Introduction
Several study results have shown that temporomandibular disorders (TMD) and headache have a reciprocal relationship and frequently occur together.1-3 Although the pathophysiology of this relationship is unclear, the head, neck, jaw, and masticatory muscles all have common neural innervation and closely related anatomical structures, thus are intrinsically connected in their ability to generate symptoms within the surrounding structures.2,4-8
Temporomandibular disorders are typical orofacial conditions that dentists and other health care professionals frequently encounter.9 The term “temporomandibular disorders” encompasses clinical problems involving the temporomandibular joint (TMJ), masticatory muscles, as well as the surrounding structures.9 Temporomandibular disorders involve the TMJ and associated structures including the TMJ disc-condyle relationship, muscles of mastication, and headache attributed to TMD.1,6,10 Temporomandibular disorders are the second-most-common musculoskeletal disorders among adults and are responsible for significant pain and disability in people with TMD.11 This condition occurs in 51% of people during their lifetime and has a severity that increases with age.2 Several studies have reported that TMD occurs in persons between 20 and 50 years of age and often peaks in the fourth decade.6,12-15
The Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) is a classification system for TMD.11,16 It is an updated version of the Research Diagnostic Criteria for TMD (RDC/TMD). According to the DC/TMD, TMD is classified into the following groups: arthrogenous TMD (including joint and disc disorders), myogenous TMD (masticatory muscle disorders), and headache (attributed to TMD).11 While the relationship between TMD and headache is yet to be clearly defined, TMD is considered a prominent comorbidity of chronic headache.17,18
Headache is one of the prevailing neurological disorders in adults.19 Primary headache is defined as a headache without anatomical or physiological explanation and an unknown pathology.20,21 According to the Global Burden of Disease, all types of headache are third on the list of disability in people under 50 years of age and migraine is ranked as the sixth most disabling condition.19 The two common subtypes of migraine are migraine without aura and migraine with aura.19,22 One in five people with migraines experiences sensation disturbances known as auras that include blind spots (scotomas), small bright dots, and flashes of light.23 Although visual auras are the most common symptom, other recognized symptoms are muscle weakness, numbness, and speech difficulty.24
Another primary headache of interest in this study is tension-type headache. Although tension-type headache is less disabling than migraine, it has a higher global prevalence of 38%.19,20,22 It is the most common type of headache in adults, and has its onset in persons between the ages of 20 and 39 years.20,25 Tension-type headache is characterized by frequent bouts of pain, usually occurring bilaterally, with a compressive or constricting quality, and is mild to moderate in intensity.25 Tension-type headache is often considered a “normal headache” and is considered one of the five most prevalent disabling conditions in women.22
A secondary headache is a headache attributed to another underlying disease or condition.4,26,27 The International Headache Society classifies secondary headaches as headaches that occur concurrently with another condition by chance and without a definitive causal agent.26 Cervicogenic headache is the only secondary headache of interest in this review. This headache type is primarily associated with myofascial pain disorder stemming from the neck.1,4 Studies show that chronic cervical spine dysfunction may contribute to TMD.9 Cervicogenic headaches can be elicited by neck movements due to cervical spine pathogenesis.4
From the literature, it is evident that both TMD and headache are prevalent conditions affecting a substantial proportion of the adult population. Additionally, it has been shown that headaches may play a role in TMD and vice versa.1-3,6,12 The pooled prevalence of this relationship should be documented by reviewing the literature available. The significance of ascertaining the prevalence will influence the treatment and management of these headache types. If there is found to be a high concurrent prevalence of headache and TMD, this means it may be prudent for health care professionals to include orofacial care in the management of patients presenting with these headache types. Orofacial care has been shown to relieve headache pain in people experiencing headaches and TMD, and it also significantly improves the headache intensity, duration, as well as cervical spine range of motion and pain.1,28,29 By adding orofacial care to headache treatments, physiotherapists could potentially reduce the frequency and intensity of the headache as well as reduce TMD pain and improve functioning of the orofacial structures.1,21,30,31
A prevalence systematic review on concurrent TMD and headache will indicate the relevance of applying an appropriate combination of treatment of both headache and the orofacial structures. There are currently no systematic reviews focusing solely on the concurrent prevalence of TMD and headache within the adult population. An initial search for headache and TMD prevalence systematic reviews in the JBI Database of Systematic Reviews and Implementation Reports, PROSPERO, MEDLINE, and the Cochrane Database of Systematic Reviews yielded no results. Therefore, the primary objective of this systematic review is to determine the prevalence of TMD in patients who are experiencing headache and vice versa. The secondary objective is to determine prevalence differences between the sexes, age groups, headache, and TMD types.
