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An enamel prism, or enamel rod, is the basic unit of
tooth enamel Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are denti ...
. Measuring 3-6
ÎĽm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: ÎĽm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
in diameter, enamel prism are tightly packed
hydroxyapatite Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities ...
crystals structures. The hydroxyapatite crystals are hexagonal in shape, providing rigidity to the prism and strengthening the enamel. In cross-section, it is best compared to a complex “keyhole” or a “fish-like” shape. The head, which is called the prism core, is oriented toward the
tooth’s crown In dentistry, crown refers to the anatomical area of teeth, usually covered by enamel. The crown is usually visible in the mouth after developing below the gingiva The gums or gingiva (plural: ''gingivae'') consist of the mucosal tissue t ...
; The tail, which is called the prism sheath, is oriented toward the
tooth cervical margin The cervical margin of a tooth is the surface above the junction of the crown of the tooth and the root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrient ...
/sup>. The prism core has tightly packed hydroxyapatite crystals. On the other hand, the prism sheath has its crystals less tightly packed and has more space for organic components. These prism structures can usually be visualised within ground sections and/or with the use of a scanning electron microscope on enamel that has been acid etched /sup>. The number of enamel prisms range approximately from 5 million to 12 million in the number between mandibular incisors and maxillary molars /sup>. Enamel prism are found in rows along the tooth. Within each row, the enamel prism's long axis is generally perpendicular to the underlying ADJ amelo-dentinal junction, which is also called the dentino-enamel junction. Such is the case in both permanent and primary dentitions; the enamel prisms following the path of the ameloblasts /sup>. In permanent teeth, the enamel prisms near the cemento-enamel junction (CEJ) tilt slightly more apically toward the root of the tooth /sup>. Knowing the orientation of enamel is very important in restorative dentistry because enamel unsupported by underlying
dentin Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by e ...
is prone to fracture /sup> and usually is avoided. The arrangement of crystals within each enamel prism is highly complex. For the most part, the enamel crystals are oriented parallel to the long axis of the prism /sup>. The further away the crystals are from the central axis, the more their own orientation diverges /sup>. Within ground sections of teeth, prisms appear to be twisted and interwoven around each other at the cusps. Such allows teeth to be able to resist strong masticatory forces without fracturing, with literature showing teeth being able to resist forces up to 20-30 pounds per tooth 0/sup>. This part of the enamel is called Gnarled enamel 1/sup>. The area around the enamel prism is known as interrod enamel. Interrod enamel has the same composition as the enamel prisms 2/sup>. Nonetheless, a
histologic Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
distinction is made between the two because crystal orientation is different in each. The crystals lie nearly perpendicular to the enamel prism 3/sup>.


References

---- University of Kentucky College of Medicine. (1996). ''Enamel Prism Morphology''. Oral Histology Digital Lab: Enamel: Enamel prism morphology (image 24). Retrieved January 24, 2022, from http://www.uky.edu/~brmacp/oralhist/module6/lab/imgshtml/image24.htm Khan, A. S., Khan, M., & Rehman, I. U. (2013). Nanoparticles, properties, and applications in glass ionomer cements. ''Nanobiomaterials in Clinical Dentistry'', 93–108. https://doi.org/10.1016/b978-1-4557-3127-5.00005-2 Ganss, B., & Pugach, M. K. (2016). ''Enamel Research: Mechanisms and characterization''. Frontiers Media S.A. Zafar, M. S., Amin, F., Fareed, M. A., Ghabbani, H., Riaz, S., Khurshid, Z., & Kumar, N. (2020). Biomimetic aspects of restorative dentistry biomaterials. ''Biomimetics'', ''5''(3), 34. https://doi.org/10.3390/biomimetics5030034 Alloing-Séguier, L., Marivaux, L., Barczi, J.-F., Lihoreau, F., & Martinand-Mari, C. (2018). Relationships between enamel prism decussation and organization of the ameloblast layer in rodent incisors. ''The Anatomical Record'', ''302''(7), 1195–1209. https://doi.org/10.1002/ar.24000 Sherwood, I. A. (2010). ''Essentials of Operative Dentistry'' (Illustrated). Boydell & Brewer Ltd. Rajkumar, K., & Ramya, R. (2018). ''Triumph’s Complete Review of Dentistry''. Wolters kluwer india Pvt Ltd. Beniash, E., Stifler, C. A., Sun, C.-Y., Jung, G. S., Qin, Z., Buehler, M. J., & Gilbert, P. U. (2019). The hidden structure of human enamel. ''Nature Communications'', ''10''(1). https://doi.org/10.1038/s41467-019-12185-7 Inés Sánchez Neira María. (2008). ''An efficient approach to the synthesis of a calcium phosphate bone-cement and its reinforcement by hydroxyapatite crystals of various particle morphologies''. Universidade de Santiago de Compostela, Servizo de Publicacións e Intercambio Científico. 0Fernandes, C. P., & Chevitarese, O. (1991). The orientation and direction of rods in dental enamel. ''The Journal of prosthetic dentistry'', ''65''(6), 793–800. https://doi.org/10.1016/s0022-3913(05)80015-0 1Gopikrishna, V. (2019). ''Preclinical Manual of Conservative Dentistry and Endodontics'' (3rd ed.). Elsevier India. 2Bartlett, J. D., & Simmer, J. P. (1999). Proteinases in developing dental enamel. ''Critical Reviews in Oral Biology & Medicine'', ''10''(4), 425–441. https://doi.org/10.1177/10454411990100040101 3Beniash, E., Stifler, C. A., Sun, C.-Y., Jung, G. S., Qin, Z., Buehler, M. J., & Gilbert, P. U. (2019). The hidden structure of human enamel. ''Nature Communications'', ''10''(1). https://doi.org/10.1038/s41467-019-12185-7 {{DEFAULTSORT:Enamel prism Dental enamel Enamel prism Tissues (biology)