Final answer:
The narrow portion where the crown and the root of the tooth join is called the neck. This is located at the area surrounded by the gums, and is essential for attaching the tooth to the periodontal ligament in the socket.
Step-by-step explanation:
The narrow portion of the tooth where the crown and the root join is commonly called the neck. When referring to the anatomy of a tooth, it comprises two main parts: the crown, which is the visible part above the gum line, and the root, which is embedded in the jaws. The area where these two sections meet, enveloped by the gingivae or gums, is the neck of the tooth. This is a significant area because it is closely associated with the periodontal ligament, which helps secure the tooth in its socket.