Review questions
- i) What is the prevalence of TMD in adult patients experiencing headaches?
- ii) What is the prevalence of headache in adult patients experiencing TMD?
The secondary review questions are:
- i) What is the prevalence of TMD in patients experiencing headache who are between 18 and 50 years of age and those over the age of 50 years?
- ii) What is the prevalence of TMD in patients experiencing headache, and conversely, in men and women?
- iii) What is the prevalence of TMD in each of the different headache classifications (such as migraine, tension-type headache, migraine with and without aura, concurrent migraine and tension-type headache, cervicogenic headache and chronic headache)?
- iv) What is the prevalence of headache in each of the TMD classifications (namely arthrogenous and myogenous)?
Inclusion criteria
Participants
The review will include studies that were conducted with male and female participants who are 18 years and older and have been diagnosed with concurrent presence of headache and TMD.
Condition
Studies that include individuals who are experiencing headache and TMD, and that state the prevalence of these conditions, will be considered for inclusion in this review. The prevalence of patients experiencing TMD in a population of patients with headache will be explored,5,17,32 and the prevalence of patients experiencing headache in a population of patients with TMD will be explored.12,33,34 Only studies that present prevalence, or where the prevalence could be calculated from the results, will be included.
Headaches, including tension-type, migraine with and without aura, cervicogenic headache, and chronic headache are the only headache types that will be included in the review. Any other headache type will be excluded. Studies that diagnosed headache according to the International Classification of Headache Disorders ICHD-II26 criteria, and where TMD diagnoses were made according to the DC/TMD or RDC/TMD axis I and II, and the American Academy of Orofacial Pain will be included in this review. Studies done where participants had a periodontal cause of orofacial pain such as gum disease, tooth abscess, or any oral cavity disease will be excluded from the review to eliminate any other cause of orofacial pain other than TMD. Temporomandibular disorders will include both arthrogenous and myogenous TMD, which can be classified as either intra-articular or extra-articular, with the latter primarily being myogenous TMD.
Context
Studies that were conducted on individuals with headache and TMD globally, in both inpatient and outpatient settings, will be considered for inclusion in this review.
Types of studies
In order to extract prevalence data, cross-sectional observational studies will be considered for inclusion. Longitudinal prospective and retrospective cohort designs will be considered where the prevalence of headache and TMD can be extracted at the start of the study. Experimental studies, such as randomized controlled trials and pre-post intervention studies, will be considered for inclusion in cases where the point-prevalence of headache and TMD are indicated pre-intervention.
Methods
The systematic review will follow the JBI methodology for reviews of prevalence and incidence.35 The protocol is registered in PROSPERO: CRD42019139689.
Search strategy
The authors will scan the words contained in the titles and abstracts, and the index terms used to characterize the article. A second search using all recognized keywords and index terms will then be carried out across all databases. The reference lists of all relevant and selected reports will be searched for additional studies.
The search will include studies written in all languages, from inception until the present date. An initial search of MEDLINE (PubMed; Appendix I) will be followed by CINAHL, the Cochrane Central Register of Controlled Trials in the Cochrane Library, EBSCO MasterFILE Premier, PEDro, ProQuest Health and Medical Complete, ScienceDirect and Scopus, Dentistry and Oral Sciences Source, and Embase.
