## 2 Materials and Methods
### Recording Equipment  
The instrumental examination consisted of electromyography (sEMG) and kinesography. Electromyographic activity was recorded using a wireless computerized instrument (Teethan BTS TMJOINT S.p.A. Garbagnate Milanese, MI, Italy), an innovative electromyograph technology using Dr. [PERSON]'s standardized protocols [30; 31; 32; 33]. Six differential satellite surface electrodes with dimensions of 16 \(\times\) 12 mm and a mother electrode of 41.5 \(\times\) 24.8 \(\times\) 14 mm were used. The sEMG signals were amplified (gain 1000), with a bandwidth of 0-10 kHz and peak-to-peak input range from 0 to 2000 \(\upmu\)V, using a differential amplifier with a high common mode rejection ratio (CMMR \(>\) 110 dB in the range 50-60 Hz, input impedance 100 MOhm), digitized (16b resolution; acquisition frequency up to 1 KHz with \(\pm\)2% accuracy) and digitally filtered (high-pass filter set at 10 Hz; low-pass filter set at 500 Hz) [34]. The muscles investigated by sEMG were the right and left temporalis muscles (TA), the right and left masseter muscles (MM) and the right and left sternocleidomastoid muscles (SCM). Six adhesive electrodes were applied to the subjects' skin of the face and neck previously cleaned with alcohol to eliminate fat and pollution residues. The electrodes were placed on temporal, facial and neck areas where most of the recorded sEMG activity \begin{table}
\begin{tabular}{c c} \hline \hline
**Inclusion Criteria** & **Exclusion Criteria** \\ \hline Patients with juvenile idiopathic arthritis & \\ diagnosed at least six months before by the & \\ Paediatric Department of the SS. Annumziata & Incomplete medical history \\ Hospital in Chieti, Italy & \\ Age between 5 and 20 years old & Congenital craniofacial syndrome diagnosis \\ No contemporary or previous & Presence of craniofacial bone fracture in the \\ orthodontic treatment & medical history \\ Compliance and ability to reliably indicate the & Previous temporomandibular joint treatments \\ presence of pain and to reliably execute & or craniofacial surgery in the medical history \\ instrumental tests & Presence of other systemic illness \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Inclusion/exclusion criteria. could be expected to come from the anterior temporalis, masseter and SCM muscles. In particular, on the anterior temporalis muscle area, the electrodes were positioned vertically, 3 cm from the zygomatic arch, just lateral to the eyebrow (lateral to the orbit of the eye); on the masseter muscle area, the electrodes were positioned between the cheek bone and the corner of the jaw [35]. On the sternocleidomastoid muscle area, one electrode was positioned in the middle of the sternal belly of the muscle. Data collection was conducted in a dental office by a single experienced examiner; the subject was seated on a comfortable chair with no headrest, with the feet resting on the floor and arms resting on the lap [35]. sEMG data were extracted with three tests lasting overall about 10 min:  
Cotton test (COT6): The subject was asked to close their mouth and clench, biting two cotton rolls positioned on the occlusal surface of the posterior teeth behind the first premolar. This test allows assessing the maximum muscle activity in the absence of dental contact. * Clenching test (CLE6): the subject was asked to close their mouth and clench in normal condition without cotton rolls (true occlusal test). * Rotation test (ROT6): The subject was asked to rotate their head, first on one side, then on the other. The operator ensured that the patient did not tilt their head or move their shoulders away from the back of the chair. For each subject, the maximum voluntary teeth clenching (MVC) value was extracted for MM and TA. The sEMG potentials recorded during the MVC tests were expressed as percent of the mean potential recorded during the MVC on the cotton rolls (unit IV/IV100). All following calculations were performed with the standardized potentials [36].