enamel

Question 1

what is the clinical crown?

Answer 1

the part of the tooth visible in the oral cavity

Question 2

what is the anatomical crown?

Answer 2

the part of the tooth that is covered by Enamel (upto the cementoenamel junction) In a healthy dentition, the anatomical crown is much larger than the clinical crown

Question 3

describe the physical properties of enamel

Answer 3

it is the white, hard wearing substance that covers the outside of the tooth. it is very hard and brittle however relies on dentine for resilience.

Question 4

can enamel be replaced?

Answer 4

nope, enamel does not have a cell population to replace lost tissue

Question 5

describe the chemical composition of enamel

Answer 5

almost purely made from the mineral (hydroxyapetite) which is also found in bone and dentine, however the crystals in enamel are much larger. Enamel is about 4% water and organic material (which is a non collagenous protein

Question 6

why do opaque white lesions appear in the early stages of a dental caries?

Answer 6

because the sub surface enamel has become porous as a result of the mineral being dissolved by the acid produced by plaque bacteria

Question 7

describe the structure of hydroxyapetite crystals

Answer 7

(Ca10(PO4)6OH2 - crystals are hexagonal in cross section, Width: 60-90 nm, Depth: 25-30 nm, and the Length: Difficult to determine, can be up to several mm long (as they may stretch from dentine to tooth surface)

Question 8

describe the rhythm of prisms in hydroxyapetite

Answer 8

Prisms have:
• A circadian rhythm (biological process that displays changes every 24 hours) is observed in enamel production, in which daily cross striations, of a 5-micron periodicity are produced

Question 9

describe the importance of interprismatic enamel

Answer 9

prevents shearing from occurring between prism rows

Question 10

Enamel structure at ADJ =

Answer 10

a. Tufts
b. Spindles
c. Lamellae

Question 11

Enamel structure not Primarily at ADJ =

Answer 11

a. Hunter-Schreger bands
b. Gnarled enamel
c. Perikymata
d. Aprismatic enamel

Question 12

Enamel at the ADJ, describe the tufts and lamellae

Answer 12

• Tufts are structures found at the amelo dentinal junction, they protrude for about 1/3 to 2/3 of thickness of the enamel
• Tufts appear to look like tufts of grass
• Lamellae run through the full thickness of the enamel, we don’t know whether they are real structures, or cracks that occur during life
• Tufts/ lamellae cannot be seen in longitudinal sections
• Scalloped nature of ADJ helps retention of enamel to the dentine surface, and resists shearing of one from the other

Question 13

what can be observed when the enamel of the crown is completely removed with acid ?

Answer 13

ribbons of protein can often be seen running down the dentine surface. These ribbons are known as tuft protein and represent areas between prisms, where enduring protein has collected

Question 14

what are hunter schreger bands?

Answer 14

are optical effects caused by a change in prism direction through the enamel (this can be seen in longitudinal sections of the enamel by reflected light and can only be seen in the inner 2/3rd of the enamel)
They appear as alternating light and dark bands

Question 15

Why are hunter schreger bands not visible in the outer third of enamel?

Answer 15

In the outer third all prisms become parallel and the Hunter-Schreger bands are no longer apparent.

Question 16

what is aprismatic enamel?

Answer 16

a region directly under the surface of newly erupted teeth where prisms are no longer evident – this is because the crystals are all arranged parallel to each other (in older teeth this may be worn away)

Question 17

what are diazones and parazones?

Answer 17

• Within longitudinal section:
o Areas sectioned transversely= Diazones
o Areas sectioned longitudinally= Parazones

Question 18

what are enamel spindles?

Answer 18

are a feature seen at the ADJ (particularly around the cusps of the teeth)
• These are dark, cigar shaped structures, penetrating up to 50μm into the enamel
• They can be seen in both transverve and longitudinal section

Question 19

When are enamel spindles formed?

Answer 19

Enamel spindles are formed during tooth development, when the odontoblasts (which make dentine) elongate into the enamel and disrupt it

Question 20

Describe the clinical significance of spindles

Answer 20

Spindles don’t have clinical significance, although in high numbers can weaken the junction between the enamel and the dentine.

Question 21

How are perkymata formed?

Answer 21

The brown Striae of Retzius run indirectly across the prisms of the enamel and on the lateral (side) of the crown reach the surface and produce a small depression running around the tooth (the perkymata)

Question 22

How are the perkymata spaced on a longitudinal section?

Answer 22

Towards the cusp the striae are irregularly spaced but become much more regular and frequent towards the cervical margin.

Question 23

What are the striae?

Answer 23

They are fossilised maps of the surface of the enamel during development

Question 24

Around the cusps, what do they striae look like?

Answer 24

like tree rings

Question 25

Where is gnarled enamel found and what does this look like?

Answer 25

Occurs under the cusps, where the prisms appear very disordered.
This disorder may have been due to an artefact in sectioning \ it is clear that the prism arrangement is abnormal
This feature appears to have evolved to break up lines of shear, directly where the maximum force will be applied

Question 26

what does the colour of enamel rely on

Answer 26

its colour is dictated by its translucency and the colour of the underlying dentine

Question 27

How are hydroxyapetite crystals arranged

Answer 27

• Crystals are arranged into prisms (may be called rods)

* Each prism spans from the dentine to just below the tooth surface and are approx. 5 microns in diameter

Question 28

How are prisms arranged

Answer 28

• In cross section, prisms are arranged perpendicular to amelo-dentinal junction (junction between enamel and dentine)

Question 29

What are brown striae of retzius

Answer 29

• Superimposed on daily cross striations are irregular cross striations (brown striae of Retzius) [towards the cusp these are irregular spaced but at the cervical margin, they are more regular]