Scoping review of systematic review abstracts about temporomandibular disorders: Comparison of search years 2004 and 2017

Introduction

The purposes of this study were to determine how many systematic reviews and meta-analyses relating to temporomandibular disorders (TMDs) had been published as of 2017 compared with those published as of 2004 and then to summarize the findings, based on an analysis of the abstracts from those studies.

Methods

A PubMed search was initiated on May 1, 2017. There were 2 separate searches. The first search was for the topic, “temporomandibular disorders.” The second search was for “temporomandibular disorders and published in the Cochrane database.” The number and the topic category of reviews for 2017 were compared with those published as of 2004.

Results

There were 120 relevant TMD systematic reviews found in search year 2017: 110 from the PubMed and 10 from the Cochrane searches. By comparison, there were only 8 TMD systematic reviews published in 2004. The abstracts for all 120 reviews indicated increased roles of genetics and psychosocial factors in the etiology of TMD. The future of TMD diagnoses appears to be toward various psychosocial and cellular tests, along with brain neuroimaging. The reviews on the topic of “treatment” supported conservative, noninvasive, reversible therapies, with a trend toward more targeted individual strategies.

Conclusions

There were only 8 TMD systematic reviews published in 2004 compared with 110 in 2017. Overall, the trend has been in the direction of better diagnostic procedures, more scientific concepts of etiology, and more conservative treatments for TMD.

Highlights

  • A 2004 literature search found 8 systematic reviews on TMD.

  • A 2017 search found 110 relevant systematic reviews in PubMed and 10 in Cochrane.

  • In 2017, 58 of the PubMed listings and all 10 of the Cochrane listings reported on treatments.

  • Conservative, noninvasive, and reversible TMD treatments are preferred.

  • No evidence was found that orthodontic treatment causes, cures, or prevent TMDs.

Once considered a single disorder with a single cause, temporomandibular disorders (TMDs) are now considered a collection of musculoskeletal conditions involving the masticatory muscles, temporomandibular joints (TMJs), and associated structures. According to the American Dental Association’s first TMD conference, held in June 1982, there are 6 subclasses of TMD: masticatory muscle disorders, derangements of the TMJs, traumatic arthritis, degenerative joint diseases, chronic mandibular hypomobility, and growth disorders. There is a multifactorial etiology for each subclass. Occlusion and specific locations of the condyles in the glenoid fossae (eg, centric relation) are no longer considered to be the primary factors in the multifactorial etiology of TMD.

For many years, orthodontists have had serious interests and concerns about TMDs. In 1988, Greene asked, “Does orthodontic treatment cause, cure, or prevent TMDs?” His answer to all 3 parts of the question was “no,” based on the limited research available at that time. Since then, there has been a tremendous increase in interest in this issue in the orthodontic specialty and the entire dental profession. The huge number of clinical and scientific studies reported in the past 30 years on TMJ topics has led to many systematic reviews and meta-analyses of that literature. In the end, the current literature has supported the 1988 conclusions of Greene; orthodontics does not generally cause, mitigate, or cure TMD, nor does it prevent the future development of TMD.

Discussions about the etiology and treatment of TMDs have moved away from a historic, dental-based model to a biopsychosocial model that integrates the host of biologic, behavioral, and social factors that are related to the onset, maintenance, and management of TMD. Many studies have led to the conclusion that TMD treatments should be, at least initially, conservative (noninvasive), reversible, palliative, and when possible based on science and evidence. A medical orthopedic approach is recommended that focuses on the biomedical sciences and musculoskeletal therapies similar to those for most chronic pain. Cognitive-behavioral therapies and biofeedback are now prominent among contemporary TMD treatment modalities. Genetics (vulnerabilities related to pain), cell studies, endocrinology, behavioral risk-conferring factors, and brain neuroimaging are the exciting future of TMD studies.

Systematic reviews (and meta-analyses) are at the highest level in the hierarchy of scientific evidence. Systematic reviews involve an exhaustive search of the literature on a topic, and then an expert panel selects a limited number of worthy studies, mostly randomized controlled trials (RCTs), to be included in the review. Depending on the nature of the review, RCTs may not be included. The relevant information from the chosen studies is then interpreted and summarized. The Cochrane database of systematic reviews takes a more discriminatory approach; authors submit proposals that are reviewed by its editorial team, with systematic reviews updated at least every 4 years.

It would be of interest for dentists, including orthodontists, to know and understand the information in TMD systematic reviews to make objective, evidence-based decisions regarding patient diagnoses and treatments. In 2006, Rinchuse and McMinn published a report in which they listed, reviewed, and discussed the 8 TMD systematic reviews (1 was a meta-analysis) published in 2004. The purpose of this current investigation was to obtain the listings and abstracts of all the TMD systematic reviews published up to 2017 and then to present this information in 6 tables arranged by topic heading: prevalence, diagnosis, etiology, treatment, surgery, and miscellaneous ( Appendix Tables I-VI ). The numeric data from the 2017 search was compared with those from 2004.

