dentin

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Dentin

By: Maaz Khan

Ashfaq Azim

Jawad Ullah Shah

Gulzar Khan2

CONTENTS• INTRODUCTION AND CHEMICAL COMPOSITION

• DENTINOGENESIS

• STRUCTURE OF DENTIN

• TYPES OF DENTIN

• INNERVATION OF DENTIN

• THEORIES OF SENSITIVITY

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Introduction and Chemical composition

• Dentin is a hard bone-like tissue that is present in the crown as well as in the root ofteeth.

• In the crown, dentin is covered by enamel and in the root it is covered by cementum

• Unlike enamel, dentin is a vital tissue containing the cell processes of odontoblasts andneuron

• Mature dentin has 20% organic, 70% inorganic and 10% water by weight .5

• The organic matrix of dentin is collagenous

• It provides resiliency to the crown which is necessary to withstand the forces ofmastication

• The principle inorganic component of dentin is hydroxyapatite crystals

• The high mineral content of dentin makes it harder than bone and cementum butsofter than enamel

• The knoop hardness for dentin is approximately 68 6

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Dentinogenesis

• The formation of dentin is called dentinogenesis, which starts before amelogenesis

• Dentin is formed by odontoblast cells

• Dentinogenesis takes place in two phases:

1. Organic Matrix Formation

2. Mineralization

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Organic Matrix Formation

• Odontoblasts then secrete matrix protein at the apical end of the cell andalong its process

• The secreted matrix is collagenous and not mineralized hence it is calledpredentin

• As the matrix is being secreted the odontoblasts move towards the centre ofthe future pulp

• The matrix that forms around the elongated cell process eventuallymineralizes and the odontoblastic process will lie within a dentinal tubule

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Contd…

• As each day passes predentin is formed along the pulpal boundary, theadjacent predentin that was formed during the previous day mineralizes andbecomes dentin

• During the period of crown development approximately 4µm of dentin is laiddown in every 24 hours

• Incremental deposition and mineralization of dentine begins below thecusps, at the tips of the pulp horns at the DEJ

• Dentinogenesis continues life long but slows down(1µm) , after the tooth iscompletely erupted

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Mineralization

• Early hydroxy apatite crystals deposition in form of fine plates on surface

of collagen fibrils and ground substance

• At first sites of calcification of dentine , crystal deposition appears to take

place radially from common centre in a so called spherulite form

• Factors controlling odontobalstic secretion and mineralization are not

known14

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• Key protiens secreted by odontoblasts that are involved in

Dentinogenesis are;

• Dentine phosphoprotien(DPP): binds to calcium and

transports it to mineralization front

• Osteonectin: inhibits growth of apatite crystal but promotes its

binding to collagen matrix

• Osteopontin: promotes mineralization

• Gla-protein(gamma carboxy glutamic acid): act as

nucleators to attract and concentrate calcium.

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Cont’d…

• Main genes involved in dentinogenesis are

1. MAP1B : For odontoblastic differentiation

2. PHEX: For dentin mineralization

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• General mineralization is slow

• Peritubular region mineralizes at early stage

• Ultimate crystal size is 3nm in thickness and 100 nm in

length

• Dentin-sialoprotien , in mineralizing dentin, affects the

rate of mineral deposition

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ASHFAQ AZIM

ROLL NO: 07

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Structure of Dentin

• Main structure appreciated in an undermicroscope dentin are;

1. Structural lines

2. Dentinal tubules

3. Peritubular dentine

4. Intertubular dentine

5. Interglobular dentine

6. Tomes granular layer 21

1.Structural lines

• Formed due to the rhythmic alternating activity and rest period

of dentin formation

• The organic matrix of dentine is deposited incrementally at A

daily rate of 4µm

• Incremental lines run perpendicular to the dentinal tubules

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3 types of structural lines are seen;

1. Incremental or imbrications' lines of von ebner

2. Contour lines of owen

3. Neonatal line

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Incremental or imbrications' lines of von ebner

INCREMENTAL LINES IN PERITUBULAR DENTIN OF THE

TOOTH THAT CORRESPOND TO DAILY RATE OF

DENTIN FORMATION

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Contour lines of owen

• Representing normal physiological

alterations in the pattern of

mineralization

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Neonatal lines

• Representing an exaggerated contour

line of owen.

• Neonatal lines are seen in all primary

teeth

and the first permanent molars

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Dentinal tubules

• Canal like branched structures extending from pulpal end

to the dentino-enamel junction

• Shallow s-shaped curvature (longitudionally) = PRIMARY

CURVATURE

• Undulations and wavy course along its length =

SECONDARY CURVATURE

• Lateral branches (1-2 microns) containing odontoblast

processes.

