In which circumstance can a dental assistant provide care without a dentist present?

The correct answer is based on the understanding of legal guidelines and the scope of practice that govern the activities of dental assistants. Dental assistants must operate under the supervision of a licensed dentist and adhere to specific regulations that define their responsibilities and actions in the clinical setting.

When a dental assistant is appropriately supervised, they may be permitted to perform certain tasks independently, as long as those tasks fall within their legally defined scope of practice and do not require the direct presence of a dentist. This ensures that patient safety and care standards are maintained while allowing for flexibility in the workflow of a dental practice.

In contrast, the other situations described do not align with the legal requirements for dental assisting. For instance, a patient's request alone does not authorize a dental assistant to provide care independently; professional and legal standards must still be upheld. Similarly, routine educational instruction typically does not necessitate direct patient care that would require the absence of a dentist's supervision. Lastly, simply because a dentist is on a break does not justify a dental assistant engaging in patient treatment without adhering to the appropriate supervisory guidelines. Thus, option C encapsulates the essential principle of supervised practice for dental assistants, emphasizing adherence to legal standards.