Lecture 3

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Enamel. Dentin and Cementum

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73 Terms

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**Enamel**
covers the anatomic crown & varies in the thickness in different areas of the tooth.
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**Structures of the Teeth**
* Enamel
* Pulp
* Dentin
* Cementum
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**Amelogenesis**
enamel formation
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**Ameloblasts**
cells responsible for amelogenesis; originate from the embryonic germ layer called ECTODERM
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**Color of enamel**
* yellowish white to grayish white
* translucent in nature
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**Color of tooth mainly depends upon three (3) factors:**

1. COLOR of underlying dentin
2. THICKNESS of enamel
3. Amount of STAINS in enamel
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**Thickness**
**decreases** gradually from **cusps or incisal**

**edges to cemento-enamel junction.**
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Tooth type:

Anterior Tooth

(incisal edges)

Premolar tooth (cusp)

Molar tooth (cusp)
Enamel Thickness

2\.0 mm

2\.3 – 2.5

2\.5 – 3.0 mm
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Enamel: Strength
HARDEST CALCIFIED TISSUE in the human body.
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Brittle
has a high modulus of elasticity, high compressive strength and low tensile strength
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specific gravity
2\.8
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Enamel: Chemical Composition
* Inorganic contents: 95% – 98%
* Organic contents: 1 – 2%
* Water: 4 – 12%
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Hydroxyapatite
largest mineral constituent
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Chemical formula of hydroxyapatite:
Ca10(PO4)6(OH)2
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Enamel is composed of:
a) ENAMEL RODS or prisms
b) ROD SHEATHS
c) CEMENTING INTERROD SUBSTANCE
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Enamel rods/ prisms
appear as oval, fish scale or keyhole shaped
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Enamel rods/ prisms
* largest structural components


* has a head and tail
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ENAMEL RODS / PRISMS
aligned perpendicularly to both the DEJ & the tooth surface in the deciduous & permanent teeth
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Gnarled Enamel
groups of enamel rods that entwine with adjacent group of rods.
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Hunter-Schreger Bands
optical appearance of bands appear to be composed of alternating light and dark zones
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Incremental Striae of Retzius
considered as growth rings
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Imbrication Lines Pickerill
incomplete circles of striae of retzius at the enamel surface formed a series of alternating grooves.
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Perikymata
elevations between the grooves; continuous around a tooth & lie parallel to the cementoenamel junction.
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Enamel Tufts
hypomineralized structures of enamel rods & inter-rod substance that project between adjacent groups of enamel rods from the DEJ.
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Enamel Lamellae
thin leaflike faults between enamel rod groups that extend from the enamel surface toward the DEJ sometimes extending into the dentin.
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Enamel Spindles
* pain receptors
* odontoblastic processes that cross the DEJ into the enamel.
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Dentino-Enamel Junction
interface of the enamel & dentin
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Fissure
failure or compromised coalescence of the enamel of developmental lobes results in a deep invagination in the groove area of the enamel surface.
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Pit
noncoalesced enamel at the deepest point of a fossa.
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Nasmyth Membrane
covers the newly erupted tooth and is worn away by mastication and cleansing.
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Pellicle
organic deposit which is a precipitate of salivary proteins.
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Dental Pulp
* considered as a single tissue with mineralized
* dentin compromising the mature end product of cell differentiation and maturation.
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Dentin
forms the largest portion of the tooth structure
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Dentinogenesis
dentin formation.
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Odontoblasts
cells responsible for dentinogenesis
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Dentin: PHYSICAL PROPERTIES
* YELLOWISH in color
* harder than bone but softer than enamel
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Dentin: Chemical Properties
* Inorganic contents- 70%
* Organic contents - 20%
* Water- 5%
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Dentinal Tubule
small canals that remain from the process of dentinogenesis & extend through the entire width of dentin, form the pulp to the DEJ
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Peritubular (Intratubular) Dentin
* **dentin that immediately surrounds the dentinal tubules**
* **more mineralized than intertubular dentin and predentin.**
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Intertubular Dentin
* located between the dentinal tubules


