Here are some examples of what a myofunctional disorder looks like. You will see how the pressure exerted by the tongue against the teeth can change tooth position. Notice the narrow palate due to lack on pressure from the tongue resting too low. There are also examples of ankyloglossia, commonly known as tongue tie, which prevents correct tongue position against the palate.
Tongue tie can prevent functional movement of the tongue. See the facial strain exhibited before releasing the tongue tie.
Where the tongue rests in the mouth can influence the way the teeth come together. The tongue resting in between the teeth is preventing this patient's teeth from biting together, but as you can see in the bottom picture, with tongue tie release and myofunctional therapy, the bite is starting to close.
This patient was in braces for 5 years because her tongue resting against her teeth was preventing the orthodontics from moving her teeth into the correct position.
Examples of tongue ties
Narrow palate due to low tongue posture and tongue thrust resulting from mouth breathing
After 4 years in braces, this patient's teeth shifted because her tongue posture was never addressed.