Dental Anatomy: Enamel Structure and Properties
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Questions and Answers

What is the primary function of enamel?

  • To aid in the formation of dentin
  • To produce the color of the tooth
  • To provide sensation to the tooth
  • To cover and protect the underlying tissues (correct)

    • When does the formation of enamel start?

  • After the tooth has erupted
  • When the embryo is 18 weeks (correct)
  • During the second year of birth
  • During the first year of birth

    • What is the hardness of tooth enamel on the Knoop hardness scale?

  • 350-500 KHN (correct)
  • 600-700 KHN
  • 500-600 KHN
  • 200-300 KHN

    • What is the origin of enamel?

    <p>Ectodermal</p> Signup and view all the answers

    What is the percentage of mineral salts in enamel?

    <p>96%</p> Signup and view all the answers

    What is the compressive strength of tooth enamel?

    <p>50x103 psi/ 350 MPa</p> Signup and view all the answers

    What is the maximum thickness of enamel over the cusps?

    <p>2.6 mm</p> Signup and view all the answers

    What is the tensile strength of tooth enamel?

    <p>1.5x103 psi/ 10 Mpa</p> Signup and view all the answers

    What is the percentage of organic content in tooth enamel?

    <p>4%</p> Signup and view all the answers

    What is the reason for the yellowish color of some teeth?

    <p>The dentin is yellow</p> Signup and view all the answers

    What is the main inorganic constituent of tooth enamel?

    <p>Hydroxyapatite</p> Signup and view all the answers

    What is the characteristic of the cervical area of the tooth in terms of enamel thickness?

    <p>Thin enamel</p> Signup and view all the answers

    What is the shape of the Hydroxyapatite crystals in tooth enamel?

    <p>Hexagonal</p> Signup and view all the answers

    What is the hardness of enamel compared to other calcified tissues?

    <p>It is the hardest</p> Signup and view all the answers

    What is the arrangement of ions within each unit cell of crystallite in tooth enamel?

    <p>Hydroxyl group surrounded by 3 uniformly spaced calcium ions</p> Signup and view all the answers

    What is the approximate percentage of lipid content in tooth enamel?

    <p>1%</p> Signup and view all the answers

    What is the process of forming enamel on teeth during tooth development?

    <p>Amelogenesis</p> Signup and view all the answers

    What is the composition of the organic matrix of enamel?

    <p>Only noncollagenous proteins</p> Signup and view all the answers

    What percentage of enamel proteins are amelogenins?

    <p>90%</p> Signup and view all the answers

    What is the function of amelogenins in enamel formation?

    <p>Regulate growth and thickness</p> Signup and view all the answers

    What is the characteristic of the N-terminal domain of amelogenins?

    <p>Tyrosine rich</p> Signup and view all the answers

    What is the stage of tooth development when amelogenesis begins?

    <p>Advanced bell stage</p> Signup and view all the answers

    What is the origin of the epithelial enamel organ?

    <p>From the stratified squamous epithelium of the primitive oral cavity</p> Signup and view all the answers

    What is the composition of the mineral phase of enamel?

    <p>Hydroxyapatite with fluoride in the hydroxyl position</p> Signup and view all the answers

    In the organizing/inductive stage, what occurs to the ameloblasts?

    <p>They elongate up to 40 microns and rest on the basement membrane.</p> Signup and view all the answers

    What happens to the basal lamina supporting the ameloblasts during the secretory stage?

    <p>It disintegrates after the deposition of predentin.</p> Signup and view all the answers

    What characterizes the maturative stage of amelogenesis?

    <p>The maturation of enamel, which occurs after most of the enamel matrix has formed.</p> Signup and view all the answers

    Where do the ameloblasts secrete enamel proteins during the secretory stage?

    <p>At the proximal and distal surfaces of the Tomes' process.</p> Signup and view all the answers

    What is the function of the Tomes' process?

    <p>It contains secretory granules and small vesicles involved in enamel protein secretion.</p> Signup and view all the answers

    Where does the formation of the enamel matrix start?

    <p>At the site of the proximal terminal web.</p> Signup and view all the answers

    What happens to the ameloblasts during the secretory stage?

    <p>They become reversely polarized with most organelles in the proximal region of the cell body.</p> Signup and view all the answers

    What is the function of the proximal terminal web?

    <p>It is the site where the formation of the enamel matrix starts.</p> Signup and view all the answers

    What is the characteristic of the ameloblasts during the secretory stage?

