Histology of Teeth

Question 1

What is the structure of enamel?

Answer 1

Tightly packed hydroxyapatite crystals
Basic unit = enamel prism
Prisms visible in ground sections of SEMs of acid etched enamel

Question 2

What are enamel prisms?

Answer 2

Complex key hole shape

Form different orientations of hydroxyapatite crytals

Question 3

What forms the prism core?

Answer 3

Tightly packed hydroxyapatite crystals

Question 4

What forms the prism sheath?

Answer 4

Boundary of clearly different crystal orientations
Crystals less tightly packed
= more space for organic components

Question 5

What is gnarled enamel?

Answer 5

At the cusps of teeth where the prisms appear twisted around eachother
Gives strength

Question 6

What are the striae of retzius?

Answer 6

Incremental growth lines
Represent weekly growth
Accentuated lines result from:
- systemic disturbance e.g. illness
- birth "neonatal line"

Question 7

What is the perikymata?

Answer 7

Shallow furrow where the striae reach the surface?

Question 8

Properties of dentine

Answer 8

Highly tubular
Tubules continuous with pulp
Tubules contain cell processes, nerves and fluid

Question 9

Where are there more and less tubules?

Answer 9

Amelodentinal junction - less around 15000-20000 per mm squared
Predentine - more around 45000-65000 per mm squared

Question 10

What nerves are present in dentine?

Answer 10

Pulp horn - 27-85%
Cervical margin - 7%
Root - <7%

Question 11

Summary of dentine innervation

Answer 11

Innervated but only in inner aspect
Most nerves in pre-dentine/inner dentine in pulp horns
Relatively few at cervical margin - clinically a sensitive area

Question 12

Dentine classification

Answer 12

Primary dentine - formed during tooth development
Secondary dentine - formed after root completion, forms slowly throughout life of tooth
Tertiary dentine - response to pulpal insult

Question 13

Properties of tertiary dentine

Answer 13

Reactioary
- uses existing odontoblasts
- slow formation
Reparative
- existing odontoblasts destroyed
- recruit newly differentiated odontoblasts
- rapid formation
- poor structure

Question 14

Function of tertiary dentine

Answer 14

remove pulp from stimulus

Question 15

Similarities between pulp and connective tissue

Answer 15

Mainly fibroblast cells
Collagen matrix
Ground substance
Blood vessel and nerves
75% water
25% organic

Question 16

DIfferences between pulp and connective tissue

Answer 16

Speciailised cells - odonotoblasts
Contained in a rigid chamber
No fat cells
No oxytalin fibres
No mast cells
Blood vessels - wide lumen, narrow wall, no valves
Densely innervated

Question 17

Pulpal innervation

Answer 17

70-80% non-myelinated
Plexus of Raschkow - clasically in cell free zone
Marginal plexus - around odontoblasts