Final answer:
A dental dam is used to keep the tongue, lip, and cheek away from the operating field.
Step-by-step explanation:
The instrument used to keep the tongue, lip, and cheek away from the operating field is called a dental dam. A dental dam is a thin sheet of latex or silicone that is placed over the area to isolate it and provide a dry working environment. It is commonly used in dental procedures to prevent contamination and ensure proper visibility.