Enamel Flashcards
(28 cards)
Maximum thickness of enamel
2-2.5mm I.e at the cusps of molars & premolars
Specific gravity of enamel
2.8
Temperature resistance of enamel
5-13 Hz
Electrical resistance
10 power 15 - 10 power 5 ohms
Amelogenins
Heterogenous group of low molecular weight.
They are rich in proline, histadine, glutamate & leucine
They account to 90% of organic materials in enamel
Non-amelogenins
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 .
Inorganic content of enamel
Hydroxyapatite
Ca10(PO4)6(OH4)2
Major constituents - Calcium, phosphorus & oxygen
Minor constituents - sodium, magnesium & carbon
Structure of enamel
It is made of enamel rods/prisms, enamel sheath & in some regions, cementing interprismatic substance
Hunter-Schreger band
Alternating dark & light bands/strips of varying widths.
They originate at the DEJ & travel outwards & end at a distance from the outer enamel surface.
Angle between Diazones & parazones
40 degrees
Incremental lines of retzius
They are brownish bands that illustrate the successive apposition of layers of enamel during formation of enamel
Mean daily rate of enamel deposition
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.
Neonatal line
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)
Cause of hunter-Schregar bands
They are a result of difference in permeability & organic content & not a result of any optical phenomenon
Prismless enamel
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.
Perikymata
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
Enamel caps
Small elevations on the surface of the enamel about 10-15 micron meter.
They are formed to die enamel deposition on non-mineralizable debris.
Enamel brochs
They are larger enamel elevations.
Enamel pits
They are about 1-1.5 micron meter in diameter.
The surface pits represent the ends of ameloblasts.
Nasmyths membrane/ primary enamel cuticle
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.
Secondary enamel cuticle
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
Pellicle
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.
Enamel spindles
Occasionally,the odontoblast processes pass across the DEJ & enter the enamel & thickened at their end & therefore known as enamel spindles.
Age changes of enamel
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
