I am 31 years old and have suffered from TMD since I was 8 years old. My jaw cracks and pops, and I live with almost constant pain. My jaw is stiff and sensitive to the touch. The tension and pain often causes neck pain, tension headaches, and migraines. My jaw often causes so much discomfort while I am eating that I have to stop or avoid certain foods altogether. I have tried soft food diets and pain medication, but it is a daily struggle. The lack of appropriate care and knowledge about the disorder make it difficult to live with.
This chapter reviews temporomandibular disorders (TMDs) from a public health perspective—examining the individual and societal burdens of living with a TMD.1 The chapter begins by summarizing TMD prevalence estimates (i.e., the number of TMD cases present in a population at a given time) for adults and children based on nationally representative population-based studies of the United States (and other countries) as well as examples from smaller regional or clinic-based surveys using more extensive assessments of TMD symptoms. These studies highlight the large, often two-fold or greater, differences in the prevalence of TMD symptoms commonly found across demographic groups by factors such as age, sex, and ethnicity.
1 This chapter draws on a paper commissioned by the Committee on Temporomandibular Disorders (TMDs): From Research Discoveries to Clinical Treatment on “Prevalence, Impact, and Costs of Treatment for Temporomandibular Disorders,” by Gary Slade and Justin Durham (see Appendix C).
Incident TMD (i.e., the rate at which new cases develop) is also reviewed, but those estimates are based on relatively few studies. Following this, the individual and social burdens of TMD are reviewed, again demonstrating the scarcity of research in this area. Finally, the chapter closes with a summary of what is known about TMD risk factors and how TMDs fit into the larger multi-system schema and other comorbidities.
The national prevalence of TMDs is difficult to estimate due to challenges in conducting clinical examinations on a large scale, such that most prevalence data are based on self-reported symptoms associated with TMDs rather than examiner-verified classification. For example, one analysis found that an estimated 11.2 to 12.4 million U.S. adults (4.8 percent of the population) in 20182 had pain in the region of the temporomandibular joint (TMJ) that could be related to TMDs (Slade and Durham, 2020). Orofacial pain symptoms may or may not be related to TMDs. These self-reported symptoms of pain in the TMJ region are not equivalent to an examiner-verified diagnosis but rather indicate the possibility of an underlying TMD being present. As discussed in Chapter 2, TMDs represent a range of diverse and multifactorial disorders that can affect individuals across the general age range of adolescence to elderly and that can have significant impacts on an individual’s health and quality of life.
Prevalence estimates of TMDs also delineate the wide range in the extent of the severity and impact of these disorders on individuals—some individuals with a TMD have an intermittent or treatable manifestation of the disorder, whereas others suffer from more severe disorders that are often intractable, persistent, and lead to significant impairment and disruption of life. By some estimates, up to 40 percent of patients with signs and symptoms of a TMD will have their symptoms resolve spontaneously (Scrivani et al., 2008). Sounds in the TMJ and deviation on opening the jaw appear
2 The prevalence estimate takes into account the survey sampling variability. The estimate is based on 2017–2018 National Health Interview Study (NHIS) data. These data are self-reported and therefore there are limitations in the data in the form of recall bias, the lack of examiner-verified diagnosis, and the fact that children, individuals in assisted living facilities, military personnel, and the incarcerated are not included in the NHIS survey population. It is also the case that the NHIS survey question related to orofacial pain symptoms is not specific to TMD and lacks the specificity to rule out non-TMD conditions. Given that many individuals may have intermittent pain that does not progress to a diagnosed TMD, the NHIS question about whether an individual experienced pain in the temporomandibular joint region for one whole day may lead an overestimation of individuals with orofacial pain. However, major health surveys such as NHIS are common sources for estimating the national or state-level prevalence of various diseases and behaviors, and the committee believes this prevalence estimate provides a valid analysis using some of the best national data available.
frequently (approximately 50 percent of the population) and are considered normal and not requiring treatment. More concerning signs and symptoms include decreased mouth opening and occlusal changes (approximately 5 percent of the population) (Scrivani et al., 2008). A complex pattern of change in biopsychosocial function is often associated with changes in TMD status (Ohrbach and Dworkin, 1998; Fillingim et al., 2018). Aside from broad patterns observed across individuals experiencing a TMD, little is known about the immediate period of painful TMD onset, the subsequent period for some individuals when acute pain transitions to chronic pain, or the later stage when chronic pain either improves or continues.
TMDs are part of the larger burden of pain. Chronic pain is estimated to affect approximately 50 million to 100 million adults in the United States (IOM, 2011; Dahlhamer et al., 2018). Annual national costs associated with chronic pain were estimated to be $560 billion to $635 billion in 2011 (IOM, 2011). The prevalence of other common chronic pain conditions such as fibromyalgia (Clauw, 2014), chronic low back pain (Meucci et al., 2015), and migraine (Burch et al., 2018) is likely comparable to that of pain in the area of the TMJ in U.S. adults. While there are limitations in comparing the relative magnitude of painful conditions (e.g., how the question was asked of study or survey participants), the committee believes estimates of the prevalence of orofacial pain or TMD symptoms place TMDs well within the context of other highly prevalent conditions and therefore demanding equal attention and care in addressing the burden of TMDs.
High-Impact Pain and TMDs
While existing data demonstrate that TMDs are highly prevalent, it is also important to consider the severity of TMD symptoms and their impact on daily life and function. Velly and colleagues (2011) recruited a mixed community-based and clinical sample of 480 adults in the Minneapolis/St. Paul, Minnesota, area with muscle or joint pain due to a TMD. At baseline, 42 percent of individuals reported high pain intensity, but only 12 percent of the sample reported higher levels of disability. At 18-month follow-up, 26 percent of the sample reported high pain intensity, and 6 percent reported higher levels of disability. Another study, which recruited 399 patients seeking care for a TMD, found that 61 percent reported no disability, 27 percent low disability, and 12 percent high disability (Kotiranta et al., 2015).
More recently, data from the Orofacial Pain Prospective Evaluation and Risk Assessment (OPPERA) study investigated the prevalence and predictors of high-impact pain among 846 people with a TMD (Miller et al., 2019). High-impact pain was defined as either having high pain intensity and low pain-related interference or having moderate to high levels of
self-reported, pain-related interference. They found that approximately one-third of the study population had high-impact pain, and individuals with high-impact pain showed greater limitations in jaw function, higher pain sensitization, and greater tenderness to palpation of multiple body sites. According to 2016 NHIS data of 42,370 adult participants, the prevalence of high-impact chronic pain was also elevated nearly four-fold (26.9 percent versus 7.0 percent) in people with orofacial pain symptoms (Slade and Durham, 2020). The TMJ may be part of a constellation of anatomic sites of high-impact chronic pain with possibly shared underlying etiology and resulting in moderate to severe pain and some level of pain-related disability for some individuals with a TMD.
Challenges Estimating TMD Prevalence
The prevalence of pain conditions such as TMDs is usually measured in cross-sectional health surveys that ask respondents about pain symptoms that are characteristic of the particular condition—in this case, TMDs. In some instances a clinical evaluation will also be conducted, with the goal of properly distinguishing pain symptoms caused by a TMD from pain symptoms caused by other types of pathology. The primary requirements for the valid estimation of TMD prevalence are a selection of a representative sample of study participants from the target population of interest; accepted case definitions based on valid and reliable questions or examination methods to classify the presence or absence of TMD pain in each study participant; and sufficient numbers of study participants to estimate the prevalence with reasonable precision. The literature reporting the prevalence of TMDs varies substantially across studies, with much of the variability attributable to differences in the methodologies used, particularly differences in case definitions (see Chapter 2 for an overview of the issues and evolution of research and diagnostic criteria used to establish case definitions for TMDs) and study populations. Sampling strategies vary considerably, ranging from large population-based studies using form survey sampling methodology to convenience samples from small clinical populations. Moreover, TMD prevalence varies as a feature of demographic factors such as age, sex, race, and ethnicity, which makes clear the need for reporting findings within demographic strata. Given these issues, making valid comparison of prevalence estimates across studies must be done with careful attention to underlying methodological differences.
