MFIQ Nonmasticatory Jaw Activities Scale, patients rate how much dif®culty they have with social activities and work and/or other daily activities, in addition to activities that depend heavily on jaw functioning, such as laughing and yawning. Of help in resolving this issue would be studies that examine the strength of association between the SOPA Disability Scale and measures of disability obtained from sources other than self-report. For example, some studies of patients with chronic pain conditions other than TMDs have obtained observer ratings of pain behaviors or signi®cant others' ratings of patient pain behaviors and physical disability. However, a challenge is posed by the fact that TMD is not associated with the overt pain behaviors (e.g. guarding and bracing) assessed by observational measures developed for back pain and other chronic musculoskeletal pain problems. Furthermore, patients may not have signi®cant others who are with them enough to be able to provide accurate information about activity limitations or interference. In the current study, we found that the SOPA Disability Scale was not correlated signi®cantly with an objective measure of jaw opening limitation. Although this might be interpreted as evidence that the associations between the SOPA Disability Scale and the self-report measures of activity interference and non-masticatory jaw activity limitations re¯ect shared method variance or measurement of the same construct, the ®nding is also consistent with the view that pain-related beliefs and activity limitations are a function of many factors in addition to physical variables. As hypothesized in this study, no process variable was associated signi®cantly with jaw opening impairment. The failure to ®nd signi®cant associations between process variables and the objective measure of jaw impairment is

49

consistent with previous research observations of only weak relationships between psychological measures and clinical signs of TMD (Rudy et al., 1989; Dworkin et al., 1994). The current study adds to the growing body of evidence that pain reports, pain-related activity limitations, and psychological distress are poorly correlated with objective measures of physical pathology in patients with TMD (Rudy et al., 1989; Dworkin, 1995; Ohrbach and Dworkin, 1998). Another limitation of the study is that all measures were completed at the same time; thus, sequential and cause± effect relations can not be determined. Further research is needed to determine whether catastrophizing and speci®c beliefs and coping strategies predict subsequent depression and disability. Electronic diaries in which patients record information daily about their activities, mood, and painrelated cognitions and behaviors may prove useful in shedding more light on the dynamic sequential relations between these variables within and across individuals. In conclusion, there is substantial empirical evidence that the physical and psychological functioning of patients with chronic disabling TMD pain is substantially associated with patients' beliefs, catastrophizing, and coping strategies, but only weakly associated with objective measures of physical impairment. Taken together, these ®ndings suggest the possibility that interventions aimed solely at identifying and correcting physical pathology in these patients may fail to be successful, and that interventions designed to change patients' pain-related cognitions and behaviors may improve patient outcomes. Furthermore, the results of the present study suggest that for patients with TMD, it may be more important to change pain beliefs (especially that one's pain is disabling) and catastrophizing than to change the pain coping strategies measured in this study (e.g. coping self-statements and attention diversion). The results raise the intriguing possibilities that for patients with chronic disabling TMD, (1) changing these coping strategies provides no bene®t beyond that provided by changing beliefs and catastrophizing, (2) changing catastrophizing adds little bene®t beyond that provided by changing beliefs, and (3) the belief that one's pain is disabling is particularly crucial. Certain behaviors not assessed in this study but commonly addressed in TMD treatment (e.g. clenching, gum chewing, and telephone posture) may also be important and should be assessed in future research. Further research is recommended to test these hypotheses and to re®ne cognitive-behavioral therapies that are maximally effective in modifying critical patient beliefs and behaviors.

Acknowledgements Support for this research was provided by the National Institute of Dental and Craniofacial Research (NIDCR # DE-08773 and P01 DE08773). Appreciation is expressed to Gayle Garson for data management and to Craig Sawchuk

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