dentin

What forms the bulk of the tooth?

What forms the bulk of the tooth?

dentin

what provides the general shape & form of tooth

dentin

what is dentin covered by

Enamel of anatomic crown Cementum of anatomic root

Enamel in decalcified section

Lost because enamel is 96% mineral Enamel is called Enamel space in decalcified sections

what structures are not seen in ground sections

Soft tissue (pulp, PDL, gingiva)

where are enamel and dentin bound

dentino-enamel junction

shape of DEJ

scalloped (convex towards dentin)

Why is the DEJ scalloped?

To provide more surface area for enamel-dentin adhesion = firm attachment

junction between root and dentin

dentino-cemental junction (less distinct & smooth)

where could DCJ be scalloped?

deciduous teeth

Dentin-pulp complex

Have same embryonic origin (dental papilla) and integrated histologically & functionally

Dentin is the calcified product of pulp Pulp provides vitality to dentin

General characteristics of dentin

Sensitive (pain) Unique to teeth Cellular (odontoblastic processes) Avascular Dynamic (ion exchange w/ environment = demineralization & remineralization) Ability to repair (tertiary dentin)

Color of dentin

Light yellow (becomes darker w/ age)

how does dentin prevent fracture of brittle enamel

Dentin is elastic

hardness of dentin

Slightly harder than bone and cementum Less hard than enamel

Resistance of dentin

Less resistant (Highly prone) to attrition, abrasion & erosion compared to enamel

thickness of enamel vs. color of tooth

Light can readily pass through enamel and reflected by underlying dentin Thick enamel does not permit light through = whiter crown

where are cells of dentin

Odontoblasts are in pulp Odontoblastic processes are in dentin

Radiographic appearance of dentin

More radiolucent than enamel More radiopaque than pulp

Strengths of dentin compared to enamel

-Less compressive strength -Higher tensile strength -Higher flexural strength -More resistant to fracture

Compressive strengths of enamel and dentin

Enamel = 384 mpa Dentin= 297 mpa

Tensile strengths of enamel & dentin

Enamel = 10 mpa Dentin = 98 mpa

Permeability of dentin

Highly permeable Decreases with age permeable to small substances

permeability of dentin depends on

size & patency of dentinal tubules

clinical significance of high permeability of dentin

Therapeutic substances applied to exposed dentin diffuse to pulp Help remineralization of dentin

Chemical composition of dentin

70% Inorganic 20% Organic 10% Water

Inorganic content of dentin (70%)

Hydroxyapatite crystals (same shape but smaller than enamel)

C10(PO4)6(OH)2

Carbonate (high), Fluoride, Sodium, Mg

Organic content of dentin

90% of organic content = Collagen 10% of organic content = Non-collagenous proteins & lipids

collagen fibers in organic content of dentin

Type 1 Type 3 Type 4

what type of collagen predominates in dentin

type 1

Non-collagenous proteins & lipids in dentin (organic)

Dentin phosphoprotein Dentin sialoprotein Dentin matrix protein Osteonectin Osteocalcin Osteopontin Bone sialoprotein Proteoglycans

Function of collagen in dentin

Rigidity Type 1 acts as scaffold to accommodate minerals in fibrils

function of phosphoproteins in dentin

Binds to calcium Binds to collagen to initiate crystal formation

function of sialoproteins in dentin

Inhibits growth of peritubular dentin to prevent occlusion of dentinal tubules

Mutation of what protein causes dentinogenesis imperfecta

Sialophosphoproteins

function of growth factors in dentin

induce production of tertiary dentin

function of enzymes in organic content of dentin

Catalyze reactions

function of phospholipids in organic content on dentin

role in Mineralization

where are phospholipids found in dentin

pre-dentin & dentin

function of proteoglycans in dentin

prevent premature mineralization until collagen fibrils attain final destination

proteoglycans are found more in

Predentin

Types of dentin according to Time of formation

-Primary dentin (predentin, mantle dentin, circumpulpal dentin) -Secondary dentin

Types of dentin according to Dentinal tubules

-Peritubular dentin (around dentinal tubule) -Intertubular dentin (between dentinal tubules)

Types of dentin according to Injury

-Tertiary dentin (reparative & reactionary) -Sclerotic dentin (dentinal tubules full of mineral) -Dead tracts (dentinal tubule full of air)

Types of dentin according to defect in mineralization

-Interglobular or globular dentin (Hypocalcified)

Sclerotic dentin & dead tracts are the

opposite of each other

When is primary dentin formed?

