Enamel

1-enamel is ectodermal in origins2-it is derived from inner enamel

epithelium of enamel organ.3-mature enamel is completely non cellular

Ameloblasts are derived from outer enamel epithelium)Mature enamel is completely acellular (True or false )

1-Thickness2-Color3- Hardness4- Tensile strength5-Permeability6-Solubility

Physical characters

thicknessIt is thick at the incisal edge and cusp tip of molars and premolars (2-2.5 mm) and ends cervically as knife edge

The thickest part of the enamel is present in---------, and………….

colorThick enamel---------------------- bluish whiteDecrease in thickness-----------------------yellow due

to the underlying dentin

Healthy thick enamel is -------- in color, while thin enamel is …………in color

hardnessEnamel is the hardest calcified tissue in the bodyBecause of its high content of minerals.Enamel can withstand load of mastication and resist wear process.

------- is the hardest calcified tissue in the body.Enamel is the hardest calcified tissue in the body (give a reason)

Tensile strengthAlthough it is hard , enamel is extremely brittle and depends on the strength of the underlying dentin.

Tensile strength of enamel is greater than that of dentin ( true or false)

permeabilityEnamel is selectively permeable, permitting partial or complete passage of ions due to the presence of microscopic pores.

Enamel is completely impermeable to ions(False or true)

solubility

Enamel dissolves in acid media. Its surface is less soluble than deep enamel.

Chemical composition

Mature enamel consists of:Mainly(96%)

inorganic substanceSmall (3%)

amount of organic substance

1%)&water

Inorganic componentMainly calcium phosphate crystals

(hydroxyapatite crystals)

organic componentMainly non collagenous proteins:

A- amelogeninsB- non-amelogenins

Microscopic structure

1-Rods (prism).2- Rod sheath.3-Inter rodal cement substance

Ground section Decalcified section

the organic substance is burnt and the inorganic substance remain

the inorganic substance is dissolved

and the organic substance remain

Enamel rods1- Course.2- Number.3- Transverse striation. 4- Direction. 5- Gnarled enamel.

the enamel rod starts straight : Courseat dentino-enamel junction (D.E.J.) for about 30 µ then has a wavy course till near the outer surface of enamel where it become straight once more.

The number of the enamel rods varies from 5 millions in lower lateral incisor to 12 millions in the upper first perm.The number of the rods equals the number of the ameloblasts.anent molar.At the tooth surface there are about 20000-30000 enamel rods in 1 mm2

The density of the rods is at the DEJ about 10% higher than at the enamel surface.

The total number of enamel rods varies from------- to ---------

transmission electron microscope

Scanning electron microscope

Transverse striation of rods

Deciduous toothpermanent tooth

Direction of rods

Gnarled enamel

D

Twisted course of enamel rods

Gnarled enamel

Give short account on gnarled enamel

Gnarled enamel is twisted and intertwined rode structure associated with increase strength of the enamel ,Present mainly in the incisal edges and tip of the cusps. (enamel rods develop in planes of tension).

Gnarled enamel

Rod sheath

distinct thin layer peripheral to the rods L.M.Different refractive index, darker and more acid resistant, and less calcified and more organic.

-not distinct layer, but organically rich interE.M.rod space devoid of crystals.

Inter rod substance

distinct cement substance with higher L.M.refractive index.

tail of the adjacent rod with different E.M.direction of the crystals

INCREMENTAL LINES OFRETZIUS

NEONATAL LINE

Neonatal line

Prenatal enamel

Postnatal enamel

PERIKYMATAThe external manifestation of the incremental lines of Retzius represented as transverse wave like grooves on the surface of the enamel are known as

.perikymata

HUNTER SCHREGER BANDS

•The dark bands (Diazones) absorb the light where the light bands (Parazones) reflect the light.

ENAMEL TUFTAND ENAMEL LAMELLAE

ENAMEL SPINDLE

It makes the area hypersensitive to pain

Enamel spindles are : A- odontoblastic processes cross the dentinoenamel junction.B- remnants of ameloblasts. C- enamel rods develop in planes of tension.

Surface structure It is relatively structure-less layer covers the cervicalregion of the teeth. 30um in thickness in 70% of People, and it is hyper-mineralized.

ENAMEL CUTICLE

It is delicate membrane coversthe crown of the newly Erupted tooth. It has the same Structure asbasement membrane

Primary cuticle secondary cuticle

It is non cellular keratinized layerformed by reduced enamel epithelium after tooth eruption,After removal of the primary oneby wear and brushing

ENAMEL pellicleIt is a glycoprotein of saliva that covers the toothimmediately after eruption. It reforms within hoursafter removal.

ENAMEL plaqueWithin a day or two after the pellicle has formed it colonized With microorganisms to form bacterial Plaque.