Structural Components of Teeth Enamel, Dentin, Cementum Dermal
Structural Components of Teeth Enamel, Dentin, Cementum Dermal denticles of sharks Enamel
Enamel Hard, vitreous-like substance that covers, protects the anatomic crown Highly mineralized - 96% inorganic Fundamental unit is the enamel
rod or enamel prism Formed by ameloblast cells (amelogenesis) Physical Properties Hardness: Mohs hardness 5 - 8 (diamond is
10) Knoop hardness number (KHN) of 300:
Dentin 65 Pure gold 32 Amalgam 90 Composite 60 Peripheral enamel harder than deeper enamel
Density: Increases from DEJ to surface Enamel thickness varies: Thicker in cusp and incisal areas Thins out towards cervical areas
Color: Semi-translucent, partly dependent on enamel thickness and underlying dentin Polychromatic (different colors) Thinner - yellow white (underlying yellow dentin) Thicker layer blue-grayish white
Tensile strength and compressibility: Hard but brittle - prone to splitting and chipping (high compressibility but very low tensile/shear strength) Cushioned and supported by
underlying dentin Solubility: Dissolved by acid (demineralization) Certain minerals (fluoride) reduce solubility and increase hardness
Surface enamel less soluble than deep enamel Permeability: Selectively permeable (shown by organic dyes) Submicroscopic pores act like a molecular sieve
Water and ions pass via osmosis Chemical Composition: Inorganic: 96% Organic: 1% Water: 3 - 4%
Inorganic Content 96% inorganic by weight Calcium + phosphate + hydroxyl ions = hydroxylapatite Hydroxylapatite crystal: Ca10(PO4)6 (OH)2 Fl combines with Ca ion to form the harder fluoroapatite crystal
Organic Content 1% organic matter Various amino acids, carbohydrates and lipids Water Content 3 - 4% by weight
Hydrated shell or covering around the apatite crystal Enamel Prisms (Rods) Fundamental unit of enamel Cross-section described as key-hole shape, interlocking
Enamel prisms... Run from DEJ to surface Essentially perpendicular to surface (fig. A & B) Primary rods perpendicular to DEJ* (fig. C) Lines of Retzius
Incremental growth lines in enamel Concentric series of brown lines (treerings) Formed by hypomineralized bands Arc-like pattern Wave-like surface characterization called
perikymata Hunter-Schreger Bands Alternating light and dark bands of enamel rods (artifact of specimen sectioning) Dark bands: diazones
Light bands: parazones Dentin Dentin Main component of tooth structure Covered by enamel (crown portion) and cementum (root
portion) Formed by odontoblast cells (dentinogenesis) Dentinal tubules: microscopic tubes that radiate outward from the pulp Dentin
Odontoblast processes: extensions of odontoblast cells within dentinal tubules Physical Properties Color is yellowish-white Knoop hardness of 65: Less than enamel
Greater than bone or cementum Elastic property: supports brittle enamel Highly permeable - decreases with age Chemical Composition
75% inorganic 20% organic 5% water, etc Inorganic composition: Calcium phosphate as hydroxylapatite Fluoride presence is 2-3X that
found in enamel Higher in permanent than primary teeth More concentrated closer to pulp Concentration increases with age Organic composition: Mainly collagen (protein)
Glycine, alanine, proline, hydroxyproline Thought to be a seeding agent in apatite crystal formation Some lipids (cholesterol) Structural Components
Odontoblasts and their processes located within dentinal tubules Tubules bigger towards pulp and narrow towards DEJ Dentinal matrix Dentinal matrix: intertubular
dentin and peritubular dentin Peritubular dentin more mineralized than intertubular dentin Dentinal matrix... Intertubular dentin mainly collagenous fibers crisscrossing between tubules
Structural morphology: Imbrication lines (Lines of Owen): incremental lines of growth similar to Lines of Retzius (e.g. tree rings) Roman
imbrice Structural morphology... Neonatal line: demarcation between prenatal and postnatal dentin (in primary teeth and permanent first
molars) Types of Dentin Primary dentin (initial formation of tooth) Secondary dentin (next to pulp,lifelong) aka Physiologic secondary dentin
Tertiary dentin (reaction to caries) PSD aka Reparative secondary dentin RSD More types of dentin
Sclerotic dentin: tubules obliterated by minerals Dead tracts: tubules with dead odontoblast processes Cementum
Characteristics Protects root dentin Provides for attachment to alveolus via Sharpeys fibers Formed by cementoblast cells (cementogenesis) Physical
characteristics: Light yellow color Chemical composition 50% inorganic (hydroxylapatite) 50% organic material and water Types of Cementum Acellular cementum
Cervical 2/3 of root Mainly calcified substance Cellular cementum Apical 1/3 of root Mainly cementocytes Secondary cementum Forms as a result of trauma or
pathology Adhesive bonding to tooth Bonding to enamel: Acid etching to remove microscopic amounts of
enamel hydroxylapatite Resin flows into roughened crevices and bonds mechanically Bonding to dentin: More complex than bonding to enamel
Etch removes mineral components leaving collagen matrix Resin primer infuses between collagen matrix and into dentinal tubules: collagen/resin hybrid layer Lab Project
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