1st BDS Lecture on tooth Enamel
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This document provides details on the structure and composition of enamel. It notes that enamel is the hardest tissue in the body, covering the anatomical crown. It is made up primarily of hydroxyapatite crystals arranged in enamel prisms/rods from the dentin-enamel junction to the surface. The direction of the prisms changes in a sinusoidal pattern. Between the prisms is interprismatic enamel. Near the surface is aprismatic enamel which is more highly mineralized. Throughout life, the crown is covered by an organic layer or integument.
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1st BDS Lecture on tooth Enamel
- 1. Dr. Varun Surya Senior resident, MAIDS delhi
- 3. Ground sections Demineralized sections
- 4. • The anatomic crown of a tooth is covered by an acellular, avascular, highly mineralized material known as ENAMEL. • Origin • Enamel : Ectodermal in origin • Dentine, cementum & pulp: Ectomesenchymal in origin
- 5. • Thickest: over cusps & incisal edges • Thinnest: cervical margin • Hardest biological tissue • While highly mineralized, withstands both shearing & impact forces well. • Its abrasion resistance is high, allowing it to wear down slowly • Neither undergo repair nor replacement.
- 6. • Surface enamel is harder, denser & less porous than subsurface enamel. • Hardness & density also decreases • from the surface towards the interior • from cuspal/incisal tip towards thee cervical margin.
- 7. • Birefringent crystalline material, the crystals reflect light differently in different directions. • Young enamel • Light is almost entirely internally reflected with no wavelength differentially absorbed. • Result in Low translucency & white color • Changes with age • Translucency increases with age-- some color of the underlying dentine is transmitted --- yellow appearance.
- 8. Hydroxyapatite crystals • Principal mineral component- calcium hydroxyapatite • By volume = 88-90% • By weight = 95-96 % • Mineral content increases from DEJ to surface • Core of crystallites- • rich in magnesium & carbonate • More soluble than periphery
- 12. • Most crystallites are regularly hexagonal in cross-section
- 13. • Water • By weight: 2 %, by volume: 5-10 % • Related to porosity of enamel • Location • Between crystals & organic material • Trapped within defects of crystallites structure • Remainder forms a hydration layer coating the crystals • Clinical importance- fluoride travel through the water component
- 14. • Organic matrix • By weight : 1-2 % • Crystallites arrangement is straight & regular - 0.05% • Crystallites arrangement is irregular – 3 % • Most important : enamel proteins • Amelogenenins & Non-amelogenenins • Lipid material: cross-striations, lines of retzius, HS bands, prism sheath & prism code
- 15. • Composite ceramic with the crystallites oriented in a complex 3-D continuum. • Basic structural unit of enamel = enamel prism/rod • Each prism consist of several million crystallites packed into long thin rods • Length= 2.5mm, diameter = 5-6 μm • Direction = from DEJ to surface • At the boundary, the crystallites deviate by 40-60o from inside of the prism
- 17. Key hole pattern
- 19. • The enamel between the prism is k/s interprismatic enamel • Its composition is similar to that of inside the prism, but it has a different optical effect because crystals deviate by 40-60o from inside the prism. Boundary Core
- 20. • Predominates in humans • Shows clear ‘head’ & ‘tail’ region • The tail of one prism lying between the head of the adjacent prisms & point cervically Head tail
- 21. • Head-crystals runs parallel to the long axis of the prism • Tail –crystals are angled 65- 70o to the long axis prisms
- 22. • The change within a single prism is gradual such that there is no clear division between the head & tail of the same prism • However, the crystals in the tail of one prism show a sudden divergence from the crystals in the head of adjacent prism Head Tail
- 24. Boundary Core
- 25. • Prismatic & Interprismatic enamel are actually continuous. • Peripheral crystallites of the prisms deviate from their long axis to form a continuum with interprismatic enamel. • Interprismatic crystallites cross prisms at an angle of approx. 60o
- 27. • When viewed in section parallel to long axis of tooth • Most prisms appear to travel in a Sinusoidal line from DEJ to the surface • The prism meet the surface at varying angles • Just above cervical margin - 60o • Within fissures - 20o
- 29. • 10-13 layers of prism follow the same direction, but prism blocks above & below follow path in different directions. • This periodic change in prism directions give rise to a banding pattern termed Hunter – Scherger bands. • Width= 50 μm • Visible because different bands of prism reflect or transmit light in different directions
- 30. Generally they are oriented at right angle to dentin. Near the incisal edge or cusp tip they change gradually to an increasingly oblique direction until they are almost vertical in the region of edge or tip of cusp.
- 31. • In cervical and central parts of deciduous tooth they are approximately horizontal.
