## 2 Materials and Methods  
A total of 32 patients affected by Temporo-Mandibular Disorders (TMDs) (26 women and 6 men), aged from 18 to 58 years (average: 38 years old; SD = 6), have been recruited. Patients were selected from a list of 321 patients recruited at the Neurosorsorial and Motor Surgery Department of the Complex Operative Unit of Odontostomatology, AOU Policlinico \"[PERSON]\" in Palermo (Italy), between January 2016 and December 2016. All the patients were found to have masticatory dysfunctions and (or) temporomandibular joint anomalies, according to the international criteria to assess the presence of Temporomandibular Disorders [33; 34]. The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board of the Neurosensorial and Motor Surgery Department of the Complex Operative Unit of Odontostomatology, AOU Policlinico \"[PERSON]\" in Palermo (Italy). (Ref. n. RIPARA project-20/01/2016). All the participants expressed their informed consent on a dedicated agreement. Inclusion criteria [33; 34]:  
* temporomandibular joint (TMJ) pain \(\geq\) 30 on the numerical visual scale (NVS);
* muscular pain (Masseters and Temporalis) \(\geq\) 30 on the NVS;
* tenseile cephalgia and (or) migraine \(\geq\) 30 on the NVS;
* cervical pain and (or) backaches of tense origin \(\geq\) 30 on the NVS. Painful symptomatology has been divided into 4 categories: mild (0-30); moderate (30-50); strong (50-80); severe (80-100). Exclusion criteria [33; 34]:  
trauma, fractures, or malformations affecting TMJ;
* recent surgery of TMJ;
* systemic pathologies (such as, rheumatoid and psoriatic arthritis, [PERSON] syndrome);
* neuropathic cephalgia;
* edentulism, involving eight or more missing teeth;  
Therapeutic indications:  
The therapeutic protocol with the lingual-ring has been articulated in the following manner: the standardized application of the device ranged from a minimum of night-only use (6-8 h) to a maximum of 12 h per day, including night, with the indication to put the tongue at the top of the spot. The maximum duration established for an entire cycle of treatment was 3 months. The recruited patients underwent the sEMG examination, with the aid of a computer-controlled technology to process the data. A dedicated software was able to digitalize the sEMG analogic signals. The sEMG recordings and signal detection were carried out following the [PERSON]'s recommendations; briefly, the operators should apply single-use, bipolar, and superficial skin-electrodes (21 \(\times\) 41 mm), placed in parallel with the muscular fibers on the Masseter and Temporal muscles (anterior fascia), on both the right and left sides. Inter-electrodes' distance should be 21 \(\pm\) 1 mm. The reference (mass) electrode is placed on the forehead (_glabella_) (Figure 1). Before placing the electrodes, the skin must be cleaned with 90% ethanol, in order to reduce the superficial electric impedance. Patients should sit in a natural position, with the head free from any support, and eyes looking to the horizon [35; 36]. The electromyographic evaluation at time zero (T0) was first performed with the aid of two 10 mm-thick cotton rolls placed between the second premolars of the mandible, with maximum voluntary tightening (MVC) lasting no less than 5 s (Figure 1). Then, the electromyographic evaluation was newly performed at time zero (T0) with the aid of the intraoral device called \"Lingual Ring\" (Figure 2). Figure 1: First recording (T0), with cotton rolls between the second premolars. Figure 2: Second recording (T0): with the intra-oral Lingual Ring application. The \"Lingual Ring\" has been previously described in the scientific literature [20; 21; 22]. Briefly, it is a medical platinic silicone, in compliance with international regulation (UNI EN ISO 10993 1:2010) and European directives number 93-42 EC (Class 1 medical devices).