Material and methods

Two PubMed searches were initiated on May 1, 2017, to look for systematic reviews and meta-analyses related to TMD. The first search was for the topic, “temporomandibular disorders.” The second search was for “temporomandibular disorders and published in the Cochrane database.” The number of reviews and categories of the topics covered in those reviews were compared with the 8 TMD systematic reviews published in 2004. For the purpose of this study, only the abstracts of the systematic reviews were obtained and analyzed to create the tables of results presented in this article.

The inclusion criteria were all systematic reviews (meta-analyses) listed in the PubMed and Cochrane databases for a search on May 1, 2017, under the title of “temporomandibular disorders.” The exclusion criterion for the general PubMed search was articles that were not TMD systematic reviews or had missing information; for the Cochrane database, the exclusion criterion was any articles that were withdrawn because they were supplanted by an updated review on a certain TMD topic.

The salient information from the systematic reviews for both searches was placed into 6 categories: prevalence, diagnosis, etiology, treatment, surgery, and miscellaneous. From the abstracts, tables were constructed for each category; the most notable information from each abstract, such as author and year, topic, number of articles meeting the selection criteria, quality of the review, and findings and conclusions are included in the 6 Appendix Tables. A table was also constructed comparing the numbers and categories of TMD systematic reviews from the 2004 search with those from the 2017 search ( Table I ). In addition, for the 2017 search, PubMed listings were compared with Cochrane listings ( Table I ). Results were summarized per numeric comparison, as well as per narrative, informational findings. The quality of the systematic reviews was evaluated and reported. The criteria and protocol for the assessment of the quality of the studies were based on what their authors stated, as well as the subjective opinions (when possible to ascertain from only reading an abstract) of the authors.

Table I
Comparison of the numbers of TMD systematic reviews (and meta-analyses) published in 2004 and 2017 in various categories
Year Prevalence Diagnosis Etiology Treatment Surgery Miscellaneous Total
2004 1 3 4 8
2017 (PubMed) 4 13 16 58 16 3 110
2017 (Cochrane) 10 10

Results

For the first PubMed search, there were 115 listings for TMDs; 110 were relevant. For the second search in the Cochrane databse, there were 19 listings; 10 were relevant; the other 9 had been withdrawn because the listings were replaced by more current reviews. The 5 articles excluded from the general PubMed listing had various deficiencies: (1) older review with no author identification, (2) article dealing with pain that was not a systematic review, (3) article on exercise and TMD with not all information reported (ie, only reported title and author), (4) article that was a critique of a publication by a world-renowned TMD expert who summarized the American Association of Dental Research 2010 Policy Statement on TMD and was not a systematic review, and (5) review that did not explicitly deal with TMD.

We divided the reviews into 6 categories: diagnosis, etiology, prevalence, treatment, surgery, and miscellaneous. The quality of the studies analyzed in all reviews was low to low-medium, with no high-level quality of evidence reported in any publication.

The 8 reviews from 2004 that had been analyzed by Rinchuse and McMinn in 2006 were compared with the 110 reviews found by searching in 2017 ( Table I ). The 10 Cochrane 2017 reviews were also compared. For 2004, half of the reviews (4 of 8) were related to treatment, and 4 were related to etiology. For 2017, most of the reviews (58 of 110) in the PubMed listing were for TMD treatments, whereas all 10 of the Cochrane reviews for 2017 were related to TMD treatment. The reviews for TMD treatment focused on conservative, reversible, low-tech, and noninvasive therapies vs aggressive, irreversible treatments ( Appendix Table IV ). For instance, there were only 3 reviews from the general PubMed search ( Appendix Table IV ) and 1 review from the Cochrane search ( Table II ) that dealt with occlusal adjustments (an irreversible form of treatment); all of those reviews reported a lack of support for this type of TMD treatment.

Table II
TMD systematic reviews published in Cochrane database
Author Topic Articles meeting criteria Quality Findings/conclusions
Aggarwal et al 2015 Treatment/psychosocial /17 Low There is weak evidence to support the use of psychosocial interventions for chronic orofacial pain. However, given the noninvasive nature of such interventions, they should be used in preference to other invasive and irreversible therapies.
Al-Ani et al 2016 Stabilizing splints 20/12 Low There is insufficient evidence either for or against the use of stabilizing splints for the treatment of TMD.
De Souza et al 2012 Treatment/TMD osteoarthritis/many types /3 Low Evaluated the most common forms of treatment for TMD osteoarthritis. The reports indicated a not dissimilar degree of effectiveness with intra-articular injections consisting of either sodium hyaluronate or corticosteroids, and an equivalent pain reduction with diclofenac sodium compared with occlusal splints. Glucosamine appeared to be just as effective as ibuprofen.
Guo et al 2015 Treatment/arthrocentesis lavage /2 Low There is insufficient, consistent evidence to either support or refute the use of arthrocentesis and lavage for TMD.
Koh and Robinson 2016 Treatment/occlusal adjustments 660/6 Medium There is no evidence from randomized controlled trials that occlusal adjustment treats or prevents TMD. Occlusal adjustments are not recommended for management or prevention of TMD.
Luther et al 2016 Treatment/orthodontics 284/55 Low There is insufficient data to answer the question whether orthodontics is a viable TMD treatment modality.
Mujakperuo et al 2010 Treatment/pharmacology /11 Low There is insufficient evidence to support or not support the effectiveness of reported drugs for the management of pain due to TMD.
Rigon et al 2015 Treatment/arthroscopy /7 Low-medium Both arthroscopy and nonsurgical treatments reduced pain after 6 months. In comparison with arthroscopy, open surgery was more effective at reducing pain after 12 months. Nevertheless, there were no differences in mandibular functionality or other outcomes. Arthoscopy led to greater improvement in maximum interincisal opening after 12 months than arthrocentesis; there was no difference in pain.
Shi et al 2013 Treatment/hyaluronate /7 Low There is insufficient evidence to either support or refute the use of hyaluronate for treating TMD.
Agostino et al 2014 Not TMD/posterior crossbite /15 Low The quad-helix may be more successful than removable expansion plates at correcting posterior crossbites for children in the early mixed dentition (ages 8-10).
/, the number before the symbol is the total number of articles accessed and the number after the symbol is the number meeting the criteria. If there is no number before the symbol, the number could not be ascertained from the abstract.

The 2017 systematic review findings indicated increased roles of genetics and psychosocial factors in the etiology of TMD. There was little to no support for a causal relationship between occlusal factors and TMD, and occlusion-changing treatments were not supported by evidence. Data do not indicate that traditional orthodontic treatment increased the prevalence or risk of TMD. The future of TMD diagnosis appears to be toward various cellular and psychosocial tests, along with brain neuroimaging. The reviews on treatment supported conservative, noninvasive, reversible therapies, with a trend toward more targeted individual strategies.

There were 4 TMD systematic reviews dealing with prevalence; 3 of those dealt with TMD prevalence in the general population, and 1 dealt with diagnostic findings in a TMD patient population. As in most reports on the prevalence of TMD, there was variability in the findings depending on age, sex, geographic region, assessment method, and so forth ( Appendix Table I ). Da Silva et al in 2016 reported that in the general population 1 in 6 children and adolescents has clinical signs of TMD, but their inclusion criteria for positive findings were questionable. Manfredini et al in 2011 reported that the most common diagnostic TMD finding in TMD populations is myofascial pain, with and without mouth-opening limitations; disc displacement with reduction was the most common finding in community samples ( Appendix Table I ).

Thirteen articles addressed TMD diagnosis ( Appendix Table II ). The listings covered a host of subtopics such as cellular, imaging, ultrasound, muscle palpation, joint vibration, and posturography. Obviously, TMD imaging had the most scientific support, followed by ultrasound. Joint vibration and posturography had no evidence-based support when subjected to critical assessments. Interestingly, muscle palpation of the lower head of the lateral pterygoid muscle lacked scientific support. Importantly, there is growing evidence for various cellular tests for TMD, and this may be the future of TMD diagnoses.

The etiology or cause of TMD has arguably been the topic of most interest in the TMD field over the past century. There were 16 general PubMed listings under this topic ( Appendix Table III ). The subtopics for etiology included bruxism, orthodontics, facial types, posterior crossbites, occlusion, heredity/genes, “brain,” hypermobility, posture, trauma/psychological, and whiplash. In the 2 reports that dealt with bruxism, there was a positive relationship between bruxism and TMD ; 1 of the reports was published in 2017, with the quality of the evidence low-moderate.

There were 3 listings for orthodontics. The meta-analysis by Kim et al in 2004 is known in the orthodontic community; they concluded that, “although no definitive conclusions could be made due to the heterogeneity of the studies, the data do not indicate that traditional orthodontic treatment increased the prevalence or risk of TMD.” The review by Iodice et al in 2013 indicated that no conclusions could be drawn related to posterior crossbites causing TMD. Also, no conclusions could be drawn by Manfredini et al in 2016 related to facial/skeletal types (ie, Class II profiles and hyperdivergent growth patterns) being associated with TMJ disc displacement and degenerative disorders. In addition, there were 2 reports dealing with occlusion and TMD. Both reviews concluded that there is little to no support for a causal relationship between occlusal factors and TMD.

Of interest is the relationship of heredity and genes in the etiology of TMD. It is common knowledge that genes play a significant role in the cause or development of most diseases and ailments, and this now includes TMD. Visscher and Lobbezoo in 2015 found evidence for the role of heritability in the development of TMD pain: genetic contributions from candidate genes that encode proteins involved in the processing of painful stimuli from serotonergic and cathecholaminergic systems. Equally important is the role of changes in the brain in the development of TMD. Further consideration of this topic ultimately leads to the question of what causes the brain changes; it is clear that these are not the primary etiology for TMD. Brain neuroimaging has demonstrated that TMD patients show consistent functional and structural changes in the thalamus and the primary somatosensory cortex, indicating the thalamocortical pathway as the major site of plasticity. There is also the suggestion that cognitive modulation and reward processing play roles in chronic orofacial pain. Brain neuroimaging will almost certainly become an important investigative tool for understanding chronic orofacial pain.

There were several other additional findings from the etiology category. One review on generalized TMJ hypermobility concluded that it was not clear whether there was an association with TMD. The role of head and cervical posture (craniocervical posture) in TMD was not clearly demonstrated in any of the 3 articles that dealt with this topic. Also, 1 review concluded that traumatic events (including psychological, emotional, sexual, or physical, including combat exposure) are associated with TMD. Whiplash trauma was considered an initiating or aggravating factor, as well as a comorbid condition for TMD; the prevalence of such trauma ranged from 8.4% to 70% in the TMD population compared with 1.7% to 13% in the non-TMD groups.

All 10 Cochrane reviews dealt with TMD treatment ( Tables I and II ). As previously mentioned, 58 of the 110 PubMed reviews were in the category of “treatment” ( Table I ; Appendix Table IV ). Several types of treatment modalities were reviewed, including various conservative and noninvasive approaches such as hypnosis and relaxation, counseling, biofeedback, acupuncture, pharmacology, physical therapy, manual techniques, and various exercises. Other modalities studied included occlusal splints, occlusal adjustments, injections, lasers, luxation, and so on. Of course, various surgical procedures were among the TMD treatments, but they are discussed below under the category of “surgery” ( Appendix Table V ).

Parenthetically, dentistry in general and orthodontics in particular have for decades had an interest in the possible relationship between occlusion and TMD, and many experts and practitioners have assumed a cause-and-effect relationship between these 2 variables. This has changed in the last several decades; by 2017, it was clear that occlusal variables are not a significant etiologic factor for the vast majority of TMD patients. We can now say that occlusal adjustments are not considered a logical and evidence-based treatment modality for TMD; there is no scientific basis, and it is an irreversible form of TMD therapy. To explain, there were 3 reviews from the general PubMed listing and 1 from the Cochrane listing dealing with this topic, and all of them pointed in the same direction: occlusal adjustments are not recommended for the management or prevention of TMD. The most recent of these reviews, from the Cochrane database, was by Koh and Robinson in 2016, and they reported that there was no evidence from RCTs that occlusal adjustment should be used to treat or prevent TMD.

There was support for the various noninvasive and conservative treatment modalities such as counseling, psychosocial therapies, biofeedback, hypnosis/relaxation, accupuncture, pharmacology, physical therapy/exercise, physiotherapy, and stabilizing splints. The efficacy of lasers was equivocal. Naeije et al found, with medium to high quality of evidence, that TMJ disc displacement with reduction is mostly stable and a life-long, pain-free condition. Therefore, because of the favorable natural course of disc displacement, active treatment is only indicated for symptomatic disc displacement without reduction. TMJ injections with sodium hyaluronate, or corticosteroids, or botulinum toxin are inconclusive.

There was no listing of orthodontics as a treatment choice among the systematic reviews for the general PubMed listing. In the Cochrane database, there was 1 article by Agostino et al in 2014 about the quad-helix appliance as a successful treatment for posterior crossbites in the early mixed dentition. This report was not a systematic review dealing with TMD. We decided to keep it in the Cochrane “treatment” listing even though it dealt with orthodontic treatment per se and not specifically TMD, because there has been a long history about the possibilities of crossbites associated with TMD.

Most of the 16 TMD systematic reviews in the “surgery” category ( Appendix Table V ) dealt with surgical treatments and could also have been placed in the “treatment” category, but we decided to place them in the separate category of “surgery” in order to highlight those findings. Surgeries for TMD are indicated only when conservative and reversible treatments fail, for chronic conditions, or for an acute, sudden traumatic event in need of immediate attention.

In the “surgery” category, 16 reviews were found in the PubMed listings ( Appendix Table V ), and 2 were found in the Cochrane listings ( Table II ). The 2 Cochrane reviews specifically dealt with surgical treatment for TMD. For the 16 PubMed listings, there were reviews that dealt with both the treatment efficacy of various surgical procedures and the effects of certain maxillofacial surgical procedures on the TMJs. In 1 Cochrane review, the authors concluded that there was insufficient evidence to either support or refute the use of arthrocentesis and lavage for TMD. The other Cochrane review was more comprehensive, comparing nonsurgical treatments with arthrocentesis, arthroscopy, and open surgery. Although both arthroscopy and nonsurgical treatments reduced pain after 6 months, open surgery was more effective than arthroscopy for pain after 12 months. In addition, there was greater maximum interincisal opening after 12 months with arthroscopy vs arthrocentesis, but there was no difference in pain.

The 16 PubMed articles that covered surgical topics dealt with a wide variety of issues; readers are encouraged to read the summaries in Appendix Table V . Two noteworthy studies are mentioned here: Al-Moraissi reported that no final conclusion could be drawn for arthroscopy vs arthrocentesis for management of TMJ internal derangements; this is similar to the conclusions from the Cochrane reviews. From the review by Al-Riyami et al in 2009, it was concluded that, although orthognathic surgery should not be advocated solely to treat TMD, it may be likely to improve TMD signs and symptoms; the quality of evidence was, however, low, and the review was dated.

There were 3 publications in the “miscellaneous” category ( Appendix Table VI ). The first one by Fricton et al alerted the reader about certain limitations of TMD systematic reviews. Foremost is the potential for systemic bias, particularly for older studies, and therefore some systematic reviews should be interpreted with caution. Of the other 2 listings, 1 dealt with an unusual TMJ case of pigmented villodular synovitis, and the other concluded that having symptomatic TMD negatively affects oral health-related quality of life, which would be an expected finding.

Results

For the first PubMed search, there were 115 listings for TMDs; 110 were relevant. For the second search in the Cochrane databse, there were 19 listings; 10 were relevant; the other 9 had been withdrawn because the listings were replaced by more current reviews. The 5 articles excluded from the general PubMed listing had various deficiencies: (1) older review with no author identification, (2) article dealing with pain that was not a systematic review, (3) article on exercise and TMD with not all information reported (ie, only reported title and author), (4) article that was a critique of a publication by a world-renowned TMD expert who summarized the American Association of Dental Research 2010 Policy Statement on TMD and was not a systematic review, and (5) review that did not explicitly deal with TMD.

We divided the reviews into 6 categories: diagnosis, etiology, prevalence, treatment, surgery, and miscellaneous. The quality of the studies analyzed in all reviews was low to low-medium, with no high-level quality of evidence reported in any publication.

The 8 reviews from 2004 that had been analyzed by Rinchuse and McMinn in 2006 were compared with the 110 reviews found by searching in 2017 ( Table I ). The 10 Cochrane 2017 reviews were also compared. For 2004, half of the reviews (4 of 8) were related to treatment, and 4 were related to etiology. For 2017, most of the reviews (58 of 110) in the PubMed listing were for TMD treatments, whereas all 10 of the Cochrane reviews for 2017 were related to TMD treatment. The reviews for TMD treatment focused on conservative, reversible, low-tech, and noninvasive therapies vs aggressive, irreversible treatments ( Appendix Table IV ). For instance, there were only 3 reviews from the general PubMed search ( Appendix Table IV ) and 1 review from the Cochrane search ( Table II ) that dealt with occlusal adjustments (an irreversible form of treatment); all of those reviews reported a lack of support for this type of TMD treatment.

Table II
TMD systematic reviews published in Cochrane database
Author Topic Articles meeting criteria Quality Findings/conclusions
Aggarwal et al 2015 Treatment/psychosocial /17 Low There is weak evidence to support the use of psychosocial interventions for chronic orofacial pain. However, given the noninvasive nature of such interventions, they should be used in preference to other invasive and irreversible therapies.
Al-Ani et al 2016 Stabilizing splints 20/12 Low There is insufficient evidence either for or against the use of stabilizing splints for the treatment of TMD.
De Souza et al 2012 Treatment/TMD osteoarthritis/many types /3 Low Evaluated the most common forms of treatment for TMD osteoarthritis. The reports indicated a not dissimilar degree of effectiveness with intra-articular injections consisting of either sodium hyaluronate or corticosteroids, and an equivalent pain reduction with diclofenac sodium compared with occlusal splints. Glucosamine appeared to be just as effective as ibuprofen.
Guo et al 2015 Treatment/arthrocentesis lavage /2 Low There is insufficient, consistent evidence to either support or refute the use of arthrocentesis and lavage for TMD.
Koh and Robinson 2016 Treatment/occlusal adjustments 660/6 Medium There is no evidence from randomized controlled trials that occlusal adjustment treats or prevents TMD. Occlusal adjustments are not recommended for management or prevention of TMD.
Luther et al 2016 Treatment/orthodontics 284/55 Low There is insufficient data to answer the question whether orthodontics is a viable TMD treatment modality.
Mujakperuo et al 2010 Treatment/pharmacology /11 Low There is insufficient evidence to support or not support the effectiveness of reported drugs for the management of pain due to TMD.
Rigon et al 2015 Treatment/arthroscopy /7 Low-medium Both arthroscopy and nonsurgical treatments reduced pain after 6 months. In comparison with arthroscopy, open surgery was more effective at reducing pain after 12 months. Nevertheless, there were no differences in mandibular functionality or other outcomes. Arthoscopy led to greater improvement in maximum interincisal opening after 12 months than arthrocentesis; there was no difference in pain.
Shi et al 2013 Treatment/hyaluronate /7 Low There is insufficient evidence to either support or refute the use of hyaluronate for treating TMD.
Agostino et al 2014 Not TMD/posterior crossbite /15 Low The quad-helix may be more successful than removable expansion plates at correcting posterior crossbites for children in the early mixed dentition (ages 8-10).
/, the number before the symbol is the total number of articles accessed and the number after the symbol is the number meeting the criteria. If there is no number before the symbol, the number could not be ascertained from the abstract.

The 2017 systematic review findings indicated increased roles of genetics and psychosocial factors in the etiology of TMD. There was little to no support for a causal relationship between occlusal factors and TMD, and occlusion-changing treatments were not supported by evidence. Data do not indicate that traditional orthodontic treatment increased the prevalence or risk of TMD. The future of TMD diagnosis appears to be toward various cellular and psychosocial tests, along with brain neuroimaging. The reviews on treatment supported conservative, noninvasive, reversible therapies, with a trend toward more targeted individual strategies.

There were 4 TMD systematic reviews dealing with prevalence; 3 of those dealt with TMD prevalence in the general population, and 1 dealt with diagnostic findings in a TMD patient population. As in most reports on the prevalence of TMD, there was variability in the findings depending on age, sex, geographic region, assessment method, and so forth ( Appendix Table I ). Da Silva et al in 2016 reported that in the general population 1 in 6 children and adolescents has clinical signs of TMD, but their inclusion criteria for positive findings were questionable. Manfredini et al in 2011 reported that the most common diagnostic TMD finding in TMD populations is myofascial pain, with and without mouth-opening limitations; disc displacement with reduction was the most common finding in community samples ( Appendix Table I ).

Thirteen articles addressed TMD diagnosis ( Appendix Table II ). The listings covered a host of subtopics such as cellular, imaging, ultrasound, muscle palpation, joint vibration, and posturography. Obviously, TMD imaging had the most scientific support, followed by ultrasound. Joint vibration and posturography had no evidence-based support when subjected to critical assessments. Interestingly, muscle palpation of the lower head of the lateral pterygoid muscle lacked scientific support. Importantly, there is growing evidence for various cellular tests for TMD, and this may be the future of TMD diagnoses.

The etiology or cause of TMD has arguably been the topic of most interest in the TMD field over the past century. There were 16 general PubMed listings under this topic ( Appendix Table III ). The subtopics for etiology included bruxism, orthodontics, facial types, posterior crossbites, occlusion, heredity/genes, “brain,” hypermobility, posture, trauma/psychological, and whiplash. In the 2 reports that dealt with bruxism, there was a positive relationship between bruxism and TMD ; 1 of the reports was published in 2017, with the quality of the evidence low-moderate.

There were 3 listings for orthodontics. The meta-analysis by Kim et al in 2004 is known in the orthodontic community; they concluded that, “although no definitive conclusions could be made due to the heterogeneity of the studies, the data do not indicate that traditional orthodontic treatment increased the prevalence or risk of TMD.” The review by Iodice et al in 2013 indicated that no conclusions could be drawn related to posterior crossbites causing TMD. Also, no conclusions could be drawn by Manfredini et al in 2016 related to facial/skeletal types (ie, Class II profiles and hyperdivergent growth patterns) being associated with TMJ disc displacement and degenerative disorders. In addition, there were 2 reports dealing with occlusion and TMD. Both reviews concluded that there is little to no support for a causal relationship between occlusal factors and TMD.

Of interest is the relationship of heredity and genes in the etiology of TMD. It is common knowledge that genes play a significant role in the cause or development of most diseases and ailments, and this now includes TMD. Visscher and Lobbezoo in 2015 found evidence for the role of heritability in the development of TMD pain: genetic contributions from candidate genes that encode proteins involved in the processing of painful stimuli from serotonergic and cathecholaminergic systems. Equally important is the role of changes in the brain in the development of TMD. Further consideration of this topic ultimately leads to the question of what causes the brain changes; it is clear that these are not the primary etiology for TMD. Brain neuroimaging has demonstrated that TMD patients show consistent functional and structural changes in the thalamus and the primary somatosensory cortex, indicating the thalamocortical pathway as the major site of plasticity. There is also the suggestion that cognitive modulation and reward processing play roles in chronic orofacial pain. Brain neuroimaging will almost certainly become an important investigative tool for understanding chronic orofacial pain.

There were several other additional findings from the etiology category. One review on generalized TMJ hypermobility concluded that it was not clear whether there was an association with TMD. The role of head and cervical posture (craniocervical posture) in TMD was not clearly demonstrated in any of the 3 articles that dealt with this topic. Also, 1 review concluded that traumatic events (including psychological, emotional, sexual, or physical, including combat exposure) are associated with TMD. Whiplash trauma was considered an initiating or aggravating factor, as well as a comorbid condition for TMD; the prevalence of such trauma ranged from 8.4% to 70% in the TMD population compared with 1.7% to 13% in the non-TMD groups.

All 10 Cochrane reviews dealt with TMD treatment ( Tables I and II ). As previously mentioned, 58 of the 110 PubMed reviews were in the category of “treatment” ( Table I ; Appendix Table IV ). Several types of treatment modalities were reviewed, including various conservative and noninvasive approaches such as hypnosis and relaxation, counseling, biofeedback, acupuncture, pharmacology, physical therapy, manual techniques, and various exercises. Other modalities studied included occlusal splints, occlusal adjustments, injections, lasers, luxation, and so on. Of course, various surgical procedures were among the TMD treatments, but they are discussed below under the category of “surgery” ( Appendix Table V ).

Parenthetically, dentistry in general and orthodontics in particular have for decades had an interest in the possible relationship between occlusion and TMD, and many experts and practitioners have assumed a cause-and-effect relationship between these 2 variables. This has changed in the last several decades; by 2017, it was clear that occlusal variables are not a significant etiologic factor for the vast majority of TMD patients. We can now say that occlusal adjustments are not considered a logical and evidence-based treatment modality for TMD; there is no scientific basis, and it is an irreversible form of TMD therapy. To explain, there were 3 reviews from the general PubMed listing and 1 from the Cochrane listing dealing with this topic, and all of them pointed in the same direction: occlusal adjustments are not recommended for the management or prevention of TMD. The most recent of these reviews, from the Cochrane database, was by Koh and Robinson in 2016, and they reported that there was no evidence from RCTs that occlusal adjustment should be used to treat or prevent TMD.

There was support for the various noninvasive and conservative treatment modalities such as counseling, psychosocial therapies, biofeedback, hypnosis/relaxation, accupuncture, pharmacology, physical therapy/exercise, physiotherapy, and stabilizing splints. The efficacy of lasers was equivocal. Naeije et al found, with medium to high quality of evidence, that TMJ disc displacement with reduction is mostly stable and a life-long, pain-free condition. Therefore, because of the favorable natural course of disc displacement, active treatment is only indicated for symptomatic disc displacement without reduction. TMJ injections with sodium hyaluronate, or corticosteroids, or botulinum toxin are inconclusive.

There was no listing of orthodontics as a treatment choice among the systematic reviews for the general PubMed listing. In the Cochrane database, there was 1 article by Agostino et al in 2014 about the quad-helix appliance as a successful treatment for posterior crossbites in the early mixed dentition. This report was not a systematic review dealing with TMD. We decided to keep it in the Cochrane “treatment” listing even though it dealt with orthodontic treatment per se and not specifically TMD, because there has been a long history about the possibilities of crossbites associated with TMD.

Most of the 16 TMD systematic reviews in the “surgery” category ( Appendix Table V ) dealt with surgical treatments and could also have been placed in the “treatment” category, but we decided to place them in the separate category of “surgery” in order to highlight those findings. Surgeries for TMD are indicated only when conservative and reversible treatments fail, for chronic conditions, or for an acute, sudden traumatic event in need of immediate attention.

In the “surgery” category, 16 reviews were found in the PubMed listings ( Appendix Table V ), and 2 were found in the Cochrane listings ( Table II ). The 2 Cochrane reviews specifically dealt with surgical treatment for TMD. For the 16 PubMed listings, there were reviews that dealt with both the treatment efficacy of various surgical procedures and the effects of certain maxillofacial surgical procedures on the TMJs. In 1 Cochrane review, the authors concluded that there was insufficient evidence to either support or refute the use of arthrocentesis and lavage for TMD. The other Cochrane review was more comprehensive, comparing nonsurgical treatments with arthrocentesis, arthroscopy, and open surgery. Although both arthroscopy and nonsurgical treatments reduced pain after 6 months, open surgery was more effective than arthroscopy for pain after 12 months. In addition, there was greater maximum interincisal opening after 12 months with arthroscopy vs arthrocentesis, but there was no difference in pain.

The 16 PubMed articles that covered surgical topics dealt with a wide variety of issues; readers are encouraged to read the summaries in Appendix Table V . Two noteworthy studies are mentioned here: Al-Moraissi reported that no final conclusion could be drawn for arthroscopy vs arthrocentesis for management of TMJ internal derangements; this is similar to the conclusions from the Cochrane reviews. From the review by Al-Riyami et al in 2009, it was concluded that, although orthognathic surgery should not be advocated solely to treat TMD, it may be likely to improve TMD signs and symptoms; the quality of evidence was, however, low, and the review was dated.

There were 3 publications in the “miscellaneous” category ( Appendix Table VI ). The first one by Fricton et al alerted the reader about certain limitations of TMD systematic reviews. Foremost is the potential for systemic bias, particularly for older studies, and therefore some systematic reviews should be interpreted with caution. Of the other 2 listings, 1 dealt with an unusual TMJ case of pigmented villodular synovitis, and the other concluded that having symptomatic TMD negatively affects oral health-related quality of life, which would be an expected finding.

Discussion

The main finding from this extensive search of the TMD literature was that there has been a marked increase in the number of TMD systematic reviews between 2004 and 2017. There were 8 reviews published in 2004 and 110 general PubMed listings and 10 Cochrane reports as of 2017. Although this increase is impressive, with few exceptions the quality of evidence for current TMD systematic reviews (2017) is low (weak); in most cases, the reviews are based on small numbers of RCTs. As a result, the intellectual yield from those studies still leaves much to be desired, with many issues remaining unresolved at this time.

From an evaluation of the 110 currently available TMD systematic reviews (and 10 Cochrane reviews), it was apparent that most are on the topic of “treatment.” Not surprising is that most treatments considered in these reviews are in the category of conservative and reversible forms of therapy, including hypnosis and relaxation, counseling, biofeedback, acupuncture, pharmacology, physical therapy, and manual techniques as well as various head and neck related exercises. Other modalities studied included occlusal splints, occlusal adjustments, injections, lasers, luxation, and so on. Whereas the findings from those reviews were generally positive for all conservative therapies, the level of evidence was low. Aggressive and irreversible forms of TMD treatments, such as occlusal adjustments, were not supported by the evidence.

The first organized attempts to deal scientifically with the issues related to TMD at a national level took place at the first TMD conference of the American Dental Association (ADA) in June 1982, with the findings published in the Journal of the American Dental Association in January 1983. A second ADA-sponsored conference took place in 1989. Current evidence-based reports and findings about TMD are often juxtaposed with the findings and recommendations from these 2 ADA conferences. The knowledge and understanding of TMD from an evidence-based perspective has certainly been bolstered by subsequent national TMD conferences including 1 sponsored by the National Institutes of Health in 1996 and several educational conferences.

