Enamel Morphology Flashcards
describe enamel
7
hardest tissue in the body
resists abrasion
brittle
supported by dentine
covers the whole crown
varies in thickness
transluscent
describe how enamel regions vary in hardness
2
surface enamel more mineralised and harder
hardness decreases from cusps/tips to cervix
describe the appearance of enamel rods
3
rods run from ADJ to surface
rods contain hydroxyapatite crystallites
crystallites are deposited at right angles to ameloblast membranes
what are the two different types of enamel rods and the differences between them?
2
long, parallel rods
* cross striations in rods
* due to daily growth
brown transveres striae
* formed at weekly intervals
what is the content of enamel?
3
hydroxyapatite: 95% weight 90% volume
water: 4% weight 5-10% volume
organic matrix: 1% weight 1-2% volume
describe the histology of enamel rods
3
rods run a sinusoidal course
adjacent groups of rods have different orientations
alternate orientation of rods causes bonding patterns (HS bands)
HS bands = Hunter-Schreger bands
name two optical enamel features
2
Hunter-Schreger bands
* alternate orientation in rods
* absent in outer enamel
Gnarled enamel
* present in cusps where mastication forces are highest
name three types of incremental lines in enamel and what are they?
3
brown striae of Retzius
* incremental growth lines of enamel deposition during tooth development
perikymata
* external expression of Striae of Retzius
neonatal line
* represents a disruption in normal distribution of enamel and dentine during birth - transition between pre and post birth enamel and dentine formation
what three features can be found at the enamel-dentine junction and what are they?
3
enamel tufts
* hypomineralised regions due to residual matrix protein at prism boundaries
enamel lamella
* incomplete maturation of groups of prisms
enamel spindles
* odontoblast processes extending into enamel
