Stuttering isn't caused by crowded teeth or by having an underbite or overbite. Also, a dentist isn't going to be knowledgeable about stuttering because it's a neurological disorder. Stuttering is something you were born with and it's an issue with how your brain developed when you were a child. There was nothing you could've done by yourself to stop the stutter from developing. You can go to speech therapy to help relearn some components of fluent speech and to reduce the tension that accompanies stuttering. But speech therapy can't completely cure stuttering (as of right now, that's impossible).