Enamel
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By what cell is enamel formed?
Ameloblasts
What is the percentage components of mature enamel?
96% mineralized, 2% organic material and 2% water
What is the mineral components of enamel?
Calcium hydroxyapatite in the form of crystals
What is the basic structural unit of enamel?
Enamel rods
How are rods arranged?
There are rods and inter-rods, which have crystals which deviate 40-60 degrees from the direction of the crystals in the rods.
What is the name given to the periodic change in rod direction, giving rise to a banding pattern?
Bands of Hunter and Schreger
What are the 4 types of incremental lines that appear on enamel?
Striae of Retzius, cross striations, Perikymata and neonatal lines
What is the name for the formation of enamel?
Amelogenesis
What are the four stages of amelogenesis?
Pre-secretory, secretory, maturation and post-maturation
Describe what happens in the maturation phase of amelogenesis.
There is a regular and repetitive modulation of ameloblast morphology between a ruffled and smooth surface in contact with the enamel, as it changes function from production to transportation.
Name some features of the enamel that are genetically passed on.
Size, shape, color and susceptibility to caries
Describe what occurs in the pre-secretory phase of amelogenesis.
The internal enamel epithelium cells begin to differentiate into ameloblasts, starting from the future dentin-enamel junction. The cells become more columnar and the nucleus moves to the part of the cell furthest from the dentin. This happens during the late bell stage of tooth development. (18 weeks)
Describe what happens in the secretory phase of amelogenesis.
The ameloblasts are more columnar and produce matrix enamel (no rods present). The enamel is only partially mineralized. As the ameloblasts move further from the dentin-enamel junction, the secretory pole of the cell forms a cone-shaped Tome’s process. Crystallites are formed at both ends of this process, and this is where the change in direction of the crystallites is produced.
Describe the maturation phase of amelogenesis.
Cell nuclei have now moved to a lower position, closer to the Tome’s process. When the full enamel is formed, the ameloblasts lose their Tome’s process and many undergo apoptosis.
Describe what happens during the post-maturation phase of amelogenesis.
Ameloblasts regress in height and serve only to protect the surface of the enamel.
What are the Striae of Retzius?
Lines that occur as concentric rings in the enamel, which occur every 7-10 days of enamel production, and mark when the ameloblasts rest.
What is the neo-natal line?
This is the particular demarcation caused by the rest of the ameloblasts during birth, marking the change from pre-natal enamel to post-natal enamel.
What is Perimykata?
These are the grooves from the end of the Striae of Retzius which run concentrically around the superficial part of the enamel. Sometimes these are visible on the outer surface of the enamel, particularly the labial surface.