Final answer:
To stop a hematoma from spreading, one should immediately apply ice on the area to reduce swelling and inflammation, without massaging, applying heat, or restricting jaw movement unless instructed otherwise.
Step-by-step explanation:
To stop a hematoma from spreading, the recommended action is to apply ice on the area. Doing so helps to reduce swelling and inflammation by causing vasoconstriction, which narrows the blood vessels, slowing blood flow to the injury site and minimizing the spreading of the hematoma.
It's important not to massage the area, as this can aggravate the condition and cause further bleeding under the skin. Applying heat or restricting jaw movement are not immediate measures for hematoma treatment and may not be relevant unless specified by the location of the hematoma.