Enamel

oral

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. 1-Thickness 2-Color 3- Hardness 4- Tensile strength 5-Permeability 6-Solubility Physical characters

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 substance is burnt and the inorganic substance remain the inorganic substance is dissolved and the organic 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 mm 2 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 ---------

18. transmission electron microscope

19. Scanning electron microscope

20. Transverse striation of rods

21. Deciduous tooth permanent tooth Direction of rods

22. 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).

23. Gnarled enamel

24. 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.

25. 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

26. INCREMENTAL LINES OF RETZIUS

27. NEONATAL LINE Neonatal line Prenatal enamel Postnatal enamel

28. 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 .

29. HUNTER SCHREGER BANDS The dark bands ( Diazones ) absorb the light where the light bands ( Parazones ) reflect the light.

30. ENAMEL TUFTAND ENAMEL LAMELLAE

31. 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.

32. 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.

33. ENAMEL CUTICLE It is delicate membrane covers the crown of the newly Erupted tooth. It has the same Structure as basement membrane Primary cuticle secondary cuticle It is non cellular keratinized layer formed by reduced enamel epithelium after tooth eruption, After removal of the primary one by wear and brushing

34. 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.