The present randomised clinical study has been carried out at College of Dentistry, Aljouf University, Kingdom of Saudi Arabia from December 2016 till October 2017. An informed consent was obtained from the patients and clearance for the study was obtained from Institutional Ethical Committee. The study subjects were selected on the basis of standardised clinical examination employing the criteria for diagnosis of TMD according to the RDC/TMD [10]. Digital panoramic radiographs and TMJ open and closed radiographic views of both sides were obtained to observe any bony changes and other related disorders.

Patients with a previous history of trauma to maxillofacial region, other orofacial pain conditions, orofacial infections, and developmental anomalies of the maxillofacial region, disc displacement, arthralgia, or osteoarthritis were excluded. The subjects with cardiac pacemaker or any serious cardiac diseases, epileptic disorders, allergy to adhesive tape or electrodes of the TENS machine were also not included in this study.

According to the diagnostic criteria, 42 patients of either gender between 18 years and 60 years of age were found eligible. Among these six of them refused to participate in the study and the remaining 36 patients were randomly assigned to TENS group and HE group comprising 18 patients each. The randomisation was carried out by casting lots, by an individual not participating in this study to allocate the subjects to either groups.

The subjects in the TENS were administered TENS therapy using HiDow FDA CLASS II Approved Wireless TENS/EMS system (The power was 20 W, with a maximum frequency of 60 Hz and amplitude ranging from 1-10 μA), each therapeutic session lasted for approximately 30 minutes, once in a week for a period of four consecutive weeks. The subjects were asked to adjust the intensity of the device according to their comfort level.

The HE group patients were briefed about modes for handling with TMJ pain through variations in the lifestyle, confronting mechanisms and ergonomic management. They were advised an exercise program comprising of active and passive jaw opening and closing exercises, isometric jaw exercises, jaw stretching exercises and resistive jaw exercises. The participants were instructed to carry out every exercise for six seconds with repetitions for 10 times. These exercises were implemented twice a day for four weeks [11-13].

All the patients were evaluated for masticatory muscle tenderness and TMJ pain on VAS using a score from 0 (no pain at all) to 100 (the worst pain imaginable) was carried out. Maximum mouth opening (The distance from the incisal edge of the maxillary incisor teeth to the incisal edge of the mandibular incisor teeth) without pain using a digital vernier calliper (Brown and Sharpe 00590302 TWINCAL IP67 Digital Caliper, 06" Range, 0.0005" Resolution, Round Depth Rod, Built in Wireless Functionality) was recorded in mm. All the above parameters were recorded at pre-treatment visit, during, and after every treatment session. The female patients were treated with the help of female staff and female dental assistants.

Independent and paired t-tests were applied respectively to assess the difference between and within groups with different parameters. The analysis was carried out with SPSS statistical software version 20.0. The statistical significance was set at 5% level of significance (p<0.05).

In TENS group, there were 11 (61.11%) females and seven (38.88%) males with the mean age of 32.91±12.57 years, and the HE group comprised of 12 (66.66%) females and six (33.33%) males with the mean age of 34±7.4 years.

The comparison of VAS scores in TENS and HE groups is represented in [Table/Fig-1]. A significant difference was observed between TENS and HE groups with respect to reduction of masseter and medial pterygoid muscle tenderness at third and fourth visit whereas significant difference was observed with respect to lateral pterygoid and temporalis muscle tenderness at fourth visit at 5% level (p<0.05). Similarly, a significant difference was observed between TENS and HE groups with respect to reduction of TMJ tenderness at second, third and fourth visit at 5% level (p<0.05).

In the TENS group, a significant reduction is observed from pre-treatment to first, second, third and fourth visit, with respect to pain, masseter, medial pterygoid, lateral pterygoid, temporalis muscle tenderness and TMJ tenderness scores at 5% level of significance (p<0.05) [Table/Fig-2]. Similarly in the HE group, a significant reduction is observed from pre-treatment to first, second, third and fourth visit, with respect to pain, medial pterygoid, lateral pterygoid, temporalis muscle tenderness and reduction of TMJ tenderness scores at 5% level of significance (p<0.05) except pre-treatment to first visit with reduction of masseter muscle tenderness scores (p>0.05) [Table/Fig-3].

