Final answer:
The first dental hygiene code was established in the early 20th century, coinciding with significant advancements in the field of dentistry.
Step-by-step explanation:
The first dental hygiene code was created in the early 20th century. The field of dentistry saw significant advancements around this time, including the establishment of dental hygiene as a profession. Addressing preventive care and oral health, registered dental hygienists could then work alongside dentists to provide comprehensive dental care to patients. These professional developments paved the way for the creation of standards and codes essential to the practice of dental hygiene.