Enamel and Cementum

Enamel

Acellular and Avascular
96% inorganic 4% water
Thin near junction and Root
hard and brittle
most highly mineralized tissue in body

Cells of the inner enamel epithelium differentiate into

ameloblasts

Tomes process

-Shovel shaped
-responsible for the orientation of the enamel rod

What shape are ameloblasts in a cross-section?

Hexagonal

Formation of enamel?

Amelogenesis

2 Stages of Amelogenesis?

1 Secretory
2 Resorbing

Secretory Stage

deposition of enamel matrix that contains both organic and inorganic material

Resorbing stage

Removal by ameloblasts of most of the water and the organic matter

Enamel rods

Interlocking rods that help resist masticatory forces to prevent fracture between rods

Rod Sheath

Formed by a change in the angulation of the crystals formed by the ameloblasts as they move
*Outline around the periphery of the rod, especially noticable in the head region of the rod

Rod Sheath resists______more than Rod core.

demineralization

Enamel rods extend from the DEJ to ?

outer enamel surface-appear wavy due to the path of ameloblasts as they migrate

Enamel rods are _____shape?

keyhole

One rod is formed by?

4 different ameloblasts

hunter-schreger bands

alternating light and dark bands in the enamel due to configuration of the enamel rods

Rodless enamel

found on all deciduous teeth and 70% of the permanent teeth
-found at the cervical area of enamel
-less frequently found over the cusp tips
-structureless layer of enamel about 30 microns thick

gnarled enamel

*formed by enamel rods that have bent in exaggerated ways

*found near the dej over areas of the cusp tips

Enamel is unable to

remodel or repair

amelogenesis occurs during which stage of tooth development?

Late Bell Stage

incremental lines

a result of rhythmic deposition of enamel

3 types of incremental lines?

1 cross striations
2 striae retzius
3 neonatal line

Perikymata

small ridges on the tooth surface

cross striations

daily apposition lines

striae of retzius

more prominent growth lines may reflect major interruptions in deposition of enamel

neonatal

a significant striae of retzius
distinguishes prenatal enamel from postnatal enamel

Enamel spindle

single extension of dentinal tubules into the enamel
*shorter than tufts*

Enamel tufts

hypomineralized inner ends of some enamel rods
*defect in enamel*Bigger than spindle

Enamel lamellae

cracks in the surface of the enamel visible to the eye
*extend from the DEJ to the surface of the enamel
*possible pathway for dental caries to spread
no greater chance for fracture/ is greater risk for caries

Tetracycline Stain

Appear as dark bands through the enamel especially near the cervix of the tooth
*Does not affect enamel
*Binds to dentin and bone
*cannot bleach/caused by dentin
*Darkend dentin that shows through translucent enamel, giving tooth a darker appearance

2 functions of cementum

1Seals the tubules of root dentin
2 serves as attachment for periodontal fibers to suspend tooth in the socket

Cementum is

*less mineralized than enamel and dentin
*continues to grow throughout life
*thinnest near the cervix
*thickest at the apex
*no nerves
*not sensitive

_______is SHiny; _______is not shiny

Enamel; cementum

Bone

Vascular
nerves
lacunae cells
canaliculi
incremental lines

Cementum

avascular
no nerves
lacunae cells
canaliculi
incremental lines
more resistant to resorption and demineralization than bone

Hertwigs epithelial root sheath is formed by______

joining of OEE and IEE

Hertwigs epithelial root sheath degenerates and the remnants are called?

epithelial rests of mallasez

Cells from the _____________differentiate into cementoblasts?

dental follicle