(2) Anatomy and Histology of the Periodontium - Enamel (A) Flashcards
Where is enamel thick and thin on a tooth?
Thickness varies from up to 2.5mm (1.3mm in primary) over cusps to feather edge at cervical margins.
occlusal surfaces on cusp tips
What structures of a tooth can regrow?
dentin and cementum
What provides the support to enamel?
dentin - resilient
Does enamel have a high or low tensile strength?
low - brittle
Where is the hardest enamel found?
Surface enamel is harder, denser and less porous than subsurface enamel.
What layer of enamel is most mineralised?
the surface
What is the gradient of hardness and density in the
Hardness and density decrease from the cusp tips to the cervical margins.
What colour is young enamel vs old enamel?
Young enamel appears white turning to a more yellow appearance as translucency increases with age.
What is the percentage breakdown of enamel?
Enamel is composed of 96% inorganic components, 2% organic component and 2% water by weight.
What is the principal mineral component of enamel?
calcium hydroxypapatite
What are examples of organic substances in enamel?
50-90%
Free amino acids, small molecules, peptides and large protein complexes (amelogenins and non-amelogenins)
What shape do hydroxyapatite crystals form?
hexagonal
What do you call a crystal of hydroxyapatite?
crystallite
What are the dimensions of an enamel hydroxyapatite crystal?
Enamel hydroxyapatite crystals are about 70nm in width, 25nm thick and of great length (almost the full thickness of enamel).
What makes up each hydroxyapatite crystal unit?
One hydroxyl group surrounded by 3 calcium ions which are surrounded by 3 phosphate ions. Six calcium ions in a hexagon enclose the phosphate ions.
What units make a hydroxyapatite crystal?
The crystal is made of a repetition of those planes of ions side by side in stacked layers.
Can there be substitutions in the hydroxyapatite crystal?
YES
What effect does the substitutions in hydroxyapatite crystals have on teeth?
The ions present in enamel may influence dental caries by affecting the dissolution of the apatite crystals and/or affecting remineralisation.
How does a fluoride substitution effect crystallites?
Fluoride’s incorporation in the crystal inhibits caries.
How does a carbonate substitution effect crystallites?
Carbonate’s incorporation in the crystal promotes the carious attack.
What is the presence of water in enamel relate to?
Water presence is related to the porosity of the tissue.
Where might water be located in enamel?
Might be present between the crystals surrounding the organic component.
Might be trapped within crystalline defects forming a hydration layer.
What can travel through the water component?
fluoride ions
What percent of the mature enamel is organic matrix?
Mature enamel 1-2%; varies from 0.05% to 3% depending on the regularity of the crystals.
What are the larger protein complexes found in the organic matrix?
amelogenins and non-amelogenins (enamelins).
What protein of the organic matrix is at the highest concentration?
Tufts
Where are tufts located?
the dentine-enamel junction
In the organic matrix, what do components with larger molecular weights contain?
rich in carbohydrates
What may lipids in enamel represent?
May represent remnants of cell membranes.
Do proteins and lipids account for more of the total enamel weight in mature or early enamel?
Proteins and peptides account for less than 2% of mature enamel weight and 25-30% of early enamel.
What is protein is the bulk of developing enamel matrix?
amelogenin
What produces amelogenin?
ameloblasts
Are amelogenins hydrophobic or hydrophilic?
hydrophobic
tend to aggregate into clumps.
Do amelogenins spread throughout the entire enamel?
They spread throughout the whole developing enamel resulting in a gel matrix through which molecules and ions spread readily.
What does the gel matrix allow?
gel matrix through which molecules and ions spread readily.
What aids in the formation of large crystals?
Amelogenins are Hydrophobic and tend to aggregate into clumps.
They spread throughout the whole developing enamel resulting in a gel matrix through which molecules and ions spread readily.
This helps in the formation of large crystals.
What is an example of a non-amelogenin?
tuftelin
What do the non-amelogenins derive form?
May be derived from plasma albumin or aminoblasts themselves
Contain distinct components secreted by ameloblasts.
Do the non-amelogenins have a role in mineralisation of enamel?
possibly
