This invention provides devices and systems and methods therefrom for properly controlling negative pressure applied to oral cavity, facilitating breathing and treating sleep apnea and snoring. The systems comprise a negative pressure system providing a vacuum source and an oral device comprising a shield, a tube passing through the shield, a flexible negative pressure deliverable part connected to the shield or the tube, an optional tongue protector, where the negative pressure deliverable part is conformable to the contour of the upper palate. Negative pressure is delivered to the front and back zones inside the oral cavity via the negative pressure deliverable part to eliminate air space in the oral cavity.
