Histology- Enamel

Question 1

How does the clinical crown differ from the anatomical crown?

Answer 1

Clinical crown is what is what enamel is seen when looking in mouth. Anatomical crown is enamel from tooth edge all the way to the root junction

Question 2

What are the properties of enamel?

Answer 2

Hardwearing/brittle structure that is resistant to wear
Teeth are not made entirely from enamel as it would shatter very easily (relies on underlying dentine for support)
Dentine gives tooth yellow appearance (enamel fades with age/wear and tooth becomes more yellow)

Question 3

What diseases affect enamel?

Answer 3

Dental caries is the main disease affecting teeth (starts as white spot that increase in porosity so takes up brown stain) gives a wedge shaped appearance under x-ray

Question 4

What are the 5 types amelogenesis imperfecta?

Answer 4

Rough hypoplastic
Local hypoplastic
Pitted hypoplastic
Hypocalcified
Hypomature

Question 5

Describe the structure of enamel

Answer 5

Hydroxyapatite crystal (Ca10(PO4)6OH2)
arranged into prisms
Width – 60-90nm
Depth – 25-30nm
Length – may be up to several mm

Question 6

Prism

Answer 6

Prisms are around 5 microns in diameter and span from dentine to tooth surface.
They run parallel at ADJ (more ordered)
Circadian rhythm is observed in enamel production
Superimposed on the lines are brown striae of Retzius (these are visible)
Cusp are irregular but at cervical margin they’re regular
When zoomed in the daily cross striations can be seen

Question 7

Describe prism orientation in human enamel

Answer 7

Alternating rows of transverse and longitudinal prism arrangement
In transverse areas ‘key hole’ appearance of prism and head + tail can be distinguished
Not as easy to observe the interprismatic enamel as seen in the rat incisor

Question 8

Describe type 1 prism

Answer 8

Hexagonal structure Rows are offset Reduced potential sheer occurring between prisms
Found in inner third

Question 9

Describe type 3 prism

Answer 9

Modified version of type 1
Classical key hole shape
Head is continuous with interprismatic enamel below
In tail crystals are angles at 60degree angle towards the tail interlocking heeds + tails break lines old shear

Question 10

Describe tufts

Answer 10

Tufts are seen at the ADJ (Junction between enamel and dentine)
Tufts protrude for about 1/3 to 2/3 of the enamel
Lamellas (may be cracks) may span though the enamel
Tuft proteins area between enamel where protein has been deposited

Question 11

Explain prism direction

Answer 11

At ADJ, the prisms may cross over each other/superimpose and tuft appearance is observed.
Change in prism direction is evolutionary mechanism resists shearing from occurring at ADJ

Question 12

Explain hunter schroeder bands

Answer 12

Optical effects caused by change in prism direction
Prism direction changing is only evident in inner 2/3 not in outer 1/3 (all parallel here)
Aprismatic enamel newly erupted teeth all of the prisms are parallel

Question 13

Describe enamel spindles

Answer 13

Found at ADJ, can project up to 50m into enamel, formed by elongating odontoblasts during tooth development, may weaken junction between enamel and dentine if in high numbers

Question 14

Describe the Brown striate of Reties

Answer 14

Superimposed onto daily incremental growth lines so run indirectly across the prisms and reach the crown surface to form a depression called Perkymata
Irregular at cusp + regular at cervical margin (Striae are continuous at the cusps)

Question 15

Describe gnarled enamel

Answer 15

Occur where maximum force is applied to the tooth (breaks up lines of shear)