I attended a stuttering research clinic for two weeks in Virginia. The guy in charge gave us a presentation on all the forefront of research into speech therapy. He said that a lot of stuttering comes from the way sounds resonate off our skulls, and people who stutter often have difficulty with resonation. He thinks placing a type of metal rod in the spot where the skull resonates sounds (the inner ear) could dramatically help. I don't have a source, I am sorry. It was a powerpoint presentation that I saw.