'Tongue Posture' is a concept I only ran into in the last year. It's quite significant. It is one of the things that meant that cave-men didn't need orthodontics as much as we do. The pressure of the tongue back then pushed quite hard on the front of the palate and avoided a lot of crowding. I have learned to feel the difference in my bite waking up after mouth breathing, compared to nose breathing, as the tongue has two completely different postures in these cases. Tongue posture can also help an appliance be more active and effective. I was told this as a youngster: The mono-block was more effective when one was awake than when one slept.