Enamel

Anything about the dental enamel

1. ENAMEL Ma. Hermie Culeen Barapon Julie Lustado Tira Abdollahi

2. Also called Substancia Adamantina or Amelo It is the hard transluscent tissue covering the anatomical crowns of the teeth of man and most mammals. Enamel

3. It acts as protective covering of the crown dentin and resist the forces of mastication. Function of the Enamel

4. 1. Because of its high content of mineral salts and their crystalline arrangement, enamel is the hardest calcified tissue in the human body. 2. Enamel is brittle and inelastic. 3. Enamel is transluscent . Physical Characteristics

5. 4. The color of enamel-covered crown ranges from yellowish white to grayish white. It depends on: Transluscency Degree of Calcification Homogeneity Physical Characteristics

6. Yellowish-white enamel Grayish-white enamel

7. 5. It is thick on cusps and incisal portions and slopes down to a thin layer at the neck of the tooth. Physical Characteristics

8. 6. Specific gravity is 2.8. 7. Enamel acts as a semi-permeable membrane from certain ions from: the saliva to the outer layer of enamel the pulp to the inner layer of enamel across dentin Physical Characteristics

9. Permeability of Enamel

10. The enamel consists mainly of inorganic material (96%) and only a small amount of organic substance and water (4%). 90% of the inorganic components is Ca 3 (PO 4 ) 2 and the rest are Mg, CO 3 -2 , F, Na, K and traces of other metals. Chemical Characteristics

11. Ca 3 (PO 4 ) 2 is in form of crytals known as hydroxyapatite crystals (3Ca 3 (PO 4 ) 2 ·Ca(Oh) 2 ) considered as the chief inorganic substance of enamel. The bulk of the organic matter in enamel is a keratin-like substance (glycoprotein). Chemical Characteristics

12. ENAMEL STRUCTURE

13. The enamel consists of the following basic structures: 1. Enamel prisms (Enamel rods) 2. Prism sheath (Rod sheath) 3. Interprismatic substance ( Interrod cementing substances) Enamel Structure

14. are long slender structures with roughly 5 or 6 sides extending from the DEJ to the surface in wavy course and oblique direction The length of the rods are greater than the thickness of the enamel. Enamel prisms (rods)

15. The diameter of the rods averages 4 um (along dej ) and becomes double at the surface. The enamel rods normally have a clear, crystalline appearance, permitting light to pass through them. They appear hexagonal, round, or oval and many resemble fish scales. Enamel prisms (rods)

16. Enamel prisms (rods)

17. Prism sheath is the outermost portion of the rod and takes stains easily because it has more organic substance Prism Sheath

18. It is the substance which cements the rods together. It is approximately 1 micron thick and believed to have proliferated from terminal bar apparatus as enamel globules are developed. Interprismatic substance

19. The rods in cross section has a common pattern: “Keyhole” or “Paddle-shaped” pattern with head and tail. In longitudinal section, the “heads” or “bodies” in between the “tails” of adjacent rods would appear like rods are separated by interprismatic substance. Submicroscopic Structure

20. The appatite crystals appear flat, ribbon-like and arranged with their long axis paralleling the long axis of rods. Some crystals may diverge as much as 40 o -65 o from the axial plane of the rods. Submicroscopic Structure

21. Transverse striations Hunter- Schreger bands Incremental Line of Retzius Enamel Lamellae Enamel Tufts Enamel Spindles Enamel Cuticle Pellicle Structural Characteristics

22. lines crossing the rods with 4 microns interval, which becomes more visible when in contact with acid It marks the daily appositional growth of the enamel rods. More prominent cross-striations occur in a regular period of about every 4 days/1 week and are known as  striae of Retzius or incremental lines. Transverse Striations

23. 4 µ / day

24. alternating light and dark bands originating from detino -enamel junction towards the surface. These are caused by the different directions of rods or criss -crossing of rods so that in longitudinal section, some rods are cut trasversely ( diazone or dark zone) and some are cut longitudinally ( parazone or light zone). Hunter- Schreger Bands

25. browish lines that mark the growth periods of enamel (beginning and ending layers of enamel). It represents every primary calcification in the enamel. Perikymata Neonatal line or ring Incremental line of Retzius

26. Imbrication lines of Pickerill Transverse wavelike grooves that are thought to be the external manifestations of Retzius lines Perikymata

27. Lines of Retzius Perikymata

28. Accentuated Retzius lines differentiating the prenatally developed enamel from postnatal enamel Present in all deciduous teeth and 1 st permanent molar This is believed to be the result of abrupt change in the environment and nutrition of the newborn infant. Neonatal Lie (Ring)

