What additional component associated with outer skin epithelium is not seen in oral epithelium?

Epithelium are the sheet of cells that covers human's body surfaces. The functions of the epithelium are: to protect the skin, to absorb intestine, to secret glands, to exchange gas ... The oral epithelium, also called oral mucosa is the "skin" inside the mouth, and it covers most of the oral cavity apart from the teeth. Keratinization is the property that distinguish the oral epithelium from the other skin epithelium. Keratinization is the process by which skin cells mature as they move from deep within the skin to the skin's surface.