Which of the following procedures can dental assistants NOT perform?

The administration of injectable local anesthetic is a procedure that falls within the scope of practice for licensed dental hygienists and dentists, but it is not permitted for dental assistants. This restriction is primarily due to the need for comprehensive training and a thorough understanding of anatomy, pharmacology, and the management of potential complications that can arise when administering anesthesia.

In contrast, the other listed procedures, such as teeth whitening, taking dental x-rays, and assisting during dental procedures, are generally within the realm of practice for dental assistants, provided they have received the appropriate training and certification. This distinction ensures that patient safety is maintained, and dental assistants are not placed in positions where they could risk a patient's well-being due to inadequate training or legal authority.