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Enamel Prisms
Tooth (Mandibular First Molar)

Enamel Prisms

Prisma enameli

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Quick Facts

The enamel prisms are the structural units of the tooth enamel, consisting of parallel rods or prisms composed mainly of hydroxyapatite crystals and organic substance and held together with a cement substance, each prism being enveloped in a sheath (Dorland, 2011).

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Structure and/or Key Feature(s)

Enamel hydroxyapatite crystallites are organized into tightly packed bundles called prisms, each of which measures approximately 5 µm in width (Standring, 2016).

Prisms are arranged in rows, with the long axis of the prism typically positioned perpendicular to the underlying dentin.

When viewed in a longitudinal section, prisms extend from the dentinoenamel junction to within 20 µm of the surface, where they are replaced by prismless enamel. In cross section, prisms are identifiable by their horseshoe shape and staggered row-like arrangement (Robinson et al., 1998).

The arrangement and pattern of crystallites within an enamel prism are affected by the local Tomes’ processes and ameloblasts that initially presented during amelogenesis. Prisms have no distinct boundaries per se, instead, the appearance of boundaries results from sudden changes in crystallite orientation. These sudden changes in orientation can be attributed to the disposition of the aforementioned ameloblasts and Tomes’ processes (Fincham, Moradian-Oldak and Simmer, 1999).

A thin zone between prisms exists which shares the same crystallite composition as prisms but a different crystalline orientation. This zone is called the interprismatic enamel or interprismatic cement.

The boundary where enamel prisms and interprismatic enamel meet is called the prism sheath. Much of the organic content of mature enamel resides at the prism sheath, which is mostly made up of a protein matrix of enamelins (Sakae et al., 2011).


Enamel prisms are the basic unit of tooth enamel and contribute to the overall structural integrity and rigidity of tooth enamel.


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

Fincham, A. G., Moradian-Oldak, J. and Simmer, J. P. (1999) 'The structural biology of the developing dental enamel matrix', J Struct Biol, 126(3), pp. 270-99.

Robinson, C., Brookes, S. J., Shore, R. C. and Kirkham, J. (1998) 'The developing enamel matrix: nature and function', Eur J Oral Sci, 106 Suppl 1, pp. 282-91.

Sakae, T., Hirayama, K., Yamamoto, H., Suzuki, K., Hayakawa, Y., Takahashi, Y., Kuwada, T., Nakao, K., Nogami, K., Inagaki, M., Tanaka, T., Hayakawa, K., Sato, I. and Kakei, M. (2011) 'Three-dimensional Orientation Analysis of Human Enamel Crystallites Using X-ray Diffraction', Journal of Hard Tissue Biology, 20, pp. 7-10.

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

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