Section 7. Scope of practice of dental hygienist. — A person shall be regarded as rendering services as dental hygienist, within the meaning and intent of this Act, who shall, with or without compensation, remove calcific deposits, accretion and stains from the exposed surfaces of the teeth, perform surface application of medicaments for the prevention and control of dental caries, or do other helpful duties in the reception and care of patients, in the sterilization of instruments, and in rendering assistance to the dentist at the chair or laboratory; and shall not perform operations on the teeth or tissues of the mouth which only the qualified dental practitioner could do under the provisions of Republic Act Numbered Four hundred and seventeen, as amended. A dental hygienist, within the meaning of this Act, shall always be understood as one working under the supervision of a registered dentist. Dentists, schools, public institutions, or commercial firms may employ registered dental hygienists but, nothing in this section shall be construed as authorizing any dental hygienist to perform any work in the mouth without the direct supervision of a licensed dentist.