Enamel

Structure and/or Key Feature(s)

Enamel is described as a highly mineralized, extremely hard and rigid material that covers the crown of the tooth. Semi-translucent and light yellow to white, the enamel lies superficial to the dentin. The boundary between these layers is known as the dentinoenamel junction. Enamel will typically reach a maximum thickness of 2.5 mm over the cusp of the tooth and become thinner at the cervical margins (Standring, 2016).

The composition of mature dental enamel is unique amongst mammal tissues, and contains 96% inorganic material, less than 1% organic material, and the rest water. Specifically, the inorganic portion of enamel is composed of hydroxyapatite; a crystalline calcium phosphate compound (Iijima et al., 2010). The organic matrix, although only making up 1% of the enamel, permeates the entire enamel and primarily consists of proteins such as amelogenin and enamelin (Standring, 2016).

At a nanoscopic level, tooth enamel is composed of needle-like apatite crystallites. These crystallites constitute the enamel prisms (Iijima et al., 2010).

Enamel is formed by the internal enamel epithelium, in a process called amelogenesis. This epithelium is composed of a closely linked sheet of narrow, cylindrical cells called ameloblasts. Ameloblast cells are responsible for the deposition of enamel during tooth development, through the process of amelogenesis. During this process, the ameloblast moves away from the enamel, forming a projection surrounding the developing enamel. These projections are a histologic landmark known as Tomes’ processes (Hillson, 2005).

Prior to tooth eruption from the gum, ameloblasts are broken down, thus removing the enamel’s ability to repair or regenerate itself (Standring, 2016).

Anatomical Relations

Enamel forms the outermost layer of the crown of the tooth, lying superficial to the dentin (Standring, 2016).

Function

Enamel is responsible for protecting the underlying tooth dentin. Its wholly mineral composition lends to the protection of the dentin against food substances as the decomposition of organic matter has little effect on it (Hillson, 2005).

List of Clinical Correlates

—Amelogenesis imperfecta

References

Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.

Hillson, S. (2005) Teeth. Cambridge University Press.

Iijima, M., Fan, D., Bromley, K. M., Sun, Z. and Moradian-Oldak, J. (2010) 'Tooth enamel proteins enamelin and amelogenin cooperate to regulate the growth morphology of octacalcium phosphate crystals', Crystal growth & design, 10(11), pp. 4815-4822.

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41 edn.: Elsevier Limited.