In this article, we examine data from a large, population-based study of people who filed collision-related personal injury claims to report the frequency of reduced or painful jaw movement after an injury related to a collision; to identify personal characteristics, crash-related factors and postinjury symptoms associated with the onset of reduced or painful jaw movement in claimants with WADs; and to report the duration of postinjury jaw pain in claimants with WADs.

	SUBJECTS AND METHODS

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Study population and design. The study population has been described in detail elsewhere.^9–11 Briefly, it included all Saskatchewan adults, 18 years or older, who filed a claim with Saskatchewan Government Insurance Corp. (SGI) for a collision-related injury that occurred between July 1, 1994, and Dec. 31, 1995. SGI is the only insurer for people who have had motor vehicle injuries in Saskatchewan, a Canadian province of approximately 1.1 million residents. Thus, the study population included all Saskatchewan residents filing a collision-related injury claim during the study period.

Of the 10,902 potentially eligible people with claims during the 19-month study period, we excluded the following from our study population: fatalities (n = 292), those unable to complete the questionnaires because of an English-language barrier (n = 81), those with serious injuries (for example, severe brain injury, n = 69) or serious unassociated illnesses (for example, Alzheimer’s disease; n = 38), those eligible for compensation through workers’ compensation rather than SGI (n = 113), those with more than one injury claim during the study period (n = 86) and those whose lawyers advised them against completing the claim form (n = 207).

Another 1,010 claims were incomplete because the person decided not to proceed with the initial claim. Of the remaining 9,006 personal injury claims, we excluded those for people who were hospitalized for more than two days owing to the collision (these people were judged to have had more serious injuries; n = 525) and nonautomotive claims (for people injured as a pedestrian, bicyclist or motorcyclist; n = 357), because the mechanism of injury in these cases was likely to be different from that in motor vehicle collisions.

Of the remaining 8,124 claims, 7,462 met our case definition for WAD in that the subject answered "yes" to the questions, "Did the accident cause neck or shoulder pain?" and "Have you felt neck or shoulder pain?" and/or "Have you felt reduced or painful neck movement since the accident?"

Design and sources of data. All data gathered in this study were self-reported. We obtained baseline information for this study from insurance claims forms (with the subjects’ names and addresses removed), which asked questions about demographic and socioeconomic characteristics, self-reported health status before the collision, details of the collision and the subject’s position in the vehicle, postcollision symptoms, and pain extent and intensity. Although there was no time limit for completing the insurance claim form, more than 80 percent of claimants completed the form within one month of their injury. We mailed questionnaires, which asked questions about symptoms and pain, at six weeks after the injury and at four, eight and 12 months to those consenting to participate in follow-up. The study was approved by the University of Saskatchewan’s Advisory Committee on Ethics.

	MEASURES

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Outcome. The outcome for this study was self-reported jaw pain after the collision, as assessed by a question on the baseline questionnaire (that is, the claims form) about the presence of reduced and/or painful jaw movement after the collision. We repeated this question in each follow-up questionnaire.

The outcome for this study was self-reported jaw pain after the collision.

Explanatory factors. All explanatory factors (such as age, sex) were self-reported. Demographic and socioeconomic factors included sex, age, marital status, education and family income. Precollision health-related factors were body mass index (calculated from weight and height), precollision general health, and answers to questions about previous presence and frequency of headaches, low back pain, neck pain, ache/pain in the jaw, general bodily discomfort, fatigue, sleep problems, depression, anxiety, memory problems, anger, frustration and fear. We assessed the following factors related to the collision: the direction of the main impact to the vehicle (such as front, side), whether a rollover occurred, the type of road (city street, rural road, highway, other) on which the collision took place, whether the vehicle was stopped at the time of the collision, seatbelt use, headrest use, head position at the time of the collision and whether the vehicle was drivable after the collision.

The questionnaire asked subjects if they had hit their head and/or lost consciousness in the collision, if they experienced broken bones in the collision and if they had been admitted to a hospital and stayed overnight after the collision. Postcollision symptoms included numbness or tingling in the arms or hands, numbness or tingling in the legs or feet, dizziness, nausea, difficulty swallowing, ringing in the ears, memory problems, visual problems, presence of low back pain and presence of dorsal back pain. Subjects marked the extent of their pain on a pain drawing of a mannequin. Using this drawing, we then calculated the percentage of the body that was in pain. In addition, subjects used a 100-millimeter visual analogue scale (VAS) to mark their neck pain, headache and other pain intensity.^12,13

Statistical analysis. We determined the overall and sex-specific prevalence and incidence of jaw pain after the collision. For the incidence proportions, we formed a cohort of subjects at risk of experiencing the onset of jaw pain by excluding people who reported having had jaw pain before the collision. Incident cases were those in subjects without prior jaw pain who reported having reduced and/or painful jaw movement after the collision. Table 1 presents the characteristics of all whiplash claimants with and without previous jaw pain. Incident cases are described in Table 2 (page 91).

