8 dentin.ppt

Dentin Dr Sandeep Gupta Oral Pathologist  INTRODUCTION Dentin is hard tissue portion Bulk of tooth Protects pulp Supports enamel 2  DENTIN PULP COMPLEX? RELATED Embryologically Histologically Functionally  Types of de...

Dentin Dr Sandeep Gupta Oral Pathologist  INTRODUCTION Dentin is hard tissue portion Bulk of tooth Protects pulp Supports enamel 2  DENTIN PULP COMPLEX? RELATED Embryologically Histologically Functionally  Types of dentin Coronal dentin Radicular dentin Primary dentin Secondary dentin Tertiary dentin  Primary dentin Mantle dentin Circumpulpal dentin Tertiary dentin Reactionary dentin Reparative dentin Osteodentin  Sclerotic dentin Intratubular dentin Intertubular dentin Interglobular dentin Predentin  Dentinogenesis Primary dentin can be of two types Mantle dentin – occupies the peripheral area where the basement membrane was earlier present Circumpulpal dentin – remaining larger segment of dentin  Odontoblast differentiation Important in understanding formation of normal dentin and reparative dentin too  Mantle dentin formation Odontoblasts differentiate from ectomesenchymal cells ↓ Secrete organic matrix collagen (type III) into preexisting ground substance of dental papilla ↓ The collagen fibrils are of large diameter (0.1-0.2μm called von Korff’s fibres) ↓ These intermingle with the aperiodic fibrils (type VII collagen ) dangling from the basal lamina and are aligned at right angles to the basal lamina  Organic matrix of mantle dentin thus contains these large diameter collagen fibrils along with the ground substance ↓ Also the odontoblast gives out short stubby processes, one of which may penetrate the basal lamina – enamel spindles ↓ The odontoblast also bud off a number of small membrane bound vesicles called matrix vesicles  Odontoblast retreat backwards towards the pulp ↓ short stubby processes of the odontoblast becomes accentuated and forms the principal extension of the cell called odontoblastic process ↓ Matrix vesicles lie between the collagen fibrils ↓ Matrix vesicles contain calcium and phosphate ions, alkaline phosphatase enzyme and calcium binding lipids ↓ This permits formation of hydroxyapatite crystals within the matrix vesicles  Once crystals are formed in the matrix vesicle, membrane around the vesicle disappears ↓ The crystals grow and more crystals form around them ↓ Islands of calcifications are formed that fuse ↓ Collagen fibrils are obscured ↓ Deposition of mineral lags behind the organic matrix formation ↓ There is always a layer of unmineralised matrix called predentin between the odontoblast and the mineralising front Circumpulpal dentin formation Intercellular space between the odontoblast is obliterated - the organic matrix has no contribution from the subodontoblastic layer Collagen fibrils are smaller, type I & closely packed and interwoven with each other and aligned at right angles to the odontoblastic process No matrix vesicles. Mineralisation involves heterogenous nucleation  Control of mineralisation Mineral deposition In matrix vesicles At the mineralization front Calcium channels Alkaline phosphatase activity Calcium ATPase activity  Pattern of mineralization 2 types – depending on rate of dentin formation Globular – best seen in mantle dentin Linear – when rate of formation is slow Both types – circumpulpal dentin  Formation of root dentin Differentiation of odontoblasts is initiated by epithelial cells of HERS Radicular dentin is structurally and compositionally different from coronal dentin  Initial collagen fibres are deposited parallel to the CDJ in contrast to mantle dentin formation (Initial collagen fibres are deposited perpendicular to the DEJ) Radicular odontoblasts differ from those of the crown in that they develop fine branches which loop. This forms the Tomes granular layer  Large number of interglobular areas and incorporation of some epithelial remnants into peripheral dentin – due to difference in the origin of IEE cells and also breakdown of HERS Radicular dentin forms at a slower rate Initial calcospherites are smaller  Physical properties Color: Light yellowish Becomes darker with age  Hardness: Harder than bone and cementum Softer than enamel – more radiolucent than enamel Harder in the central part than near the pulp or on its periphery Dentin of primary teeth slightly harder than that of