Orthodontics as risk factor for temporomandibular disorders: a systematic review

Machado, Eduardo; Machado, Patricia; Cunali, Paulo Afonso; Grehs, Renésio Armindo

doi:10.1590/S2176-94512010000600005

Abstracts

INTRODUCTION: The interrelationship between Orthodontics and temporomandibular disorders (TMD) has attracted an increasing interest in Dentistry in the last years, becoming subject of discussion and controversy. In a recent past, occlusion was considered the main etiological factor of TMD and orthodontic treatment a primary therapeutical measure for a physiological reestablishment of the stomatognathic system. Thus, the role of Orthodontics in the prevention, development and treatment of TMD started to be investigated. With the accomplishment of scientific studies with more rigorous and precise methodology, the relationship between orthodontic treatment and TMD could be evaluated and questioned in a context based on scientific evidences. OBJECTIVES: This study, through a systematic literature review had the purpose of analyzing the interrelationship between Orthodontics and TMD, verifying if the orthodontic treatment is a contributing factor for TMD development. METHODS: It was conducted a survey in research bases (MED-LINE, Cochrane, EMBASE, Pubmed, Lilacs and BBO) between the years of 1966 and 2009, with focus in randomized clinical trials, longitudinal prospective non-randomized studies, systematic reviews and meta-analysis. RESULTS: After application of the inclusion criteria 18 articles were used, which were 12 longitudinal prospective non-randomized studies, 4 systematic reviews, 1 randomized clinical trial and 1 meta-analysis, which evaluated the relationship between orthodontic treatment and TMD. CONCLUSIONS: According to the literature, the data concludes that orthodontic treatment cannot be considered a contributing factor for the development of temporomandibular disorders.

Temporomandibular joint dysfunction syndrome; Temporomandibular joint disorders; Craniomandibular disorders; Temporomandibular joint; Orthodontics; Dental occlusion

INTRODUÇÃO: nos últimos anos, a inter-relação entre a Ortodontia e as disfunções temporomandibulares (DTMs) tem despertado interesse crescente na classe odontológica, sendo tema de discussões e controvérsias. Em um passado recente, a oclusão era considerada como principal fator etiológico das DTMs, sendo o tratamento ortodôntico uma medida terapêutica primária para um restabelecimento fisiológico do sistema estomatognático. Assim, passou-se a investigar o papel da Ortodontia na prevenção, desencadeamento e tratamento das DTMs. Com a realização de estudos científicos com metodologias mais rigorosas e precisas, a relação entre o tratamento ortodôntico e as DTMs pôde ser avaliada e questionada dentro de um contexto baseado em evidências científicas. OBJETIVO: o presente trabalho, através de uma revisão sistemática de literatura, teve como objetivo analisar a inter-relação entre a Ortodontia e as DTMs, verificando se o tratamento ortodôntico é fator contribuinte para o desenvolvimento de DTM. MÉTODOS: foi realizado um levantamento em bases de pesquisa (Medline, Cochrane, Embase, Pubmed, Lilacs e BBO) entre os anos de 1966 e 2009, com enfoque em estudos clínicos randomizados, estudos longitudinais prospectivos não randomizados, revisões sistemáticas e meta-análises. RESULTADOS: após a aplicação dos critérios de inclusão, chegou-se a 18 artigos, sendo que 12 eram estudos longitudinais prospectivos não randomizados, 4 revisões sistemáticas, 1 estudo clínico randomizado e uma meta-análise, os quais avaliaram a relação entre tratamento ortodôntico e DTM. CONCLUSÕES: pela análise da literatura, conclui-se que o tratamento ortodôntico não pode ser considerado fator contribuinte para o desenvolvimento de disfunções temporomandibulares.