Conclusion 3-1: The prevalence of temporomandibular disorder (TMD) symptoms varies widely across studies depending on the assessment used and the population studied. Based on one analysis of 2017–2018 data, an estimated 4.8 percent of U.S. adults
(an estimated 11.2 to 12.4 million U.S. adults) had pain in the region of the temporomandibular joint that could be related to TMDs. Based on this information, it is likely that TMDs are the most prevalent type of chronic orofacial pain and TMDs may be comparable in prevalence to other chronic pain conditions such as fibromyalgia, chronic low back pain, and migraine disease.
Prevalence of TMDs in Adults
National Population-Based Studies
NHIS is a federally sponsored recurring survey that provides nationally representative measures of many health conditions, along with health-related behaviors and socio-demographics. The NHIS uses rigorous sampling methodology to collect data annually from approximately 87,500 civilian, non-institutionalized persons. In most of its annual surveys conducted since 1987, orofacial pain symptoms have been assessed using a single-item question asked of all respondents age 18 years or older:
The following questions are about pain you may have experienced in the PAST <REFERENCE PERIOD>. Please refer to pain that LASTED A WHOLE DAY OR MORE. Do not report aches and pains that are fleeting or minor. During the PAST <REFERENCE PERIOD>, did you have facial ache or pain in the jaw muscles or the joint in front of the ear?
This question serves as the assessment tool for TMDs for NHIS surveys. A limitation of this assessment tool is that it lacks sufficient specificity to rule out other non-TMD conditions that can present with similar symptoms (e.g., other orofacial pain conditions), likely leading to an overestimation of TMD prevalence. It may also miss non-painful TMDs and will not reflect the various types of TMD an individual may have (see Chapter 2 for an overview of TMD types).
The period prevalence of occurrence of at least 1 day of symptoms depends on the timeframe over which the respondents are asked about having a 1-day episode of symptoms. In 1989, when the reference period was 6 months, the period prevalence3 of at least 1 day of TMD symptoms in the U.S. adult population was 6.0 percent (see Appendix C). In subsequent years, the reference period was reduced to 3 months, resulting in somewhat lower prevalence estimates, ranging from 4.3 percent in 1999 to 5.2 percent
3 Period prevalence is the proportion of a population that has the condition at some time during a given period (e.g., 12-month prevalence), and includes people who already have the condition at the start of the study period as well as those who acquire it during that period.
in 2018, a numerical difference that is not statistically different. Overall, the findings represent a fairly consistent period prevalence over the past 20 years.
Socio-Demographic Variation in Prevalence of TMD Symptoms (NHIS 2017–2018)
The NHIS collects extensive data about socio-demographic characteristics, other health conditions, and the health care usage of study participants, making it possible to examine cross-sectional variations in the prevalence of TMD symptoms (pain) according to those characteristics. However, it should be emphasized that any observed cross-sectional associations do not necessarily signify a causal relationship, in either direction, between those characteristics and TMD symptoms.
In 2017–2018 the 3-month period prevalence of orofacial pain symptoms, according to the NHIS wording, differed appreciably according to age, gender, race, and income (see Table 3-1; see Appendix C). Specifically, prevalence was elevated approximately two-fold in females compared to males, whites compared to Asian Americans, and individuals in low-income households compared with those in high-income households. There was an inverted-U relationship with age, with prevalence greatest in 45- to 54-year-olds and lower in both the youngest (18 to 24 years) and oldest age groups. In contrast, the prevalence did not vary appreciably according to ethnicity or geographic region.
Prevalence of TMD Symptoms According to Health Care Usage and Other Pain Conditions (NHIS 2017–2018)
In 2017–2018 the prevalence of orofacial pain symptoms tended to be greater among people who had used health care in the preceding year than among those who had not (see Table C-3 in Appendix C). Specifically, there was an approximately two-fold higher orofacial pain symptom prevalence associated with having seen a physical or occupational therapist, chiropractor, or medical specialist and a 1.5-fold higher orofacial pain symptom prevalence associated with having seen a general physician. In contrast, the prevalence of orofacial pain symptoms did not differ according to whether participants had seen a dentist within the preceding year. It must be emphasized that the 2017–2018 surveys did not inquire as to the reasons for health care visits or, in particular, whether people with orofacial pain symptoms sought health care because of those symptoms.
Larger differences in prevalence were seen relative to the presence of other pain conditions (i.e., other than orofacial pain symptoms; see Table C-3 in Appendix C). People reporting headache or pain symptoms
TABLE 3-1 Socio-Demographic Characteristics Associated with Orofacial Pain Symptom Period Prevalence in U.S. Adults, 2017–2018
|Population Group||% of Population||TMD Prevalence*
(%, 95% CL)
|All adults||100.0||4.8 (4.5, 5.0)|
|18–24||11.8||4.2 (3.5, 5.0)|
|25–34||17.8||4.9 (4.3, 5.4)|
|35–44||16.4||5.2 (4.6, 5.8)|
|45–54||16.7||5.4 (4.9, 6.0)|
|55–64||16.8||5.1 (4.6, 5.7)|
|65–74||12.1||3.7 (3.3, 4.2)|
|Female||51.7||6.2 (5.9, 6.6)|
|Male||48.3||3.2 (2.9, 3.5)|
|Northeast||17.8||4.4 (3.8, 4.9)|
|Midwest||21.9||4.9 (4.3, 5.4)|
|South||36.6||4.5 (4.1, 4.9)|
|West||23.7||5.4 (4.9, 5.9)|
|White||77.7||5.0 (4.8, 5.3)|
|Black/African American||12.4||3.6 (3.0, 4.2)|
|Native American||1.2||4.1 (2.8, 5.5)|
|Asian||6.4||3.0 (2.3, 3.7)|
|Other/multiple||2.4||7.1 (5.4, 8.8)|
|Hispanic||16.2||4.4 (3.8, 5.0)|
|Not Hispanic||83.8||4.8 (4.6, 5.1)|
|<1.0||10.4||7.3 (6.5, 8.2)|
|1.0–<2.0||16.1||5.9 (5.3, 6.5)|
|2.0–<4.0||26.6||4.8 (4.4, 5.2)|
|≥4.0||40.5||3.7 (3.3, 4.0)|
|Unknown||6.4||4.5 (3.6, 5.4)|
NOTE: CL = confidence limit.
*Jaw or face pain that lasted ≥1 day in the 3 months preceding the NHIS interview. From the author’s analysis of data from n=52,159 participants in the 2017–2018 NHIS surveys.
SOURCE: Appendix C.
in the neck, back, or joints had at least three times the prevalence of orofacial pain symptoms as people without those respective symptoms (see Table C-3 in Appendix C). Using a simple count of those four body pain symptoms, the 3-month period prevalence of orofacial pain symptoms was 32.4 percent among people with all four body pain symptoms, compared with 1.1 percent among people with no body pain symptoms.
