Mo. Rev. Stat. § 332.366

Any person who provides teeth whitening services to another person by use of products not readily available to the public through over-the-counter purchase shall be deemed to be engaging in the practice of dentistry. Licensed dental hygienists or dental assistants may apply teeth whitening formulations, but only under the appropriate level of supervision of a licensed dentist as established by rule. Any individual who take the dental impression of another person or who performs any phase of any operation incident to teeth whitening, including but not limited to the instruction or application of on-site teeth whitening materials or procedures, except under the appropriate level of supervision of a licensed dentist, shall be deemed to be engaging in the practice of dentistry.