29. Neonatal Line Prenatal Enamel Postnatal Enamel

30. Leaf-like structural defects extending from the surface of the enamel towards the interior Enamel Lamellae

31. Narrow, ribbon-like structure composed of bundles of poorly calcified rods and interrod cementing substance originating from dentino -enamel junction. The term tuft is used because the structure resembles the blades of grass attached to a parent stem. Enamel Tufts

32. Enamel Lamellae Enamel Tufts

33. Club-shaped extensions or projections of the dentinal tubules into the enamel. It is an odontoblastic process which extends in between the cells of inner dental epithelium before the formation of enamel This is one of the factors that causes the hypersensitivity of d.e.j . Enamel Spindles

34. Enamel Cuticle ( Nasmyth’s membrane) is a delicate membrane that covers the crown of the newly erupted tooth but is probably soon removed by mastication. Pellicle are precipitates of salivary proteins covering the erupted enamel and may be colonized later by bacteria and food debris. Enamel Cuticle and Pellicle

35. The dentin surface on the crown has shallow depressions or pits where the enamel caps are fitted resulting to the irregular or scalloped appearance of the junction of enamel and dentin. This provides a firm attachment of enamel to the dentin surface. Scalloped Dentino -Enamel Junction

36. ENAMEL DEVELOPMENT

37. The enamel organ, originating from the stratified epithelium of the stomodeum , consists of four distinct layer: Outer enamel epithelium Stellate reticulum Stratum intermedium Inner enamel epithelium Epithelial Enamel Organ

38. The borderline between the inner enamel epithelium and the connective tissue of the dental papilla is the subsequent dentino -enamel junction . Cervical loop is the part where the inner enamel epithelium reflects onto the outer enamel epithelium

39. Outer cuboidal cells of enamel organ which becomes irregular producing loops where capillaries are found It serves as a protective barrier for enamel organ During enamel formation, cells develop vesicles and villi and large number of mitochondria indicating the active participation of cells in the transmission of nutrition. Outer Enamel Epithelium

40. Star-shaped cells in many layers forming a network within the enamel organ It supports the production of the enamel matrix. It is resistant and inelastic, therefore it acts as buffer against physical forces that might distort the conformation of the developing dej . It becomes reduced in size, thus it shortens the path of nutrition that comes from the outside. Stellate Reticulum

41. More inner compressed layer of flat to cuboidal cells Also supports the production of enamel matrix The cells show mitotic division even after the cells of the IEE cease to divide. Stratum Intermedium

42. Innermost tall columnar cells of enamel organ It will differentiate into ameloblast that form enamel matrix. Inner Enamel Epithelium

43. When the crown has been formed, the cells of this portion give rise to Hertwig’s epithelial root sheath. Cervical Loop

44. AMELOGENESIS

45. Also called the apposition of enamel matrix It is the process of development of enamel consisting of 2 phases: Formative phase (organic matrix formation) Mineralization and Maturation phase Amelogenesis

46. where there is formation of enamel matrix Formation of dentino -enamel membrane - the ameloblast deposit a thin matrix extracellularly on the surface of the dentin uniting with the membrana preformativa to become the dej Formative Phase

47. 2. Formation of Tomes' process - the protoplasmic projections of ameloblasts into the matrix are the Tomes' processes that appear as rows of projections extending intracellularly - responsible for the way the enamel matrix is laid down Formative Phase

48. 3. Isolation of Tomes' process from the cell body of ameloblast by condensation of cytoplasmic substance closely associated with thickened cell membrane called terminal bar (distal terminal bar). Formative Phase

49. 4. “Filling-in” of the distal end of Tomes’ process with matrix material from the ameloblast . 5. Formation of the fully formed segments of rods or the pre-enamel rods. Formative Phase

50. The first stage an immediate partial mineralization occurs in the matrix segment and the interprismatic substance as they are laid down. The first mineral is actually in the form of crystalline apatite. The second stage or maturation starts the height of the crown and progresses cervically , seems to begin at the dentinal end of the rods. It begins before the matrix has reached its full thickness. Mineralization and Maturation

51. Enamel maturation: From cusp tip or incisal edge and progress cervically The maturation of the crystals begins at its dentinalend and progress to the outer surface. At first parallel to D.E.J and later to the outer surface of enamel Maturation occurs by the growth of the primary crystals till they fuse together The fibrils between the crystals will become thinner Mineralization and Maturation

52. After eruption, the maturation continues by deposition of ions from saliva to reach 96 % of its weight inorganic substance.