The general guidelines and recommendations about diagnosis and treatment of TMDs from those conferences still hold true today, but there definitely is more evidence to support them. For example, the recommendations of the ADA conferences regarding treatment were that TMD management should be based on conservative and reversible (noninvasive) treatment modalities and, when possible, have a scientific basis for the recommended treatment. Evidence-based recommendations for TMD treatments that followed shortly after the ADA conferences were consistent with the conference recommendations. For instance, they emphasized that TMD treatments should generally be symptomatic and palliative; rarely do TMD treatments address causation or etiology. The more aggressive and irreversible types of TMD treatments were only necessary as a “when all else fails” option. As we learn more about chronic pain, it is clear that escalation to aggressive treatments is often inappropriate. In addition, the gold standard for TMD diagnosis in the early years was rather simplistic (but nonetheless true): (1) medical and dental histories, (2) TMJ clinical examination, and (3) when indicated, TMJ imaging. Parenthetically, orthodontics was considered TMJ neutral; it neither caused, prevented, nor cured TMD.

Certainly, a consideration of these systematic reviews should be important to both the clinician and the academic with an interest in TMD. All general dental and orthodontic clinicians need to have current, evidence-based knowledge of the TMD literature to properly manage patients with signs and symptoms of TMD; this information also would be useful for patient referrals to other professionals. Furthermore, as stated by Mullmani : “[It is] crucial for orthodontists to step up to the challenge and equip themselves with biologically sound scientific rationale and evidence-based facts to face the Google-equipped and informed patients and their interrogations.” By giving the reader succinct summaries of all 110 TMD reviews (and 10 Cochrane reviews), arranged in tables by topic categories, we hope that clinicians will find this updated information useful in dealing with TMD patients in their practices.

After our data collection process in May 2017, another important TMD systematic review about TMD and occlusion was published in July 2017. Manfredini et al reviewed 822 citations and chose 25 studies that met their inclusion criteria (17 were case control studies of TMD vs non-TMD subjects). They believed that only 2 studies had high quality, whereas most fell into the moderate category. The general conclusion was that there was a lack of a clinically relevant association between TMD and dental occlusion; this means that occlusion should not be viewed as the critical host factor in the pathophysiology of TMD. This leads to the clinical implication that TMD treatments based on altering the dental occlusion should be viewed with caution, and patients should be advised of this current state of the evidence.

As the past concepts of etiology and treatment fade away, there are important developments in the TMD field. Current evidence suggests that TMDs should be viewed as a group of orthopedic disorders, with strong genetic and psychosocial factors playing important roles. Of course, these developments were not expected by all previous TMD conferences. Experts now view TMD as a chronic musculoskeletal disorder, with all considerations of diagnosis and treatment based on those for orthopedics and physical therapy and physical medicine, as well as those related to chronic pain mangement. Regarding the genetic considerations for TMD, there are candidate genes that encode proteins involved in the processing of painful stimuli from serotonergic and cathecholinergic systems. Brain neuroimaging will increase to identify changes in brain areas related to chronic orofacial pain.

No discussion of contemporary TMD research would be complete without noting the recent high level, evidence-based TMD study that was not a systematic review; it deals with one of the largest TMD research projects ever conducted. It was a 2016 report from 4 OPPERA studies that included the combined data from 4300 adults from sites in the United States: ie, 1 large cohort study and 3 case control studies. The findings from this report were that (1) there were higher rates of TMD in subjects with poor health and those who smoke and had deteriorating sleep quality, (2) participants’ self-reports of jaw parafunction more strongly predicted TMD than did examiners’ assessments such as tooth wear and TMJ derangement, and (3) among the 300 genes that were investigated, 6 loci were associated with chronic TMD, and 6 were associated with intermediate phenotype of TMD.

This study was limited, since we evaluated only the abstracts from the systematic reviews in PubMed and the Cochrane database for 2017, and did not evaluate the full publications. Therefore, no assessment of the methodologic strengths and weaknesses of the these systematic reviews was undertaken. In addition, no conclusions could be drawn regarding the quality of the reporting of the systematic reviews in relation to PRISMA or the risk of bias at the review level. However, the analysis of only the abstracts was a deliberate choice, allowing us to present the complete panorama of what researchers have been reporting in their systematic reviews in this complex field. Also, it enabled us to edit those abstracts into readable summaries as presented in Appendix Tables I through VI . Furthermore, it was clear from reading these abstracts that all studies had not defined and classified TMD in the same manner. For instance, they did not always use the classic research diagnostic criteria/TMD criteria to describe their patient populations. The reader should therefore be cautious about interpreting the findings of each study, since it may include a mixed population of TMD subjects. At best, systematic reviews per se have limitations and shortcomings, so it is necessary to consider and evaluate all newly published literature.

When the evidence-based paradigm was initially conceived, it was assumed that clinicians would merely need to wait and read published systematic reviews to be totally up to date on the literature in a field. Clearly, this is not the current belief regarding the utility of systematic reviews, including TMD systematic reviews. Therefore, clinicians should not abrogate their responsibility for acquiring the current best evidence in the TMD field by depending only on systematic reviews.

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Dec 10, 2018 | Posted by in Orthodontics | Comments Off on Scoping review of systematic review abstracts about temporomandibular disorders: Comparison of search years 2004 and 2017
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