Amelogenesis is the
- Amelogenesis is formation of enamel on tooth Â and
- occurs during the crown stage of tooth development
- Amelogenesis occurs after dentinogenesis,
- Since dentin must be present for enamel to be formed,
- laying down of dentine induces ameloblasts to secrecte enamel
- this is termed reciprocal induction.
Amelogenesis occurs in 3 stages.
- The first stage is known as the Pre-secretaryÂ phase,
- the second stage is known as the secretary phase and
- third stage is called the Â maturation stage.
There is morphogenesis and alignment of secretary cells.
In secretary phase,
- there are histological changes in cells which prepare cells to secret enamel .
- The ameloblasts retreat from the newly formed dentine Â and
- laying down of mineralized Â enamel with no pre enamel
- The ameloblasts retreat as soon as the enamel is laid down without leaving any process behind
- enamelÂ is laid down in the form of Proteins and an organic matrix to form a partially mineralized enamel in the secretary stage.
In the maturation phase,
- The full thickness of enamel has been laid down
- The excess proteins and water is removedÂ fronm the enamel matrix
- Mineral ions are added Â Â in the enamel matrix
- Growing crystals remove water resulting completes enamel calcification and mineralization.
- ameloblasts are polarized columnar cells.
- In the rough endoplasmic reticulum of these cells,
- enamel proteins are released into the surrounding area and
- contribute to what is known as the enamel matrix,
- which is then partially mineralized by the enzyme alkaline phosphatase.
When this first layer is formed,
- the ameloblasts move away from the dentin,
- Allowing for the development of Tomesâ€™ processes at the apical pole of the cell.
Enamel formation continues,
- around the adjoining ameloblasts,
- resulting in a walled area, or pit,
- that houses a Tomesâ€™ process, and
- also around the end of each Tomesâ€™ process,
- resulting in a deposition of enamel matrix inside of each pit.
The matrix within the pit will eventually become,
- an enamel rod, and
- the walls will eventually become interrod enamel.
The only distinguishing factor between the two is,
the orientation of the calcium crystals.
In the maturation stage,
- the ameloblasts transport substances used in the formation of enamel.
- Microscopically, the most notable aspect of this phase is that these cells become striated, or have a ruffled border.
These signs demonstrate that the ameloblasts have changed their function from,
Production, as in the secretary stage, to transportation.
The noteworthy proteins involved are ,
- enamelins, and
During this process,
- amelogenins and
- ameloblastins are removed after use,
- leaving enamelins and tuftelin in the enamel.
- By the end of this stage, the enamel has completed its mineralization.
Neo natal lines in enamel:
1.Â Â Formed as a result of trauma of birth
2.Â Â Are excentuated incremental lines
3.Â Â Formed as the anamel rods the prism direction and thickness is changed
Prisms do not follow a straight path from dentino enamel junction to the surface.
1.Â Â Enamel prisms are perpendicular to dentine enamel junction to the surface
2.Â Â Their direction reflect the direction of movement of ameloblast during enamel formation
Their changing direction and arrangement makes,
Hunter â€“Scherger bands
Changing direction of enamel prism between different layers makes enamel:
1.Â Â Increases strength of enamel
2.Â Â Less prone to fracture
3.Â Â More resistant to wear
Dentino enamel junction:
1.Â Â Is not a straight line but is interlocking of 2 tissues
2.Â Â This prevents shearing apart of the 2 tissues during mastication
3.Â Â The dentino enamel junction appearnce is Scalloped
4.Â Â Where the concavities of scalloped project in to the dentine
This scalloped appearance is prominent:
1.Â Â Beneath the cusps
2.Â Â Enamel and dentine crystals difference
3.Â Â Hydroxyappatite crystals in dentine are smaller then enamel
Histological structures apper at the dentino enamel junction:
- Enamel spindles
- Enamel tufts
- Enamel lamella
- Are found in the inner 1/3 of enamel
- Attached to enamel dentine junction
- Are hypo mineralised
- Recur at intervals
- Have more organic matrix
- Are hypomineralised sheets
- Run full length of enamel
- Are less common then tufts
- Are irregularly arranged
- Are the projection of dentinal tubulesÂ which cross dentino enamel junction and pass in to denamel
- And appear as enamel spindles
- They project 10 â€“ 40 micron meter in to enamel
- They are common beneath cusps and sdges
- The spindles sre continuous with the dentinal tubules
Normally the dentinal tubules terminate at the:
- Dentine enamel junction
- But some of the dentinal tubules enter the enamel and appear poreÂ like structures microscopicallyÂ Â appear as enamel spindles
Contain odontoblast process
- Is physically and chemically different from the sub- surface enamel
- Surface enamel is harder
- Less porous
- Less soluble
- More radio- opaque then sub surface enamel
Surface enamel has a wavy surface:
- Called perikymata
- On newly erypted tooth
- With elevations called imbrications and
- Furrows prikymata