Final answer:
The provided historical context discusses the Hill Burton Act of 1946, which influenced hospital construction and healthcare services in the U.S., but does not provide the exact year dental hygiene was designated under the Health Professions Act.
Step-by-step explanation:
The question pertains to the history of healthcare legislation, particularly relating to dental hygiene. While the information provided does not contain the specifics about when dental hygiene was designated under the Health Professions Act, it discusses the historical context of the Hospital Survey and Construction Act, known as the Hill Burton Act, which was passed in 1946.
This Act was significant for the expansion of hospitals and healthcare services in the United States, though it initially permitted segregated facilities. However, the specific designation of dental hygiene under the Health Professions Act would require further research since it is not mentioned explicitly in the reference information.