Dentine

Dentine

Physical properties

• Pale yellow • HardnessE>d>bone and cementum . (compressive,tensile,flexural )strength >E

CHEMICAL PROPERTIES

• BY WEIGHT BY VOLUME 70%INORGANIC 50%INORGANIC 20%ORGANIC 30%ORGANIC 10%WATER 20%WATER

CHEMICAL PROPERTIES

Inorganic : (hydroxyapetite crystals ):Smaller than E.Found between collagen fibrils Calcium poor Carbonate rich

Organic(organic matrix ):Similar to boneFibrils in amorphous ground substance

Organic

Fibrils: 90% of fibrils collagen Collagen type I traces of III +IVRun parallel to pulpal surface

Proteins

Non-collagenous proteins :1. Dentine phosphoproteins (PP-H)Main non-collagenous prtn.Most acidic protein known .Implicated in the process of mineralization .

2.Proteoglycans Decorin BiglycanGlycosaminoglycans(chondrotin-4-sulphate,chondrotin-6-sulphate)Implicated in the process of fibrils assembly,cell adhesion,migration,proliferation,differentiation.

3. δ-carboxyglutamate-containing proteins(Gla-prtns)Implicated in the mineralization process.

4.Acidic proteins OsteonectinOsteopontinGrowth factors:Insulin like growth factor(IL-GF) ,Transforming growth factor (TG-F)Their role is hard to investigate .

lipids

• 2% of the organic content • Role in mineralization • Predentine near mineralizing front • Mineralized dentine”crystal ghosts”…needle

like ..role in growth of crystals ..interglobular dentine .

Dentine tubules

• Run From pulp to D-E junction ,C-E junction.• Sigmoid ,curved course (primary curvature)

(primary curvature ):

• convexity nearest pulp faces rootward

• In root and under cusps its less pronounced .

Secondary curvatures

TRANSVERSE SECTIONS:Appear Circular • Taper 2.5ɱm to 1ɱm from pulp to periphery .• During formation of dentine tubules by the

odontoblasts the cells migrate inward and occupy a smaller surface area,hence the tubules are separted more widely at the periphery .

So …

Dentinal tubules

• Branch profusely near E-D junction .(a reflection of the branching of odonoblastic process ).

• In the root tubules branch and loop (“grandular layer of Tome’s) ..the branching becomes obvious near pulp (predentine )

Peritubular dentine(intratubular dentine )

• Walls of tubules are made of collagen typeI• Peritubular dentine lacks collagenous fibrous

matrix.• Layed down on walls and narrows the size of

the lumen untill obliterates tubule completely.

• 15% more mineralized

• Saliva occluding factor in

• Found around the same time we start seeing intertubular dentine …by eruption we can see it from E-d junction to 100-50ɱm of predintine .

Intratubular dentine

• In root they occlude tubules completely with age “transluscent dentine “Transulscent dentine increases with age Tubules filled with water appear opaque This feature used in forensic medicine to age teeth

Contents of dentinal tubules

1) Odontoblastic process Higher in no. in predentineOccupies most of the tubule in areas near pulp . The process contains :filaments,mitochondria,RER.2) Afferent nerve endingsCrown below cuspsRadioactive aminoacids to view them .3) Antigen presenting cells processes 4) Extracellular fluid (dentinal fluid)Different from other extracellular matirices in higher potassium ions lower sodium ions .

Regional variations

• Mantle dentine (crown)• Granular dentine (root)• hyaline layer(root)• Interglobular dentine(outermost part of

circumpulpal )(crown and root )• Circumpulpal dentine (crown and root)• Intermediate dentine • Predintine

Regional variations

Enamel or cementum

Mantle dentine

Circumpulpal dentine

Intermediate dentine (minerilization)

Predentine

pulp

• Outermost layer in the crown earliest formed dentine

• Outer layer sometimes incomplete minerilization”interglobular dentine”

• Pulpal part secondary dentine• Pulpal to secondary dentine(if present) tertiiary dentine)

Mantle dentine

• 20-150 ɱm• Earliest formed dentine in crown (near e-d junction).• Different from circumpulpal dentine:1. Less mineralized 2. Collagen fibers perpendicular to E-D junction.3. Tubules branch profusely here.4. Mineralization in the presence of matrix vesicles.• Seen in light microscopy of ground and

demineralized sections.

Interglobular dentine

• Beneath mantle in crown ,beneath granular in root .

• Fusion of globules and calcospherites at mineralization is incomplete.

• Tubules pass through this area withouit deviation but LACK peritubular dentine in this area .

