Enamel - Prismatic structure

Question 1

Enamel microstructure:
How many and how are crystallites packed

Answer 1

• Several million crystallites
• Packed into long, thin units - run from ADJ to the tooth surface

Question 2

Enamel microstructure:
In longitudinal sections, how are tooth prisms lined up with the ADJ

Answer 2

Perpendicular

Question 3

Enamel microstructure:
In cross-section, how are the enamel prisms seen

Answer 3

• Run in offset rows
• Resemble a repeating ‘keyhole’ pattern

Question 4

Enamel microstructure:
Explain the prisms keyhole shape

Answer 4

• Boundary is horseshoe shaped
• Prismatic enamel is the head of the prism and ‘keyhole’
• Interprismatic enamel is the tail of the prism and ‘keyhole’

Question 5

Enamel microstructure:
What is the advantage of having more porosity (gaps)

Answer 5

There’s more space for water, enamel proteins and the organic matrix

Question 6

Enamel microstructure:
How does the orientation of the head and tail of the prism region differ

Answer 6

Head - runs parallel to the longitudinal axis
Tail - Crystalites gradually diverge and are at a 60º angle

Question 7

Enamel microstructure:
Why is there no clear difference between the orientation of the head and tail of a prism

Answer 7

The change is very gradual

Question 8

Enamel microstructure:
Why is there porosity between prisms

Answer 8

Not all prisms run horizontally so:
- There’s gaps
- The joint is not neat

Question 9

Enamel microstructure:
Describe Pattern I

Answer 9

• Found less frequently
• Near the ADJ + surface
• Prisms have complete boundaries
• Offset rows relative to those above + below

Question 10

Enamel microstructure:
Describe Pattern II

Answer 10

• Incomplete prism boundaries
• No offsetting rows

Question 11

Enamel microstructure:
Describe Pattern III

Answer 11

• Most common pattern found in human enamel
• Incomplete prism boundaries
• Offsetting rows
• Offsetting + interlocking of heads & tails breaks up lines within enamel + dissipate forces applied to the tissues

Question 12

Enamel microstructure:
How can the offsetting of rows and arrangement of prisms be considered a structural adaptation

Answer 12

• Increase strength of enamel
• Increase resistance to fracture - the force is dissipated

Question 13

Enamel prismatic structure:
Where are the changes in direction of groups of prisms most prominent

Answer 13

Beneath cusps and incisal edges

Question 14

Enamel prismatic structure:
Explain what is meant by gnarled enamel

Answer 14

Groups of prisms spiral around others, giving the appearance of gnarled enamel

Question 15

Enamel prismatic structure:
What is the advantage of gnarled enamel

Answer 15

Helps to increase resistance to occlusal masticatory forces

Question 16

The Amelodentinal Junction (ADJ):
Describe the structure of the ADJ

Answer 16

• Where enamel and dentine meets
• Marks site of initial deposition of enamel and dentine
• Non-linear - has a scalloping pattern
• Less mineralised than enamel and dentine
• Scalloping pattern is more pronounced beneath cusps + incisal edges

Question 17

The Amelodentinal Junction (ADJ):
What are the microstructural adaptations of the ADJ

Answer 17

• Scalloped shape aids retention of enamel on dentine surface & resists shearing of one from the other
• Scalloping helps limit propagation of cracks from the surface towards dentine