permanent teeth Viscoelastic and subject to slight deformation  Strength: Organic matrix and tubular architecture – greater compressive strength, tensile and flexural strength than enamel Permeability: Depends on size and patency of tubules which will decline with age  Chemical composition Inorganic content: 70% Hydroxyapatite crystals – plate shaped and smaller than enamel Phosphates, Carbonates, sulfates, Fluoride Organic content: 20% Collagen type I, III, V – not arranged in bundles Lipids Non collagenous proteins Water: 10% NON COLLAGENOUS PROTEINS- Includes-  Amelogenins  Dentin Phosphoprotein/Phosphoryn(DPP)  Dentin Sialoprotein(DSP)  Dentin Glycoprotein(DGP)  Mantle dentin First formed mineralised dentin Outermost part of primary dentin Seen in the crown between DEJ and interglobular dentin  Seen in the root underlying the Tomes granular layer About 20 μm thick Fibrils are perpendicular to DEJ and are larger in size than those in circumpulpal dentin Has fewer defects than circumpulpal dentin  Circumpulpal dentin Forms the bulk of the tooth and the dentin that is formed before the root formation is complete Collagen fibrils are smaller, closely packed More mineralised than mantle dentin (4%)  Secondary dentin Represents dentin formed after the root formation is complete A narrow band of dentin bordering the pulp Has fewer tubules than primary dentin There is a bend between primary dentin and secondary dentin  Tertiary dentin Reactive, reparative, or irregular secondary dentin Localised formation of dentin on the pulp dentin border - Produced only by cells directly affected  Produced in reaction to various stimuli – attrition, caries, restorative procedures Tubules may be Regular Irregular and sparse in number No tubules at all Osteodentin – odontoblasts entrapped in dentin; mimicking osteocytes in bone  Dentinal tubules COURSE: S shaped curve - called PRIMARY CURVATURE Doubly curved course starting at right angles to the pulpal surface and ending perpendicular to the DEJ and CDJ  First convexity is directed towards the apex of the tooth Course taken by odontoblasts during dentinogenesis. They crowd as they move from DEJ towards the pulp SECONDARY CURVATURES Smaller oscillations within the primary curvatures  EXTENT: Crown – DEJ to pulp Root – CDJ to pulp Tubules are longer than the thickness of dentin DIAMETER: 2.5μm near pulp 1.2μm in mid portion 900nm near the DEJ  DENSITY Tubules are farther apart in the periphery and closer near the pulp Number of tubules per unit area on the pulpal and outer surface of dentin is about 4:1 Near the pulpal surface – 50,000 – 90,000 tubules per square mm More tubules per unit area in the crown than in the root  BRANCHING Major: 500-1000μm in diameter Represent terminal branching of tubules More frequent in root dentin than in coronal dentin  Intratubular dentin Also known as peritubular dentin A hypermineralised ring of dentin found within the dentinal tubule (9% or 40% more than that of intertubular dentin) Lost in decalcified sections as they are highly mineralised and appear as empty space surrounding the odontoblastic process  Intertubular dentin Constitutes the main body of the dentin Located between the dentinal tubules or between zones of peritubular dentin Mineralised but retained after decalcification  Interglobular dentin Areas of hypomineralised / unmineralised dentin Found in crown of teeth in the circumpulpal dentin just below mantle dentin where pattern of mineralisation is largely globular  Normal architecture of dentinal tubules remains unchanged as they run uninterruptedly through the interglobular area No intratubular dentin where the tubules pass through the globules  Incremental growth lines Dentinogenesis occurs rhythmically Alternating phases of activity and quiescence Daily rhythmic recurrent deposition of matrix as well as hesitation in daily formative process is represented as incremental lines of von Ebner  Seen best in longitudinal sections Run at right angles to the dentinal tubules Distance between the lines varies from 4-8 μm in crown and much less in root Daily increment decreases after a tooth reaches functional occlusion  Contour lines of Owen Accentuated incremental lines Disturbance in matrix and mineralisation process They represent hypocalcified areas Earlier referred to a line resulting from coincidence of