Preliminary keywords include headache, cervicogenic headache, tension-type headache, migraine with and without aura, orofacial pain, orofacial care, temporomandibular disorder, temporomandibular joint, arthrogenous and myogenous TMD. Additionally, MeSH terms will be used where possible (see Appendix I). Peer-reviewed published studies as well as unpublished studies (gray literature) will be considered for inclusion.
Study selection
Titles and abstracts of studies will be reviewed, and full-text articles will be selected if the inclusion criteria are met. Two reviewers (NM and UB) will review the titles, abstracts, and full texts based on the inclusion criteria. Should disagreements between reviewers exist, a third reviewer (BO) will be consulted. EndNote X8.2 (Clarivate Analytics, PA, USA) will be used to manage all records. Duplicates will be removed and all studies that do not meet the criteria will be excluded. All excluded full-text studies will be documented with reasons in the review.
Assessment of methodological quality
Studies that meet the eligibility criteria will be assessed by two independent reviewers (NM and UB) for methodological quality using the JBI System for the Unified Management, Assessment and Review of Information (JBI SUMARI; JBI, Adelaide, Australia)35 critical appraisal checklist for studies reporting prevalence data. Any disagreements between the two reviewers will be resolved through discussion, or a third reviewer (BO) will be consulted where needed.
Data extraction
The standardized data extraction tool from JBI SUMARI will be used. The authors will extract the following information from the included studies: citation details, study design/type, location of the study, setting/context, time frame for data collection, participant characteristics (study inclusion/exclusion information), sample size, condition and measurement method, and description of main results related to prevalence (n/N).
Data synthesis
The results from the included studies will be analyzed using JBI SUMARI software. Meta-analyses will be conducted by pooling the proportions from all included studies. Pooling of data from studies where the prevalence of TMD in those with headache have been established will be done. In addition, data from studies that determined the prevalence of headache in individuals with TMD will also be pooled. Sub-group analysis will be performed in the different headache classifications (such as migraine, tension-type headache, migraine with and without aura, concurrent migraine and tension-type headache, cervicogenic headache, and chronic headache). Similarly, sub-group analysis will be performed in the different types of TMD (arthrogenous and myogenous). Male and female prevalence within each sub-group will be determined where possible. A meta-analysis will also be performed according to age in those between 18 and 50 years, as well as participants older than 50 years.19
The I2 statistic will be calculated as well as 95% confidence intervals and a probability value shown for significance of effect. In order to allow for the expected high heterogeneity values from the variance of the studies, a random effects model will be utilized for the meta-analysis.36 The weighted summary proportions will be assessed using the Freeman-Tukey transformation (arcsine square root transformation) and the Logit transformation. Sample size, proportion (expressed as a percentage) and 95% confidence interval for the results of each individual study and the pooled result will be presented. Effect sizes of each included study and the summary effect will be presented in forest plots. The authors anticipate that a random effects model will need to be applied to account for within- and between-study variability; however, a fixed effects model will be applied when the heterogeneity between studies is low as determined by the I2 test. Potential publication bias will be presented through funnel plots.
If the heterogeneity between studies is high and it becomes impossible to pool findings into a meta-analysis, studies will be summarized in a narrative format and sources of heterogeneity, such as clinical, methodological, or statistical sources, will be discussed. All study data, including the quantitative results (point and interval estimates) from each study, will be presented in table format to ensure that the findings are transparent.
Appendix I: Search strategy
Search conducted in MEDLINE (PubMed): 21 July 2020
Results retrieved: 1207
Where possible, terms were searched for in MeSH as well as Text Word.
Search: (((((temporomandibular[Text Word]) OR (tmd[Text Word])) OR (tmj[Text Word])) OR (temporomandibular joint disorders[MeSH Terms])) AND (((((pathology[Text Word]) OR (pain[Text Word])) OR (dysfunction[Text Word])) OR (arthrogenous[Text Word])) OR (myogenous[Text Word]))) AND (((((((headache[Text Word]) OR (tension-type headache[Text Word])) OR (migraine[Text Word])) OR (cervicogenic headache[Text Word])) OR (cervical headache[Text Word])) OR (headache disorders[MeSH Terms])) OR (migraine disorders[MeSH Terms]))
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