(Finals) OHE Laboratory: Enamel, Dentin, and Pulp

Enamel

Hardest calcified matrix of the body.

Ameloblasts

The cells that are responsible for formation of enamel, the ________, are lost as the tooth erupts into the oral cavity, and hence enamel cannot renew itself.

Because it has a complex structure and is highly mineralized, thanks to having almost no organic material when mature.

Why is enamel strong despite having limitations?

Translucent, light yellow - grayish white

Color of Enamel?

On its thickness

More translucent = more yellow (because the underlying dentin becomes more visible)

Where does the color of the Enamel depends on?

Because enamel is translucent—when it’s thinner, more of the yellow dentin underneath shows through.

Why does enamel sometimes look yellow?

Acids

Enamel is soluble in ______.

Inorganic Material: 96% Hydroxyapatite Crystals

Organic Material: 4% Proteins & Water

What are the chemical conposition of enamel?

Enamel is very hard due to its high mineral content and structure, helping it resist chewing forces. But it's also brittle, so it needs the softer dentin underneath for support.

Very hard = bcos of high mineral content

Brittle = needs softer dentin for support

Why is enamel hard but brittle?

Enamel Rods

• Basic structural units of enamel.

• AKA enamel prisms.

• First described as hexagonal and prism-like in cross-section.

• They have a fishtail appearance, extend through the entire enamel thickness perpendicular to the DEJ, are thickest at cusps/incisal edges, and thinnest at the cervical region.

• Gnarled enamel rods refer to their intertwining pathways.

Gnarled Enamel Rods

Refers to enamel rods intertwinning pathways.

Enamel Rod Sheath

• Covers enamel rods

• Slightly more mineralized than the rod itself.

• Has a fish scale appearance.

Interrod Enamel

• AKA interprismatic substance

• Ccements enamel rods together

Aprismatic Enamel

Prismless and is more mineralized than enamel beneath it

Incremental Lines of Retzius

• Brown lines extending from the DEJ to the tooth surface (longitudinal section); dark concentric rings (transverse section)

• Appositional or incremental growth of enamel

• Marks primary calcification of enamel

Neonatal Line

Accentuated or more pronounced incremental line (of Retzius)

Transverse Striations

• Crosses bands of Retzius

• Appositional growth of enamel of 4 μm/day

Hunter-Schreger Bands

• Alternate light and dark banding pattern resulting from changes in the direction of enamel rods

• Prevents fracture of enamel

Enamel Tufts

• Hypomineralized groups of enamel rods that appear as short, fan-shaped, dark projections near or at the DEJ

• Originates from dentino-enamel junction

• Lateral spread of caries happen through this structure

• Sheet-like cracks on the surface of enamel extending to its entire thickness

• Pathway for bacteria to penetrate the enamel

Enamel Spindle

• Extensions of dentinal tubules that cross into the enamel through the DEJ.

• May cause hypersensitivity.

• Remnants of odontoblastic processes that became entrapped.

Dentino-enamel Junction

• Scalloped appearance

• For attachment

1. Pits and Fissures

2. Mamelons

3. Perikymata/Imbrication Lines of Pickeril

What are the macroscopic structures for ENAMEL?

Perikymata/Imbrication Lines of Pickeril

Termination of line of Retzius on the tooth surface

DENTIN

hard tissue portion of the pulp-dentin complex that forms the bulk of the tooth

DENTIN

• Bonelike matrix characterized by multiple closely packed dentinal tubules that traverse its entire thickness

• Contain the cytoplasmic extensions of odontoblasts that once formed the dentin and then maintain it.

Yellow

What is the color of Dentin?

Dentin

Avascular

Dentin

Harder than bone but softer than enamel.

Inorganic material: 70% - Made up of hydroxyapatite crystals

Organic material: 30% - Type I collagen and water

What are the chemical composition of dentin?

Primary Dentin

• Starts to form from odontogenesis until apical foramen formation

• Formed before root completion

Secondary Dentin

• Slower deposition

• Formed after root completion

Secondary Dentin

• Formed in response to outside or noxious stimuli

• Two forms:

  1. Reactionary dentin: formed by existing odontoblasts

  2. Reparative dentin: formed by new odontoblasts in response to trauma (e.g. caries, restorations, attrition, erosion, abrasion, etc.)

