Pain Neuroscience Education, Motor Imagery and Action Observation in Patients With Chronic Temporomandibular Disorders.

The Numerical Pain Rating Scale (NPRS) will be used to assess pain intensity. This scale consists in a sequence of numbers from 0 to 10, in which 0 represents "no pain" and 10 represents "worst pain imaginable".

The Craneofacial pain and disability inventory (CF-PDI) is a self-administered questionnaire that has been designed to obtain information on how pain in the orofacial region affects the patient's daily life. It consists of 21 items, with the final score ranging from 0 to 63 points. Each question is scored on a 4-point ordinal scale, ranging from 0 to 3. A higher score reflects higher pain and disability levels.

The Pressure Pain Threshold (PPT) will be measured through a pressure algometer in 3 different sites; 1) Anterior temporalis muscle, 2) upper trapezius muscle and 3) thenar eminence (non-dominant hand). At each site, 3 measurements will be made with an interval of 30 seconds, and the mean will be registered. To determine the PPT, the pressure will be increased at a rate of approximately 1 kg/second and patients will be asked to raise their arm the moment the pressure begins to change to a sensation of pain, at which point, the evaluator will stop pressing. PPT values will be expressed in kg/cm2.

Temporal Summation (TS) will be induced using a pressure algometer. For TS, 10 consecutive pressure pulses will be elicited using the PPT (obtained before). For each pulse of the TS procedure, the pressure will increase at a rate of 1 kg/second until the PPT is reached, where it will remain for one second before being released. The pressure pulses will be repeatedly performed with an interval between stimuli of one second. Participants will be instructed to assess the pain intensity of the first and tenth pressure pulses according to the NPRS. The TS score will be obtained by subtracting the first NPRS score from the last score. The higher the TS score, the more efficient nociceptive signaling for the brain.

For the Conditioned Pain Modulation (CPM) a occlusion cuff will be used as a conditioning stimulus. The cuff will be inflated in the non-dominant arm at approximately 20 mm Hg/second until the subjects report experiencing pain at a value of 5/10 using the NPRS, when inflation will stop. Subjects will adapt to the stimulus for 30 seconds, and the first PPT measurement will be performed. Then, the cuff will then be deflated and 1 minute later the second PPT measurement will be taken.

The Central Sensibilization Inventory (CSI) is a self-report outcome measure that consists of two parts. Part A consists of 25 statements where the participant must answer how often he/she experience each symptom. Individual items are scored from "0" (never) to "4" (always), resulting in a total score range for all 25 items from "0" to "100". Part B asks if the participant have been previously diagnosed by a doctor for some diseases (YES/NO). Part B of the CSI is for information only and is not qualified. A score of more than 40 indicates the presence of central sensitization.

The Pain Catastrophizing scale (PCS) is a 13-items instrument that ask participants to reflect on past painful experiences, and to indicate the degree to which they experienced each of 13 thoughts or feelings when experiencing pain, on 5-point scales with the end points being (0) not at all and, (4) all the time. A total score (ranging from 0 to 52) is obtained, along with three subscale scores that assess rumination, magnification, and helplessness. A higher total PCS score of 30 represents a clinically relevant level of catastrophizing.

The Spanish version of the Tampa Scale of Kinesiophobia for Temporomandibular Disorders (TSK-TMD-S) consists of 10 items formulated positively and distributed in 2 subscales as follows: (1) somatic approach (items 1, 2, 3, 4 and 10) and (2) avoidance of activities (items 5 to 9). The total score can range from 10 to 40 (somatic focus, 5-20; avoidance of activity, 5-20), with higher scores indicating an increased fear of jaw movement and re-injury. The cut-off point to consider kinesiophobia is 23 points.

To assess adherence to home exercise, a google form will be sent weekly to the volunteers. It will consist of questions related to the number of times patients performed the exercises during the week and to the difficulties they encountered. Adherence to exercises will be expressed as a percentage [(number of exercise sessions performed / number of exercise sessions prescribed) X100].