I dropped a table on my right big toe a month ago. The X-rays were negative for a fracture but my toe is still swollen and painful and it still hurts too much to wear shoes. I have an old air cast from an Achilles tendon injury and it feels much better to walk in that as opposed to shoes, so should I keep my cast on until I am fully healed to take the pressure off my toe so it can mend faster? And does it sound as if I have a bad bone bruise?
By AirCast, I assume you mean a fracture brace for the ankle, which has a solid, inflexible sole. (AirCast is a company that makes many different types of braces.)
The reason it does not hurt as much in the brace, is the solid sole. You do not have to bend the joints of the great toe. So, as long as you do not let the ankle get stiff, it is probably fine to use the brace. They do make smaller shoes/braces that have stiff soles (called wooden soled shoe, stiff soled shoes, or something similar) that may be easier to get around in than the large ankle brace. Some also come with toe cutouts, so there is no pressure on the toe. They are also called post-op shoes sometimes.
Again, anything that makes the toe hurt less is probably okay, as long as your ankle does not get stiff, or your Achilles becomes tight. Move the ankle around and stretch your Achilles tendon every day.
You may have bruised the underlying bone, and you probably also bruised the heck out of the soft tissues around the great toe. Those can also take some time to heal. But, four weeks is quite a period for the soft tissues to remain that swollen (even with an uderlying bone bruise). If the swelling does not seem to start to get better in a little while, you may need to have this reevaluated.
(PS The only way to tell if a bone is "bruised", is to have an MRI. That is the only study that can pick up the edema within the bone marrow.)