The reasons for jaw cramps when yawning include the following: 1. Having the habit of clenching teeth in daily work or study can put the masticatory muscles in a spastic and tense state, and can cause soreness of the masticatory muscles when yawning with a wide mouth; 2. When the teeth are crowded, misaligned or have the habit of chewing on the lateral side, it can trigger the temporomandibular joint dysfunction syndrome, and the joint area on both sides produces unequal wear and tear. The pain can be produced in front of the ear screen; 3. After trauma, the joint disk is perforated or ruptured, and it is unable to do normal opening and closing of the mouth movement, which can cause pain in the joint when yawning; 4. When chronic inflammation occurs in the joint cavity and produces adhesions, excessive mouth opening movement can induce joint movement disorder and produce local swelling and pain.