What device helps to isolate and protect the oral cavity by placing a barrier?

The rubber dam is the correct answer because it serves a critical function in dental procedures by isolating the teeth and gingival areas from the rest of the oral cavity. This barrier helps maintain a dry working field, preventing saliva, blood, and other fluids from interfering with the dental work. Additionally, the rubber dam protects the patient's mouth and throat from potential injury by keeping instruments and debris contained.

While a protective shield may offer some level of protection during procedures, it does not specifically isolate the oral cavity in the same way that a rubber dam does. A cotton roll holder can assist in moisture control but is limited in its effectiveness and scope. Similarly, a dental bib is intended to protect the patient’s clothing during treatment rather than isolating or protecting the oral cavity itself. Each of these additional devices serves important purposes, but the rubber dam uniquely fulfills the role of creating a controlled environment for dental procedures.