The superintendent of any facility may admit for purposes of receiving dental services not otherwise available in the community any mentally retarded person 18 years of age or older requesting dental services; any mentally retarded person for whom such a request is made by his parents, guardian, or person standing in loco parentis; or any mentally retarded person who has been declared legally incompetent and for whom such a request is made by his guardian. Such admission shall be for no longer than necessary to receive those dental services, including the normal time for recovery from such services, as are deemed appropriate by persons authorized to practice dentistry in this state.