Dental Enamel Properties Quiz

Study Notes

Enamel covers the anatomical crown of the human tooth.
Enamel is 2-2.5mm thick at the cusps of molars and premolars, thinning to almost a knife edge at the cervical margin of the tooth.
Awareness of enamel thickness is beneficial in treatment plans, such as partial dentures.

Color: Yellowish teeth have translucent enamel, while white or greyish teeth have opaque enamel. Natural color depends on calcification and enamel translucency.
Thickness: Enamel thickness varies across the tooth, from 2-2.5 mm at cusps to a thinner edge at the cervical line.
Hardness: Enamel is the hardest calcified tissue in the human body due to its high mineral salt content and crystalline arrangement. Permanent teeth enamel is harder than deciduous teeth enamel. Micro-hardness is greatest at the surface and decreases toward the cervical line, highest at cusps and incisal ridges.
Brittleness: Enamel's hardness makes it brittle, especially when its connection to healthy dentin is compromised.
Permeability: Enamel acts as a semipermeable membrane for certain ions and dyes. Permeability mostly occurs from saliva to the outer layer of enamel, whereas movement from pulp to inner enamel layer is lessened.

Composition: Inorganic materials make up 96% of enamel weight and 88-90% by volume. Organic materials make up 4% by weight and 12-10% by volume.
Crystalline Arrangement: Enamel's basic unit is calcium phosphate (hydroxyapatite crystals).
Hierarchical Structure: The smallest unit is the calcium phosphate crystal, then enamel prisms, which appear after 30 microns from the dentin.

Enamel Rod (Prism): Parallel-arranged hydroxyapatite crystals that are coated with a layer of enamel protein, and have inter-rod areas with more organic materials. Enamel rod types have oval, keyhole, racket or fish-scale patterns and their cross sections are in the form of cylinders.
Incremental Lines (Retzius): Show alternating periods of formation and rest during enamel development. Short lines represent daily secretion rate and longer lines represent weekly rate. Neonatal line is a line separating pre and post-natal formed enamel, evident in primary and some permanent teeth.
Amelo-dentinal Junction (DEJ): The border between enamel and dentin; enamel prisms end and form a knife edge in permanent teeth and end horizontally in deciduous teeth. The bond between enamel and dentin is chemical, not mechanical.
Enamel Lamellae: Thin, hypocalcified sheets of enamel that extend from the outer surface to the DEJ.
Enamel Tufts: Hypocalcified enamel structures, most evident in transverse ground sections, and rare in longitudinal sections.
Enamel Spindles: Odontoblastic processes that form between cells of the inner dental epithelium before enamel formation, especially apparent underneath cusp tips and incisal edges.

Outer Rodless/Aprismatic Enamel: Outer layer of enamel; this is a different form of enamel from the inner prismatic layer.
Perikymata: Wave-like grooves running horizontally and circumferentially across the surface of the crown; more numerous near the cervical line and decreasing occlusally.

Tooth Whitening: Processes designed to lighten tooth color; can be done chemically or mechanically.
Acid Etching: Technique used to roughen enamel surface by dissolving minerals, especially for bonding restorations. Results in a greater surface area for bonding; three distinct patterns result: enamel rod dissolution, inter-rod dissolution, or no enamel rod residue.

Hunter-Shreger Bands: Optical phenomenon from changes in enamel rod course. Seen clearly in longitudinal ground sections viewed by reflected light as varied appearances (Parazone - light reflects; Diazone - light is transmitted). This explains the natural appearance of teeth, despite not entirely reflecting dentin color.
Rod Ends: Rod ends form shallow concavities in the cervical region and become deeper occlusally.
Cracks: Can occur (especially with issues of undermined enamel), and identifying this feature is important for conservative dentistry.
Afibrillar Cementum: This makes up the attachment at the tooth root and neck.