Impact of temporomandibular disorders on quality of life

Introduction: Temporomandibular dysfunction (TMD) may have a major impact on quality of life. Objective: Thus, this integrative review assessed the impact of TMD on quality of life. Method: An electronic and manual search was conducted to identify studies that evaluated the impact of TMD on an individual’s quality of life. After the inclusion and exclusion criteria were met, seven articles were included and evaluated according to the quality of evidence using the Newcastle-Ottawa assessment. Results: The selected studies used different instruments to diagnose temporomandibular joint disorders and measure the quality of life. Only three studies used the RDC/TMD. As for quality of life, the most used instrument was the SF-36, followed by Br-MPQ and WHOQOL-Bref. Conclusion: The findings show that there is a negative impact of temporomandibular dysfunction on quality of life, especially regarding its severity. However, further studies are needed to confirm these results.


Introduction
Temporomandibular dysfunction (TMD) involves musculoskeletal pain, disorders of mandibular movement patterns and/or impairment of functional movement [1][2][3][4][5]. It is also recognized as the most common non-odontogenic chronic condition of orofacial pain, in which pain is its main characteristic and the main reason for seeking treatment [6][7][8][9][10][11][12][13][14][15]. In addition to pain that is mostly aggravated by chewing and mandibular functions, individuals with TMD have asymmetric mandibular movements, joint noises and headache. In cases of constant and recurrent pain in the masticatory muscles, temporal region and/or the joint region itself, TMD may become a chronic condition; in these cases, although not risky, quality of life may be negatively affected [6,[16][17][18]. Therefore, the use of instruments to assess the impact of TMD on quality of life is important to determine treatment needs and subsequent therapeutic successes [4].
In examining the literature, we only found one systematic review by Dahlström and Carlsson [19] showing that TMD has a negative impact on oral healthrelated quality of life, and we then realized that TMD could also affect overall quality of life. Therefore, this integrative review was performed to assess this issue. Impact of temporomandibular disorders on quality of life 3

Focus question
This study was conducted to answer the question: "What is the impact of temporomandibular dysfunction on overall quality of life?"

Search strategy
The following databases were searched: PubMed, LILACS, SciELO, Cochrane, as well as a manual search of the reference lists of selected studies to include articles that met the eligibility criteria. Only articles published between 2000 and 2017 were included. A search strategy was adapted for use in each database, and the keywords used for the search were: "Temporomandibular joint disorders" (MESH), "Facial pain" (MESH) AND "Quality of life" (MESH); "Temporomandibular Joint Disorders" (DECS), "Facial Pain" (DECS) AND "Quality of Life" (DECS). We also searched for articles from the references of the selected articles and in gray literature. Studies were identified first by reading titles and abstracts, then followed by full-text reading of potentially eligible studies.

Inclusion and exclusion criteria
Articles were selected according to the following inclusion criteria: articles published after 2000, in Portuguese or English, and addressing crosssectional, case-control and/or cohort studies that related TMD and overall quality of life.
We excluded the articles that were a literature review, case report and/or case series that evaluated TMD in individuals with degenerative diseases, such as juvenile idiopathic arthritis, and individuals with dentofacial deformities. Articles that evaluated only chronic TMD, populations of children and adolescents under 18, and that used quality of life instruments specific for determining impact of oral health were also excluded [20,21].

Main outcome
The main outcome was to determine the impact of TMD on quality of life.

Quality assessment
Quality assessment for cross-sectional studies was performed using the Newcastle-Ottawa Quality Assessment Scale, as recommended by the Cochrane Collaboration Guidelines for the evaluation of nonrandomized studies [22,23].
Studies were evaluated in three categories (selection, comparability, and results) based on the incorporation of design elements associated with decreased bias. The study received stars (*) if it complied with the scale [23].

Study selection
The search strategy yielded a total of 205 articles; 19 articles were selected for full-text reading, and 13 were excluded for not meeting the eligibility criteria; five evaluated TMD and quality of life. In patients with degenerative diseases, four used specific instruments to determine the impact of oral health on quality of life, two were case series, one was a case report and one evaluated a population under 18 years. At the end, a total of 6 articles were included, as illustrated in Figure 1. A total of 463 patients were included in the studies. Articles excluded by title and abstract: 180 Articles excluded due to repetition: 6 Excluded due to inclusion and exclusion criteria: 13 Figure 1 -Study selection.
One of the articles divided the sample into three different subgroups: patients with TMD complaints for less than 1 year (subgroup 1), patients with TMD complaints for 1 to 3 years (subgroup 2) and patients with TMD complaints for more than 3 years (subgroup 3) [11]. Subsequently, two studies [11,28] classified the patients according to RDC/TMD criteria: group A -myofascial pain; group B -disk displacement; and group C -arthralgia, osteoarthritis and osteoarthrosis.
All articles concluded that there was a negative impact on the quality of life of patients with TMD, especially regarding the social, psychological and mental aspects of the individuals; one article also concluded that there was a relation between TMD severity and worsening of quality of life [11]. No article described sample calculation.

