Enamel

Question 1

Maximum thickness of enamel

Answer 1

2-2.5mm I.e at the cusps of molars & premolars

Question 2

Specific gravity of enamel

Answer 2

2.8

Question 3

Temperature resistance of enamel

Answer 3

5-13 Hz

Question 4

Electrical resistance

Answer 4

10 power 15 - 10 power 5 ohms

Question 5

Amelogenins

Answer 5

Heterogenous group of low molecular weight.
They are rich in proline, histadine, glutamate & leucine
They account to 90% of organic materials in enamel

Question 6

Non-amelogenins

Answer 6

They are high molecular weight proteins.
They are rich in glycine, aspartic acid & serine.
They account to 10% of organic materials.
Enamelin, tuftelin & ameloblastin are the most important non-amelogenins .

Question 7

Inorganic content of enamel

Answer 7

Hydroxyapatite
Ca10(PO4)6(OH4)2
Major constituents - Calcium, phosphorus & oxygen
Minor constituents - sodium, magnesium & carbon

Question 8

Structure of enamel

Answer 8

It is made of enamel rods/prisms, enamel sheath & in some regions, cementing interprismatic substance

Question 10

Hunter-Schreger band

Answer 10

Alternating dark & light bands/strips of varying widths.

They originate at the DEJ & travel outwards & end at a distance from the outer enamel surface.

Question 11

Angle between Diazones & parazones

Answer 11

40 degrees

Question 12

Incremental lines of retzius

Answer 12

They are brownish bands that illustrate the successive apposition of layers of enamel during formation of enamel

Question 13

Mean daily rate of enamel deposition

Answer 13

3.5-4mm & it is denoted by cross straitions.

There are 7-10 cross straitions between 2 incremental lines therefore denoting about a weeks deposition.

Question 14

Neonatal line

Answer 14

It is an accentuated incremental line that demarcates the prenatal & postnatal enamel.
Neonatal line is present in all deciduous teeth & only the permanent molars as their enamel formation begins before birth
(Mostly just 1st molar)

Question 15

Cause of hunter-Schregar bands

Answer 15

They are a result of difference in permeability & organic content & not a result of any optical phenomenon

Question 16

Prismless enamel

Answer 16

A relatively structureless layer of enamel about 30 micron meter thick. Found mostly towards the cervical areas. Contains no prisms & apatite crystals are arranged parallel to each other.

Question 17

Perikymata

Answer 17

They are transverse wave like grooves believed to be external manifestations of the striae of retzius
They are continuous around a tooth, parallel to each other & to the CEJ

Question 18

Enamel caps

Answer 18

Small elevations on the surface of the enamel about 10-15 micron meter.
They are formed to die enamel deposition on non-mineralizable debris.

Question 19

Enamel brochs

Answer 19

They are larger enamel elevations.

Question 20

Enamel pits

Answer 20

They are about 1-1.5 micron meter in diameter.

The surface pits represent the ends of ameloblasts.

Question 21

Nasmyths membrane/ primary enamel cuticle

Answer 21

It covers the entire crown of the newly erupted tooth but removed by mastication.
It is a typical basal lamina found in most epithelia.
It is secreted by the ameloblasts after enamel formation is completed.
It’s function is to protect the enamel surface from the resorptive action of the surrounding vascular tissues.

Question 22

Secondary enamel cuticle

Answer 22

The cervical region of the enamel is covered by afibrillar cementum, continuous with the cementum.
It is of mesodermal origin.
This cuticle is secreted after the epithelial organ retracts form the cervical region during tooth development

Question 23

Pellicle

Answer 23

Erupted enamel is normally covered by a pellicle which is a precipitate of salivary proteins.
This pellicle reforms within hours after an election enamel surface is mechanically cleaned.
Within a day or two after the pellicle is formed it becomes colonized by microorganisms to form a bacterial plaque.

Question 24

Enamel spindles

Answer 24

Occasionally,the odontoblast processes pass across the DEJ & enter the enamel & thickened at their end & therefore known as enamel spindles.

Question 25

Age changes of enamel

Answer 25

Loss of mamelons
Loss of perikymata,enamel brochs, pits,rod ends etc
Decrease in permeability
Color darkens
Localized increase in fluoride & nitrogen
Increase in hardness & modulus of elasticity by 12%
More brittle

Question 26

Reversal of polarity

Answer 26

The migration of centrioles & Gogol bodies from the proximal states ends of the cell to the distal ends takes place in the organizing stage of life cycle of ameloblasts

Question 27

Reversal of nutritional source

Answer 27

After the appearance of dentin the nutritional supply to the ameloblasts from the dental papilla is cut off & the nutrition is now derived from the surrounding capillaries.
This is facilitated by the disappearance of the stellar reticulum & the proliferation of the capillaries

Question 28

Tomes process

Answer 28

The projections of the ameloblasts into the enamel matrix

Question 29

Modulation

Answer 29

Ameloblasts alternate cyclically in developing smooth & ruffled borders in the apical cytoplasm during the maturative stage, this is called modulation