Introduction

Temporomandibular disorders (TMD) are associated with some signs and symptoms such as tinnitus, earache, jaw locking, limitations and deviations in the mandibular trajectory, in addition to joint clicks during mouth opening or closing [1, 2]. According to the Diagnostic Criteria for TMD (DC/TMD) Axis I, TMD can be divided into myogenic disorders (Group I) and intra-capsular disorders, including disc displacements (Group II) or arthralgia, arthritis, and arthrosis (Group III) [1].

TMD is the second most common musculoskeletal disorder that causes pain and disability [3]. Although the therapy of temporomandibular joint disorders remains controversial [4], the first line TMD treatment is still considered a conservative approach, including physical therapy, oral nonsteroidal anti-inflammatory drugs (NSAIDs), laser therapy, transcutaneous electrical nerve stimulation (TENS), occlusal splints, extracorporeal shockwave therapy, and oxygen-ozone therapy [1].

In some cases, the click is usually caused by the anterior disc displacement with reduction, which can also be displaced to the posterior, medial, and lateral portion [2, 3]. This condition occurs both at the mouth opening and closing, and it can be painful or not [5,6,7]. Some factors can influence the disc displacement with reduction (DDWR), such as: micro or macro-trauma, lack of muscle coordination, joint hypermobility, severe injury or deviation in the condyle surface or in the temporomandibular joint (TMJ) fossa, decreased lubrification, TMJ flaccidity, among others [3, 5, 8, 9].

The prevalence of DDWR increases with age [10]. This may be related to the TMJ morphology and the dimensions of the joint space that change with aging, and the space decreasing can cause a disc dislocation [11, 12]. DDWR prevalence is higher in females, which may be related to a greater joint laxity [13, 14].

Clinically, DDWR can manifest in three patterns: the first is painless and discovered during a routine physical examination; the second is also painless but the patient seeks care to reduce or eliminate the click; and the third, when the click appears along with pain, is treated focusing on eliminating the arthralgia [15].

Some therapies, such as physiotherapy, pharmacotherapy, occlusal devices, and psychological therapy are used to treat DDWR. Arthrocentesis and viscosupplementation are also used as therapies for DDWR and can be performed alone or together [16, 17]. Non-invasive treatments, such as counselling for behavioral changes, are generally chosen as the first approach [1, 4]. In addition, jaw exercises can be effective for most patients with TMD-related pain [18]. Both above mentioned therapies have a high acceptance rate by the patients and are easily executed at home [18].

Thus, the aim of this study was to evaluate and compare the effectiveness for reducing pain and click perception in patients who received counseling only with those who received counseling associated with jaw exercises. Furthermore, the secondary objective was to assess the presence of parafunctional habits.

Material and methods

Study design

This study is a randomized single-blind clinical trial composed of two groups of 34 patients each, and it was conducted following the Consolidated Standards of Reporting Trials (CONSORT) [19]. This clinical trial was registered at Brazilian Clinical Trials Registry (http://www.ensaiosclinicos.gov.br/rg/RBR-7t6ycp/) on 26/06/2020. The follow-up period was 30 days. This study was approved by the Research Ethics Committee of the Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), protocol #1.843.016, and conducted in accordance with the Helsinki declaration, revised in 2013.

Patients seeking for treatment at the Surgery and Periodontics Clinic of the UFVJM, with diagnosis of TMD, were recruited for the study. These patients were examined by a professional and those who met the inclusion criteria were invited to participate in the study, after signing a consent form. Those excluded patients were referred to appropriate treatment.

The inclusion criteria were patients aged 18 years or older, complaining of TMJ click (audible) during mouth opening/closing, followed or not by pain in the facial region, who never underwent any type of treatment for TMD’s. Exclusion criteria were: edentulous patients, patients who have already undergone any treatment for TMD’s; those patients with any systemic disease that could cause joint and/or muscle changes; and patients who were undergoing drug treatment for the condition.

Study settings

This study was carried out at the Surgery and Periodontics Clinic of the UFVJM. A researcher (MAMS), properly calibrated and trained according to the video available on the RDC/TMD website (https://ubwp.buffalo.edu/rdc-tmdinternational), was responsible for carrying out all evaluations. Each patient was evaluated in four appointments: baseline, 24 h, seven and 30 days after the interventions. Another researcher was responsible for teaching the participants the jaw exercises and for giving the instructions (counselling).

Questionnaire

After the patients’ admissions to the study, a specific clinical form for TMD, the Research diagnostic criteria for TMDs (RDC/TMD) [20], was filled out. At this point, the presence of TMJ clicks was investigated through clinical examination. Pain was analyzed by palpation, and measured based on the RDC/TMD. The patients were asked if the click was causing discomfort. The Oral Health Impact Profile (OHIP-14) questionnaire was also applied [21].

