Which of the following actions can be taken by a dental hygienist under direct supervision?

A dental hygienist operates under direct supervision when a licensed dentist is present and overseeing the procedures being performed. Among the options, removing sutures is the action that can be undertaken under this level of supervision. This task typically requires the dentist's direction and may involve the hygienist working closely with the dentist to ensure the patient's safety and comfort during the procedure.

Performing dental hygiene assessments involves evaluating a patient's oral health, which is within the hygienist's scope of practice, but it's generally not classified as an action that requires direct supervision since it can be performed independently based on the hygienist's training.

Placing sutures is usually reserved for dentists due to the complexity and potential complications involved in the procedure. It requires a higher level of expertise than what is standard for dental hygienists.

Developing treatment plans often falls under the responsibilities of the dentist who diagnoses and develops comprehensive plans for patient care, while hygienists may contribute information but do not typically create these plans independently without dentist oversight.

Thus, the removal of sutures, being a task that falls within the proper scope of practice for a dental hygienist while directly supervised by a dentist, is correctly identified in this context.