Smaller regional studies of TMD prevalence have used varying assessment methods and case definitions. For example, Manfredini and colleagues (2011) conducted an analysis that included 21 papers, 15 of which dealt with populations of patients with a TMD who underwent clinical examination and 6 of which examined community-based samples. The studies of patient populations reported an average prevalence of 45.3 percent for TMD-related muscle disorder diagnoses, 41.1 percent for disc displacements, and 30.1 percent for TMD-related joint disorders. Results from the community studies showed an overall 9.7 percent prevalence for muscle disorder diagnoses. The prevalence estimates by subtypes of TMD diagnoses showed substantial variation across these diagnostic groups.
Due to their similarities to U.S. populations, results from regional studies in Canada are worth examining. Using formal sampling methodology, Locker and Slade (1988) assessed TMD-associated symptom prevalence in adults 18 years and older in Toronto, Canada. Using a self-reported measure of pain in the region of the TMJ (i.e., “pain in front of the ear”), they reported a prevalence of 5.0 percent among men and 9.5 percent among women, whereas functional pain (i.e., “pain while chewing”) was similar between men and women, at 7.4 percent and 7.7 percent, respectively. No difference in pain measures was found between the younger (<45 years of age) and older (≥45 years of age) age groups. When study participants were given a list of nine questions about TMD symptoms, 48 percent endorsed at least one symptom, with joint sounds, tiredness or stiffness of jaw muscles, and an uncomfortable bite being most common (Locker and Slade, 1988). A telephone survey of a representative sample of the French-speaking population of Quebec (Goulet et al., 1995) reported a similar overall prevalence among men (5 percent) and women (9 percent), with no age trend noted for either group. Frequent episodes of TMJ clicking and difficulty in jaw opening were found in 9 percent and 4 percent of the respondents, respectively.
Prevalence of TMDs in Children and Adolescents
Reports of the prevalence of TMDs in children and adolescents vary widely. A systematic review (Christidis et al., 2019) that included six studies (List et al., 1999; Nilsson, 2007; Wu and Hirsch, 2010; Franco-Micheloni et al., 2015; Al-Khotani et al., 2016; Graue et al., 2016) reported prevalence in children or adolescents based on clinical evaluations using the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) or the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) measures (see Table 3-2). Overall prevalence estimates ranged from 7.3 percent to 30.4 percent. A systematic review by da Silva and colleagues (2016), which was also based on the use of the RDC/TMD and which included a clinical evaluation, reported the results from 11 studies from 8 countries. The prevalence estimates ranged from 4.0 percent to 42.7 percent. The meta-analysis associated with this study reported an overall prevalence across all 11 studies of 16 percent, with clicking and jaw locking being the most commonly reported symptoms. There was no overlap in the included studies between the da Silva and colleagues’ (2016) and Christidis and colleagues’ (2019) systematic reviews.
Studies of the prevalence of TMDs among children have reported mixed results on gender differences, with some studies reporting no difference in prevalence (LeResche, 1997; List et al., 1999; Magnusson et al., 2005; Köhler et al., 2009; Marpaung et al., 2019). Care seeking and pain intensity were reported to be higher among girls. There is evidence that the prevalence of TMDs in children and adolescents increases with age (Magnusson et al., 2005; Köhler et al., 2009; da Silva et al., 2016; Marpaung et al., 2019). One study reported that pain severity was greater in older than in younger adolescents (Howard, 2013).
Determining the incidence (i.e., the rate at which new cases develop) of TMDs requires longitudinal (cohort) studies, where individuals are followed over time and their symptoms assessed periodically. No nationally representative cohort studies of TMD have been reported. Incidence data, consequently, comes from smaller, community-based studies such as the OPPERA study. This study provides the latest and best estimates to date of the incidence of TMDs (see Box 3-1 for an overview of the OPPERA study).
Early Studies of TMD Incidence
Prior to the OPPERA study, investigators at the North Carolina study site conducted a 3-year prospective cohort study of women age 18 to 34
TABLE 3-2 Prevalence of TMDs in Children and Adolescents from Six Studies
|Reference||Number of Participants||Age Interval (mean age in years)||Girls/Boys (%)||Prevalence of TMDs (%)||Self-Reported TMD Pain (%)||Most Common Diagnosis|
|Al-Khotani et al., 2016||456 (GP)||10–18 (14.0)||59.6/40.4||27.2||32.2||Myofascial pain|
|Franco-Micheloni et al., 2015||1307 (GP)||12–14 (12.72)||43.2/56.8||30.4||—||Myofascial pain|
|Graue et al., 2016||167 (DC)||12–19||51.0/49.0||11.9||7.2||Disc displacement with reduction|
|List et al., 1999||862 (DC)||12–18||45.5/54.5||7.3||11.0||Myofascial pain|
|Nilsson, 2007||28899 (DC)||12–19 (15.3)||47.9/52.1||—||4.2||Myofascial pain|
|Wu and Hirsch, 2010||561 (DC) German||13–18 (15.7)||50.1/49.9||13.0||16.0||Disc displacement with reduction|
|497 (DC) Chinese||13–18 (15.7)||50.9/49.1||14.9||19.7|
NOTES: DC = dental clinic; GP = general population. The prevalence of TMD was determined according to the RDC/TMD or DC/TMD. In the study by Wu and Hirsch there were 561 German participants and 497 Chinese participants.
SOURCE: Christidis et al., 2019.
years at the time of enrollment (Slade et al., 2007). When a participant was enrolled, examiners verified that she did not have TMD, and symptoms were monitored during follow-up with quarterly questionnaires. Any symptomatic subjects were re-examined to determine the incidence of examiner-classified TMD. The annual incidence rate that this approach yielded was 3.5 percent.
In a prospective cohort study of 11-year-olds who were enrollees in the Group Health Cooperative in Washington State, 6.8 percent developed examiner-verified TMD during the 3-year follow-up period, for an annualized incidence rate of 2.3 percent (LeResche et al., 2007). Study participants were monitored during the follow-up period using quarterly questionnaires to screen for new symptoms of TMDs, similar to the methodology used in the OPPERA study. The incidence rate in adolescents was nearly twice as high in female as males, and it was greater in whites than in other racial groups. Among the strongest predictors of elevated incidence was the presence of other pain conditions at baseline (i.e., headache, back pain, and stomach pain).
Adult enrollees in the same health maintenance organization who had first been enrolled in 1986 were also followed prospectively and re-interviewed after 3 years, with no intervening surveys (Von Korff et al.,
1993). Among those subjects who had no history of a TMD when enrolled, 6.5 percent reported TMD symptoms 3 years later.
Another community-based study (Plesh et al., 2012) reported a similar overall annual incidence (3.9 percent) of facial pain in a biracial cohort; the prevalence and incidence were higher in white women than in black women.
TMD Incidence in the OPPERA Study
In the OPPERA prospective cohort study, facial pain symptoms were assessed by questionnaire once every 3 months among 2,719 adults aged 18 to 44 years who had no history of a TMD when enrolled (Slade et al., 2013c). During the median 2.3-year follow-up period, one-third of cohort members developed at least one symptom episode (e.g., facial pain for ≥5 days per month for ≥1 month during a 3-month reporting period). This represented an initial symptom rate of 18.8 episodes per 100 people per annum. For those who developed one such episode, the rate of recurrence doubled, and it doubled again in the follow-up of those with recurrent symptoms. For one-quarter of the episodes, symptom severity was rated as 7 or higher using a 0 to 10 rating scale, consistent with “severe” clinical pain (Slade et al., 2013c).