Randomizing process and blinding

The randomization process was previously conducted by an independent researcher who was blinded to the patients and interventions. Each intervention was written, drawn, and sealed in opaque envelopes before starting the study. The interventions were drawn as “A” for the test group, which received jaw exercises and counselling, and “B” for the control group, which received only counselling program. Only the researcher responsible for the interventions knew the envelope content. The numbers corresponding to the patients and the interventions (classified as “A” and “B”) were placed in opaque envelopes. Thus, each patient had their corresponding numbers placed on the envelopes along with the intervention, assigned by lottery. Each patient received the allocated intervention, which was taken from the envelope at the appointment time, and the clinician only knew the intervention to be applied at the time to execute it. The allocation remained hidden until the time of the intervention. The interventions were always executed by the same researcher, who did not participate in the evaluations.

Interventions

The patients were divided into two groups: the test group received a counselling program (Table 1) [22] plus jaw exercises (Table 2) [23], and the control group received only counselling. All exercises were instructed to be performed in a total of 20 repetitions, thrice a day, with no pre-established time restriction for each repetition, every day until the end of the research. The instructions for the counselling program and jaw exercises were read and explained in a standardized way by the same researcher. In addition, the patients received all written instructions.

Table 1 Counselling Program
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Table 2 Jaw Exercises
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Outcomes

The RDC/TMD questionnaire for muscle and joint palpation at specific points, which uses a pain scale from zero to three (0: pressure only; 1: mild pain; 2: moderate pain; 3: severe pain), was applied in the baseline and 24 h, seven and 30 days after the interventions. At each evaluation, the patients were asked if the pain level was “better”, “worse” or “the same” in relation to the previous evaluation, and if the click was still making them uncomfortable.

Sample size

The sample size calculation was based on the following parameters: the standard deviation obtained from pain intensity through the visual analogic scale (13.1 mm) [18]; the difference stipulated between groups, which was 9 mm; a significance level of 95%; and a power of 80%. Thus, it was required 34 participants per group in the study.

Statistical methods

Statistical analyzes were performed using the statistical package SPSS® (Statistical Package for the Social Sciences Inc.) version 23.0. Exploratory analyzes provided frequencies, means and standard deviations. 95% confidence interval was used, and 5% level of significance was adopted. The data normal distribution was verified through the Shapiro–Wilk test. Chi-square test was used to verify the association between categorical variables. The inter- and intra-group comparisons were performed using the Mann–Whitney and Friedman tests (post hoc Wilcoxon) respectively.

Results

The number of participants and the losses with the reasons are described in the Flowchart (Fig. 1). The prevalence of females (n = 48, 68.4%) was higher in the sample. The mean age was 25.88 (± 7.26) years.

Fig. 1
figure 1

Flowchart of the included participants

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The click during mouth opening was present in 60 patients (85.7%), while the click during mouth closing was observed in 29 patients (41.4%). Pain during maximum mouth opening (n = 30, 42.9%), mandibular protrusion (n = 16, 22.9%), and right and left laterality (n = 13, 18.6%) movements was present in the minority of patients.

Some types of habits were present: gnashing teeth (n = 25, 35.7%), biting nails (n = 19, 27.1%), chewing gum (n = 20, 28.6%), and using the phone (n = 21, 30%). Other habits, such as clenching teeth (n = 46, 65.7%), talking a lot (n = 42, 60%), stress (n = 40, 57.1%), and using computers (n = 46, 65.7%) were present in most of the participants.

In the baseline, patients of the counselling plus exercises group showed higher mean pain in the right side compared with the left side in five palpation points: medium temporal muscle (p = 0.027), anterior temporal muscle (p = 0.006), superior masseter muscle (p = 0.030), posterior mandibular (p = 0.023), and posterior ligament (p = 0.026) (Table 3).

Table 3 Palpation – Inter-groups comparisons
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In the 24-h evaluation, the left side of the anterior temporal muscle showed higher mean of pain on palpation in the inter group analysis (p = 0.041) (Table 3).

No statistically significant difference was found at any point in the seven-day assessment (Table 3). In the 30-day evaluation, the right medium temporal muscle showed higher mean pain in the inter group analysis (Table 3).

In the counselling group, there was a significant intra-group difference in the lateral pole (TMJ) on the right side (p = 0.016) (Table 4) and on the left side (p = 0.033) evaluation (Table 4).

Table 4 Palpation – Intra-group comparison
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In the intra-group analysis, the right side showed higher mean of pain on palpation in five muscles, in the counselling plus exercises group: upper masseter muscle (p = 0.049), medium masseter (p = 0.004), lateral pole (TMJ) (p < 0.001), lateral pterygoid muscle (p = 0.02), and temporal muscle tendon (p = 0.021) (Table 4). On the left side of this group, it was observed that two palpation sites did not show statistically significant results: submandibular (p = 0.08) and lateral pterygoid (p = 0.125) (Table 4).

