I went to see my horse one day and his entire left side jawbone was rock hard and swollen an extra two inches out in some spots. I quickly asked my barn owner what I should do, Was he in pain? Should I call the vet? Would it go away?
He told me (because the swelling was so hard) that it was probably a permanent thing, and that his bone was probably displaced. He said I could just leave it and live with a funny-faced-horse, or I could have a (very expensive) surgery to correct it, not that there would be a point, other than aesthetics.
So I left it, and lo and behold, when I went to visit him a week later it was completely gone!