- 32. Diazones (transverse) Parazones (longitudinal) Angle between diazones & parazones is 40o In outer quarter of the enamel, all prism runs in same direction- hence No Hunter – Scherger bands
- 33. • The Sinusoidal directions of prisms in alternating sheets result in alternating reflecting bands on cut surface. • Different sheets exhibit different crystal orientations & thus different degrees of polarization
- 37. • As prisms are arranged in a spiral pattern, in some area beneath the cusps & incisal edges , the changes in the direction of the prisms appear more marked & irregular • The groups of prisms seem to spiral around each other, giving the appearance of “Gnarled” enamel • Gnarled= full of knots
- 38. Aprismatic enamel Prismatic enamel • Newly erupted primary teeth = outer 20-100 μm of enamel • Newly erupted permanent teeth = outer 20-70 μm of enamel • Here enamel crystallites are aligned at right angles to the surface & parallel to each other
- 39. Aprismatic enamel Prismatic enamel • This surface layer is more highly mineralized than the rest of enamel because of absence of prism boundaries • It occurs because of absence of tomes process from the ameloblasts in the first & final stages of enamel deposition
- 40. • During development changes in the enamel secretory rhythm, chemical composition and /or the position of the developing enamel front are recorded as Incremental lines • 2 types • Short period = cross – striations • Long period = enamel striae
- 41. • Lines that cross prisms at right angles • Interval = 3-6μm • These are diurnal being formed every 24 hours parallel to the secretory face of the ameloblasts
- 43. • Prominent lines that runs obliquely across the prisms to the surface • They represent the successive positions of the enamel-forming front
- 48. Enamel striae 7 cross striations Perkymata groove Between adjacent striae=7-10 cross striations Middle portion of enamel Cross striations= 4μm Enamel striae=25-30μm Cervical enamel Cross striations= 2μm Enamel striae=15-20μm
- 49. • Over the whole of lateral surface of enamel , enamel striae reach the surface in a series of fine grooves running circumferentially • These are k/s Perikymata grooves & are separated by Perikymata ridges • In deciduous tooth, these features are ever clearly visible in cervical enamel of deciduous 2nd molar
- 51. Striae of Retzius Perikymata
- 52. • Enamel striae are less pronounced or absent from enamel formed before birth. • A particularly marked striae is formed @ birth - Neonatal line • It reflect the metabolic changes at birth • Prism change both direction & thickness at this event
- 53. Neonatal line
- 54. • Surface enamel, in most areas is, Aprismatic & thus more highly mineralized
- 55. • Small elevations of 10-15 μm • Caps may result from enamel deposition on top of small deposits of non- mineralized debris late in development
- 56. • Depressions, particularly on lateral surface. • Results from loss of enamel cap & underlying material by abrasion or attrition
- 57. • Large surface elevations • 30-50μm in dia. • More common in premolars • Unknown origin
- 58. Permits strong union between two dissimilar tissues Enamel Dentin
- 59. • First, scalloping pattern; 25-100 μm, cusp & incisal edges • DEJ is smooth on lateral surface of crown • Second, smaller, micro-scallops 2-5 μm in size • Third, a nano-structural level of organization, the ends of fine collagen fibrils from the dentine mingling with the initial crystals of enamel • DEJ is less mineralized than either Enamel or Dentine
- 61. Enamel Dentin
- 63. • Narrow (up to 8μm in dia), round, sometimes club-shaped tubules • Extend upto 25 μm in enamel • Result of some odontoblastic process that, during the early stages of enamel development, insinuated themselves between the ameloblasts • Not aligned with the prisms Enamel spindle
- 64. • Junctional structures in the inner 3rd of enamel that, in ground section, resemble tufts of grass. • Same direction as that of prisms • They are hypomineralized • Recur at approx. 100μm intervals along the junction Enamel tufts
- 65. • Each tuft is several prism wide. • This appearance result from protein, presumed to be residual organic matrix, at the prism boundaries of hypomineralized prisms. • Best visualized- transverse sections • Highest concentration of ‘Tuftelin’ protein.
- 66. • Sheet-like, apparent structural faults • Run through entire thickness of enamel • Hypomineralized, narrow, longer & less common than enamel tufts • Best visualized- transverse sections
- 67. Lamellae may arise • Developmentally due to incomplete maturation of groups of prisms, leading to deposition of enamel protein • After eruption, cracks produced due to loading of enamel, in which saliva and oral fluids accumulates.
- 68. • Small isolated spheres of enamel • Occasionally found on the root, generally found on the cervical margin. • Enamel is prismatic, with prisms following an irregular course • Particularly common in the root bifurcation region where they may predispose to plaque accretion following gingival recession.
- 72. • Throughout its life, crown is covered by an organic layer or integument • Before eruption, crown is covered by • Overlying oral mucosa • Coronal part of dental follicle • Vestiges of the enamel organ (plus its associated 1o enamel cuticle)
- 73. Enamel space Dental follicle Oral epithelium Reduced enamel epi.
- 74. • After eruption, parts of integument of enamel organ origin are lost by • Degeneration of its epithelial component • Attrition & abrasion of the underlying cuticular component • Primary (pre-eruptive) enamel cuticle acquires additional matter form • Region of gingival sulcus-from lining epithelium • Coronal to gingival margin – from saliva • This salivary layer-Acquired pellicle • Bacteria : adhere to cuticle----pellicle----plaque
- 75. • Nasmyth’s membrane • Reduced enamel epithelium+ primary enamel cuticle • Basal lamina (primary enamel cuticle) • Not evident at the light microscopic level • Interposed between enamel surface & REE
- 76. Enamel space Dental follicle Oral epithelium Reduced enamel epi.
- 80. • Part of crown well exposed in mouth is covered by • REE- soon lost • 1o enamel cuticle- soon acquires organic elements of salivary origin- acquired pellicle • Above gingival margin –tooth covered by—plaque • Region of gingival crevice-tooth covered by- 1o enamel cuticle • Below this layer-- tooth covered by--- junctional epithelium
- 84. • Lies in intimate contact with the underlying organic enamel matrix • Approx. 30 nm thick • Acquires accretions in gingival crevice from crevicular epithelium & plasma---- 5 μm thick • Contiguous soft tissue: proteoglycans & glycoproteins • Plasma : immunoglobulins