Lecture 3

Enamel. Dentin and Cementum

**Enamel**

covers the anatomic crown & varies in the thickness in different areas of the tooth.

**Structures of the Teeth**

• Enamel

• Pulp

• Dentin

• Cementum

**Amelogenesis**

enamel formation

**Ameloblasts**

cells responsible for amelogenesis; originate from the embryonic germ layer called ECTODERM

**Color of enamel**

• yellowish white to grayish white

• translucent in nature

**Color of tooth mainly depends upon three (3) factors:**

1. COLOR of underlying dentin

2. THICKNESS of enamel

3. Amount of STAINS in enamel

**Thickness**

**decreases** gradually from **cusps or incisal**

**edges to cemento-enamel junction.**

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

Enamel: Strength

HARDEST CALCIFIED TISSUE in the human body.

Brittle

has a high modulus of elasticity, high compressive strength and low tensile strength

specific gravity

2\.8

Enamel: Chemical Composition

• Inorganic contents: 95% – 98%

• Organic contents: 1 – 2%

• Water: 4 – 12%

Hydroxyapatite

largest mineral constituent

Chemical formula of hydroxyapatite:

Ca10(PO4)6(OH)2

Enamel is composed of:

a) ENAMEL RODS or prisms
b) ROD SHEATHS
c) CEMENTING INTERROD SUBSTANCE

Enamel rods/ prisms

appear as oval, fish scale or keyhole shaped

Enamel rods/ prisms

• largest structural components

• has a head and tail

ENAMEL RODS / PRISMS

aligned perpendicularly to both the DEJ & the tooth surface in the deciduous & permanent teeth

Gnarled Enamel

groups of enamel rods that entwine with adjacent group of rods.

Hunter-Schreger Bands

optical appearance of bands appear to be composed of alternating light and dark zones

Incremental Striae of Retzius

considered as growth rings

Imbrication Lines Pickerill

incomplete circles of striae of retzius at the enamel surface formed a series of alternating grooves.

Perikymata

elevations between the grooves; continuous around a tooth & lie parallel to the cementoenamel junction.

Enamel Tufts

hypomineralized structures of enamel rods & inter-rod substance that project between adjacent groups of enamel rods from the DEJ.

Enamel Lamellae

thin leaflike faults between enamel rod groups that extend from the enamel surface toward the DEJ sometimes extending into the dentin.

Enamel Spindles

• pain receptors

• odontoblastic processes that cross the DEJ into the enamel.

Dentino-Enamel Junction

interface of the enamel & dentin

Fissure

failure or compromised coalescence of the enamel of developmental lobes results in a deep invagination in the groove area of the enamel surface.

Pit

noncoalesced enamel at the deepest point of a fossa.

Nasmyth Membrane

covers the newly erupted tooth and is worn away by mastication and cleansing.

Pellicle

organic deposit which is a precipitate of salivary proteins.

Dental Pulp

• considered as a single tissue with mineralized

• dentin compromising the mature end product of cell differentiation and maturation.

Dentin

forms the largest portion of the tooth structure

Dentinogenesis

dentin formation.

Odontoblasts

cells responsible for dentinogenesis

Dentin: PHYSICAL PROPERTIES

• YELLOWISH in color

• harder than bone but softer than enamel

Dentin: Chemical Properties

• Inorganic contents- 70%

• Organic contents - 20%

• Water- 5%

Dentinal Tubule

small canals that remain from the process of dentinogenesis & extend through the entire width of dentin, form the pulp to the DEJ

Peritubular (Intratubular) Dentin

• dentin that immediately surrounds the dentinal tubules

• more mineralized than intertubular dentin and predentin.

Intertubular Dentin

• located between the dentinal tubules

• less mineralized than peritubular dentin

• main body of dentin.

Predentin

layer that lines the innermost (pulpal) portion of dentin.

Types of DENTIN:

• PRIMARY DENTIN

• SECONDARY DENTIN

• TERTIARY DENTIN

Primary Dentin

• outlines the pulp chamber;

• forms the initial shape of the tooth;

• formed before root completion.

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.

Tertiary Dentin

* produce in reaction to noxious stimuli, such as caries or a restorative dental procedure.

Tertiary Dentin

also referred to as:

• REACTIVE,

• REPARATIVE or

• IRREGULAR SECONDARY DENTIN

Sclerotic Dentin

results from aging or mild irritation & causes change in the composition of the primary dentin.

Dead Tracts

areas of dentinal tubules that are empty & are black when viewed microscopically.

Eburnated Dentin

• outward (exposed) portion of reactive

• sclerotic dentin where slow caries has destroyed formerly overlying tooth structure, leaving a hard, darkened cleanable surface.

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

Deep Dentin

less effective pulpal barrier than superficial dentin near the DEJ or dentinoenamel junction.

Smear Layer

composed of denatured collagen, hydroxyapatite & other cutting debris.

Smear Plugs

serves as a natural bandage over the cut dentinal tubules because it occludes many of the dentinal tubules with debris

Smear Plugs

formed from cutting debris forced into the tubules

Pulp

soft connective tissue that occupies the central portion of the tooth.

Pulp organ is divided into:

• CORONAL PULP

• RADICULAR PULP

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.

Radicular Pulp

located in the pulp canal/s in the root portion of the tooth.

Pulp is composed of

• MYELINATED & UNMYELINATED FIBERS,

• ARTERIES,

• VEINS,

• LYMPH CHANNELS,

• CONNECTIVE TISSUE CELLS,

• INTERCELLULAR SUBSTANCE,

• ODONTOBLASTS,

• FIBROBLASTS,

• MACROPHAGES,

• COLLAGEN, &

• FINE FIBERS

Functions of the Pulp:

• FORMATIVE

• NUTRITIVE

• SENSORY

• DEFENSIVE

Formative

production of primary & secondary dentin by the odontoblasts

Nutritive

supplies nutrients & moisture to the dentin through the blood vascular supply to the odontoblasts & their processes.

Sensory

provides sensory nerve fibers within the pulp to mediate the sensation of pain.

Defensive

related to its response to irritation by mechanical, thermal, chemical or bacterial stimuli

Cementum

hard connective tissue that covers the roots of the teeth.

Cementoblasts

cementum formation

Cementoblasts

developed from undifferentiated mesenchymal cells in the connective tissue of the dental follicle

Cementum: Chemical Formation

Inorganic material: 45 – 50%

* HYDROXYAPATITE

ORGANIC MATTER & WATER: 50 – 55%

Sharpey’s Fibers

are portions of the collagenous principal fibers of the periodontal ligament embedded in both the cementum & alveolar bone

2 kinds of Cementum

• ACELLULAR

• CELLULAR

Acellular

living tissue that does not incorporate cells into its structure & usually predominates on the coronal half of the root

Cellular

occurs on the apical half

Cervical line

refers to the cementoenamel junction that is formed when cementum joins the enamel