With regards to mouth opening, a non significant difference was observed between TENS and HE groups at pre-treatment and first, second, third and fourth visit at 5% level (p<0.05) [Table/Fig-4]. A significant reduction is observed from pre-treatment to first, second, third and fourth visit with respect to maximum mouth opening in TENS group, whereas a significant reduction is observed from pre-treatment to second, third and fourth visit at 5% level of significance (p<0.05) except pre-treatment to first visit (p>0.05) in HE group [Table/Fig-5].

Masticatory muscle tenderness, joint pain and sounds are the most common presenting features of the TMDs, which can limit the jaw movements leading to a compromise in quality of life of the patients with an abrogating impact on social function and emotional health [14]. Despite the fact, that a wide assortment of remedial methodology, for example, medicinal treatment, occlusal splints, physical therapy, orthodontic therapy, and so on, have been utilised to limit the pain in TMD subjects. Still there is shortage of randomised controlled clinical studies, to recommend suitable management protocol of these subjects. Albeit different treatments seem to bring about comparable recovery in pain and dysfunction, discretion is recommended concerning utilization of intrusive and other irreversible therapies [15].

In the present study, majority of the subjects were in third and fourth decades of life, this was in consistent with the studies by Moger G et al., Juniper RP et al., Shanavas M et al., and Riden DK et al., [15-18]. It has been proposed that the limited prevalence of TMD signs and symptoms in geriatric individuals reinforce the anticipation that a compelling portion of TMDs are self-limiting [1]. This study comprised of 63.79% of females and 36.20% males, this was in accordance with Shahanavas M et al., Dworkin SF et al., Rai S et al., and Jensen R et al., [17,19-21]. The reason for this is thought to be the sex hormones which regulate the pain sensitivity; the threshold and tolerance for the pain among females [22]. In contrast to this Beaton RD et al., and Patil S et al., did not observe any significant gender difference in their studies [23,24].

In the present study, the patients in the TENS group, showed a significant reduction from pre-treatment to fourth visit, with respect to masseter, medial pterygoid, lateral pterygoid, temporalis muscle tenderness and TMJ pain. In accordance to our findings, many previous studies in the literature reported the effectiveness of TENS therapy in reducing pain and discomfort of TMD patients [20,24-26].

Singh H et al., and Johnson and Tabassam observed that TENS therapy was significantly better than placebo in subjects with pain in TMJ region [25,26]. Kato MT et al., conducted a study in 18 TMD patients and found that TENS therapy significantly reduced pain and discomfort [27]. In the studies conducted among patients with TMD, by Moger G et al., Rai S et al., and Patil S et al., it was found that TENS therapy helped in relieving muscular and chronic pain and improvement in mouth opening [15,20,24]. Shanavas M et al., recommended from the observations of their study that the use of TENS therapy in the treatment of TMD can be justified [17].

A significant improvement is also noted with respect to tenderness of the muscles of mastication and reduction of pain in TMJ in the subjects of HE group from the commencement till the completion of the study. This observation was similar to Bae and Park and Ucar M et al., who observed in their studies that passive and active stretching exercises, isometric tension and relaxation exercises are efficient at relieving the pain and improve jaw opening [13,28].

A reduction in muscular and TMJ tenderness is observed in TENS and HE groups but when both the therapies were compared, a significant reduction in muscular tenderness and TMJ pain is noted in TENS group at the end of fourth week. This finding confirmed that TENS therapy is more effective in reduction of muscular and joint pain when compared to HE therapy. Although, a significant reduction is observed with respect to maximum mouth opening in TENS group and in HE group at the end of the treatment period but a non-significant difference was observed when both TENS and HE groups were compared, which suggests that both the therapies were equally effective in improving the mouth opening of TMD patients.

The limitation of our study was limited sample size and absence of placebo-controlled group. Further, longitudinal studies are warranted to evaluate the long-term effects of both treatment modalities.

From the results of this study, it can be concluded that, both TENS and HE therapies were effective in the reduction of masticatory muscle tenderness and joint pain after treatment, but the TENS therapy showed better results in reducing the muscle and joint with a statistically significant difference when compared with HE therapy. TENS and HE treatment modalities demonstrated similar effectiveness in the improvement of mouth opening.

Thus, the observations from the present study justify the use of TENS therapy as well as HE therapy in the management of TMD.

Financial support: This study was funded by the Aljouf University, Kingdom of Saudi Arabia - Research project No. (407/37).