Síndrome da disfunção da articulação temporomandibular; Transtornos da articulação temporomandibular; Transtornos craniomandibulares; Articulação temporomandibular; Ortodontia; Oclusão dentária

ORIGINAL ARTICLE

^ISpecialist in Temporomandibular Disorders (TMD) and Orofacial Pain, Federal University of Paraná (UFPR). Dental Degree, Federal University of Santa Maria (UFSM)

^IISpecialist in Prosthetic Dentistry, Pontifical Catholic University of Rio Grande do Sul (PUCRS). Dental Degree, UFSM

^IIIPh.D. in Sciences ,Federal University of São Paulo (UNIFESP). Professor of Graduate and Post-graduate Course in Dentistry, Federal University of Paraná (UFPR). Coordinator of the Specialization Course in TMD and Orofacial Pain, UFPR

^IVPhD in Orthodontics, UNESP. Professor of Graduate and Post-graduate Course in Dentistry, UFSM

Contact address

ABSTRACT

INTRODUCTION: The interrelationship between Orthodontics and temporomandibular disorders (TMD) has attracted an increasing interest in Dentistry in the last years, becoming subject of discussion and controversy. In a recent past, occlusion was considered the main etiological factor of TMD and orthodontic treatment a primary therapeutical measure for a physiological reestablishment of the stomatognathic system. Thus, the role of Orthodontics in the prevention, development and treatment of TMD started to be investigated. With the accomplishment of scientific studies with more rigorous and precise methodology, the relationship between orthodontic treatment and TMD could be evaluated and questioned in a context based on scientific evidences.

OBJECTIVES: This study, through a systematic literature review had the purpose of analyzing the interrelationship between Orthodontics and TMD, verifying if the orthodontic treatment is a contributing factor for TMD development.

METHODS: It was conducted a survey in research bases (MED-LINE, Cochrane, EMBASE, Pubmed, Lilacs and BBO) between the years of 1966 and 2009, with focus in randomized clinical trials, longitudinal prospective non-randomized studies, systematic reviews and meta-analysis.

RESULTS: After application of the inclusion criteria 18 articles were used, which were 12 longitudinal prospective non-randomized studies, 4 systematic reviews, 1 randomized clinical trial and 1 meta-analysis, which evaluated the relationship between orthodontic treatment and TMD.

CONCLUSIONS: According to the literature, the data concludes that orthodontic treatment cannot be considered a contributing factor for the development of temporomandibular disorders.

Keywords: Temporomandibular joint dysfunction syndrome. Temporomandibular joint disorders. Craniomandibular disorders. Temporomandibular joint. Orthodontics. Dental occlusion.

INTRODUCTION

In recent years a considerable increase in the prevalence of signs and symptoms of temporomandibular disorders (TMD) has been observed.⁴⁴Several theories have been proposed to determine the etiology of TMD, but a single and specific factor was not detected.^44,47The etiology of TMD has a multifactorial nature and is associated with muscle hyperactivity, trauma, emotional stress, malocclusion and other predisposing, precipitating or perpetuating factors of this condition.⁴⁷Due to the etiological complexity and variety of signs and symptoms that may, generally, also represent other conditions, recognition and differentiation of temporomandibular disorders can present itself in a very unclear way to the professional.⁵

Epidemiological studies show that the signs and symptoms of TMD are commonly found in children and adults,^9,32and may reach up to 31% of the population⁴²and it affects more than 10 million people in the USA.⁴¹Usually the signs and symptoms are milder in childhood and increases in adolescence both in prevalence and severity.⁴⁹

Some studies have attempted to evaluate the possible effect of occlusal factors on the development of TMD. The results of these studies indicate that occlusal factors have small etiological importance in relation to pain and to the functional alterations of the stomatognathic system, but the role of occlusion in the etiology of TMD is still a subject of discussion.¹⁷

Thus, the role of orthodontics in the development, prevention and treatment of TMD remains controversial. This study aimed to analyze by a systematic literature review the inter-relationship between orthodontic treatment and TMD and specifically verify if orthodontic treatment is a contributing factor to the development of TMD.

MATERIAL AND METHODS

A computerized search in MEDLINE, Cochrane, EMBASE, PubMed, Lilacs and BBO was performed for the period from 1966 through January 2009. The research descriptors used were "orthodontics", "orthodontic treatment", "temporomandibular disorder," "temporomandibular joint", "craniomandibular disorder", "TMD", "TMJ", "malocclusion" and "dental occlusion", which were crossed in search engines. The initial list of articles was submitted to review by two reviewers, who applied inclusion criteria to determine the final sample of articles, which were assessed by their title and abstract. If there was any disagreement between the results of the reviewers, a third reviewer would be consulted after reading the full version of the article.

Inclusion criteria for article selection were:

» Studies that evaluated orthodontics in relation to its role in the development of TMD and in which orthodontic treatment is already finished in the samples.

» Randomized clinical trials (RCTs), longitudinal prospective non-randomized studies, systematic reviews and meta-analysis. Clinical trials should present control group.

» Clinical trials in which clinical examination in patients were performed and at least one clinical evaluation was done after the end of orthodontic treatment. Studies based only on nuclear magnetic resonance imaging (MRI), computed tomography (CT), electromyography, cephalometry and conventional radiographs were excluded.

» Studies written in English, Spanish and Portuguese and published between 1966 and January 2009.

Thus, cross-sectional studies, clinical case reports, case series, simple reviews and opinions papers were excluded, as well as studies in which orthodontic treatment had not yet been completed and studies based only on imaging tests.

RESULTS

After applying the inclusion criteria 18 articles were selected: 12 longitudinal prospective non-randomized studies, 4 systematic reviews, 1 randomized clinical trial and 1 meta-analysis, as shown in Figure 1.

The final sample of selected articles was divided into two groups: 1) clinical trials, in which clinical evaluations were performed and 2) systematic reviews and meta-analysis, as presented in Tables 1, 2 and 3.

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DISCUSSION

Considerations about the subject should always be performed through a critical reading of the methodology used by different authors. The use of the basic research principles allows the researchers to try to control as best as possible the biases of the study generating higher levels of evidence. Thus, the sample size calculation becomes important, so that the sample becomes representative and the results can be extrapolated to the studied population. Moreover, the calibration intra and inter-examiners should be performed to assure the reliability of diagnostic criteria, as well as adoption of randomization and blinding criteria. Likewise, careful matching for age and sex between the test and control groups should also be observed.⁵³

Within this context of an evidence-based dentistry, it appears that the most common types of studies published in Brazilian journals correspond to studies of low potential for direct clinical applications: in vitro studies (25%), narrative reviews (24%) and case reports (20%). The low number of studies with greater strength of evidence shows the necessity to expand the knowledge of evidence-based methods among Brazilian researchers.⁴⁵

The supposed relationship between orthodontics and temporomandibular disorders has attracted the interest of the orthodontic class in last years. Despite significant advances in diagnostic capability due to advanced techniques such as nuclear magnetic resonance imaging, 3D computed tomography, volumetric Cone-Beam tomography and application of more sophisticated clinical procedures, this possible relationship remains unclear. A reflection of this controversy is the way that orthodontic treatment is considered in several publications. If, for some authors, orthodontic correction may be the cure for TMJ dysfunction, for others it may predispose patients to pain and dysfunction of the stomatognathic system.⁵

For the establishment of a risk factor, it must fill out several methodological criteria to qualify as a true risk factor. Thus, the factor should be identified with the outcome in longitudinal studies, must be present before the establishment of the disease and show a biological plausibility with the disease. Moreover, the factor remains associated after being controlled for other risk factors, a dose-response relationship must exist, that is, the higher the risk factor, the higher the outcome and this factor must be identified in different populations.²

Cross-sectional or retrospective studies allow the study of associations that identify risk indicators and generate hypotheses. Subsequently, these hypotheses need to be tested in longitudinal studies to identify true risk factors, because only longitudinal studies can be used as generators of cause and effect evidence due to its temporal component.⁵⁴Therefore, the clinical trials included in this systematic review show longitudinal design, whereas it should be in this point of view that the interrelationship between orthodontics and TMD must be considered.

There is a difference in the quality of the designs of clinical studies before and during the 80s, and the most recent ones.³⁵Studies of cross sectional and observational nature, methodological errors-such as lack of information about randomization, blinding, sample size calculation, calibration and control of factors- and inadequate quality of study designs compromised the power for generating scientific evidence. Furthermore, the heterogeneity of results in published studies makes an adequate meta-analysis more difficult to be obtained. Added to this, there is a lack of a standardized classification system for TMD diagnosis. Thus, you can always find a scientific article to prove a point of view.²⁷

Another important factor, as previously mentioned, when evaluating studies involving the interrelation of orthodontics and TMD, are the diagnostic criteria adopted by the authors. Due to the lack of a universal classification system and validated for TMD, in this systematic review various diagnostic methods used by the authors of the included studies can be found: Helkimo index,^18,19craniomandibular index,^15,16as well as adaptations of these or other questionnaires. This fact complicates the comparison and analysis of results obtained in the studies evaluated in this systematic review.

In order to standardize the diagnostic criteria and facilitate future clinical trials, the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) was formulated, which examined jointly the physical and psychosocial aspects of TMD, in the axis I and II, respectively.⁸This diagnostic method has been translated, culturally adapted and validated in Brazil.^31,48Thus, future clinical studies may use a standardized and universal index, which will facilitate comparison of study results. It is important to be noted that none of the studies evaluated in this systematic review used the RDC/TMD as a diagnostic criteria.

Studies also analyzed the relationship between TMJ sounds and its morphology. Sounds can be associated with various pathologies and the presence of clicks and crackles does not necessarily indicate a TMJ with abnormal morphology.¹⁴It becomes important to acknowledge situations of disk displacement with and without reduction, as well as the presence of crackles as indicative of osteoarthritis. It is important to emphasize that the absence of TMJ sounds, not necessarily characterized a situation of normality.^14,52

There are many factors that may cause or aggravate TMD. A review of the literature did not find a positive association between orthodontic treatment in children and adolescents and future risk of TMD development. In addition, orthodontic mechanotherapy performs gradual changes in a system that has a great capacity of adaptation.⁵¹

Similar results were obtained in other studies, and worsening of signs and symptoms of TMD pre-treatment were not observed.²⁰

In a critical review of the literature, a low association between occlusal factors that characterize TMD was noted. Moreover, orthodontic treatment performed during adolescence usually does not increase or decrease the probability of developing TMD in the future. Some occlusal factors, such as skeletal anterior open bite, overjet greater than 6-7 mm, retruded cuspal position/intercuspal position slides greater than 4 mm, unilateral posterior crossbite and absence of five or more posterior teeth may be associated with specific diagnosis of TMD.³⁶

In another critical review, it was found that the signs and symptoms of TMD can occur in healthy individuals, increasing with age, particularly during adolescence, until menopause, and that the TMD that begin during orthodontic treatment may not be related to the treatment. Moreover, there is no risk for TMD associated with any type of orthodontic mechanics and there is no evidence that a stable occlusion, as ideal objective of orthodontic treatment, prevents signs and symptoms of TMD. Still, the extraction of teeth as part of orthodontic treatment plan does not increase the risk for development of TMD.³⁵

Current studies, within a context of an evidence-based Dentistry, such as randomized clinical trials, longitudinal prospective nonrandomized studies, systematic reviews and meta-analysis, through the use of more rigorous methodological criteria and adequate designs, evaluated more precisely the interaction between orthodontic treatment and temporomandibular disorders.

