Dental Enamel Flashcards
What does the enamel do
- Forms outer covering of tooth
- Modifies colour of tooth
Why are younger teeth whiter
Less translucent enamel
Where is enamel thickest
Over cusps and incisal edges
Where is enamel thinnest
At cervical margin
How does enamel thickness evolve with time
Thickness declines gradually to become a very thin layer at the cervical margin
What is the composition of enamel
Almost pure mineral - hydroxyapatite
What are the physical properties of enamel
- Very hard due to high mineral content & its unique microstructural organisation
- Withstand forces from mastication
- High abrasion resistance so it wears down slowly
- Cannot be repaired or replaced
- Brittle so it depends on dentine for resilience
What proteins comprise the matrix of immature enamel
- Amelogenin
- Ameloblastin
- Enamelin
What are the chemical properties of human enamel
- Hydroxyapatite in enamel forms larger crystalites
- Crystalites are long, ribbon-like
- Tightly packed with pores
How are crystallites grouped
Grouped as prisms - some form the interprismatic enamel
Where do enamel spindles arise
At the ADJ, particularly around the cusps of teeth where most crowding of odontoblasts occurs
What are enamel tufts
- Hypomineralised structures coming from the ADJ
- Tufts are spaces between prisms that contain the enamel protein ‘tuftelin’
What are enamel lamellae
- Fine cracks in the surface of enamel
- Extend from surface of enamel to ADJ
When and why are enamel lamellae formed
- During enamel development
- Due to incomplete maturation of enamel development or stress cracks
Describe the structure of the newly erupted outer enamel
Non-prismatic
Why is surface enamel more highly mineralised
Absence of prism boundaries
Whats the advantage of surface enamel containing more fluoride than subsurface enamel
- Increased density
- Increased hardness
- Decreased solubility in comparison to subsurface enamel
Whats the advantage of surface enamel being aprismatic
- Not subject to abrasion
- Less porous
- Less susceptible to acid dissolution
Explain the Perikymata Grooves
Fine ridges resulting from the termination of the incremental striae of Retzius on the enamel’s surface
Describe the sheets of enamel prisms forming the Hunter-Schreger bands
- Prisms are grouped into sheets of 10-13 layers, following a sinusoidal path
- Groups of prisms above and below them going in different directions
Explain how the optical effect (Hunter-Schreger bands) are formed
Periodic changes in the direction of prism sheets
Why are Hunter-Schreger bands visible
Different bands of prisms transmit light in different directions
Whats the advantage of the complex pattern of prisms
Makes enamel resistant to a fracture
What happens to enamel as age increases
Becomes progressively thinner due to tooth surface loss
Why does the tooth darken as enamel age increases
Enamel becomes thinner + reduced translucency of tooth
Why does enamel become less permeable with age
- Microporosity reduces - less spaces between crystallites
- Crystals acquire more ions
- Crystals increase in size
What dissolves enamel mineral
Acids produced by plaque biofilm
Where do early lesions develop and where do they progress
- Develop at the surface of enamel
- Progress through the tissue following the orientation of prisms
What does the microporus prismatic structure allow acids to do?
Allows acids produced by plaque biofilm to penetrate surface enamel and begin dissolving enamel prisms and crystallites
Where will acids penetrate more readily?
- Where there’s greater porosity
- May tend to progress down paths provided by prism boundaries
Why is removal of unsupported enamel an important element in cavity preparation design
Caries penetrates to the underlying dentine, leaving overlying enamel unsupported and prone to fracture during mastication
What can lead to microleakage
Fracture of unsupported enamel
What happens to prisms during tooth preparation
Prisms are sectioned, cracked and pulled apart