Results for quality of life
The SF-36 instrument [29,30], used by most of the selected studies to measure quality of life, is currently one of the most used instruments in literature; it is composed of 36 items in 8 domains, of which 4 correspond to physical aspects (functional capacity, physical ability, general health and pain) and 4 to mental aspects (emotional aspect, social aspect, mental health and vitality) [11]. Of the four studies that used SF-36 to measure quality of life [11,24,25,26], three showed that the vitality domain had the worst score among TMD patients [11,23,24], and one compared patients who had TMD for less than one year (group I), for 1 to 3 years (group II) and for more than 3 years (group III) [11]. There was a statistically significant difference between patients in group I versus group III, with physical functioning and pain scores being worse in group III patients; no such difference was found between group II and III patients.
Another instrument to assess quality of life was Br-MPQ [27], which analyzes the findings regarding the impact of pain on the individual's life. The authors reported that the impact of pain on daily living activities, the subtypes sleep (68.18%) and appetite/eating (63.64%) showed the highest percentages of responses with some degree of impairment (p > 0.05). In addition, 77.27% of individuals with TMD had difficulty tolerating pain (p > 0.05%) [26].
One study used the quality of life instrument WHOQOL-Bref [28], which consists of 26 questions divided into four domains: physical, psychological, social and environmental [28,31]. The results showed an association between the social domain of quality of life in the disk displacement group, with and without reduction with limited opening in the RDC-TMD. Higher physical and social function: groups II and III scored significantly worse than the general population. None of the groups differed from the general population when comparing mental items.

Impact of temporomandibular disorders on quality of life
Pain duration was significantly correlated with the physical function subscale of SF-36 and mandibular involvement.
Patients with painful TMD for less than one year. Better score when compared to population norm. Long duration of pain. Mental health score and function limitation due to emotional problems were not seriously affected by reduced physical health. Social functioning seemed to be considerably affected.

(Conclusion)
Impact of temporomandibular disorders on quality of life 7

Discussion
TMD has been the subject of both clinical and epidemiological studies, not only in investigations regarding treatment, but also to find out how much does this disease, which is becoming increasingly common among people, negatively affects quality of life [32][33][34][35][36]. The results of this review showed that TMD has a negative impact on people's quality of life.
Different results were reported regarding the diagnostic classification of TMDs found in the participants, and this discrepancy was due to the use of different assessment and diagnostic instruments and to the way data was collected. Studies which evaluated patients from specialized clinics or who sought treatment [11,28] had more patients with moderate or severe TMD, while patients from a population that was not seeking treatment [24,26] showed a more pronounced percentage of mild TMD. Defining exactly how data will be collected and which population will be studied is of utmost importance for the analysis of the final results, since results found in a population seeking specific treatment for dysfunction are not considered valid for the general population. This issue should be analyzed in future studies.
It is known that systemic and/or degenerative diseases, and musculoskeletal diseases as well, might be a confounding factor in the diagnosis of TMD, since they have a multifactorial etiopathogenesis [8,37,38]. Along the same line, it is clear from scientific literature that only three articles included in this review considered systemic, degenerative and/or musculoskeletal diseases as exclusion factors [24,26,28]. The other studies did not report these diseases as such.
An important issue that has been suggested is the standardization of the instruments for TMD assessment and diagnosis, since it is very difficult to compare studies that diagnosed TMD more fully, such as those with the use of RDC/TMD [28,39], with studies that used simpler diagnostic instruments. Only three articles used the RDC/TMD, which were also the studies that obtained the best classification in the quality assessment according to the Newcastle-Ottawa instrument [22]. According to these studies, the presence of muscle disorders (group I), osteoarthritis (group III) and orofacial pain had a major impact on the quality of life of individuals with TMD. In addition, the long duration of pain seriously affected social functioning [11,28].
Despite the differences in the studies regarding the instruments used for TMD diagnosis and quality of life measurement, homogeneity could be observed, since we used a rigorous methodological design in the quality assessment of the studies performed, by the application of the Newcastle-Ottawa Scale [22,40]. However, the risk of bias due to the small number of articles included cannot be excluded.
The results of our integrative review showed that TMD has a negative impact on quality of life, especially regarding its severity, seriously affecting social functioning [41]. A limitation of this review was that, of the six studies eligible for inclusion in this review, no study reported sample calculation. Quality assessment revealed that three articles were at risk of bias. The adequate methodological design of the studies, as well as sample calculations to define the sample size, with the objective of internal and external validations, will be necessary in future studies to confirm the results obtained in this review.

Conclusion
TMD has a negative impact on quality of life, especially regarding its severity. Important questions were reported on the standardization of the instruments used for TMD diagnosis and assessment, and also on the confounding factors caused by the non-exclusion of individuals with systemic/degenerative and musculoskeletal diseases in the samples studied. Due to the small number of studies available, further research is needed.
Impact of temporomandibular disorders on quality of life