	RESULTS

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All subjects. This group includes all subjects, regardless of their history of jaw pain. Of the 8,109 people meeting our inclusion criteria and responding to the question about postcollision jaw pain, 1,329 (16.4 percent) (95 percent confidence interval [CI], 15.6 to 17.2) reported experiencing prevalent reduced and/or painful jaw movement after the collision (12.4 percent in men and 19.1 percent in women). The incidence of new onset of reduced and/or painful jaw movement in the 7,763 subjects who reported never or almost never having experienced jaw pain before the collision was 14.9 percent (n = 1,158; 95 percent CI, 14.1 to 15.7). The incidence was higher in women (17.2 percent) than in men (11.6 percent).

Subjects with WADs. The prevalence of reduced and/or painful jaw movement in the subcohort of 7,452 subjects meeting our case definition for WAD and responding to the postcollision jaw pain question was 17.4 percent (n = 1,295; 95 percent CI, 16.5 to 18.3); again, the prevalence was higher in women (20.0 percent) than in men (13.2 percent). After we excluded those with pre-existing jaw pain, 1,128 (15.8 percent) of 7,127 subjects (95 percent CI, 15.0 to 16.7) reported experiencing new onset of reduced and/or painful jaw movement after the collision. The incidence was higher in women (18.4 percent) than in men (12.4 percent). By comparison, the incidence in claimants without WAD was 4.7 percent (n= 30 of 636; 95 percent CI, 3.2 to 6.7), which means that WAD claimants had 3.36 times greater risk (95 percent CI, 2.36 to 4.78) of experiencing reduced and/or painful jaw movement after the collision than did injured claimants without WAD. Table 1 presents the characteristics of WAD claimants with and without new onset of reduced and/or painful jaw movement.

Factors associated with postcollision onset of reduced and/or painful jaw movement in WAD claimants. Table 3 lists the factors associated with incident jaw pain in WAD claimants. Women were almost 50 percent more likely than men to experience the onset of jaw pain after a collision, and people older than 50 years were 35 percent less likely, even after we adjusted for all other factors in the model. People with greater pain were slightly more likely to report experiencing postcollision onset of jaw pain. For each additional percentage of body pain, the risk of experiencing onset of jaw pain rose by 1.8 percent, and for each additional point in pain intensity (on a 100-mm VAS), the risk of experiencing jaw pain rose by 0.4 percent for neck pain intensity and by 0.6 percent for headache intensity. People reporting difficulty with swallowing after the collision were 3.75 times more likely to also experience onset of jaw pain, and those with ringing in the ears were twice as likely to report experiencing jaw pain.

Recovery from jaw pain. In the subcohort of 1,128 people with incident jaw pain after the collision, the median time for this symptom to resolve was 120 days (95 percent CI, 113 to 128). Of this subcohort, 497 (44.1 percent) participated in at least one follow-up questionnaire. Participation was not associated with the presence of jaw pain. Participants in follow-up questionnaires were more likely to be women, to have a high school education or greater and to have had very good or good health before their injury. Homemakers, divorced or widowed people, those who consulted a lawyer before filing their insurance claim and those with greater headache pain were less likely to participate in follow-up questionnaires (Table 3).

Of those who participated in at least one follow-up questionnaire, 236 (47 percent) reported that they no longer experienced jaw pain at six weeks, and by four months, 348 (70 percent) of those with new jaw pain after the collision reported experiencing complete resolution of this symptom. By the end of the one-year follow-up period, 390 subjects (78 percent) reported that they had recovered, 51 (10 percent) reported experiencing continued reduced and/or painful jaw movement and the remainder dropped out of the study before recovering.

	DISCUSSION

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This is the first population-based survey, to our knowledge, to examine the occurrence of the main symptom of TMD: namely, reduced or painful jaw movement after a collision-related whiplash injury. Although only 4.3 percent of the subjects reported having experienced jaw pain before the collision, more than 15 percent of claimants reported experiencing this symptom within the first few days of the collision, with women having a higher rate of both preinjury and postinjury jaw pain.