* less mineralized than peritubular dentin
* main body of dentin.
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Predentin
layer that lines the innermost (pulpal) portion of dentin.
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Types of DENTIN:
* PRIMARY DENTIN
* SECONDARY DENTIN
* TERTIARY DENTIN
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Primary Dentin
* outlines the pulp chamber;
* forms the initial shape of the tooth;
* formed before root completion.
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Secondary Dentin
* forms on all internal aspects of the pulp cavity.
* Represents the continuing, but much slower, deposition of dentin by the odontoblasts after root formation has been completed.
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Tertiary Dentin
* produce in reaction to noxious stimuli, such as caries or a restorative dental procedure.
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Tertiary Dentin
also referred to as:

* REACTIVE,
* REPARATIVE or
* IRREGULAR SECONDARY DENTIN
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Sclerotic Dentin
results from aging or mild irritation & causes change in the composition of the primary dentin.
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Dead Tracts
areas of dentinal tubules that are empty & are black when viewed microscopically.
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Eburnated Dentin
* outward (exposed) portion of reactive
* sclerotic dentin where slow caries has destroyed formerly overlying tooth structure, leaving a hard, darkened cleanable surface.
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Hydrodynamic Theory
* The most accepted theory of pain transmission
* This accounts for pain transmission by the small rapid movement of fluids that occur within the dentinal tubules
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Deep Dentin
less effective pulpal barrier than superficial dentin near the DEJ or dentinoenamel junction.
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Smear Layer
composed of denatured collagen, hydroxyapatite & other cutting debris.
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Smear Plugs
serves as a natural bandage over the cut dentinal tubules because it occludes many of the dentinal tubules with debris
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Smear Plugs
formed from cutting debris forced into the tubules
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Pulp
soft connective tissue that occupies the central portion of the tooth.
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Pulp organ is divided into:
* CORONAL PULP


* RADICULAR PULP
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Coronal Pulp
located in the pulp chamber in the crown portion of the tooth, including the pulp horns that are directed toward the incisal ridges & cusps tips.
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Radicular Pulp
located in the pulp canal/s in the root portion of the tooth.
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Pulp is composed of
* MYELINATED & UNMYELINATED FIBERS,
* ARTERIES,
* VEINS,
* LYMPH CHANNELS,
* CONNECTIVE TISSUE CELLS,
* INTERCELLULAR SUBSTANCE,
* ODONTOBLASTS,
* FIBROBLASTS,
* MACROPHAGES,
* COLLAGEN, &
* FINE FIBERS
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Functions of the Pulp:
* FORMATIVE
* NUTRITIVE
* SENSORY
* DEFENSIVE
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Formative
production of primary & secondary dentin by the odontoblasts
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Nutritive
supplies nutrients & moisture to the dentin through the blood vascular supply to the odontoblasts & their processes.
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Sensory
provides sensory nerve fibers within the pulp to mediate the sensation of pain.
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Defensive
related to its response to irritation by mechanical, thermal, chemical or bacterial stimuli
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Cementum
hard connective tissue that covers the roots of the teeth.
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Cementoblasts
cementum formation
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Cementoblasts
developed from undifferentiated mesenchymal cells in the connective tissue of the dental follicle
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Cementum: Chemical Formation
Inorganic material: 45 – 50%

* HYDROXYAPATITE

ORGANIC MATTER & WATER: 50 – 55%
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Sharpey’s Fibers
are portions of the collagenous principal fibers of the periodontal ligament embedded in both the cementum & alveolar bone
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2 kinds of Cementum
* ACELLULAR
* CELLULAR
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Acellular
living tissue that does not incorporate cells into its structure & usually predominates on the coronal half of the root
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Cellular
occurs on the apical half
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Cervical line
refers to the cementoenamel junction that is formed when cementum joins the enamel