53. LIFE CYCLE OF AMELOBLASTS

54. According to their function, the life span of the cells of the inner enamel epithelium can be divided into six stages: Morphogenic stage Organizing stage Formative stage Maturative stage Protective stage Desmolytic stage Life Cycle of Ameloblasts

55. Before the ameloblasts are fully differentiated and produce enamel, they interact with the adjacent mesenchymal cells, determining the shape of the dej and the crown. During this stage, the cells are short and columnar with large nuclei that almost fill the cell body. Morphogenic Stage

56. The ameloblasts interact with the cells of the dental papilla at the periphery which later differentiates into odontoblasts . The cells become longer, and nucleus-free zones at the distal ends of the cells become almost as long as the proximal parts containing the nuclei. Organizing Stage

57. After the first layer of dentin has been formed The presence of dentin seems to be necessary for the beginning of enamel matrix formation. Changes in the organization and number of cytoplasmic organelles and inclusions are related to the initiation of enamel matrix. Formative Stage

58. Enamel maturation occurs after most of the thickness of the enamel matrix has been formed in the occlusal or incisal area. Ameloblasts display microvilli at their distal extrimities , and cytoplasmic vacuoles. These structures indicate an absorptive function of these cells. Maturative Stage

59. When the enamel has completely developed and has fully calcified, the ameloblasts cease to be arranged in a well-defined layer and can no longer be differentiated from the cells of the stratum intermedium and OEE. These cell layers then form stratified epithelial covering of the enamel called reduced enamel epithelium (REE) that protects the enamel by separating it from the connective tissue until the tooth erupts. Protective Stage

60. The REE proliferates and seems to induce atrophy of the connective tissue separating it from the oral epithelium, so that fusion of the two epithelia can occur. It is probable that the epithelial cells elaborate enzymes that are able to destroy connective tissue fibers by desmolysis . Desmolytic Stage

61. CLINICAL CONSIDERATIONS

62. 1. How does a knowledge of enamel affect cavity preparation? A. Directs acid etching of enamel & bonding properties (restorations, sealants) B. Directs removal of unsupported enamel rods (enamel fragile when unsupported)

63. 2. What makes enamel structure susceptible to caries? Crystals dissolve at low pH, acid produced by cariogenic bacteria Enamel surface is porous and imperfect (pits, fissures, lamellae)

64. 3. How are caries & dental erosion similar? different? Same: Both involve chemical (acid) insult Different: Caries due to bacterial action Erosion due to enviromental factors

65. At what pH does enamel undergo dissolution? (dissolve) What common dietary substances have a low ph? pH 5.0 - 5.5 Soda pop, sports drinks, citrus, pickles, etc. The average American drinks more than 53 gallons of carbonated soft drinks each year, more than any other beverage, including milk, beer, coffee or water. Pop is a poor dietary choice for 3 reasons. Can you name them?

66. 4. What accounts for the natural coloration of teeth? What accounts for white spots? Enamel translucent & porous, dentin shows through Contrast with facial/hair color Impaired translucence of enamel creates optical white spots

67. 5. What are some environmental factors that affect enamel formation? How do these occur? Nutrition, systemic diseases, high fevers, tetracycline, trauma, fluoride, etc. Occur during tooth development

68. 5. How does fluoride affect enamel? Protective function: inhibitor of crystal dissolution & remineralization with fluoroapatite Too much affects ameloblasts ( fluorosis )

69. 6. What are some hereditary conditions affecting enamel? amelogenesis imperfecta , ectodermal dysplasias , etc.

70. Amelogenesis Imperfecta is a condition where there is disturbance in the formation and maturation of the enamel matrix. 1. Enamel Hypoplasia – result of the disturbance in matrix formation. Clinically, the surface of enamel may develop pits, fissures or grooves or enamel may be very thin. 2. Enamel Hypocalcification – result of disturbed mineralization of enamel matrix. Clinically, the enamel appears chalky white or opaque and soft.

71. USE YOUR SMILE TO CHANGE THE WORLD, BUT DON’T LET THE WORLD CHANGE YOUR SMILE!  Thanks for Listening!

72. Avendano , Estela Vizcarra . Compendium of Oral Histology and Embryology. Bhaskar , S.N. Orban’s Oral Histology and Embryology. 11 ed. Naim , Jamal. Tissue of the Teeth: Enamel. http://up.edu.ps/ocw/repositories/pdf-archive/oralbiologey209092008ReadOnly/body.html References: