INTRODUCTION

Temporomandibular disorder (TMD) is a collective term that described a heterogeneous group of conditions that involve the masticatory musculature, the temporomandibular joint (TMJ) and associated structures (^{Dimitroulis, 1998}; ^{Shaffer et al., 2014}). Its most common features are regional pain in the face, limitations in jaw movements, and noises from the TMJs during jaw movements (^{List & Jensen, 2017}; ^{Manfredini & Poggio, 2016}; ^{Schiffman et al., 2014}). It can also be manifested through articular noises, difficulties in chewing and cutting food, headaches and pain in the TMJ region, ear fullness, earache, tinnitus, dizziness and articular disc displacements (^{Conti et al., 2007}; List & Jensen).

The etiology and pathogenesis of TMD are still unclear. This disorder seems to have a multifactorial cause with interaction of psychological, genetic, neurological and anatomic factors (^{Chisnoiu et al., 2015}; Manfredini & Poggio). Factors such as depression, stress and anxiety seem to be directly involved into the development and progression of TMD (^{Rollman & Gillespie, 2000}; ^{Licini et al., 2009}). Anatomical factors such as occlusal disharmony, when associated to psychological findings, can release tensions through the stomatognathic system potentiating the symptoms of pain and joint disorders (^{Rugh & Solberg, 1976}; List & Jensen).

Orthodontic treatments have been extensively discussed in the current literature due to its possible association with the development of TMD. The literature suggests the imbalances in the dental occlusion in primary or permanent dentitions may be factors linked to TMD (^{Bourzgui et al., 2010}; ^{Fernández-González et al., 2015}). The actions of orthodontic treatments on TMD have not already been completely elucidated. The aim of the current study was to evaluate the relationship between the use of fixed orthodontic appliances and symptoms of temporomandibular disorders.

MATERIAL AND METHOD

This cross-sectional study was performed with sample of 336 undergraduate dental students at School of Dentistry of the northeastern region of Brazil. All of the individuals answered a structured questionnaire about the use of fixed orthodontic appliances and TMD symptoms. To compose this study, individuals of different sex and over age 18 years old were selected. The sample was paired for sex and use of complete fixed orthodontic appliances in maxillary and mandibular teeth. This study was approved by the research ethics committee (protocol nº 1.430.327).

The questionnaire used for the current work was previously described (^{Conti et al., 1996}, 2003). This instrument is composed of 10 objective questions related to TMD symptoms that approach questions linked to emotional tensions, parafunctional habits consciousness and articular symptomatology. Three types of answers where available for questions about TMJ: “yes”, “no” or “sometimes”. For determining the presence and degree of TMD, values “0”, “1” and “2” were attributed to the answers of the questionnaire.

For each answer indicating the presence of TMD, a value of “2” was given. The value “0” indicated the absence of symptoms. The value “1” was given when occasional occurrence of TMD symptoms was reported. The sum of the values was used for classifying the samples in three categories: Absence of TMD for values ranged from 0 to 3; mild TMD from 4 to 8; moderate/severe TMD from 9 to 20. Furthermore, questions about sex, age and use of fixed orthodontic appliances were added (Table I).

The data obtained were inserted in software SPSS for Windows version 17.0. The data were performed with frequency, Chi-Square and Fischer Exact tests with a confidence interval of 95 % (p ≤ 0,05).

Table I Anamnestic questionnaire. 

RESULTS

Table II shows all results of descriptive analysis of the data. From of total of 336 individuals, 50 % (n=168) was female and 50 % (n=168) male, with an average age of 27,60 years (median of 24 years), varying from 18 to 37 years old. About the use or not of orthodontic appliances, 50 % (n=168) of sample reported that they use fixed orthodontic appliances meanwhile 50 % (n=168) reported that they have never used orthodontic appliances.

Table II Descriptive analysis of data. 

The results highlighted that the most prevalent symptoms of TMD were the headaches (21.4 %, n=72), temporomandibular joint noises (21.4 %, n=72) and head and/or neck pain (20.0 %, n=67). From the answers given, it was observed that the majority of the sample (72.6 %, n=244) presented some degree of TMD symptoms. The analysis of TMD symptomatology showed that 60.4 % of sample (n=203) has a mild symptoms and 12.2 % (n=41) showed moderate/ severe.

The analysis of association between the symptoms of TMD (absent, mild, moderate/severe) and the variables of the research were studied. The symptoms of TMD was not associated with the sex of subjects neither to use of orthodontic appliances (p=0.985 and p=0.121 respectively).

DISCUSSION

The etiology of TMD is complex and may not be explained on a cause-and-effect basis (^{Talic, 2011}). The results of this study did not show any association between the use of orthodontic appliances and temporomandibular disorders. These findings suggest that the orthodontic treatment with the use of fixed appliances is not an etiological factor related to TMD symptoms. The literature describes that TMD has multifactorial etiology and unpredictable nature, highlighting that malocclusion or use of orthodontic appliances does not configure triggering factors for these disorders (^{Greene et al., 1999}; ^{Conti et al., 2007}; ^{Machado et al., 2010}).

Several authors describe that orthodontic treatment does not increase the risk for TMD (^{Sadowsky et al., 1991}; ^{Rendell et al., 1992}; ^{Egermark et al., 2005}; ^{Mohlin et al., 2007}). A prospective cohort study performed in South Wales, United Kingdom, investigated the relationship between orthodontic treatments and TMD and concluded that treatments do not cause nor it prevents TMD (^{Macfarlane et al., 2009}). ^{Ruf & Pancherz (1998}) described in their study that the correct orthodontic treatment does not seem to have adverse results in the TMJ in the long term.

Scientific evidences point out that orthodontic treatments do not seem to be linked as an etiologic factor for the beginning, maintenance or evolution of TMD. A study performed at Iowa University for evaluating the incidence of TMD symptoms with a sample of 109 subjects post orthodontic treatment concluded that orthodontics was not associated with causes of TMD (^{Kremenak et al., 1992}). The cohort study, followed by Egermark, analyzed patients who had orthodontic care between 1981 and 1983 and followed up of 20 years. The presence of TMD was investigated is all patients. In conclusion, no statistically significant difference was found between the prevalence of TMD in patients who had received orthodontic treatment and those who had not received orthodontic intervention (Egermark et al., 2003, 2005). Another twenty-year cohort study, described by Macfarlane et al., concluded that participants with history of orthodontic treatment did not have higher risk of new or persistent TMD.

These findings suggest that, in general, orthodontic treatment does not provide any further advantages for management or prevention of TMD (^{Imai et al., 2000}; ^{Henrikson & Nilner, 2003}; FernándezGonzález et al.; ^{Manfredini et al., 2016}). In addiction, ^{Luther et al. (2010}), in a Cochrane review, points out that there is no evidence that orthodontic treatment can treat or prevent TMD.

Our results showed that the majority of participants of the research presented TMD symptoms. ^{Medeiros et al. (2011}) performed a study with a sample of 347 students from the first and the last year of School of Dentistry, Medicine, Pharmacy, Physiotherapy and Nursing. It was verified that most of the individuals, 54.5 %, presented a mild TMD, 17.9 % showed moderate TMD and 2.6 % had a severe TMD (Medeiros et al.). These results suggest that TMD may be high prevalence and it’s underdiagnosed.

Due to the etiological complexity and physiopathology of TMD their signs and symptoms can appear before, during or after orthodontic treatment (^{Conti et al., 2003}; Henrikson & Nilner; Conti et al., 2007; Macfarlane et al.; Bourzgui et al.). In this sense, a complete articular diagnosis of patient prior to orthodontic treatment is advisable. Orthodontic treatment should not be started in patients with acute signs and symptoms of TMD (Talic). In cases where the patient shows TMD, the treatment should be postponed until that the disorder be controlled.

CONCLUSION

It can be suggested that the use of fixed orthodontic appliances is not a factor associated with symptoms of TMDs. Still, it is possible to note that the prevalence of mild TMD symptoms in dentistry students is high.