secondary curvatures of neighbouring dentinal tubules  Neonatal line Accentuated contour line Seen in deciduous teeth and permanent first molars Reflects abrupt change in environment that occurs at birth  Separates prenatal dentin and post natal dentin Dentin matrix formed before birth is of better quality May be a zone of hypocalcification  Tomes granular layer In dry ground sections – granular zone adjacent to cementum in transmitted light Increases in amount from CEJ to root apex Caused by coalescing and looping of terminal portions of dentinal tubules  Earlier thought to be minute hypomineralised areas of interglobular dentin These are spaces seen only in ground sections and not in H&E stained sections OR electron micrographs Looping is said to be related to lower rate of dentin formation in the root  Predentin Located adjacent to pulp tissue 2-6 μm wide unmineralised dentin  As collagen fibres undergo mineralisation at the predentin-dentin junction, predentin becomes dentin and a new layer of predentin forms circumpulpally In mineralised dentin, collagen fibrils are of larger diameter (100nm) and more closely packed than in predentin Odontoblastic process / Tomes fibres These are cytoplasmic extensions of the odontoblasts Odontoblasts are seen at the pulp- predentin border and the processes extend into the dentinal tubules  Largest in diameter near the pulp (3-4 μm) In dentin it tapers to 1 μm Diameter of cell body of odontoblast is 7 μm and length is 40 μm  Extent of odontoblastic processes into dentin – Enamel spindles  Dentinal junctions Dentinoenamel junction (DEJ) Cementodentinal junction (CDJ)  Age changes Vitality of dentin Reparative dentin Dead tracts Sclerotic dentin  Vitality Has odontoblast and its process as an integral part Has the capacity to react to physiologic and pathologic stimuli Dentin is laid down throughout life  Reparative dentin Abrasion, erosion, caries, operative procedures – odontoblast processes are exposed or cut, odontoblasts die or form reparative dentin Odontoblasts killed are replaced by migration of undifferentiated cells (cell rich zone / undifferentiated perivascular cells)  Dead tracts Odontoblastic process may be lost – caries, attrition, abrasion, cavity preparation, erosion especially in area of narrow pulp horns due to crowding of odontoblasts Odontoblastic processes disintegrate and the empty tubules are filled with air  Sclerotic dentin Also called transparent dentin – similar refractive indices Stimuli - caries, attrition, abrasion, cavity preparation, erosion Reparative dentin formation Collagen fibres and apatite crystals appear in the dentinal tubules Seen in older individuals especially in the roots  Blocking of tubules – a defensive mechanism of dentin Sclerosis Reduces the permeability of dentin Prolongs pulp vitality Appear white in transmitted light & black in reflected light  Dentin sensitivity 3 theories for pain transmission through dentin Direct neural stimulation Fluid/hydrodynamic theory Transduction theory  Direct neural stimulation Stimuli in some unknown manner reach the nerve endings in the inner dentin  Hydrodynamic theory Most popular and accepted theory Stimuli affect fluid movement in the dentinal tubules Stimuli could be – heat, cold, air blast dessication, mechanical or osmotic pressure Fluid movement – inward/outward causes mechanical disturbance of the nerves closely associated with odontoblast and its process. They act as mechanoreceptors  Transduction theory Odontoblastic process is excited by the stimulus and impulse is transmitted to nerve endings in the inner dentin  CONTENTS OF DENTINAL TUBULES Odontoblastic process Dentinal fluid – dental lymph? Lamina limitans Peritubular dentin Nerve endings – predentin and inner dentin no farther than 100-150 μm from the pulp  Clinical considerations 1mm2 of exposed dentin – 30,000 cells damaged Not be insulted by bacterial toxins, drugs, undue operative trauma, unnecessary thermal changes, irritating restorative materials Sealed with non irritating insulating substance  Spread of caries – Tubular system undermining of enamel at the DEJ Invasion of micrcoorganisms Dentin sensitivity – not a symptom of caries unless pulp is affected  Trauma from operative instruments Aspiration of odontoblast within the tubule Reperative dentin formation – sub odontoblastic layer Thank You