As used in this act, “Assignment of Duties” shall mean the assignment by a dentist to another person of services and procedures which are performed in the office of a dentist. A dentist may assign to such competent person or persons as the dentist deems appropriate those services and procedures performed in the dental office in which the dentist is practicing but which do not require the professional competence and skill of a dentist or dental hygienist or expanded function dental assistant. Such assignment of services and procedures shall be under the direct supervision of a licensed dentist. This section shall not be construed as authorizing the delegation or assignment of diagnosing, treatment planning and writing prescriptions for drugs or writing authorizations for restorative, prosthetic or orthodontic appliances.