Reactionary dentin

Formed by existing odontoblasts.

Reparative denti

Formed by new odontoblasts in response to trauma (e.g. caries, restorations, attrition, erosion, abrasion, etc.)

Dentinal Tubules

• Extends from the DEJ to the pulp chamber

• Diameter gets wider as it gets closer to the pulp

• Contains three structures

Odontoblastic Process (Dentinal Tubules)

Extension of odontoblast

Periodontoblastic space (Dentinal Tubules)

Contains dentinal fluid

Intratubular Nerve

From plexus of Raschkow

• Peritubular Dentin

• Intertubular Dentin

• Interglobular Dentin

By proximity to Dentinal Tubules

• Coronal Dentin

• Radicular Dentin

By location

• Mantle Dentin

• Circumpulpal Dentin

By time of formation

Peritubular Dentin

• Hypermineralized dentin formed within the perimeter of dentinal tubules as odontoblastic processes shrink

• Covers dentinal tubule

Intertubular Dentin

• Hypomineralized dentin located between the dentinal tubules

• Makes up the bulk of the dentin formed

Interglobular Dentin

• Hypomineralized dentin located between improperly fused globules of hydroxyapatite

• Found chiefly in primary dentin especially in the crown)

Coronal Dentin

May contain hypomineralized interglobular dentin and dead tracts

Radicular Dentin

May contain hypomineralized Tomes’ granular layer

Mantle Dentin

Outermost layer of dentin; first formed dentin located closest to enamel and cementum

Circumpalpal Dentin

All dentin formed thereafter until tooth formation is complete; dentin intervening between mantle dentin and predentin

Predentin

• AKA Dentinoid

• A narrow layer of uncalcified dentinal matrix immediately next to the odontoblasts.

• Significance: as long as the pulp remains vital there will be continuous deposition of dentin

Intermediate Dentin

Dentin found between primary and predentin

Incremental or Imbrication line

Fine lines or striations that mark the daily appositional growth of dentin (4-8 micron interval).

• Wide rings produced by metabolic disturbances during odontogenesis that run perpendicular to dentinal tubules

• Neonatal line: a more pronounced contour line of Owen formed during the physiologic trauma at birth

Granular Layer of Tomes

Looping of terminal tubules

Sclerotic Dentin

• Part of primary dentin where there is calcification of the vital contents of dentinal tubules

• Results as one ages over time to help prevent pulpal irritation

Dead Tracts

Part of primary dentin where the vital contents of tubules degenerate leaving the tubules empty and filled with air

Hydrodynamic Theory of Brannstrom

Movement of dentinal fluid in tubules irritates odontoblastic processes sending pain signals to the brain.

PULP

Soft, specialized connective tissue that supports the dentin

PULP

Contained inside the pulp chamber of the tooth and communicates to the periodontal tissues via the apical foramen and accessory canals

PULP

Consists of lymphatics, nerves, and blood vessels

Organic material: 100% - Collagen Type Iand III

What is the chemical composition of the Pulp?

Formative (Function of a Pulp)

Has mesenchymal cells that ultimately form dentin

Nutritive (Function of a Pulp)

Nourishes the avascular dentin

Sensory (Function of a Pulp)

Free nerve endings provide pain sensation

Protective (Function of a Pulp)

Produces reparative as needed

• Odontoblastic zone

• Cell-free zone of Weil

• Cell-rich zone

• Pulp core

When its histologic appearance is examined, four distinct zones can be distinguished (from outermost to innermost):

Odontoblastic Zone

A signle layer of odontoblast lining the pulp chamber

Cell-free zone of Weil

Devoid of cells (except during dentinogenesis). Contains the parietal plexus of nerves (Raschkow’s plexus) and a plexus of blood vessels (including arteriovenous anastamoses)

Cell-rich Zone

Contains fibroblasts and undifferentiated mesenchymal cells

Pulp Core

Contains fibroblasts, macrophages, leukocytes, blood and lymph vessels, myelinated (mostly Aδ) and unmyelinated (C) sympathetic nerve fibers, collagen types I and III, and ground substance