When you aren’t using your mouth your lips should be sealed, your teeth slightly apart, your tongue tip should be up and not touching your teeth, your tongue should be suctioned to the roof of your mouth and your chin should be relaxed. This is optimal oral rest posture.
Optimal oral rest posture > Suboptimal oral rest posture
I encourage you to strive for correct oral rest posture.
So why is the way you hold your mouth so important?
If your lips are constantly parted this could result in mouth breathing. Mouth breathing can alter facial growth and development for the worse. If you aren’t using your nose to breathe, then your overall health is affected for the worse as mouth breathing does not provide the positive benefit that nasal breathing provides.
If you constantly clench and grind your teeth, then this could result in your teeth to wear down and your temporomandibular joint could be negatively impacted.
If your tongue is constantly pressing against your teeth, then this could result in your teeth shifting even after you have had braces, and your speech could be distorted due to incorrect oral placement of the tongue when talking.
If your tongue is resting low in your mouth, then this could negatively impact facial growth and development, speech production, the way your teeth look, your temporomandibular joint and much more.