Difficulty in opening the mouth is a symptom that occurs when there is a problem with the jaw joint or with the masticatory muscle group. Difficulty in opening the mouth after local anesthesia is mainly due to soft tissue injury. Diagnosis: The causes are muscle injuries that may occur during local anesthesia, hematomas caused by bleeding, and infection at the injection site. The most likely cause, especially in the case of inferior alveolar nerve conduction anesthesia, is injury to the medial pterygoid muscle or blood vessels in the temporomandibular space by the injection needle. When a local anesthetic is injected into or around the muscle, the muscle fibers are stimulated and stiffen and gradually become necrotic, which may become worse if vasoconstrictors are applied. Bleeding within the muscle fibers can cause compression of the surrounding tissues, either by triggering a chemically noxious irritation that results in muscle twitching, or by continuing irritation as the blood is slowly absorbed, or by secondary infections that cause the muscle stiffness to become more and more severe, with prolonged difficulty in opening the mouth. Muscle twitching can also be triggered by contaminants in local anesthetics or by harmful stimuli from antiseptic solutions. Infection at the injection site, even if mild, can cause difficulty in opening the mouth. Particularly minor abscesses in the temporomandibular space are difficult to detect and are likely to develop into chronic inflammation. These mouth opening difficulties may manifest immediately after anesthesia or slowly over several days. Difficulty in opening the mouth can occur quickly when the chewing muscle is directly stimulated by a needle prick or local anesthetic injected during local anesthesia. If bleeding or infection occurs, the longer the chewing muscle is stimulated the stronger the stimulation becomes and the more severe the difficulty in opening the mouth becomes. Treatment: The mainstay of treatment for dysphagia is intermittent warm compresses, as well as analgesics for pain relief and muscle relaxants if the muscle spasm is severe. Self-physical therapy is practiced every three or four hours by having the patient do five minutes of jaw opening and closing and lateral movements. In most cases, it is easy to heal, and symptoms improve in about 2-3 days. If the headache or difficulty in opening the mouth persists afterward, consider whether it is infected and take antibiotics. If penicillin does not help, consider whether the infection is caused by anaerobic bacteria, if so, just take a few days of metronidazole and you will be fine. If the difficulty in opening the mouth persists for a long time, the unabsorbed bleeding can become scar tissue and organize or transform into a chronic infection, at which point it is best to consult an oral and maxillofacial surgeon in order to reevaluate and treat the problem. For proper prevention, uncontaminated anesthetics should be used with a sharp needle. Anatomically, local anesthesia should be administered accurately to avoid injuring unnecessary tissues.