Our finding that female sex is a risk factor for jaw pain after a collision causing whiplash injury is consistent with the results in other reports.^3–5 Subjects older than 50 years reported having less jaw pain before the collision and were 35 percent less likely than younger subjects to report experiencing the onset of this symptom after the collision. Previous health had little influence on the risk of experiencing jaw pain after a collision, although those who reported having hit their head in the collision were almost 40 percent more likely to report experiencing new onset of jaw pain after the collision than were those who did not hit their head.

As might be expected, people who developed reduced and/or painful jaw movement after the collision also reported having concurrent symptoms of difficulty swallowing and ringing in the ears. However, despite greater frequency of these and other postcollision symptoms in those reporting onset of jaw pain after the collision, the association between pain intensity and the onset of jaw pain is equivocal. Although mean pain scores were higher in those reporting jaw pain after the collision, the size of the effect was less marked after we adjusted for other factors in the multivariable model. Although still statistically significant, increases in headache and neck pain intensity were associated with only very small increases in the likelihood of experiencing new onset of jaw pain.

Study strengths and limitations. Our study has several important strengths. First, we used a large, unselected sample of claimants with collision-related injuries. Because there is only one insurer in Saskatchewan for collision-related injuries, we were able to ascertain the eligible subjects completely. Selection bias is reduced further by the fact that our baseline data are from the insurance claims form, which was filled out by everyone filing a personal injury claim. It is possible that some people with whiplash injuries did not file a personal injury claim, but these likely would have been trivial injuries, because all people seeking health care after a collision-related injury were included. There were no barriers to obtaining health care, because Saskatchewan has universal health care coverage. In addition, we had access to a large range of potential explanatory factors through the insurance claims form.

However, our data regarding jaw pain were self-reported and we did not have clinical diagnoses of TMD. Therefore, we can make inferences only about self-reported jaw pain rather than TMD as a clinical finding. If over-reporting of symptoms occurred, our incidence estimate would be inflated.

Recovery. Recovery from jaw pain appears to be good, with almost one-half of the people participating in follow-up reporting no longer having jaw pain within six weeks of their injury, and almost 80 percent recovering during the course of the one-year follow-up. These recovery findings should be interpreted cautiously, however, because only 44.7 percent of the eligible cohort participated in follow-up, thus introducing the likelihood of selection bias. In addition, we have no information with regard to the proportion of participants with jaw pain who sought treatment for this symptom, and what impact such treatment might have had on the course of jaw symptoms after the injury.

Heise and colleagues¹⁴ were among the first to question the tendency to associate a cervical musculoskeletal injury with the development of TMJ dysfunction. In a study of 155 patients who had sustained whiplash injuries in motor vehicle collisions, these authors found no clinical evidence of a significant relationship between cervical musculoskeletal injury and the development of TMJ dysfunction. In addition, a previous study of another Canadian sample suggested that jaw pain is relatively uncommon (prevalence < 5 percent) in the general population, and our findings of jaw pain before an injury (4.3 percent) support these data.¹⁵

We found that after a motor vehicle collision resulting in whiplash injuries, 17.4 percent of people reported experiencing jaw pain in the collision; among those with no history of jaw pain, 15.8 percent reported experiencing jaw problems after the collision. Although reduced or painful jaw motion does not necessarily equate with a diagnosis of TMD, it is one of the primary symptoms of TMD and suggests that whiplash injuries in a motor vehicle collision are associated with TMD.

Factors listed in Table 2 were statistically significant in the multivariable logistic model at P < .05. Other factors included in the model but not reported above (that is, a crude relationship of P < .10, but not statistically significant in the multivariable model) were family income, position in the vehicle, direction of impact to the vehicle, use of a seatbelt, use of a headrest, broken bones, filing a claim under the tort or no-fault system, percentage of body in pain, neck pain intensity and pain intensity in other parts of the body. Other factors considered, but with a univariate relationship of P > .10, were age, hitting one’s head in the collision, crash involving a rollover, whether the vehicle was drivable after the collision, head position at the time of impact, admission to a hospital and loss of work time due to the injury.

	CONCLUSION

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We found that reduced and/or painful jaw movement was more common after a collision-related whiplash injury than after other collision-related injuries. Within WAD injuries, jaw pain after a collision was slightly more frequent among those with a history of jaw pain than among those without such a history. However, although jaw pain was a common symptom after a whiplash injury, almost one-half of people affected had recovered from this symptom within six weeks of their injury, and 70 percent had recovered from jaw pain within four months of their injury. By one year, however, 10 percent of those affected had not recovered from their injury.

Further research is needed to identify people at risk of experiencing poor recovery of reduced and/or painful jaw movement after a whiplash injury so that clinicians can target them for effective intervention.