The self-administered therapy programme will consist of prevention of parafunctional activities, information about sleep hygiene and home exercise programmes, the effectiveness of which has been reported in the literature and is in line with the International Delphi Guidelines. Home exercises will start with 2 times a day, 8 repetitions and progress will be made weekly according to the patient's condition.

For Placebo Non-Invasive Auricular Transcutaneous Vagal Nerve Stimulation, the technique will be similar to active stimulation. The VaguStim device will be set to 0 Hz by the practitioner, indicating that no actual stimulation is being delivered. Patients will be told that they will not be able to feel the current due to its lower intensity during the intervention, without explaining the true nature of the placebo stimulation.

Non-Invasive Auricular Transcutaneous Vagal Nerve Stimulation, CE certified (CE No: 2460) non-invasive stimulation device will be applied with. The application will be performed with 3 different sized electrodes (small, medium, large) specially designed according to the size of the inner ear. The stimulation will be delivered bilaterally from the symba concha and tragus regions innervated by the auricular branch of the n.vagus, which guarantees effective and targeted vagal modulation. With reference to the studies in the literature; VaguStim application frequency will be 25 Hz, pulse width 250 µs, current level 0.5 mA with biphasic waveform.

The treatment will continue 3 days a week for a total of 6 weeks, with each session lasting 20 minutes.

Participants in this group will receive self management therapy. The self-administered therapy programme will consist of prevention of parafunctional activities, information about sleep hygiene and home exercise programmes, the effectiveness of which has been reported in the literature and is in line with the International Delphi Guidelines. Home exercises will start with 2 times a day, 8 repetitions and progress will be made weekly according to the patient's condition.

Jaw and neck joint pain intensity will be assessed using the Visual Analogue Scale (VAS),which is reported to be valid and reliable.The individuals included in the study will be asked to indicate the jaw and neck joint pain intensity they have experienced at rest and during chewing in the last 1 week on a 100 mm long line positioned vertically.The marked points will be measured and recorded in millimetres.An increase in VAS indicates pain of higher intensity Pressure-pain threshold measurement will be performed using a digital algometer.Before starting the tests, the individuals will be informed about the test and one trial session will be performed. The tests will be performed using a 1 cm2 headgear with a 1 kg/cm2 increase in pressure intensity every second and the participants will be asked to tell the evaluator the point at which the pressure to be applied turns into mild pain. The average of three consecutive tests performed at 30 s intervals will be taken and recorded in kg/cm2.

The TheraBite® Range of Motion Scale (TheraBite ®, Platon Medikal Ltd., United Kingdom) will be used to assess the range of motion of the participants' jaw joint. TheraBite is a scale with high intra-observer reliability that is frequently used in the literature for the assessment of jaw joint range of motion and is accepted as the standard for clinical use. Participants will be placed supine on a therapy table in an examination room and asked to open their mouths as far as they can and the range of motion will be recorded in millimetres (mm). The measurements will be repeated three times and the average of the three measurements will be taken as reference.Higher values obtained from this scale represent an increase in the range of motion of the mouth.