A statistically significant difference in the intergroup analysis was found in the self-perception of the treatment result (p = 0.002) and in the click discomfort (p < 0.001), after 30 days of intervention (Table 5). In the intra-group comparison, a statistically significant difference was found in the self-perception of the treatment result (p < 0.001) and in the discomfort (p < 0.001), when evaluating the counselling plus jaw exercises group (Table 6). Outcomes collected from patient reports were published in another study [20].

Table 5 Questionnaire – Inter-groups comparison
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Table 6 Questionnaire – Intra-group comparison
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Discussion

Both the counselling group and the counselling plus jaw exercises group showed effectiveness in the TMD treatment, improving the patients’ symptoms when comparing the follow-up evaluations to the baseline. This study reported a statistically significant difference for the resolution of the TMJ click at the end of the follow-up period when comparing the two treatment groups, in which the counselling plus jaw exercises group showed better results.

Regarding the palpation, the counselling plus jaw exercises therapy showed higher efficacy throughout the evaluations when compared to the control group. This may be related to the fact that the exercises contribute to an improvement in the biomechanical activity of the articular disc and help reestablishing the muscular function [24].

Palpation on the condyle lateral poles showed statistically significant results at all evaluations in both comparison groups. This may suggest that treatment including only the counselling program is effective to treat DDWR. Corroborating this fact, a systematic review [25] reported that counselling was able to improve the sensitivity to muscle palpation and the maximum mouth opening. In addition, another study demonstrated that only counselling was effective to treat TMDs, resulting in significant improvements in pain and quality of life [26].

In the 30-day evaluation, the patients who received the counselling plus jaw exercises were unanimous when reporting that the treatment did not worsen the condition, unlike the patients who received only counselling. This may be linked to the fact that the exercises included in the present study protocol are efficient for the DDWR [7], since another study [27] reported that the exercises of their protocol were seen as a limitation. Thus, in that study, there was no statistically significant difference between the comparison groups (with and without the exercises) in a follow-up period of four to six weeks [27].

The TMJ click is one of the most common complaints among TMD patients, what was also verified in this study [28]. After 30 days of follow-up, most of the patients in the counselling plus exercises group showed that the click was not bothering them anymore, unlike the group treated with counselling only. This reinforces the effectiveness of the jaw exercises also reported in other studies [7, 15, 23, 29, 30].

The sample was composed mainly of female patients, who are more likely to develop DDWR because they have a looser joint and, when aging, this tends to worsen since the disc position usually changes [10, 13, 14]. Among the parafunctional habits reported by the patients, it is important to highlight the “stress” and “clenching teeth”, which are directly connected to each other, and can lead to the development of TMDs or even aggravate the condition already present [31, 32].

To reduce the risk of bias and to present a high level of evidence and internal validity, this study followed the CONSORT checklist for a clinical trial, including randomization, allocation concealment, blinding, sample size calculation, and analysis by protocol [33].

Limitations

There are limitations to be considered in this study: the absence of a group treated only with exercises and a control group without any treatment. The latter would probably not be approved by the University Research Ethics Committee due to the presence of patients with pain. Therefore, it was decided for a group with orientations/ counselling.

The follow-up period may also be seen as a limitation, as some studies suggest a follow-up of more than 30 days to assess the therapies effectiveness [18, 26]. However, this randomized clinical trial showed significant results within 30-days.

Regarding pain, it is also important to consider that the clinical improvement of the DDWR can be attributed to the cyclical aspect of the dysfunction itself [34], or even an improvement due to the simple fact that the patient was included in a clinical trial, phenomenon known as the Hawthorne effect [35]. In other patients, the pain may have a reason other than DDWR.

Clinical implication

This clinical trial has a high external validity because it evaluates therapeutic approaches easy to conduct and can be taught and monitored remotely [18, 36]. In the current global pandemic stage, with the restrictions of human proximity and mobility imposed by the consequences of the Sars-CoV-2, these treatment options become even more valid and useful [37]. Moreover, the low number of clinical trials comparing the two therapeutic approaches for DDWR, with high methodological rigor, make this study relevant [38]. The treatment evaluated herein demonstrated to be efficient, easy to understand, low cost, and it can be used by clinicians as a viable alternative therapy. Future research on this subject must focus on negative control group comparison and a long follow-up [39].

Conclusion

There was no difference between the two treatments in the improvement of the pain level. Patients that received counselling plus exercises showed greater results regarding the palpation points in the intra-group comparisons, TMJ click resolution, and self-perception of the treatment effectiveness when compared to the patients that received only counselling.