- The fundamental structural unit of dental enamel is the enamel rod (also known as the enamel prism).
- These enamel rods are tightly packed, highly organized, and extend from the dentinoenamel junction (DEJ) to the outer surface of the tooth.
- Each enamel rod is formed by a group of enamel crystals arranged in a specific pattern, which provides mechanical strength and resilience to the enamel.

Key points:
- The enamel rod (prism) is the basic building block of enamel.
- It consists of hydroxyapatite crystals tightly packed in a prism-like structure.
- Enamel rods are produced by ameloblasts during tooth development but ameloblasts themselves are not structural units; they are the cells that form enamel.
- Unlike enamel rods, dentin tubules are part of dentin, not enamel.
- Enamel lamellae are enamel defects or structural anomalies, not fundamental units.

Thus, knowing that the enamel rod is the smallest discrete structural unit helps in understanding enamel’s properties in terms of both function and pathology.

Reference: Craig's Restorative Dental Materials, 13th Edition, Chapter 2 / Page 45