Exercise Therapy and Jaw-Mobilizing Device for Trismus in Head and Neck Cancer Patients

Inclusion Criteria: * Age ≥ 20 years. * Ability to communicate in Mandarin or Taiwanese, without significant reading, hearing, or writing impairments, and capable of completing questionnaires independently or with researcher assistance. * Diagnosed with head and neck cancer and scheduled for initial radiotherapy to the head and neck region. * Clear consciousness without severe cognitive or psychiatric disorders. * Presence of intact central incisors (#11, #41) on the right side or (#21, #31) on the left side of both the upper and lower jaws. * Baseline maximal mouth opening (MMO) ≥ 25 mm. * Willingness to participate in the study with signed informed consent. Exclusion Criteria: * Known temporomandibular joint disorders. * Postoperative wound healing complications diagnosed by a physician that prevent participation in mouth-opening rehabilitation exercises.