• TEMUNCALCIFIED INTERGLOBULAR AREAS APPEAR DARK

Granular dentine(root)

• Ground sections:peripheries of dentine in root appear dark • Seen in root and not in crown due to different

rate in formation of dentine .• “tree top “appearance • Hypomineralized in comparison to

circumpulpal dentine .

Hyaline layer (root)

• Outside granular layer • Origin is obscure • Narrow band (20ɱm )• Non-tubular,structureless• Bond dentine to cementum • Great importance in periodontal regenration .

Circumpulpal dentine

• Basic structure of dentine (bulk)• Uniform in structure except at its edges Peripherallyinterglobular dentine marks incomplete minerlization intially.Centrallyminerlizing front .In older teeth ,pulpal surface modified secondary and tertiary denitne .

predentine

• Function of odontoblastic process here issecretion of matrix component .

While in minerlizing dentine modificatuon of matirx. And mineraliztion .Width vary(10-40 ɱm) according to rate of dentine deposition,so its wider in young teeth .

Structutral lines

• originatinf from• 1-tubular curvatures• 2-incrimintal deposition .

Primary curvature lines “shreger lines”

• Longitudenal sections Peaks of primary curvatures coincide Broad band• Horizontal sections:Difficult to be seen Seem like a broad concentric bands in circumpulpal dentine

Secondary curvature lines“contour lines of owen “

• Secondary curvature lines coincide • Unusal in primary dentine but sometimes

seen

Exaggerated lines

• Between primary and secondary dentine • Between dentine formed before birth and

after “neonatal line “ marking different mineralization and matirx composition

Incrimintal lines

• Seen in ground,demenralized,under polarized light and in microradiographs.

• Long period lines “andersen lines”:changes in collagen fibril orientation . In polarized light enhanced lines.16-20ɱm apart Between each 2 long period lines 6-10 pairs of short lines. (similar to enamel striae and cross striations )

• Short period”von ebner’s lines” :

• alternating dark and light bands.• Under cusps(formation of dentine is fast ).

Age related and posteruptive changes

• Secondary dentine • Tertiary dentine • Sclerotic dentine • Dead tracts

Secondary dentine

• Very similar to primary dentine • Change in the direction of odontoblast • Tubular pattern is a little less regular • Incremental markings closer together • Begins at the completion of root formation.• Tooth comes into occlusion but Seen in

unerupted teeth .• Mostly on pulpal floor

Tertiary dentine (irregular secondary dentine,reparative dentine,reactionary dentine,response

dentine,osteodentine)

• In response Stimuli:caries,attrition,leakage,trauma.• Could be tubular or atubular• Contiuity with normal dentine is lost • Process:pulp induces odontoblast-like cells to produce mineralized tissue.• Similar in producing collagen type I and sialoprotein.• What about epithelial cells /mesenchymal cells

interaction ?

Sclerotic dentine

• Like intratubular dentine but as a result of stilmulus(slowly advancing caries,areas of severe attrition.

• Appear transparent • Material that fills is diffenert from intratubular

dentine.• Could be derived from saliva .

Dead tracts

• Empty tubules Due to dead odontoblast,or odontoblast retracts before intratubular dentine occludes tubule.

• Ground sections:Mounting medium will not enter Transmitted light will be reflected completelyDark

Clinical considerations

• Permeability • Response to external stimuli (actually from

pulp)• Bonding • Endodontics• sensitivity

permeability

Bacteria and its toxins,restoartive materials (itchants ) may pass through tubules .To be considered patent :• Could be exposed by caries,attrition ,abrasion,trauma .• Tubules must be patent Might be occluded by 1peritubular dentine 2exogenous3tertiary dentine• That the interstitial fluid doesn’t wash them out• Able to pass through odontoblast layer (a barrier).

Bonding

• More complex than E . Due to high organic content

• Smear layer

Sensitivity

• Sensitivity :in exposesed dentine (but not always )is sensitive.

Patent dentinal tubules

Could be solved by occluding tubules by smearing or precipitation of fluoride or oxalates.

hypothesis

1. nerves in tubulesScarse Absent in outer parts Application of local anesthesia doesn’t abolis sensitivity .

2.Odontoblastic process not proven to work as nerves Doesn’t reach e-d junctiom Not synaptically connected to nerves

3.Fluid movement in tubule(hydrodynamic hypothesis)Movemet of fluid is sufficent to depolrize nerve endings present deep in tubule Heat ,osmotic pressure,dryingfluid movememt outward.Coldinward Chemicals and thermal stimuli induce a much quicker response than can be explained with diffusion or conduction . But there could be a mix of both ,while hydrodynamic predominates when there is pulpal inflammation.