During tooth development (before closure of apical foramen)

when does primary dentin formation end

when root formation is complete

Outermost layer of primary dentin

mantle dentin

main bulk of primary dentin

Circumpulpal dentin

when does secondary dentin formation start

after root formation is complete

secondary dentin occurs due to

continuous slow deposition of dentin

where is secondary dentin seen

Roof & floor of pulp chamber

Pulp recession

Sign of aging in pulp; decrease in size due to the formation of secondary or tertiary dentin = pulp horns recede down

In cavity preparation in elderly, less chance of pulp exposure

Inorganic:organic content of secondary dentin

Similar to primary dentin # of dentinal tubules is less

junction between primary and secondary dentin

Slight diff staining and Less regular organization of dentinal tubules

what is the first formed dentin

Mantle dentin Formed even before enamel

where does mantle dentin lie

below dentinoenamel junction

Adjacent to DEJ and DCJ

mantle dentin is

Outermost layer of dentin Closest to enamel

thickness of mantle dentin

20um

Korff's fibers

First formed large, distinct collagen fibers of dentin (collagen type 3)

type of collagen in korff's fibers

type 3 collagen

what is predentin

Initial, non-mineralized layer of dentin close to pulp

thickness of predentin

2-6 microns thick

Predentin becomes

dentin, and a new layer of predentin forms below it

content of predentin

Only collagen No mineral (phospholipids help mineralization)

Type of predentin depends on

time of formation / time of sectioning

predentin before root completion belongs to

primary dentin

predentin after root completion belongs to

secondary dentin

predentin after injury belongs to

Tertiary dentin

tertiary dentin is deposited at specific sites in response to

injury (caries, attrition, abrasion, cavity preparation)

rate of deposition of tertiary dentin is proportional to

injury

tertiary dentin is seen anywhere along

pulp-dentin complex

dentinal tubules in tertiary dentin

Irregular Cell inclusions

Osteodentin

Dentin that resembles bone (having cell inclusions) Formed in tertiary dentin in response to injury

Types of tertiary dentin

Reparative Reactionary

Reparative tertiary dentin

Formed by newly differentiated odontoblasts

Reactionary tertiary dentin

Formed by pre-existing odontoblasts

What is peritubular dentin?

dentin that forms walls around dentinal tubules

mineralization of peritubular dentin

40% more mineralized than intertubular dentin

collagen in peritubular dentin

less than intertubular dentin

location of intertubular dentin

between dentinal tubules Form main body of dentin

intertubular dentin forms

main body of dentin

intertubular dentin represents

primary secretory product of odontoblasts

intertubular dentin consists of

Type 1 collagen network in which apatite crystals are deposited

histology of dentin

¢Dentinal tubules & Odontoblastic process ¢Peritubular dentin ¢Intertubular dentin ¢Interglobular dentin ¢Incremental lines of von Ebner ¢Tomes granular layer ¢Sclerotic dentin ¢Dead tracts ¢Enamel spindles

# of dentinal tubules

30,000 - 70,000 /mm2

diameter of dentinal tubules

Near pulp: 3 um Near enamel: 1 um

Taper from pulp to be narrowest at DEJ

dentinal tubules extend from

pulp to DEJ and DCJ

shape of dentinal tubules

Curved S shape

why are dentinal tubules branched

form a network for nutrients diffusion

lateral branches of dentinal tubules are called

Canaliculi

diameter of canaliculi

1 um

canaliculi are at right angle to

main dentinal tubule

function of dentinal tubules

Responsible for permeability of dentin Pathway for microbial invasion of dentin

content of dentinal tubules

-Odontoblastic processes (microtubules & intermediate filaments) -Dentinal fluid -Thin nerve fibrils -Peritubular dentin -Inner organic lining (Lamina limitans)

what is lamina limitans

Plasma membrane of odontoblastic processes that is rich in GAG

what is the major component of dentinal tubules

odontoblastic processes

enamel spindles

-Extensions of odontoblastic processes into enamel crossing DEJ -Odontoblastic processes dont withdraw quick enough after stimulating pre-ameloblasts & remain stuck in enamel

curvatures of dentinal tubules

Primary curvature Secondary curvature