A large majority of these symptom episodes were subclinical, in that a subsequent examination found that the episode in question did not meet the criteria for a clinical TMD, as determined using the RDC/TMD (Slade et al., 2013c). These criteria are both the self-reported symptom episodes, as defined in the preceding paragraph, and examiner findings of arthralgia (i.e., pain in the TMJ) during jaw maneuver or digital palpation or myalgia (i.e., pain during jaw maneuver or digital palpation in ≥3 of 8 muscle groups, each assessed bilaterally: temporalis, masseter, lateral pterygoid, submandibular) or both. The annual incidence rate of clinically classified TMD was 3.9 percent per annum, which was one-fifth of the rate of symptom onset (Slade et al., 2013a). This discrepancy in rates is one reason that the impact of TMD in the community at large represents a “symptom iceberg,” a term referring to symptoms that are not managed by health care professionals (Slade et al., 2013c, 2016).
Stated another way, the 3.9 percent per annum rate of examiner-classified TMD means that for every 100 TMD-free people enrolled, nearly 4 individuals per year developed the condition. Among those who became symptomatic and were found to have an examiner-classified TMD, pain occurred as a singular episode in 12.3 percent, as a recurrent episode in 65 percent, and as a persistent episode in 19.2 percent. Among all incident cases in the OPPERA study, pain was most commonly reported as arthralgia and myalgia (73 percent of the incident cases); the next most
common presentation was myalgia alone (23 percent of incident cases). The incidence was greater in the older age groups, but it did not vary significantly by gender. With respect to race and ethnicity, there was a three-fold greater incidence in the highest group (blacks) than in the lowest (Asians). The threshold for incident case classification was ≥5 days with TMD pain symptoms per month over more than 1 month during a 3-month reporting period (Slade et al., 2013a).
From the original group of 260 people with first-onset TMDs, 147 were re-examined 6 months later, and 49 percent of those (n=72) had persistent TMDs and 51 percent (n=75) had transient TMDs (Meloto et al., 2019). Persistence of symptoms was more likely in the younger age groups, in females, and in non-Hispanic whites. Several other characteristics were also predictive of persistence, including clinical pain and the degree of limitation in jaw opening. However, DC/TMD psychosocial variables did not improve the ability to predict an individual’s risk of developing a persistent TMD (Meloto et al., 2019).
Data Collection Challenges and Opportunities: Prevalence and Incidence Studies
The overall prevalence estimates from the NHIS have been consistent for decades and suggest that additional cross-sectional national surveys of TMDs (when defined as symptoms related to facial pain) are unlikely to result in substantially different findings. As with many other studies there are limitations in the NHIS datasets:
- The data are self-reported and subject to recall bias.
- The data are cross-sectional, precluding causal inferences. This may be particularly relevant for many of the associated factors such as socioeconomic status, which can be both a risk factor for TMDs and a result of TMDs.
- There was no TMD treatment information to assess the prevalence of TMDs among those with and without treatment.
- NHIS excludes important populations, including active-duty military, residents of long-term care facilities or prisons, and children.
As made clear by the data above, one message that emerges from prevalence and incidence studies of TMDs in adults and children is that pain in the region of the TMJ is common, although it varies significantly by demographic groupings. For example, in most studies women report experiencing symptoms more often than men, African Americans report fewer symptoms than whites, and the overall prevalence varies with age although not always in consistent ways. The case definitions for diagnosing a TMD include a
physical examination in addition to symptom elicitation, and these have been included in several high-quality incidence studies but appear infrequently in population-based prevalence studies. There are also important differences in prevalence reported between child and adolescent populations and adult populations.
The above research suggests that there are important subtypes of TMDs that have highly variable clinical presentations and natural histories. Identifying a patient’s disease subtype is likely to be indispensable for assigning patients to appropriate treatment pathways. Unfortunately, little is now known regarding how to assign patients to appropriate care pathways. The current lack of population-based longitudinal studies is a clear gap in TMD research. This gap hampers efforts to understand risk and prognostic factors, which impedes the selection of optimal treatment pathways. Additional clinical and epidemiological research is needed to close this research gap. Longitudinal, population-based research could identify predictive factors or prodromal stages that precede clinical disease manifestation and guide the development of prevention interventions.
When the prevalence of signs and symptoms varies across demographic categories, there is a suggestion that non-clinical factors (e.g., social determinants) may also play a role in the onset and persistence (clinical course) of TMD symptoms. Thus, additional epidemiological studies that include non-clinical factors such as social determinants could shed new light on the etiology and prognosis of the various TMDs.
As with all epidemiological and clinical research, standardized definitions and methods aid in comparing research results across studies. Variation in case definitions among TMD studies has historically been one of the biggest challenges in this regard. Fortunately, efforts to develop a consistent and reliable case definition have seen the TMD-focused clinical and research communities begin to come together with the development and use of the DC/TMD (see Chapter 2). This should lead to improved research methods and, ideally, to better outcomes from TMD treatment.
Conclusion 3-2: Nationally representative longitudinal studies of the incidence, prevalence, and disease course of temporomandibular disorders (TMDs) using the Diagnostic Criteria for Temporomandibular Disorders would advance understanding of TMD etiology, risk, and prognosis and support the ability to develop clinical practice guidelines and treatment pathways.
The committee heard from a number of individuals about the high financial and emotional toll of living with a TMD. A number of patients
reported having had significant challenges working with dental and medical insurance companies to cover TMD-related care. Patients said they spent many thousands of dollars (e.g., $25,000) out of pocket for tests, appliances, and care not covered by insurance. Some patients noted that they had to quit their jobs because the symptoms made working unbearable. In addition to financial burdens associated with living with a TMD, the voices of patients provide real-world situations and experiences that illuminate and provide important context to the scientific literature. These individual experiences have been shared through the TMJ Patient-Led RoundTable (Kusiak et al., 2018, pp. 9–11) and include the following barriers, challenges, and experiences:
- “Women treated in a male-dominated environment;
- Failure of health professionals to acknowledge or explain the severity and complexity of TMD in marketing to the public;
- Chaos and controversy that abounds in the TMD treatment arena where patients receive different diagnoses and treatment plans from different practitioners, risking patient healthcare decisions in the face of sometimes conflicting information;
- Patient abandonment when the treatments prescribed by the provider doesn’t alleviate their condition or worsen it;
- Patients blamed when the treatments fail;
- Financial loss and bankruptcy due to the costs of TMD health care, unpredictable insurance coverage for TMD treatments, requirement by practitioners for patients to pay for services in cash in advance, encouraging patients to take personal loans, and sign contracts with financial companies affiliated with the dental practice;
- Harm from treatments that received FDA approval;
- Betrayal by and loss of trust in dentists and other practitioners with whom they have entrusted their well-being;
- Desperation to get relief trying any treatment, regardless of its scientific validity;
- The stigma of a condition that isn’t readily obvious to friends, family, and the general public;
- Social isolation from friends and family leading to loneliness, anxiety, and depression;
- Dramatic changes in physical appearance resulting from the disorder, treatment, nutritional problems, and severe weight gain/loss. Facial deformities causing diminished self-esteem, shame and revulsion, the shock of no longer recognizing themselves when looking in the mirror, and the ultimate shame of being stared at in public;
- Social consequences such as: job loss; divorce; abandonment of career, educational, and personal ambitions; abandoning the idea
of having children; inability to assume household and child-rearing responsibilities; and changed family roles;
- Physical inability for restaurant dining—society’s way of interacting in a social or business setting. Those who feel like going out suffer the embarrassment imposed by the masticatory inadequacy, such as having food fall out of their mouths or choking;
- Loss of valuable friendships and inability to participate in daily experiences and pleasures normal people take for granted;
- The effect TMD on the sex lives of both the patient and partner—the once pleasurable sensations of being touched, hugged, kissed, having one’s face stroked, and all the things that are an integral part of lovemaking and affection sharing, are, for many, excruciatingly painful;
- Thoughts and attempts of ending one’s life/suicide.”
