There are three causes of disorders that can be considered for pain in the junction under the ear when opening the mouth: 1. Temporomandibular joint disorder syndrome. This is due to painful injury around the temporomandibular joint, resulting in dysfunction of the masticatory muscle groups. It occurs mostly in young adults aged 20-40 years old, and is generally prevalent in people who are accustomed to chewing unilaterally, with the majority producing pain and joint popping during jaw movement. Pressure points are often palpable in the first 10-12 mm of the temporomandibular joint. Combined with X-rays, a clear diagnosis can be made. 2. Due to facial soft tissue injury. This is due to acute trauma resulting in localized bruising and ecchymosis, swelling, and restricted movement of the facial muscles including (facial muscles, masticatory muscles, etc.). If the injury is chronic, it is mostly due to local tissue adhesions and scarring that have not fully healed during the acute period. 3. It may also be due to the dislocation of the temporomandibular joint or even habitual dislocation caused by the relaxation of the ligaments and other tissues around the temporomandibular joint.