Enamel

Question 1

What are some physical properties of enamel

Answer 1

Thickest over cusps, thinner at cervical margin

Hardest biological tissue to withstand shearing and impact forces

Compared to subsurface enamel: harder, less porous, less soluble, more fluoride, less carbonate

Brittle due to hardness

White with low translucency when young, turning yellow and more translucent when old

Question 2

What is the chemical composition of enamel

Answer 2

96% inorganic material, mostly calcium hydroxyapatite

10% water (by volume)

• extra crystalline water: mobile, bulk of enamel
• caged water: caged in apatite crystals, not tightly bound
• intra crystalline water: associated with lattice or hydroxy group

1% organic material

Question 3

The 2 diffusion pathways in enamel

Answer 3

Intraprismatic space:

• between hydroxyapatite crystals
• filled with water and organic material
• slow

Interprismatic space:

• principle diffusion pathway
• empty and fast

Question 4

What is gnarled enamel

Answer 4

Rods appear twisted around cusp/incisal edge

Question 5

What are cross striations

Answer 5

Perpendicular to long axis of enamel rods. Incremental lines that record daily increments of growth

Diurnal rhythmicity, primarily active in the day

Question 6

What are the lines of retzius/perikymata

Answer 6

Dark lines that extend obliquely from EDJ towards the incisal edge. Transversely, striae run circumferentially (in rings)

Perikymata demarcates groups of prisms formed by different cohort of ameloblasts, reflecting weekly rhythmicity

Enamel is formed more slowly at cervical region. Incremental lines are closer

Question 7

What are hunter schreger bands

Answer 7

Alternating light and dark bands that form due to changes in direction between adjacent groups of enamel rods

Question 8

Describe the 3 structures at the EDJ (scalloped)

Answer 8

Enamel spindles

• trapped odontoblastic processes which extend into ameloblast layers before enamel forms
• shortest

Enamel tufts

• branching defects at EDJ protruding 1/3 into enamel
• hypomineralised, more enamel protein
• occur dye to abrupt changes in direction of rods arising from different regions of scalloped EDJ

Enamel lamellae

• linear enamel defect through entire thickness of enamel
• occur due to incomplete maturation of grouops of prisms
• hypomineralised

Question 9

What happens to enamel as it ages

Answer 9

Reduced permeability