OB D8 - Enamel histology

Question 1

why can you not study enamel by a decalcified section?

Answer 1

• mineral removed
• 7-10 microns thick
• no enamel

Question 2

How do you study enamel histologically?

Answer 2

Ground section:

• cut with a diamond saw
• 150microns
• mineral present

Question 3

when does enamel appear darker?

Answer 3

• contain less mineral
• light doesnt pass through as well
• demineralised due to caries

Question 4

what is the enamel structure?

Answer 4

tightly packed hydroxyapatite crystals

Question 5

what is the basic unit of enamel?

Answer 5

enamel prism (or rod)

Question 6

what are prisms visible in?

Answer 6

• ground sections

- SEM’s of acid etched enamel (Scanning electron micrograph)

Question 7

what are the two parts of enamel in cross section?

Answer 7

• prism core

- prism sheath

Question 8

what does every dash cross sectionally represent?

Answer 8

hydroxyapatite crystal

Question 9

what is the shape of enamel prisms?

Answer 9

complex “key hole” shape

Question 10

what gives the prisms their key hole shape?

Answer 10

from different orientations of the hydroxyapatite crystals

Question 11

what is the structure of prism core?

Answer 11

tightly packed hydroxyapatite crystals

Question 12

what is the structure of prism sheath?

Answer 12

– boundary of clearly different crystal orientations – crystals less tightly packed
– more space for organic components

Question 13

what is the significance of the prism sheath structure?

Answer 13

more vulnerable to acid attacks

Question 14

what is the enamel prisms shape governed by?

Answer 14

– The presence of the Tomes process
– The shape of the Tomes process
– The direction of movement of the ameloblast

Question 15

what are regions formed without a tomes process?

Answer 15

aprismatic

Question 16

what areas are aprismatic?

Answer 16

– 1st formed (i.e. innermost) 5μm

– last formed (i.e. outmost) 30μm

Question 17

what is the significance of acid etch/conditioning?

Answer 17

• remove top prism sheath or core
• get grooves - put resin/fissure sealant on tooth
• capillary action- sucked into grooves- gives micro mechincal attachement /retentition
• resin flows in crevices between prisms and locks it on

Question 18

what size are enamel prisms?

Answer 18

3-6microns in diameter

Question 19

what path of enamel prisms follow?

Answer 19

ameloblasts so 90 degrees to ADJ

Question 20

what course to the enamel prisms take?

Answer 20

although they look straight in longitudinal section - they take an undulating course

Question 21

what type of enamel is at the cusps of the tooth and why?

Answer 21

• Gnarled enamel
• the prisms appear twisted around each other
• give strength due to most forces at the cusps

Question 22

what is striae of retzius?

Answer 22

incremental growth lines

Question 23

what is the appliance of striae of retzius?

Answer 23

brown lines

Question 24

what does striae of retzius represent?

Answer 24

weekly growth

Question 25

what results from systemic disturbances ( e.g. illness) / birth (neonatal line) ?

Answer 25

accentuated lines

Question 26

which teeth have neonatal line?

Answer 26

• all primary teeth

- permanent 6’s

Question 27

what is perikymata?

Answer 27

shallow furrow where the striae reach the surface?

Question 28

what is imbrication lines of peckerill?

Answer 28

ridges between perikymata

Question 29

why is perikymata important?

Answer 29

aesthetically - difference in crown

Question 30

what are hunter-schreger bands?

Answer 30

An optical effect reflecting the sinusoidal path of enamel prisms in alternating sheets

Question 31

what are enamel spindles?

Answer 31

dentinal tubules in enamel

Question 32

what are enamel tufts?

Answer 32

hypomineralised

Question 33

what are enamel lamellae?

Answer 33

• developmental
• acquired
• preparation artefact

Question 34

what are the 3 type of amelogenesis imperfecta (enamel anomalies)?

Answer 34

• type I -hypoplastic
• type II - hypomaturation
• type III- hypocalcified

Question 35

Describe type I - hypoplastic.

Answer 35

Features - less matrix formed
Clinical :Small crown or pitted/grooved enamel Small–normal crown
Colour: Normal or white or yellow/brown

Question 36

Describe type II - hypomaturation.

Answer 36

Features- reduced crystal growth
Clinical :
Opaque cream to yellow brown
Surface soft and rough – easily chips/abrades

Question 37

Describe type III - hypocalcified.

Answer 37

Features - reduced crystal formation
Clinical :
Opaque white – yellow brown
Surface soft and rough - easily chips/abrades

Question 38

what results from molar incisor hypomineralisation (enamel anomalies)?

Answer 38

•  Discrete opaque white soft enamel
•  Altered localised ameloblast function 
• ?Due to systemic childhood illness

Question 39

what results from fluororosis (enamel anomalies)?

Answer 39

- Ameloblasts susceptible to environment
- Reduced enamel matrix protein degradation
 -Incomplete crystal growth

Question 40

what can cause trauma to primary incisors (enamel anomalies)?

Answer 40

•  Intrusion of primary incisors
•  Damage to successional tooth germ
•  Damage to reduced enamel epithelium