1-enamel is ectodermal in origins2-it is derived from inner enamel epithelium of enamel organ.3-mature enamel is completelynon cellularAmeloblasts are derived from outer enamel epithelium)Mature enamel is completely acellular (True or false )
thickness It is thick at the incisal edge and cusp tip of molars and premolars (2-2.5 mm) and ends cervically as knife edgeThe thickest part of the enamel is present in---------, and………….
colorThick enamel---------------------- bluish white Decrease in thickness-----------------------yellow due to the underlying dentinHealthy 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 andresist 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 extremelybrittle and depends on the strength ofthe underlying dentin.Tensile strength of enamel is greater than that of dentin ( true or false)
permeabilityEnamel is selectively permeable,permitting partial or complete passageof ions due to the presence ofmicroscopic pores. Enamel is completely impermeable to ions (False or true)
solubilityEnamel dissolves in acid media. Itssurface is less soluble than deepenamel.
Chemical compositionMature enamel consists of: Mainly(96%) inorganic substance Small (3%) amount of organic substance & 1%) water
Course: the enamel rod starts straightat dentino-enamel junction (D.E.J.)for about 30 µ then has a wavycourse till near the outer surface ofenamel where it become straightonce 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
Direction of rodspermanent tooth Deciduous tooth
Gnarled enamel Twisted Gnarled course of enamel enamel rods DGnarled enamel is twisted and intertwined rodestructure associated with increase strength of theenamel ,Present mainly in the incisal edges and tipof the cusps. (enamel rods develop in planes oftension).Give short account on gnarled enamel
Rod sheathL.M. distinct thin layer peripheral to the rods Different refractive index, darker and more acid resistant, and less calcified and more organic.E.M. not distinct layer, but organically rich inter- rod space devoid of crystals.
Inter rod substanceL.M. distinct cement substance with higher refractive index.E.M.tail of the adjacent rod with different direction of the crystals
INCREMENTAL LINES OF RETZIUS
NEONATAL LINE Prenatal enamel Neonatal line Postnatal enamel
PERIKYMATAThe external manifestation of theincremental lines of Retzius representedas transverse wave like grooves on thesurface of the enamel are known asperikymata.
HUNTER SCHREGER BANDSThe dark bands (Diazones) absorb the •light where the light bands (Parazones)reflect the light.
ENAMEL TUFTANDENAMEL LAMELLAE
ENAMEL SPINDLEIt makes the area hypersensitive to painEnamel spindles are :A- odontoblastic processes cross the dentinoenamel junction.B- remnants of ameloblasts.C- enamel rods develop in planes of tension.
Surface structureIt is relatively structure-less layer covers the cervical region of the teeth. 30um in thickness in 70% ofPeople, and it is hyper-mineralized.
ENAMEL CUTICLEPrimary cuticle secondary cuticleIt is delicate membrane covers It is non cellular keratinized layer the crown of the newly formed by reduced enamelErupted tooth. It has epithelium after tooth eruption,the same Structure as After removal of the primary one basement membrane by wear and brushing
ENAMEL pellicleIt is a glycoprotein of saliva that covers the tooth immediately after eruption. It reforms within hours after removal. ENAMEL plaqueWithin a day or two after the pellicle has formed itcolonized With microorganisms to form bacterialPlaque.