• Tubular population ranges from 15000/mm²(at DEJ) and

30000-75000/mm²(at pulpal region)

• Contains: odontoblasts processes, non myelinted nerve

fibres

and dental lymph28

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Peritubular dentine

• Also called INTRA TUBULAR DENTINE

• Hypermineralized dentin(40% more) surrounding the

dentinal tubules

• Formation continues throughout life at very slow rate

which narrows the lumen of dentinal tubules leading

to obliteration and results into formation of sclerotic

dentine

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Intertubular dentine

• Dentin present between adjacent dentinal tubules

• Less mineralized

• Formed by the cell bodies of odontoblasts

• Major organic component is collagen arranged in

bundles perpendicular to D.Tubules

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Interglobular dentine

• Seen when mineralization of dentin begins in

small globular areas that fail to coalesce into a

homogenous mass.

• It’s a mineralization defect

• Generally star shaped with curved outlines of

globular masses

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CONT’D…

• During section preparation organic

matrix in interglobular proteins is lost

and these areas get filled with air,

appearing

• Dark (under transmitted light) and

• Bright(under reflected light)

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Granular dentine

• Also called as Tome’s Granular

Layer

• In longitudional section,

peripheral layer of radicular

dentin adjacent to cementum

appears granular

• Exact nature is not known

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CONT’D…

• Recent review shows that these granules

represent true spaces created by extensive

looping and coalescing terminal portions of

dentinal tubules

Appearing;

• Dark (under transmitted light) and

• Bright(under reflected light)35

Predentin

• Nonmineralized dentine

• Present on pulpal surface

• Comparable to osteoid of bone

• 2-6 micron thick (maybe upto 20 microns)

• Mineralizing front present throughout the life

• Exists due to the mineralization lag

• Act as covering of mineralized dentin and

prevent resorbption

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GULZAR KHAN

ROLL NO: 72

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Types of

dentin

On basis of

Time of Formation

1. Primary Dentine

2. Secondary

Dentine

3. Tertiary Dentine

On Basis of

Relation to Dentinal

tubules

1. Peritubular

Dentine

2. Intratubular

Dentine

3. Intertubular

Dentin

Other

types

1.Predentin

2. Interglobular

Dentine38

1. Primary Dentin

• Physiological dentin formed till root formation completion

• Its of two types;

A. Mantle dentin

B. Circumpulpal dentin

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A. Mantle dentine

• First formed dentin

• 20 microns in thickness

• Derived from dental papilla and lacks

phosphophoryn

• Extends from dej upto zone of interglobular

dentin

• Contains large diameter collagen fibre40

B. Circumpulpal dentin

•Forms remaining part of primary dentine

•Matrix with smaller diameter collagen fibres

•Secreted by odontoblasts and contains phosphophoryn

•More mineralized than mantle dentin41

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2. Secondary dentin

• Physiological dentine formed after root completion

• Formed throught out life

• Continous formation reduces the size of pulp chamber

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3. Tertiary dentin

• Also referred to as IRREGULAR SECONDARY DENTINE

• Tertiary dentin can be reactionary or reparative

• Reactionary dentin is that type of tertiary dentin that isdeposited by the pre-existing odontoblasts

• Reparative dentin is deposited by newly differentiatedodontoblasts

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JAWAD ULLAH SHAH

ROLL NO: 04

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Innervation of dentin

• Innervation throught intratubular nerves

• Nerves accompany 30-70% odontoblastic process in close association

with them

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CONT’D…

• It is believed most of these are terminal processes of the myelinated

nerve fibres of the dental pulp

• Primary afferent somatosensory nerves of the dentine and pulp project to

the descending trigeminal nuclear complex

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3 Theories of dentine sensitivity

1. Direct nerve stimulation

2. Transduction theory

3. Hydrodynamic theory

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1. Direct nerve stimulation

• Nerves present in the dentinal tubules are reponsible

Failure:

• Extreme sensitivity

• Marked sensitivity in pehripehral dentine

• Sensitivity in newly erupted teeth 51

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2. Transduction theory

• Odontoblast act as receptor cells transmitting the impulse to

pulpal nerves

• Odontoblast origin from neural crest cells

Failure:

Experimental studies shows membrane potential of

odontoblast was too low to permit conduction53

3. Hydro-dynamics theory

• Nerves located in peripheral portion of pulp react to local

changes are brought about by mechanical factors

• When dentin is exposed , fluid( dental lymph) is lost

• Hydrostatic equilibrium is disturbed in peripheral pulpal

environment

• Pressue changes stimulate nerves and initiate pain

• Explains why local anesthetics doesnot reduce sentivity in

dentin

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