Which of the following duties is within the scope of practice for a Licensed Dental Assistant?

The correct answer is placing orthodontic separators, which is a task typically included in the duties of a Licensed Dental Assistant. Licensed Dental Assistants are trained to perform various supportive tasks in dental practices, and placing orthodontic separators falls within their scope of practice. This procedure involves inserting special devices between teeth to create space for orthodontic appliances, and it does not require a dentist's direct involvement for every step.

In contrast, the other options represent duties that are generally beyond the scope of practice for a Licensed Dental Assistant. Administering nitrous oxide requires specialized training and is typically restricted to licensed dentists or dental anesthesiologists due to the complexities and risks involved in sedation. Performing surgical extractions is a more advanced procedure that must be carried out by a licensed dentist or oral surgeon. Likewise, diagnosing periodontal disease is a diagnostic responsibility that requires education and training specific to dentists, as making a diagnosis involves assessing a patient’s overall health, probing into deeper tissue assessment, and treatment planning, which are outside the realm of a dental assistant's duties.

Thus, the role of a Licensed Dental Assistant is focused on supportive functions that assist the dentist, and placing orthodontic separators is an appropriate task that aligns with that role.