Final answer:
The cementoenamel junction is the anatomical boundary that separates the enamel covering the tooth crown from the cementum on the root.
Step-by-step explanation:
The cementoenamel junction is what separates the enamel from the cementum of a tooth. Enamel is the hardest material in the body and covers the crown of the tooth, which is the visible outer surface. The cementum is a layer that covers the root of the tooth and some of the crown, working with the periodontal ligament to anchor the tooth in place in the jaw bone. The cementoenamel junction, also known as the CEJ, is the boundary where these two hard tissues meet. It is crucial in providing a smooth transition between the crown and root of the tooth, which are necessary for tooth function and oral health.