Subjects
A blinded, randomized, clinical trial was conducted. The procedures of the present study received approval from the Human Research Ethics Committee of Nove de Julho University, Sao Paulo, Brazil (protocol number 133012). This study is registered in August, 2014 in the ClinicalTrials.gov (NCT01874041). Prior to participation, all volunteers signed a statement of informed consent.
Individuals diagnosed with TMD and sleep bruxism aged 18 to 40 years were recruited from the university community of the city of Sao Paulo, Brazil, through notices placed on information boards located in general areas of the university and the Internet between June 2011 and December 2012. Neither the examiner in charge of the surface electromyography (EMG) nor the researcher in charge of the data analysis was aware of the allocation of the volunteers to the different groups.
The volunteers received an intra-oral examination by an experienced dentist for signs of sleep bruxism. Those with incisal and/or occlusal tooth wear and clinical signs in the buccal mucosa and tongue of clenching or grinding were diagnosed with bruxism based on the criteria of the American Academy of Sleep Medicine [12] and a positive self-report of awake bruxism [13].
The Fonseca Patient History Index was used to diagnose the presence and intensity of TMD, which is an adequately valid, reliable measure for identifying individuals with TMD that has been widely used in recent studies [14]-[18]. This Portuguese-language measure for the assessment of TMD severity has 10 items, each with three response options: “yes” (scored as 10 points), “sometimes” (5 points) and “no” (0 points). The sum of the points for all items gives the overall score and allows the following classification: absence of TMD (0 to 15 points), mild TMD (20 to 45 points), moderate TMD (50 to 65 points), and severe TMD (70 to 100 points) [18]. Only individuals with severe TMD and bruxism for at least one year were included in the present study.
The following were the exclusion criteria: occurrence of missing teeth (except third molars); current use of an orthodontic appliance; history of neuromuscular disease; current use of analgesic, anti-inflammatory agent or muscle relaxant; and currently undergoing physical therapy for TMD.
One hundred nine male and female individuals were consecutively recruited and screened based on the eligibility criteria. During this process, 49 volunteers were excluded. Thus, the final sample was made up of 60 volunteers with severe TMD and sleep bruxism. Block randomization was employed and opaque envelopes were used to conceal the allocation of the volunteers to the four treatment groups described below (Additional file 1: Figure S1).
The massage group (MG) (n =15; 13 women and 2 men; mean age: 29.32 ± 4.31 years) was submitted to three weekly 30-minute sessions of massage therapy performed by a physiotherapist who had undergone a training exercise for the administration of sliding and kneading maneuvers of the masseter and anterior temporal muscles, bilaterally, over four consecutive weeks (total: 12 sessions) [19]. Sliding consisted of a unidirectional movement in which part of the therapist’s hand (mainly the fingertips) was used, moving from the proximal to the distal portion of the face with constant, progressive pressure compatible with the status of each tissue. The degree of pressure varied depending on the level of pain, sensitivity and tension in each individual. Kneading consisted of a gripping maneuver of a muscle group or portion of a muscle, with intermittent movements of compression and decompression. The therapist performed circular movements with the fingertips such that the skin and subcutaneous tissues were moved over the subjacent structures. A facial massage cream was used to facilitate the manual procedures [15].
The conventional occlusal splint group (COSG) (n =15; 12 women and 3 men; mean age: 27.89 ± 5.82 years) was submitted to treatment with an occlusal splint for four weeks. The aim of this form of treatment was to promote greater stability of the joint components, establish a more favorable occlusal relationship, promote the reorganization of neuromuscular activity, reduce hyperactivity of the masticatory muscles and reestablish balanced muscle function. After a clinical examination by a dentist, the upper arch of each volunteer was molded with irreversible hydrocolloid for the fabrication of a Michigan-type occlusal splint with canine and protrusive guides as well as a flat occlusal surface for contact with the antagonist teeth. The volunteers were instructed to wear the splint while sleeping. Adjustments were made after two weeks by the same dentist in charge of the evaluation and splint fabrication [20],[21],[15].
The massage + conventional occlusal splint group (MCOSG) (n = 15; 14 women and 1 man; mean age: 26.05 ± 3.32 years) was submitted to combined treatment with massage and occlusal splint as described in the previous two paragraphs.
