Dentin-Pulp Complex

Types of dentin

Type	When and how it forms	Notes
Mantle dentin	First dentin, just under the DEJ	Less mineralized; larger collagen fibers
Primary (circumpulpal) dentin	Bulk of dentin, until root completion	Regular tubules
Secondary dentin	After root completion, slowly for life	Physiologic; pulp chamber shrinks with age (roof and floor most)
Tertiary: reactionary	Surviving original odontoblasts respond to a mild stimulus	Tubules continuous with primary dentin
Tertiary: reparative	New odontoblast-like cells after the originals die	Irregular, few or no tubules (e.g., dentin bridge under a pulp cap)
Sclerotic dentin	Tubules filled with mineral (age, slow caries, abrasion)	Glassy look; harder to bond to
Peritubular vs intertubular	Peritubular lines each tubule and is more mineralized; intertubular lies between	Peritubular dentin narrows tubules over time

Dentin is about 70% mineral by weight; its matrix is mainly type I collagen with noncollagenous proteins such as DSPP (mutated in dentinogenesis imperfecta).

Tubules run in a gentle S-curve (primary curvature) in the crown and nearly straight in the root; they are wider and more numerous near the pulp, so deep dentin is more permeable.
Predentin: the unmineralized layer next to the odontoblasts.
Incremental lines: von Ebner lines (daily) and contour lines of Owen (accentuated disturbances).
Interglobular dentin: hypomineralized areas between calcospherites (prominent in vitamin D deficiency); Tomes' granular layer: a granular zone in root dentin beneath cementum.
Dentin sensitivity is explained by the hydrodynamic theory: fluid movement in open tubules stimulates nerve endings near the pulp.

Zone	Contents
Odontoblastic layer	Odontoblast cell bodies; processes extend into tubules
Cell-free zone (of Weil)	Capillaries and the subodontoblastic nerve plexus (of Raschkow)
Cell-rich zone	Fibroblasts and undifferentiated mesenchymal cells (source of replacement odontoblast-like cells)
Pulp core	Larger vessels and nerves

Fibroblasts are the most numerous pulp cells. A-delta fibers (myelinated) give sharp, quick pain to cold; C fibers (unmyelinated) give dull, lingering pain with inflammation.
With age: fewer cells, more fibers, more pulp stones, smaller chamber and canals.

Calling reparative dentin the type made by original odontoblasts: that is reactionary; reparative comes from new cells.
Saying secondary dentin forms only after injury: it forms physiologically after root completion.
Assuming deep dentin is less permeable: tubule density and diameter rise toward the pulp.
Swapping A-delta (sharp) and C fibers (dull, lingering).

Pick an answer to see right away whether it is correct and why.

A dentin bridge forms under a calcium hydroxide pulp cap after the original odontoblasts died. This is:
Which theory best explains dentin hypersensitivity?
The cell-free zone of Weil contains:
Which statement about secondary dentin is correct?
Which pulpal nerve fibers produce dull, poorly localized, lingering pain?

0 of 5 answered

Answer key: 1 A · 2 A · 3 C · 4 A · 5 C