Amelogenesis and Enamel Flashcards
physical characteristics of enamel
1) hardest substance in body
2) composition
- 96% mineral (calcium hydroxyapatite)
- 1% organic and 3% water
Dentin composition
1) 70% mineral
2) 20% organic and 10% water
enamel crystal formation
1) calcium hydroxyapatite
- calcium ions, phosphate groups, hydroxyl groups
2) changes can happen in the structure of the apatite crystal
- Ca2+ for other mono and divalent cations
- PO43- for CO32-
- OH- for F-, Cl-, or CO32-
substitution of OH- for F-
increases acid resistance
OH- for CO32-
increases acid solubility
dental fluorosis
1) taking too much fluoride when the teeth are developing under the gingiva
- children 8 or younger are at risk
enamel matrix structure
1) specialized proteins
2) amelogenins 90%
- hydrophobic and regulate crystal growth and location
3) non amelogenins (10%)
- function in nucleation of enamel crystals and crystal growth
—
only about 30% hydroxyapatite right now
non amelogenins proteins
1) ameloblastins. enamelings, tuftlin, serum proteins, serine and metalloproteinases
amelogenesis imperfecta
1) if defects in GENES for enamelin, amelogenin, and proteases
2) enamel will not develop properly, will not assemble
3) affect 1-14000 people in US
organization of enamel crystals
1) long mineral crystals
2) calcium hydroxyapatite
3) organized in rod and interrod enamel
4) enamel rod sheath
- contains organic materials (white lines)
rodless enamel
1) no rod or interrod enamel is seen at the beginning of enamel secretion and at the end
acid etch
1) affects the direction of the rods and interrods
2) effective way to bond the sealants, restorative materials, and brackets
- micromechanical interlock
amelogenesis
1) process of enamel formation
2) ameloblasts secrete matrix proteins
- create and maintain and extracellular environment for mineral deposition
stages of amelogenesis
1) pre-secretory
2) secretory
3) maturation
—
all this occurs during the bell stage of odontogenesis
pre-secretory stage
1) morphogenic phase (shape)
- IEE cells elongate (tall columnar)
- stimulate dental papilla cells to become odontoblasts
- make dentin, which triggers the differentiation phase below
2) differentiation phase
- IEE cells become ameloblasts
layers of tip of enamel organ (bell stage)
1) stellate reticulum
2) stratum intermedium
3) ameloblast
- migrate towards the crown
4) dentin
5) odontoblasts
- migrate towards pulp
6) dental papilla
secretory stage
1) enamel matrix secretion
- 30% mineralized
2) matrix composition
- amelogenin (90%) and non-amelogenins proteins (10%)
3) tome’s process formation
- responsible for rods and interrod formation
- apical specialization
tomes process
1) distal portion
- rods
2) proximal portion
- interrod
maturation stage
1) after the full thickness of immature enamel has formed
2) transitional phase
- ameloblast reduce in height and volume (no tome’s process)
3) 25-50% of the cells undergo apoptosis
maturation proper
1) principal activity of ameloblasts is the bulk removal of water and organic material, and introduced more inorganic ions
2) release of proteinases (MMP-20 and KLK-4)
smooth ended ameloblast
1) resorption of water and degraded matrix proteins
2) triggered by low pH
ruffle ended ameloblasts
1) release MMP20 and KLK4
2) transport calcium and phosphate into maturing enamel
reduced enamel epithelium
1) when enamel maturation is complete, the ameloblast layer and the adjacent layers (stratum intermedium, stellate reticulum, and other enamel epithelium will fuse to form the reduced enamel epithelium
life cycle of ameloblasts in a human tooth
1) morphogenetic stage
2) histodifferentiation stage
3) initial secretory stage
- no Tome’s process
4) secretory stage
- Tome’s process
5) ruffle ended
6) smooth ended ameloblast
7) protective stage
enamel hypoplasia
1) underdevelopment of the ameloblasts
2) environmental factors
- deficiency of vitamin A, C, D
- febrile diseases (measles and scarlet fever)
- hypocalcemia
- local infection or trauma and drugs
lines of retzius and perikymata
1) due to repetitive change (every 7-9 days) in the formation of rod vs interrod substance
- due to changes in the shape of tome’s process
2) serious of dark lines extending from the DEJ toward tooth surface
- the tiny groove on the surface is the perikymata
cross striations
1) thought to represent the daily rhythm of enamel formation and mineralization
2) regular intervals of 4 microns
3) different direction than retzius
- sort of perpendicular
hunter Schreger banding
1) optical phenomenon
2) when light goes through dry section of tooth
3) differences in orientation of groups of enamel rod
gnarled enamel
1) variability in the direction of individual enamel rods at the cusp tips and incisal edges
enamel spindles
1) trapped odontoblasts in the enamel layer
2) migrated towards enamel accidentally
enamel tufts
1) projects from DEJ outward
2) appear branched and contain greater concentrations of enamel proteins
enamel lamellae
1) extend from the surface inward
2) filled with organic material
