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Components of Enamel

1. Mineral Content (Hydroxyapatite) - 96% 2. Enamel Matrix 1% 3. Water 3%

Enamel structures

1. Prisms (Rods) 2. Sheath

Enamel Prisms (Rods)

Mineralized crystalline structure of enamel. Extends width of enamel from DEJ to outer surface. Perpendicular to DEJ. "Keyhole shape", largest mass

Enamel Sheath

Water and Matrix present. Formed by ameloblasts. Interprismatic or Interrod region covers rod/prism.

How many ameloblasts does it take to make a complete rod and sheath?

It takes 4 ameloblasts

How many cells does it take to make the head?

1 cell

How many cells does it take to make the tail?

3 cells

Ameloblasts must have

Tome's process present to lay down enamel and form prism

Amelogenins

Proteins found in developing enamel. Form bulk of matrix

Enamelins

Proteins found in mature enamel

Enamel development stages

1. Formative 2. Calcification 2. Maturation

Formative stage

There are two groups of matrix proteins (Amelogenins and Enamelins). Ameloblasts lay matrix but then break it down to allow room for hydroxyapatite

Calcification stage

Crystals are deposited

Maturation stage

Crystals enlarge (more amelogenins are removed to allow for growth of crystals)

Enamel Protective Stage

Enamel complete so enamel organ is now reduced enamel epithelium. Reduced enamel epithelium covers and protects new enamel prior to eruption. Ameloblasts secrete basal lamina to cover enamel (important in establishment of DGJ).

Newest enamel is located

Close to CEJ

Junctional epithelium is located

Directly above Connective Tissue

Sealants are placed on

Permanent teeth that have been in the oral cavity for about 1 year

Hunter-Schreger Bands

Taking enamel and cutting it cross-sectional and longitudinal and laying those 2 cuts next to each other. Band appearance

Gnarled Enamel

Enamel prisms that are twisted around each other at cusps or incisal edges.

Enamel Lamellae

Runs from DEJ to very outside. Fracture line. Only seen microscopically. Sensitivity because tubules are open to outer environment.

How many different ways may Lamellae form?

3 different ways

Enamel Tufts

Found from DEJ to inner 1/3 of enamel. May be calcified or not. Resembles bundles of grass. Bigger than spindles.

Enamel Spindles

Develop when odontoblastic processes are not withdrawn quickly. Tiny. Non-calcified enamel. Located next to DEJ.

Scalloped DEJ

Length of rods and tubules are irregular. Scalloped ridge increases adherence and strength. Prismless area.

Outer surface of enamel

Is prismless on a newly erupted tooth

Fluoride uptake requires

Hydroxyapatite

Enamel mineral content

96%

Dentin mineral content

70%

Bone and Cementum mineral content

40 - 45%

Which is a larger crystal, fluorapatite or hydroxyapatite?

Fluorapatite

Pre-Eruptive Calcification Stage

Fluoride is deposited during formation of Enamel crystals and incorporated as fluorapatite. Benefit from systemic fluoride.

Pre-Eruptive Maturation Stage

Fluoride Deposition continues after calcification. Benefit from systemic fluoride.

Post-Eruptive Stage

After eruption and throughout life of teeth. Topical uptake and rapid uptake during 1st years after eruption.

Types of developmental lines

1. Cross Striations 2. Incremental Lines 3. Lines of Retzius (Neonatal)

Cross Striations

Normal, growth lines

Incremental Lines

Same thing as imbrication lines or Perikymata

Lines of Retzius/Neonatal

Occurs if stress or trauma is experienced during birth

Incipient Carious Lesion

Has not completely broken through the enamel

Full blown Carious Lesion

Lost enamel structure and must restore tooth

Fluoride may be given

1. Systemically 2. Topically

Fluoride will not help the tooth

In Stage 1 of development, only during Stages 2 and 3

Fluoride uptake is more rapid on enamel

During the 1st years after eruption

Fluoride takes away

Hydroxy ion which was becoming demineralized and replaces it with the fluoride ion and you now have fluorapatite.

In the head, hydroxyapatite crystals run

Parallel to the Long Axis of the Rod

In the tail, hydroxyapatite crystals run

Perpendicular to the Long Axis

Zones of Enamel

1. Surface 2. Body 3. Dark 4. Translucent 5. Sound enamel

In the Surface, Body, Dark and Translucent zones

Hydroxyapatite is taken away, the crystals are larger and enamel is demineralized.

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