Ohio Rev. Code § 4715.23
The practice of a dental hygienist shall consist of those prophylactic, preventive, and other procedures that licensed dentists are authorized by this chapter and rules of the dental board to assign only to licensed dental hygienists or to qualified personnel under section 4715.39 of the Revised Code.
A licensed dentist may assign to a dental hygienist intraoral tasks that do not require the professional competence or skill of the licensed dentist and that are authorized by board rule. Such performance of intraoral tasks by a dental hygienist shall be under supervision and full responsibility of the licensed dentist, and at no time shall more than four dental hygienists be practicing clinical hygiene under the supervision of the same dentist. The foregoing shall not be construed as authorizing the assignment of diagnosis, treatment planning and prescription (including prescriptions for drugs and medicaments or authorizations for restorative, prosthodontic, or orthodontic appliances); or, except when done in conjunction with the removal of calcarious deposits, dental cement, or accretions on the crowns and roots of teeth, surgical procedures on hard and soft tissues within the oral cavity or any other intraoral procedure that contributes to or results in an irremediable alteration of the oral anatomy; or the making of final impressions from which casts are made to construct any dental restoration.
A licensed dentist may assign to a dental hygienist the application of silver diamine flouride if the dentist has examined the patient and diagnosed the need for such treatment and the dental hygienist has completed a course approved in accordance with rules adopted under division (B) of section 4715.436 of the Revised Code.
The state dental board shall issue rules defining the procedures that may be performed by licensed dental hygienists engaged in school health activities or employed by public agencies.
R.C. § 4715.23