Enamel
- 1. Enamel
- 2. 1-enamel is ectodermal in origins 2-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 )
- 3. Physical characters 1-Thickness 2-Color 3- Hardness 4- Tensile strength 5-Permeability 6-Solubility
- 4. thickness It 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………….
- 5. color Thick enamel---------------------- bluish white Decrease in thickness-----------------------yellow due to the underlying dentin Healthy thick enamel is -------- in color, while thin enamel is …………in color
- 6. hardness Enamel is the hardest calcified tissue in the body Because 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)
- 7. Tensile strength Although 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)
- 8. permeability Enamel 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)
- 9. solubility Enamel dissolves in acid media. Its surface is less soluble than deep enamel.
- 10. Chemical composition Mature enamel consists of: Mainly(96%) inorganic substance Small (3%) amount of organic substance & 1%) water
- 11. Inorganic component Mainly calcium phosphate crystals (hydroxyapatite crystals)
- 12. organic component Mainly non collagenous proteins: A- amelogenins B- non-amelogenins
- 13. Microscopic structure 1-Rods (prism). 2- Rod sheath. 3-Inter rodal cement substance
- 14. Ground section Decalcified section the organic the inorganic substance is burnt substance is dissolved and the inorganic and the organic substance remain substance remain
- 15. Enamel rods 1- Course. 2- Number. 3- Transverse striation. 4- Direction. 5- Gnarled enamel.
- 16. Course: the enamel rod starts straight at 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.
- 17. 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 ---------
- 21. Transverse striation of rods
- 22. Direction of rods permanent tooth Deciduous tooth
- 23. Gnarled enamel Twisted Gnarled course of enamel enamel rods D 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). Give short account on gnarled enamel
- 24. Gnarled enamel
- 25. Rod sheath L.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.
- 26. Inter rod substance L.M. distinct cement substance with higher refractive index. E.M.tail of the adjacent rod with different direction of the crystals
- 27. INCREMENTAL LINES OF RETZIUS
- 28. NEONATAL LINE Prenatal enamel Neonatal line Postnatal enamel
- 29. PERIKYMATA The external manifestation of the incremental lines of Retzius represented as transverse wave like grooves on the surface of the enamel are known as perikymata.
- 30. HUNTER SCHREGER BANDS The dark bands (Diazones) absorb the • light where the light bands (Parazones) reflect the light.
- 32. 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.
- 33. Surface structure It is relatively structure-less layer covers the cervical region of the teeth. 30um in thickness in 70% of People, and it is hyper-mineralized.
- 34. ENAMEL CUTICLE Primary cuticle secondary cuticle It is delicate membrane covers It is non cellular keratinized layer the crown of the newly formed by reduced enamel Erupted tooth. It has epithelium after tooth eruption, the same Structure as After removal of the primary one basement membrane by wear and brushing
- 35. ENAMEL pellicle It is a glycoprotein of saliva that covers the tooth immediately after eruption. It reforms within hours after removal. ENAMEL plaque Within a day or two after the pellicle has formed it colonized With microorganisms to form bacterial Plaque.