Final answer:
A registered dental assistant notices that the oxygen pressure gauge registers 15 psi. This indicates a low oxygen pressure in the tank and may require refilling or replacing the tank soon.
Step-by-step explanation:
The oxygen pressure gauge registering 15 psi indicates that the oxygen pressure in the tank is 15 pounds per square inch. In a dental setting, this pressure is typically considered low and may indicate that the tank needs to be refilled or replaced soon. It is important for the Registered Dental Assistant to ensure that there is sufficient oxygen supply to meet the needs of the dental procedures.