    <p>They are reversely polarized with most organelles in the proximal region of the cell body.</p> Signup and view all the answers

    What is the fate of the ameloblasts after the formation of the enamel matrix?

    <p>They migrate away from the dentin surface, allowing the formation of Tomes' process.</p> Signup and view all the answers

    What is the process of forming enamel on teeth called?

    <p>Amelogenesis</p> Signup and view all the answers

    In which stage of enamel formation do matrix proteins continue to be secreted by ameloblasts until the entire thickness of enamel is laid?

    <p>Secretory phase</p> Signup and view all the answers

    What is the percentage of mineralized enamel formed at the end of the secretory phase?

    <p>30%</p> Signup and view all the answers

    What is the function of proteases secreted by ameloblasts in the maturative phase?

    <p>Remove enamel proteins</p> Signup and view all the answers

    What is the composition of mature enamel?

    <p>96% mineral, 4% protein, 5% water</p> Signup and view all the answers

    How many stages are there in the life cycle of ameloblasts?

    <p>6 stages</p> Signup and view all the answers

    What is the shape of cells in the morphogenic stage of ameloblast life cycle?

    <p>Low cuboidal</p> Signup and view all the answers

    Where are Golgi apparatus and centrioles located in ameloblasts during the morphogenic stage?

    <p>Proximal end of cell</p> Signup and view all the answers

    Study Notes

    Introduction to Enamel

    • Enamel is the hard, vitreous-like substance that covers the outer regions of the tooth crown, protecting the underlying tissues.
    • Enamel starts to form when the embryo is 18 weeks old and has an ectodermal origin.

    Physical Properties of Enamel

    • Enamel is the hardest calcified tissue in the human body, with a high content of mineral salts and a crystalline arrangement.
    • It is extremely hard, enabling it to withstand mechanical forces during tooth functioning.
    • Enamel thickness varies, with a maximum thickness of over 2.6 mm on cusps/incisal edges and thinning to a knife edge at the neck of the tooth/pit/groove area.
    • Enamel color ranges from yellowish white to greyish white, with underlying dentin being yellow.
    • Cervical areas have thin enamel, reflecting the yellow color of dentin, while incisal areas have a bluish tinge due to the thin edge of the double layer of enamel.

    Mechanical Properties of Enamel

    • Hardness: 350-500 KHN
    • Compressive strength: 50 x 10^3 psi/ 350 MPa
    • Shear strength: 13 x 10^3 psi/ 90 MPa
    • Tensile strength: 1.5 x 10^3 psi/ 10 MPa (low)
    • Abrasion resistance: high
    • Modulus of elasticity: 19 x 10^6 psi/ 130 GPa
    • Specific gravity: 2.95 (deciduous teeth) and 2.97 (permanent teeth)
    • Permeability: refractive index 1.655 (in comparison, porcelain is 1.5 and quartz is 1.54)

    Chemical Properties of Enamel

    • Inorganic content: 96% (calcium hydroxyapatite)
    • Organic content: 4% (water, proteins, carbohydrates, and lipids)
    • Minor constituents: fluoride, zinc, silver, aluminum, barium, copper, nickel, selenium, titanium, vanadium, and lead.

    Enamel Proteins

    • Enamel proteins are made up of non-collagenous proteins only.
    • Amelogenins (90%): heterogeneous group of low molecular weight proteins.
    • Non-amelogenins (10%): enamelin, ameloblastin (amelin or sheathlin), and tuftelin.
    • Amelogenins regulate growth and thickness.

    Enamel Formation (Amelogenesis)

    • Amelogenesis begins during the advanced bell stage of tooth development after dentinogenesis.
    • Enamel formation occurs in two phases: secretory and maturative.
    • During the secretory phase, ameloblasts secrete enamel proteins and form the organic matrix.
    • During the maturative phase, the organic matrix is mineralized, and the enamel crystallite forms and grows in length.

    Life Cycle of Ameloblasts

    • According to function, the life span of cells of the inner enamel epithelium is divided into six stages: morphogenic, organizing/inductive, formative/secretory, maturative, protective, and desmolytic.
    • During the morphogenic stage, the cells are low and cuboidal, resting on the basement membrane.
    • During the formative/secretory stage, ameloblasts become elongated, and the Golgi apparatus and centrioles are located in the proximal end of the cell.

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    Description

    Test your knowledge of enamel, the hard outer layer of tooth crowns, including its physical and chemical properties, formation, and functions. Learn about the structure, thickness, color, hardness, strength, and resistance of enamel.

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