The burden, costs, and public health significance of TMDs in the general population can be directly quantified using objective measures of treatment costs available through clinical studies or insurance claims data on usage (e.g., the number of visits to health care professionals for TMD-associated services). More challenging to obtain are estimates of indirect or opportunity costs such as time lost from work, but these too can be translated into economic terms.
Subjective measures such as quality of life are important to measure when considering TMDs, as they are associated not only with facial pain and functional limitations but also with alterations in activities of daily living, disruption of work and social life, poor sleep, and other disrupted activities. These impacts on quality of life can be converted to quality-adjusted life years or disability-adjusted life years for use in economic analysis. An assessment of the burden of TMDs begins with the prevalence estimates discussed above, which indicate how significant a percentage of the population has suffered at any one time from TMD symptoms.
The costs of care associated with TMDs are not well captured in insurance claims data in the United States for several reasons. First, TMDs are managed in both dental and medical settings, leading to a split in where cost information is located. Furthermore, when care is paid out of pocket, as much of dental care is, there is little opportunity to capture the cost.
TMD Care Usage and Costs
The health impacts of TMDs have been examined primarily in smaller clinical studies or with surveys, with the general finding that both acute and chronic TMD-associated pain motivate most individuals to seek professional health care. Moreover, chronic TMD pain is often comorbid with migraine, fibromyalgia, and other forms of widespread pain.
In a study of chronic orofacial pain (not specific to TMDs), the Developing Effective and Efficient Care Pathways for Patients with Chronic Pain (DEEP) study, Durham and colleagues (2016b) estimated the direct costs for care in a primary care population of 198 patients recruited across 10 dental and 25 medical practices in the United Kingdom. Individuals were also recruited from secondary care facilities including emergency dental clinics. The costs were calculated for three categories of care: consultation costs (visits to health care professionals for discussion), medication costs, and appliance (dental/surgical) and intervention (dental/medical/surgical) costs. The mean duration of pain in these patients was 108.4 months, and they averaged consultations with four health care professionals during this time, with 93 percent receiving at least one treatment. Women made up 81 percent of the patients seeking treatment. The total health care usage costs (compiled since each patient’s orofacial complaints began) averaged £1,751 (approximately $2,280), with consultations having the highest cost. The DEEP study found that orofacial pain had a substantial impact on the individual and the UK economy through lost productivity and on the health care system due to disorganized care pathways increasing the number of consultations required to diagnose the condition and care for the patient. (See Slade and Durham, 2020, in Appendix C for a detailed report of the UK study’s methodology and outcomes.) The direct costs from DEEP are not easily translated from the United Kingdom to the United States due to the substantial differences in how health care is paid for in the two countries. It is also possible that the care pathways typical for TMD patients in the United Kingdom differ from those in the United States. Further research using representative datasets or cohorts within the United States will be required to fully understand the care usage and costs for TMDs in this country.
Katsoulis and colleagues (2012) reported cost results from a Swiss study of 242 clinical TMD patients and found that the average cost for just the dental treatment (splint, findings, diagnostics, and planning and manufacturing splints) was 1,778 Swiss francs (approximately $1,800). However, for many patients additional costs were incurred for ancillary, non-dental services such as physiotherapy, physician’s services, and loss of earnings.
Riley and colleagues (1999) measured health care usage related to painful orofacial symptoms, including jaw joint pain, in a telephone survey of 1,636 older adults (≥65 years of age) in the United States. The researchers found that 125 (7.6 percent) reported jaw joint pain and 56 percent of those with jaw-related symptoms reported using health care services in the past 12 months with 41 percent visiting a physician, 11 percent a dentist, 6 percent a nurse practitioner, and 11 percent other caregivers. Those with jaw joint pain who reported service use averaged 6.7 visits with health care professionals in the prior 12 months.
Macfarlane and colleagues (2002) surveyed 2,504 adults (18 to 65 years of age) from general medical practices in the United Kingdom with respect to broadly defined orofacial pain. The overall prevalence of orofacial pain was 26 percent with symptoms decreasing with age and being more common in women (30 percent) than in men (21 percent). Among all orofacial pain patients, 46 percent sought advice from dentists or physicians, and 17 percent took time off from work or had a disruption of activities of daily living as a consequence of their pain.
Hobson and colleagues (2008) found that patients with a TMD used 10 to 20 percent more general dental services than individuals without a TMD, and White and colleagues (2001) found that patients with a TMD used more health services overall. In a survey sent to school-aged adolescents, those with TMD pain reported more school absences than healthy age- and sex-matched individuals (Nilsson, 2007).
It is clear both from the quantitative data presented in the DEEP study and from other reviews of the qualitative data that the journey to seek appropriate diagnosis and care can be long and costly in terms of both the impact on the individual and the effect on an individual’s personal finances. This is mirrored on a societal level in the health care usage costs and the economic costs of TMDs. The personal impact on an individual’s quality of life is consistent over the entire course of their search for diagnosis and care, and it is similar to the impact of other, more well-known conditions such as arthritis and depression. The health care usage costs remain consistent over time and are all dominated by the cost of multiple consultations with different specialties or providers. Despite the level of intervention received, within the DEEP dataset, at least, it seems that the probability of improvement from high-impact pain was low (48 percent probability of moving from a high score on the Graded Chronic Pain Scale to a low score on this scale over a 6-month period) (Durham et al., 2016b).
In a secondary analysis of results from the DEEP study that used the results for participants indicating TMD/musculoskeletal as the source of their persistent orofacial pain (Slade and Durham, 2020), researchers found that those individuals living with TMDs differ from those with other persistent pain conditions in that they have an exceedingly low absenteeism rate, but the quality and quantity of the work that they can provide for their employer is affected (12 percent decrease for each) (Slade and Durham, 2020). This results in a considerable “hidden” cost to the employer—calculated to be between £584 and £1,225 in lost productivity for each 6-month period they are at work with a TMD (Slade and Durham, 2020). The researchers found that these data on absenteeism were less than work absenteeism for individuals with migraines (Slade and Durham, 2020).
TMDs are characterized by and often defined by a wide range of symptoms. These can include acute or chronic pain in masticatory muscles and the pre-auricular region, jaw muscle soreness, limited range of jaw movement, and TMJ noises. Those with a TMD often have comorbid conditions such as headache, sleep disturbances, and bruxism as well as more generalized conditions (e.g., fibromyalgia). The impact of these TMD-associated symptoms on an individual’s quality of life varies by the specific symptoms as well as by their severity and chronicity.
Quality of life can be measured using simple questionnaires asking an individual to endorse items from a list of symptoms and inferring their impact. This approach tends not to be very generalizable, because the impact of signs or symptoms of a disease on overall quality of life can vary in unknown ways among individuals and across cultures. As a result, instruments have been developed specifically to measure quality of life. Such instruments tend to be of two types, generic health-related, quality-of-life measures and disease-focused or topically focused instruments such as the Oral Health Impact Profile (Locker and Slade, 1993).
Generic health-related, quality-of-life instruments can be as simple as a single item asking a person to rate his or her overall well-being or as complex as instruments that assess quality of life across multiple domains. These instruments vary in their validity and in their mode of administration (e.g., self, interviewer, telephone). Detailed descriptions of the numerous health-related, quality-of-life instruments is beyond the scope of this report, but further information is available on quality-of-life instruments as applied to TMDs (Ohrbach, 2010). It can be argued that overall health-related quality of life is in fact the most important thing to measure if one wants to understand the extent to which a disease state affects an individual’s psychosocial well-being. Oral-health-focused instruments were developed out of concern that generic health-related, quality-of-life instruments might be insensitive to oral health status. With their focus on oral health conditions and concerns, the instruments were thought to be useful in directing attention to oral health and to have the sensitivity to measure changes in oral health status over time. Commonly reported instruments include the Oral Health Impact Profile (Locker and Slade, 1993) and the Oral Health Impact Profile-14 (Locker and Allen, 2002).
Psychosocial Measures of TMD Impact
In the UK DEEP study (Durham et al., 2016b; Slade and Durham, 2020), quality of life was consistent across study time points. When the results were pooled across all five time points (347 complete observations),
the mean utility value of an individual’s quality of life was 0.68 (95% confidence interval [CI] 0.66–0.71). Compared with other datasets from the United Kingdom, this impact on the quality of life was similar to that exerted by diabetes (0.72), arthritis (0.64), depression (0.64), and myocardial infarction (0.64) and was greater than that of stroke (0.80) and lower than that of back pain (0.47). There was also a degree of consistency across time points in the multidimensional nature of the pain. When the data were pooled across time points (358 complete observations), the mean (95% CIs) scores per domain were pain severity (39.4, 95% CI 37.4–41.2); interference (36.8, 95% CI 34.9–38.6); life control (61.9, 95% CI 59.8–64.1); affective distress (46.2, 95% CI 44.3–48.0); and support (49.8, 95% CI 47.0–52.7). The DEEP study compared these values with normative values for low back pain, burning mouth syndrome, and fibromyalgia and found a comparable pain intensity, affective distress, and level of support for the patient between burning mouth syndrome and painful TMDs. TMDs are associated with less loss of control in life circumstances than burning mouth syndrome, but they exert higher levels of interference in daily activities. In comparison to the more generalized persistent pains of low back pain and fibromyalgia, TMDs seem to exert less impact across most domains, with the exception of affective distress, where it would appear they cause more affective distress.
Several recent systematic reviews have confirmed that TMDs are associated with a decrease in oral health–related quality of life. Bitiniene and colleagues in a 2018 systematic review of 12 studies reported that 10 studies documented correlations between TMDs and lower quality of life. Similar results were found in a 2010 systematic review (Dahlstrom and Carlsson, 2010), where all 12 of the reviewed studies found oral health–related quality of life was negatively impacted in individuals diagnosed with a TMD. The reviewers did not report the magnitude of the impact, but they reported that pain was the most important aspect of TMDs associated with reduced oral health–related quality of life. John and colleagues (2007), using the 49-item Oral Health Impact Profile, reported that quality of life was negatively impacted in TMD patients; disc displacement with reduction had the least impact on quality of life of all of the RDC/TMD diagnoses.
Many of the studies of quality of life report no difference between the sexes. Increasing age has been shown to be associated with worse quality-of-life measures (John et al., 2007; Rener-Sitar et al., 2013). There was also a clear dose–response relationship reported across 12 studies in the systematic review by Bitiniene and colleagues (2018), where the more severe the TMD symptoms, the lower the quality of life. Importantly, the impact of TMDs on oral health–related quality of life is reported to be greater than almost all other orofacial diseases and illnesses or conditions (Dahlstrom and Carlsson, 2010).
Data Collection Challenges and Opportunities: Cost Studies
Studies assessing the direct and indirect costs specific to a TMD diagnosis are rare. Research into the direct and indirect costs of TMD is needed, especially in light of the changing policies around health care delivery. As value-based care takes hold, the personal, social, and economic impact of chronic TMD will need to be included as part of the value proposition for health care coverage. Associated with this will be the need to accurately characterize patient outcomes of care so that interventions can be assessed through comparative effectiveness studies.
TMDs have a high comorbidity with multiple medical conditions, including other idiopathic pain conditions, systemic medical conditions that include pain as a primary symptom, and health conditions whose primary symptoms are not pain (Hoffmann et al., 2011; see Box 3-2). For example, results from the OPPERA study demonstrate that individuals with a painful TMD reported more pain conditions (e.g., back pain, irritable bowel syndrome, headaches) and a greater number of medical comorbidities, particularly neural/sensory and respiratory conditions, than did controls (Ohrbach et al., 2011). Also, individuals with a TMD reported significantly poorer general health than controls. Similarly, population data from the NHIS revealed significant comorbidity of jaw/face pain with other pain conditions (back pain, neck pain, headache, joint pain) and with non-painful medical conditions (e.g., hypertension, heart disease, asthma, sinusitis) (Plesh et al., 2011b; Maixner et al., 2016). More recently, in a primary care setting, treatment-seeking patients with a TMD with low or high levels of disability reported more comorbid pain conditions and more general health-related diagnoses than patients with no disability (Kotiranta et al., 2018). It is important to recognize that these comorbidities could reflect pre-existing conditions that increase the risk of a TMD. For example, systemic conditions such as rheumatoid arthritis or Ehlers-Danlos syndrome could lead to the development of TMD symptoms. Alternatively, TMDs may predate and potentially increase the risk of other conditions, such as headache conditions or psychological symptoms.
TMDs and Painful Comorbidities
TMDs are among the group of chronic pain conditions that have been identified as chronic overlapping pain conditions due to their frequent comorbidity and shared risk factors (Maixner et al., 2016). Other chronic overlapping pain conditions frequently included in this group are
fibromyalgia, irritable bowel syndrome, vulvodynia, chronic fatigue syndrome, interstitial cystitis/painful bladder syndrome, endometriosis, headache conditions, and low back pain, although this is not an exhaustive list. As noted above, the OPPERA study showed significant comorbidity of TMDs with several other pain conditions, including back pain, headache, and irritable bowel syndrome (Ohrbach et al., 2011). Similarly, an
analysis of the NHIS data revealed a significantly increased risk of TMDs among individuals with headache, neck pain, low back pain, or painful joints (Maixner et al., 2016). Other studies have found that among people with fibromyalgia, back pain, headache, irritable bowel syndrome, chronic fatigue syndrome, and vulvodynia, the likelihood of having a TMD is significantly greater than in the general population (Aaron et al., 2000; Whitehead et al., 2002; Wiesinger et al., 2007; Nguyen et al., 2013; Robinson et al., 2016; Florencio et al., 2017; Gallotta et al., 2017). Moreover, the presence of comorbid pain conditions is associated with a greater severity of TMD symptoms (Visscher et al., 2016; Florencio et al., 2017). The associations of TMDs with these comorbid pain conditions are likely bidirectional in nature, such that these other pain conditions may develop following TMD onset; however, some evidence suggests that premorbid presence of other pain conditions increases the risk of developing a TMD (Sanders et al., 2013a).
TMDs have also been associated with a variety of systemic conditions that often include pain as a common symptom. Several rheumatologic diseases show significant comorbidity with TMDs, including rheumatoid arthritis, ankylosing spondylitis, systemic lupus erythematosus, and Sjogren’s syndrome (Aliko et al., 2011; Sidebottom and Salha, 2013; Yildizer Keris et al., 2017; Zhang et al., 2017). TMJ osteoarthritis is one subtype of TMD (Wang et al., 2015), but TMD symptoms are also more prevalent in patients with osteoarthritis at other sites such as the hand (Abrahamsson et al., 2017) and knee (Zhang et al., 2017). Moreover, TMDs are substantially more prevalent in patients with rheumatoid arthritis than in the general population (Bracco et al., 2010; Mortazavi et al., 2018), and rheumatoid arthritis disease activity has been correlated with the severity of TMD symptoms (Alstergren et al., 2008; Ahmed et al., 2013, 2015). A high prevalence of TMDs has been reported in children with newly diagnosed juvenile idiopathic arthritis (Weiss et al., 2008; Muller et al., 2009; Stoll et al., 2018). TMD signs and symptoms are also more common in patients with Sjogren’s syndrome and psoriatic arthritis than in controls (Crincoli et al., 2015; Zanin et al., 2019).
TMDs and Non-Painful Comorbidities
TMDs have also been associated with health conditions that do not include pain as a primary symptom. An analysis of the NHIS data revealed an association of TMDs with a variety of non-painful medical conditions (Maixner et al., 2016).
Respiratory and Sleep Conditions
The OPPERA study demonstrated a link between TMDs and various respiratory conditions (Ohrbach et al., 2011). Specifically, individuals reporting at least one of five respiratory conditions (sinus trouble, allergies or hives, asthma, tuberculosis, breathing difficulties) were 2.5 times more likely to be chronic TMD cases than were controls. In addition, the occurrence of a TMD was 3.1 times higher among those reporting a history of obstructive sleep apnea. Similarly, a population-based study in Korea reported increased odds of TMDs among individuals with asthma and rhinosinusitis (Song et al., 2018a), and a recent case–control study reported an association between having a TMD and pneumonia, asthma, and allergies (Fredricson et al., 2018). These cross-sectional findings do not address the direction of the association between TMDs and respiratory symptoms; however, findings from the OPPERA prospective cohort study showed that the presence of one or more respiratory conditions predicted the future development of a TMD (Sanders et al., 2013a).
Sleep disorders also show high comorbidity with TMDs (Olmos, 2016; Almoznino et al., 2017). Smith and colleagues (2009) found that the majority of people with a TMD met the criteria for at least one sleep disorder, and primary insomnia was associated with increased pain sensitivity. More generally, patients with a TMD report poorer sleep quality, longer sleep latency, and lower sleep efficiency (Sener and Guler, 2012; Lavigne and Sessle, 2016). Furthermore, women with a TMD showed increased respiratory-related arousals during sleep (Dubrovsky et al., 2014). As noted above, self-reported obstructive sleep apnea was associated with a chronic TMD in the OPPERA study (Ohrbach et al., 2011), and more symptoms of sleep apnea conferred an increased risk of future TMD onset (Sanders et al., 2013b). Sleep bruxism has also been linked with TMDs in some studies; however, recent meta-analyses describe the evidence linking sleep bruxism and TMD pain as inconclusive (Jimenez-Silva et al., 2017; Baad-Hansen et al., 2019). Sleep and pain are likely reciprocally related, such that sleep disturbance may be not only a consequence but also a risk factor for TMDs. Indeed, the OPPERA findings showed that reduced sleep quality and sleep apnea were pre-existing risk factors for TMD onset (Sanders et al., 2013b).
Hypermobility and Ehlers-Danlos Syndromes
Ehlers-Danlos syndrome, a group of heritable connective tissue disorders, represents another set of systemic conditions associated with an increased risk of TMDs and other chronic pain conditions (De Coster et al., 2005; Chopra et al., 2017; Mitakides and Tinkle, 2017). Chronic pain is highly prevalent in this syndrome, including both regional and widespread
pain, and TMD pain has been reported in up to 71 percent of patients with Ehlers-Danlos syndrome (De Coster et al., 2005). TMD symptoms in this syndrome are generally attributed to joint hypermobility and the resultant instability of the mandible during masticatory function as well as during maximal opening, which leads to protective muscle contraction and subsequent further problems in functioning (see Chapter 2). Previous findings have demonstrated associations between joint hypermobility and TMD symptoms among individuals without Ehlers-Danlos (Perrini et al., 1997; Ogren et al., 2012). However, pain in the syndrome has also been associated with other mechanisms, including neuropathic features and signs of central sensitization (Syx et al., 2017; Benistan and Martinez, 2019) as well as myofascial pain due to protective muscle contraction.
Altered jaw function, including pain during eating and chewing, can substantially affect nutritional habits among people with a TMD, which can in turn reduce eating-related quality of life (Nasri-Heir et al., 2016). However, information regarding the nutritional habits in patients with a TMD is quite limited. A small cohort study of patients seeking treatment for TMDs reported that eating was a problem for the vast majority of the patients and that most reported eating a softer diet (Irving et al., 1999). Raphael and colleagues (2002) reported that higher pain severity was associated with a lower intake of dietary fiber among people with myofascial TMD pain. While nutritional modifications are often a consequence of the “soft diet” component of most TMD self-management programs (Durham et al., 2016a; The TMJ Association, 2017), little evidence has addressed the benefits and adverse effects of addressing nutritional needs (Durham et al., 2015; Nasri-Heir et al., 2016). Additional research is needed to elucidate the role of nutritional factors in TMDs and to determine the clinical benefit of nutritional interventions in these conditions.
Tinnitus and Vertigo
TMD has been associated with multiple otologic symptoms, such as tinnitus and vertigo (Porto De Toledo et al., 2017; Manfredini, 2019). Recent meta-analyses have reported bidirectional associations between tinnitus and TMDs, with tinnitus being substantially more frequent in patients with a TMD than in controls and TMDs being more common among individuals with tinnitus than in those without (Bousema et al., 2018; Omidvar and Jafari, 2019). Furthermore, the severity and duration of TMD pain have been related to tinnitus in some studies (Hilgenberg et al., 2012; Akhter et al., 2013). Other otologic symptoms have also been
associated with TMDs, including hearing loss and vertigo/dizziness (Pekkan et al., 2010; Effat, 2016). Regarding the direction of association, one study found that palpation tenderness in the masticatory muscles predicted an increased risk of future development of tinnitus over the ensuing 5 years (Bernhardt et al., 2011).
General Somatic and Psychological Symptoms
Individuals with TMDs report a greater number of subclinical somatic symptoms assessed via questionnaires (de Leeuw et al., 2005; Fillingim et al., 2011; Chen et al., 2012). These assessments include many of the symptoms described above (e.g., otologic symptoms, respiratory symptoms) as well as symptoms affecting other bodily systems (e.g., cardiovascular, gastrointestinal, musculoskeletal). TMDs are also associated with an increased likelihood of psychological symptoms, including depression, anxiety, and posttraumatic stress disorder, perceived stress, and pain-related psychological processes, such as pain catastrophizing (negative cognitive-emotional processing including rumination about pain) and kinesiophobia (fear of movement) (Manfredini et al., 2009; Fillingim et al., 2011; Bertoli and de Leeuw, 2016; Reiter et al., 2018; Tay et al., 2019). Moreover, pain severity has been positively associated with these psychological factors (Guarda-Nardini et al., 2012; Su et al., 2017; Natu et al., 2018). While these somatic and psychological symptoms may reflect the consequences of TMDs, as described below, some of these symptoms also represent important risk factors for the future development of a TMD.
Conclusion 3-3: Even with a fragmented understanding of temporomandibular disorders (TMDs) according to traditional public health measures (e.g., prevalence, incidence), it is clear that TMDs have a large public health impact and a significant health, social, financial, and emotional burden on many individuals and families.
As described above, multiple painful and non-painful conditions and symptoms have been associated with TMDs. It is impossible to determine from cross-sectional studies whether these represent risk factors, consequences, or coincidences, but numerous prospective studies have identified premorbid factors that confer an increased risk of TMD onset or persistence, or both. Furthermore, several socio-demographic factors are known to be related to TMD risk.
Family History and Genetic Factors
While chronic pain conditions have been found to show familial aggregation (Matsudaira et al., 2014; Zadro et al., 2017), few studies have examined this in people with painful TMDs. It is likely that TMDs have a polygenetic underpinning although much remains to be discovered (see Chapter 4 for more discussion of TMD genetics). Raphael and colleagues (1999) found that TMDs and other painful conditions were no more common in first-degree relatives of people with a history of TMDs than in first-degree relatives of people with no history of TMDs. Several twin studies have also reported that TMDs appear to have limited heritability, although these studies have generally been small and underpowered (Visscher and Lobbezoo, 2015). A more recent and larger twin study suggested that 27 percent of the variance in TMD pain can be attributed to genetic factors (Plesh et al., 2012). Genetic contributions to TMDs have also been explored in candidate gene association studies, which have found evidence that serotonergic and catacholaminergic genes are associated with TMDs (Diatchenko et al., 2013; Visscher and Lobbezoo, 2015). More recently, genome-wide association studies have identified novel genetic pathways that may be related to TMDs, including the sarcoglycan alpha gene (Sanders et al., 2017) and the muscle RAS oncogene homolog (MRAS) gene (Smith et al., 2019). Notably, several of these studies have reported that associations of some genetic factors with TMDs vary based on other risk factors, such as sex and psychological factors (Belfer et al., 2013; Slade et al., 2015; Meloto et al., 2016; Sanders et al., 2017; Smith et al., 2019). One study illustrated the potential for the existence of a gene–environment interaction that influences TMD risk (Slade et al., 2008). In this prospective cohort study of 186 females, individuals with a genetic variant associated with pain responsiveness had a significantly greater risk of developing TMD if they had reported a history of orthodontic treatment compared to subjects who did not (Slade et al., 2008).
TMDs in Females
TMDs are significantly more common in females than in males, with population-based studies indicating that females are at approximately twice the risk of experiencing a TMD as males (LeResche, 1997; Bueno et al., 2018). The OPPERA study observed a slightly but non-significant increased incidence of first-onset TMDs in females, while female sex was strongly associated with chronic TMDs, suggesting that females have an increased risk of TMD persistence (Slade et al., 2013a,b, 2016). Indeed, in OPPERA’s nested case–control study, 54 percent of females transitioned from first onset to persistent TMDs, as compared with 41 percent of males (Slade et
al., 2016). This is consistent with prior findings that among patients with acute TMDs, women were more likely than men to progress to chronic TMDs (Garofalo et al., 1998), and that this sex differential may increase as chronicity persists. This increased risk of TMDs among females is observed primarily during the reproductive years (LeResche, 1997; LeResche et al., 2005; Slade et al., 2011; Song et al., 2018b). Age has also been shown to be a factor in the incidence of TMDs, with peak prevalence occurring in women in the 35–44 age group (Slade et al., 2011) and decreasing beyond reproductive age (Plesh et al., 2011a). The OPPERA study reported that TMD incidence increased with age across the age range from 18 to 44 years (Slade et al., 2013a,b), but age-related incidence information beyond 44 years of age was not available.
Women exposed to emotional, physical, or sexual abuse may also be at an increased risk for TMDs. In one study of 40 women of ages 16 to 45 years with an idiopathic TMD, the women were more likely to report emotional abuse, exposure to insults, and being diminished or humiliated in front of other people than women without a TMD (Grossi et al., 2018).
TMDs in Different Races and Ethnicities
The association of race/ethnicity with TMDs is currently not well understood. Janal and colleagues (2008) reported that myofascial TMDs were more common among black women and Hispanic women than among white women. In a study of 4- to 6-year-olds, TMD symptoms were found to be more common among African American children than among Caucasian children (Widmalm et al., 1995). In contrast, Plesh and colleagues (2002) found a lower prevalence of TMDs among African Americans than among Caucasians after controlling for socioeconomic status. As yet another contrast, in the OPPERA study non-white racial/ethnic groups had significantly lower odds of chronic TMDs than whites, while African Americans showed an increased incidence of first-onset TMDs compared with whites (Slade et al., 2011, 2013a,b). This paradox is explained by lower risk of symptom persistence in African Americans, as OPPERA data showed that after onset, TMDs persisted in 61 percent of whites versus 35 percent of African Americans (Slade et al., 2016). The association between race/ethnicity and TMDs likely involves the contribution of other underlying factors, such as socioeconomic status (Poleshuck and Green, 2008). Recent findings demonstrate that lower socioeconomic status (i.e., education and wealth) is associated with a higher prevalence and severity of general chronic pain (Grol-Prokopczyk, 2017), and racial/ethnic differences in pain were not significant after controlling for these socioeconomic influences. Specific to TMDs, the OPPERA study found that low satisfaction with material standards conferred an increased risk
TABLE 3-3 Potential Predictors of Future TMD Onset Identified in the OPPERA Study
|Clinical and Health Variables||Psychological Variables||Pain Sensitivity Variables|
The OPPERA study identified numerous premorbid predictors of future TMD onset, including clinical, psychological, and pain sensitivity measures, and the strongest predictors from each domain are listed in Table 3-3 (Fillingim et al., 2013; Greenspan et al., 2013; Ohrbach et al., 2013; Sanders et al., 2013b).
Data Collection Challenges and Opportunities: Studies on Risk Factors
In addition to the risk factors for TMD onset, several factors appear to increase the risk of the transition from acute to chronic TMD pain, including female sex, acute pain severity and related disability, and depressive and somatic symptoms (Garofalo et al., 1998). However, there is limited information regarding risk factors for the persistence of TMD symptoms, and virtually no data addressing protective factors. Chapter 4 contains additional information regarding the need for genetic and mechanistic studies of TMDs.
Conclusion 3-4: Risk factors for persistent temporomandibular disorders (TMDs) and the protective factors that prevent an individual from transitioning to painful, chronic TMDs are poorly understood and need to be a priority for clinical epidemiological research on TMDs.
Throughout the report, the substantive burdens to individuals with a TMD and their families are documented, and actions are proposed to
improve the treatment and management of TMDs. This chapter highlights the significant health, quality-of-life, and cost burdens that TMDs place on society. The committee’s recommendations on the actions needed to strengthen population-based data on TMDs are provided in Chapter 8. The research priorities highlighted in Box 3-3 supplement and expand on those recommendations.
Conclusion 3-1: The prevalence of temporomandibular disorder (TMD) symptoms varies widely across studies depending on the assessment used and the population studied. Based on one analysis of 2017–2018 data, an estimated 4.8 percent of U.S. adults (an estimated 11.2 to 12.4 million U.S. adults) had pain in the region of the temporomandibular joint that could be related to TMDs. Based on this information, it is likely that TMDs are the
most prevalent type of chronic orofacial pain and TMDs may be comparable in prevalence to other chronic pain conditions such as fibromyalgia, chronic low back pain, and migraine disease.
Conclusion 3-2: Nationally representative longitudinal studies of the incidence, prevalence, and disease course of temporomandibular disorders (TMDs) using the Diagnostic Criteria for Temporomandibular Disorders would advance understanding of TMD etiology, risk, and prognosis and support the ability to develop clinical practice guidelines and treatment pathways.
Conclusion 3-3: Even with a fragmented understanding of temporomandibular disorders (TMDs) according to traditional public health measures (e.g., prevalence, incidence), it is clear that TMDs have a large public health impact and a significant health, social, financial, and emotional burden on many individuals and families.
Conclusion 3-4: Risk factors for persistent temporomandibular disorders (TMDs) and the protective factors that prevent an individual from transitioning to painful, chronic TMDs are poorly understood and need to be a priority for clinical epidemiological research on TMDs.
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