Significant current scientific evidences, such as longitudinal and experimental-interventionist studies, point to a tendency of no association between orthodontic treatment and TMD,^{10,11,21,22,23,25,26,40} and and the presence or absence of extractions during orthodontic treatment did not increase the prevalence or worsened signs and symptoms related to TMD.^11,23Randomized clinical trials²⁶and longitudinal prospective non-randomized studies,^{10,11,21,23,25}as well as meta-analysis²⁷and systematic review,³⁹besides presenting more rigorous methodologies, generate a greater power of scientific evidence. Moreover, the correct occlusal relationship between the teeth did not cause a change in the physiological position of the condyles and articular discs in TMJ when examined MRIs and CT.^3,28,29

Reviewing the literature in search of randomized clinical trials-studies that generate a high level of scientific evidence-about the interrelation of orthodontic treatment and TMD, there is only one study in the evaluated period in this systematic review.²⁶This fact occurs due to difficulties in the accomplishment of randomized clinical trials evaluating orthodontic treatment and TMD, due to ethical and practices reasons.²⁷Difficulties are also present when assessing other forms of irreversible therapies such as TMD treatment protocols. An example of this situation is the occlusal adjustment, from 1966 to 2002, there are only 6 RCTs evaluating the occlusal adjustment as treatment and prevention option for TMD in a systematic review published in Cochrane Library.³⁰

Regarding to the role of orthognathic surgery and orthodontic treatment with the Herbst appliance in relation to TMD, the literature analysis shows that there is a necessity for a higher number of longitudinal studies, controlled and randomized, to obtain more precise conclusions about the role of these treatment modalities in relation to TMD. Systematic reviews that attempted to assess both therapeutics and their relationship with signs and symptoms of TMD were inconclusive, due to small number of significant scientific evidences.^1,50In relation to the role of therapy with Bionator²⁶and headgear,²⁶it appears that they have no association with the development of TMD. It is important to be noted that the use of chincup^4,6,7and facial mask⁴³shows weak or nonexistent associations in relation to TMD, but studies with this conclusions were not included due to the methodological criteria of this systematic review.

Before the beginning of orthodontic treatment, in asymptomatic patients, a full history and physical examination on signs and symptoms of TMD should be performed by the orthodontist.³⁴Studies evaluating the attitude of orthodontists to TMD show that this interrelationship is viewed differently as the possibility of orthodontic treatment increase the probability of developing of TMD.^33,34

Assessing the attitudes and beliefs of orthodontists regarding TMD, in a cross-sectional study, the authors obtained results as the majority of respondents did not feel secure about the diagnosis, therapeutic decision and assessment of treatment outcomes of TMD. The vast majority of respondents reported believing that orthodontic treatment does lead to a higher incidence of TMD and orofacial pain, but believe that it can be a form of prevention and treatment of these disorders. It is important to noted that most participants reported knowledge at a basic level or no knowledge about TMD and orofacial pain during their postgraduate course in orthodontics.³⁸

On the other hand, the results of a research examining the attitudes of Chinese orthodontists, regarding orthodontic treatment and TMD, using a questionnaire, showed that most orthodontists think that an inadequate orthodontic treatment could increase the development of TMD and an adequate orthodontic treatment could prevent it.³³

In the presence of signs and symptoms of TMD, the primary treatment protocol should be minimally invasive and with reversible nature. Therapies that change the occlusal pattern irreversibly, such as orthodontic treatment and occlusal adjustment, should be indicated in a conscious and precise way. Furthermore, this decision should be based on significant scientific evidences.

CONCLUSIONS

» Many of the available studies in literature have limitations in their designs and methodologies, as well as heterogeneity of results, which reduces the power of evidence generated. Current studies, with rigorous methodological criteria and adequate designs, present more precise evidences of the interrelationship of the orthodontic treatment and TMD.

» The systematic literature review shows that there is no increased in prevalence of TMD due to traditional orthodontic treatment, either with protocols for extractions or not, with significant scientific evidences, such as longitudinal controlled randomized and non-randomized trials, systematic reviews and meta-analysis, concluding for a tendency of no association. However, it is necessary to perform further randomized clinical trials, with standardized diagnostic criteria for TMD for the determination of more accurate causal associations.

» It is important to perform, during the diagnostic phase of the pre-orthodontic patients, a full assessment of the presence or absence of signs and symptoms of TMD and orofacial pain, making use of complementary examinations for a correct diagnosis. In the presence of TMD, an integration with the Temporomandibular Disorders and Orofacial Pain specialty becomes important for an appropriate treatment decision, due to the high prevalence of TMD in the general population.

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