Fifty individuals who have undergone orthognathic surgery of the mandible alone or concurrently with the maxilla will be randomly assigned to the control group, which involves practicing a control task (completion of Sudoku or crossword puzzles) in addition to a self-rehabilitation program and physiotherapy. Patients will be instructed to engage in the task for approximately 10 minutes per day, equivalent to the duration of motor imagery practice in the group 1. Adherence to the program will be monitored by the physiotherapist. The program has been standardized across all participating centers, as the study is multicentric.

Active range of motion for maximum mouth opening in millimeters measured using a caliper between the maxillary and mandibular incisors on the midline. Forward and lateral jaw movements will be measure by the same evaluator blinded to the randomization group.

Pain at rest and during jaw movements will be assessed using the 0-100mm Visual Analog Scale (VAS) (0=no pain, 100=maximum imaginable pain). In the evaluation of acute pain, the Visual Analog Scale is commonly used as it is a reliable, valid, sensitive, and suitable measurement tool (Sirintawat et al., 2017). Analgesic consumption will be recorded through patient inquiry at each physiotherapy session.

The patient will be weighed using a scale at the end of each physiotherapy session.

Orthodontic treatment concurrent with physiotherapy will be systematically assessed at each physiotherapy session by questioning the patient, including an inquiry about any prescribed orthodontic measures and the use of retention elastics, as these factors may impact the maximum mouth opening.

This will include i) the physiotherapy number (n=8) and duration (each session duration = 30 min), ii) the compliance with active movement performed self-rehabilitation (both motor imagery control groups) indicated by the number of movement practiced per day, iii) compliance with intervention (motor imagery or control). The physiotherapist will supervised and verify the patient's compliance all along the study.

It will be measured using the Jaw Functional Limitation Scale 8 items. The patient will rate each item from 0 (no discomfort) to 10 (complete limitation). The maximum total score is 80. This scale includes items specifically assessing chewing, vertical jaw mobility, as well as verbal and emotional expression. The questionnaire is reliable (Ohrbach, Larsson, et al., 2008).

It will be measure using the Orthognathic Quality of Life Questionnaire with 22 items. Each item is assessed from 0=no discomfort to 4=major discomfort, with a maximum total score of 88. Four sub-domains are evaluated: aesthetics (max subscore=20, items 1, 7, 10-11, 14), function (max subscore=20, items 2-6), awareness of facial deformity (max subscore=16, items 8-9, 12-13), and social impact (max subscore=32; items 15 to 22) (Cunningham et al., 2000).

We will use the Goal Attainment Scale (Krasny-Pacini et al., 2013). Before surgery, the patient will choose the 3 items that they consider to be the most critical/disturbing among the various domains impacted by dento-maxillary dysmorphosis, The patient will indicate the level of achievement for each of these goals [initial pre-treatment level = -2 ; progress toward the goal without reaching it = -1 ; expected level after treatment = 0 ; "most likely" level after treatment = +1 ; successful goal better than expected = +2]

Motor imagery capability will be measured by the Tongue Mouth Imagery Questionnaire by the same blind and experienced physical therapist. It consists in scoring the vividness of motor imagery movement using a 5-point Likert scale separating the visual and kinesthetic modalities (1: no image/sensation, 5: image as clear / sensation as intense as during overt movement).