Dental enamel

Location and borders

The enamel externally covers the clinical crown of the tooth (corona dentis), the part of the tooth protruding from the dental alveolus. Beneath the enamel lies the main bulk of the tooth — dentin (dentinum).

At the boundary between the crown and the root lies the neck of the tooth (cervix dentis). In this contact zone (area contingens), the enamel joins the root cementum. There are four variants of their junction:

• Enamel and cementum meet end-to-end.
• Enamel overlaps cementum.
• Cementum overlaps enamel.
• Enamel does not reach the edge of the cementum (leaving an exposed area of dentin between them).

On the surface of intact teeth, there is the enamel cuticle, a thin and fairly durable film.

Clinical note: In a newly erupted tooth, the clinical crown is smaller than the anatomical crown. With age, as areas of the tooth not covered by enamel become exposed, the clinical crown becomes larger than the anatomical crown.

Chemical composition and origin

Dentin and cementum are hard tissues of connective tissue origin, whereas tooth enamel is of epithelial origin.

The high hardness of enamel is due to its high mineral salt content:

• Inorganic substances: 96–99% (mineral salts).
• Organic substances: 1–4% (proteins and water).

Histological structure

The primary structural unit of the tissue is the enamel prism. There are several million such prisms in the enamel.

• Characteristics of the prism: the diameter is 4–6 µm, and the cross-sectional shape is predominantly arcade-like. Structurally, the prism consists of calcified ultrafine fibrils.
• Arrangement: prisms originate at the dentinoenamel junction and terminate on the surface of the crown. Their length varies and most frequently exceeds the thickness of the enamel layer itself.
• Bundles: enamel prisms are grouped into bundles of 10–20. Along their course, they form S-shaped curves.

Histological ground sections of enamel reveal characteristic optical phenomena:

• Hunter–Schreger bands — alternating light and dark bands. Optical inhomogeneity occurs because some bundles of enamel prisms are cut in transverse section, while others are cut longitudinally.
• Retzius lines — oblique lines. Their formation is associated with the cyclic nature of enamel mineralization processes during its development.

Clinical significance: caries pathogenesis

On the tooth enamel, Streptococcus mutans and Streptococcus sanguis dominate, which is associated with their high ability to adhere to hard dental tissues.

The leading role in the development of dental caries is attributed to the pathogenic effect of microbial dental plaque:

1. Pellicle formation: an acquired pellicle forms on the tooth surface — a film of salivary mucopolysaccharides and glycoproteins. The biofilm is fixed to the tooth surface via an electrostatic mechanism, which also ensures bacterial attachment.
2. Colony growth: in the absence of regular removal of dental deposits, plaque accumulates, and active growth of microorganism colonies occurs.
3. Fermentation: acid-producing microorganisms participate in the fermentation of dietary sugars; this is promoted by a cariogenic diet high in carbohydrates.
4. pH drop: as a result of fermentation, organic acids are produced, and the local pH level in the plaque drops to a critical level (4.5–5.0).
5. Demineralization: at the critical pH, the process of enamel demineralization is triggered, and a demineralized lesion is formed.

Class and exam questions

What else to study on this topic

• Dentyn (dentinum)
• Cementum of the tooth (cementum)
• Crown and neck of the tooth
• Microbial dental plaque and pellicle

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.