The silicone occlusal splint group (SOSG) (n = 15; 10 women and 4 men; mean age: 28.92 ± 6.78 years) was submitted to treatment with a silicone splint for four weeks fabricated from a 3-mm soft polyvinyl sheet in a vacuum pressure molding device with a thermally controlled infrared heater. This machine performed vacuum suctioning of the warmed sheet of thick, resilient mouth-guard material over the maxillary cast. When the sheet had properly adapted to the cast in the vacuum former, the splint was separated from the cast with a laboratory knife/scissors, the edges were smoothed and the palatal area was removed. Chair-side occlusal fitting was made by evenly warming the occlusal surface of the splint with an alcohol torch before placement in the patient’s mouth. The soft splint was then polished with pumice, disinfected and placed in the oral cavity. The soft, resilient material is believed to help distribute the load during parafunctional activity (bruxism) [22]. The volunteers were instructed to wear the splint while sleeping.
Electromyographic analysis
The right and left masseter and anterior temporal muscles were analyzed using surface EMG. EMG signals were obtained using an eight-channel module (EMG System do Brasil Ltda®) consisting of conditioner with a band pass filter with cut-off frequencies at 20–1000 Hz, an amplifier gain of 1000 and a common mode rejection ratio >120 dB. All data were acquired and processed using a 16-bit analog to digital converter (EMG System do Brasil Ltda®) with a sampling frequency 2 kHz. The system was composed of active bipolar electrodes with a pre-amplification gain of 20 x.
The volunteer was instructed to remain seated in a chair, feet apart, shoulders relaxed and hands resting on thighs, with the head on the Frankfurt parallel to the ground and no visual feedback of the signals registered on the computer. The sites for the electrodes were cleaned with a cotton ball soaked in alcohol to diminish impedance between the skin and electrodes. Disposable circular electrodes (Ag/AgCl – Medical Trace©) measuring 10 mm in diameter were attached to the belly of the muscle in the region with the greatest tonus after the volunteer performed moderate clenching. Bandage tape was used to secure the electrodes further, with care taken to avoid micro-movements. The inter-electrode distance was 20 mm from center to center, as suggested by the European Recommendations for Surface Electromyography [23]. A rectangular metallic electrode measuring 3 x 2 cm coated with Lectron II conductive gel (Pharmaceutical Innovations®) to increase the conduction capacity and impede interference from external noise was attached to the left wrist of the volunteers for reference [23].
Three EMG readings were taken before and after treatment in all groups during maximum voluntary clenching for 10 seconds, with a five-minute rest period between readings. To avoid direct occlusal contact between the dental cusps, a strip of Parafilm M® (American National Can TM, Chicago, USA) with texture and dimensions similar to commercial chewing gum was folded into five parts and positioned in the molar region bilaterally.
The initial two seconds and final three seconds of the EMG signal were discarded. Thus, a five-second reading was considered for each test. The signal was analyzed using Fast Fourier Transform computed with a 2048-point hamming window processing (50% overlap). The median frequency (MDF) of the power spectrum was calculated for each five-second period analyzed. All EMG signal processing was performed using specific routines carried out in the Matlab program, version 7.1 (The MathWorks Inc., Natick, Massachusetts, USA).
Data analysis
The sample size was calculated with the aid of the Ene software, version 3.0 (Barcelona, Spain) and based on the findings of a pilot study. The data were collected during maximum voluntary clenching for eight seconds before (T0) and after five sessions of massage therapy (T1). Considering an 80% test power and α of 0.05, the suggested sample size was 13 individuals (T0 = 1.19; T1 = 1.08; SD =0.14) per group.
As the Shapiro-Wilk test revealed that the MDF was not normally distributed (p <0.05), the data were analyzed using nonparametric tests and expressed as median and inter-quartile range (25% and 75%). The Kruskal-Wallis test used to determine the similarity in the MDF among the groups (MG, COSG, MCOSG, SOSG) before treatment (baseline). The Wilcoxon test was used to evaluate the effects of the treatments. TMD intensity before and after treatment was determined using the Fonseca Patient History Index and verified through repeated-measures analysis of variance (ANOVA) considering two factors: group (MG vs. COSG vs. MCOSG vs. SOSG) and treatment (pre-treatment vs. post-treatment). Specific differences were analyzed using Tukey’s post hoc test. The significance level was set to 5% (p <0.05). All data were analyzed using the Statistical Package for the Social Sciences, version 17.
