K.L.
The image you describe is just adorable! You probably need to do something to get his muscles working in balance so he doesn't grow up with something that could cause pain and other problems when he is older. Some problems like this can result in wearing down teeth, chronic headaches, and even hearing loss. Best to look into it while he is young, but make sure you get this on video first!
I am trained in a variety of therapies, including muscle re-activation and kinesiology (the study of muscle movement and inter-muscular relationships). To state this simply, MDs are not trained to adequately diagnose functional muscular disorders. Dentists and orthodontists may suggest traction methods to forcefully align the teeth or balance the bite. Traction therapies, such as braces, are rarely, if ever, done on baby teeth. If the bite is imbalanced, you would more likely notice this when he chews, not when he talks. If it is a bite imbalance, a dentist might simply grind a tooth down so that the bite is more comfortable.
In my experience, I would not assume this was a dental problem and would not subject a child to unnecessary sedatives for dental procedures until I had reason to believe it is a dental problem. This sounds to me more like an issue of the TMJ (jaw joint), the muscles used to control that joint, and the muscles used for speech. I would consult a licensed practitioner that better understands muscle function and balance, as well as how to easily manipulate joint relationships. I would seek a doctor of chiropractic, an osteopathic doctor, a cranio-sacral therapist, or someone trained in neuro-cranial restructuring. Since most of these types of practitioners do not specialize as pediatric practitioners, do ask around and/or search the web for those who work best with children. You may find a pediatric DO. I've known many a happy parent who decided to try the methods that were least uncomfortable, least risky, and usually least expensive first. If it doesn't work, you can always try the methods that are more uncomfortable and invasive. In your son's circumstance, these more natural options are not only more comfortable and less challenging for your son, they are also far more likely to be truly effective. If you live in the St. Louis area, I would be happy to refer you to some excellent practitioners.