Dentinogenesis and dentin permeability

Dentinogenesis

and dentin permeability

Dr. Gábor Varga

February, 2016

Department of Oral Biology

Faculty of Dentistry, Semmelweis University

Radiograph of teeth – dentin is the major component

Molar

longitudinal

section

Dentin is the

major

component

of the pulp

Pulp Horn

mantle dentin

tertiary dentin

primary dentin

secundary dentin

predentin

Section of the tooth– types of dentin

I

W

O I

W

O

Wet weight Volume

Constituents of dentin

Water, Inorganic, Organic

Tooth development – details 1

Tooth development – details 2

Section of tooth – pulp is inside

Gene activation during tooth development

Epithelium

Mesenchyme

Differentiation of

odontoblasts

Formation of mantle dentin

during the early phase of

mineralization

Section of the developing tooth

Dentin is produced by odontoblasts

dentin

Predentin

Odontoblasts

Mineralization

front

Mesenchyme

Cross section of a rat insicor illustrating mature secretory odontoblasts

Odontoblast

structure

Mature secretory odontoblast

Involvement of hard tissue proteins in mineral

formation

Interaction of odontoblast secretory products

in predentin, dentin and the mineralization

front

Light microscopic autoradiographs of the

utilization of tritiated proline by odontoblasts at

various time periods after intravenous injection

Collagen fibers are visible after

dissolution of the mineral phase

- dentine tubules are visible

Collagen fibers around

tubules

(A) Primary, (B) secondary and (C) tertiary

or reparative dentin

Dentinogenesis Imperfecta

Dentin phosphoprotein (DPP), a highly acidic

protein, is the major noncollagenous component of

dentin, being solely expressed by the ectomesenchymal

derived odontoblast cells of the tooth. Takagi and

Sasaki (1988) suggested that a deficiency of this protein

is a causative factor factor in dentinogenesis

imperfecta (DGI1; 125490). MacDougall et al. (1997)

demonstrated that 2 major noncollagenous dentin matrix

proteins, dentin sialoprotein (DSP) and dentin

phosphoprotein (also known as phosphophoryn) are

encoded by a single

gene termed dentin sialophosphoprotein (DSPP).

Dentinogenesis Imperfecta

Characteristics

– autosomal dominant

(1:8000)

– Opalescent teeth

– Irregular structure and

hypomineralized dentin,

grey or dark

yellow/brown

Dentinogenesis Imperfecta

Radiology

Onion- or tulip-like tooth

crown

large pulp chamber, narrow

dentin matrix

Dentin permeability, dentin sensitivity

Dentin tubules, inter tubular

and intratubular dentin

Components of dentin

20000/mm2

45000/mm2 0,2-1,0 μm

Number

Diameter

Permeability: the number and the

diameter change depending on the dentin

tubules

Entrance of a dentine tubule

The empty dentin tubules provide the basis

for permeability - longitudinal section

Mineral deposits narrow down dentin

tubules

Debris closing the entrance of dentin tubules

Components of dentin tubules besides

extracellular fluid

Electron micrographs of the odontoblastic process

and nerve ending in dentin

Neuronal network of pulp/dentin

Nerve endings in dentin

Diffusion - Fick’s 2nd law

Js=DsAs / (∆Cs∆x)

• Js: diffusion rate

• Ds: diffusion coefficient

• As: size of cross sectional surface

• ∆Cs: concentration gradient

• ∆x: length

Hagen – Poiseuielle equation

- fluid movement -

basis of the hydrodynamic theory

V=π∆Pr4 / 8ηL

• V: fluid movement

• ∆P: pressure difference

• r: radius

• η: viscosity

• L: length

Dentine sensitivity

• Dentinal tubules pass from pulp to dentine

surface

• Contain dentinal fluid

• Pulpal one third of dentine contains

odontoblast processes and some nerve fibres

• Problem: how can dentine transmit stimuli?

Dentine sensitivity

• Hydrodynamic theory of dentine sensitivity

- fluid movement and pressure changes

• Is sensitivity due to nerve fibers in tubules?

• or movement of odontoblasts?

• Could odontoblasts be sensory endorgans?

• Are nerve fibers in the subodontoblastic plexus

the actual sensors?

Dentine sensitivity

• Great variation between subjects

• secondary dentine and sclerosis of dentine

In a caries lesion, cariogenic bacteria invade the

dentinal tubules, demineralizing sclerotic and

peritubular dentin in the process

Current concepts of the generation of dentinal pain

General position of afferent nerve endings in the

odontoblastic layer, the predentin, and the dentin

Od: odontoblastic layer, SP: substance P, CGRP: calcitonin gene- releated peptide, BV: blood

vessels, PAN: primary afferent nociceptor, SPGN: sympathetic postganglionic nerves

Substance P-

immunreactive nerve

fibers (Nf) and nerve

endings ( ) of the

odontoblastic plexus

beneath a pulp horn.

D: dentin

Potential mechanisms that lead to the sensitization of

primary afferent nociceptors (PAN)

Sensitization of primary afferent nociceptors (PAN)

by arachidonic acid (AA) cascade and phospholipase A-

aktivating protein (PALP)

The rate of pain also depends on the level of heat

exposure

Pain development: gate control theory

A: stimulator effect, SG: spinal ganglion, B: interneuron, T: transmitting neurons

Dentine hypersensivity

Treatment

• To obliterate tubules by deposition of calcium salts

• To block tubules by protein precipitation

• To hyperpolarize or depolarize nerve fibers by altering ionic environment