dentin

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Presentation by:Garima singh

1st yr PG

Dentin

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• Primary dentin Vs permanent dentin

• Infected dentin Vs affected dentin

• Smear layer

• Dentin bonding system

• Conclusion

• References

• Introduction

• Composition of dentin

• Dentinogenesis

• Physical properties of dentin

• Histology of dentin

• Types of dentin

• Innnervation of dentin

• Age and functional changes

Contents :

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• Dentin is a mineralized, elastic, yellowish-white, avascular tissue enclosing the central pulp chamber.

• Dentin is characterized by multiple closely packed dentinal tubules that traverse its entire thickness and contain the cytoplasmic extensions of odontoblasts that once formed the dentin and then maintain it.

Introduction

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• Inorganic material 70%– Consist of hydroxyapatite in form of small plates

• Organic material 20%– It is about 90% collagen (mainly type I with small

amount of type III and type V)– noncollagenous matrix proteins and lipids

• Water 10%

Composition of dentin

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• It is a two phase sequence – collagen matrix formation– Mineralization

• Outlines are– Differentiation of odontoblast– Formation of mantle predentin– Mineralization

Dentinogenesis

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• Differentiation of odontoblast is brought about by the expression of signaling molecule and growth factors in cells of IEE

Odontoblast differentiation

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• The first sign of dentin formation is the appearance of distinct, large-diameter collagen fibrils (0.1-0.2 mm in dia) called von Korff’s fibres.

• As odontoblast continue to increases in size, they also produce smaller collagen type I fibrils that orient themselves parallel to future DEJ.

• In this way a layer of mantle predentin appears.

Fromation of mentle predentin

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• Throughout dentinogenesis, mineralization is achieved by continuous deposition of mineral, initially in the matrix vesicle and then at the mineralization front.

• Factors :‽

• Proteins are :– Dentin phosphoprotien (DPP)- key protein– Osteonectin-inhibitory effect – Osteopontin- promoter– Gla protein- seeder / nucleaator– Chondrointin sulphate-

Mineralization

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• Two pattern:1) Globular

mineralization Deposiotion of crystals in several discrete areas of matrix by heterogenous capture in collagen.

2) Linear mineralizationWhen the rate of formation progresses slow, the mineralization front appears more uniform.

Pattern of mineralization

Scanning electron micrograph of globular

dentin

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• Dentin formation begins at the bell stage of tooth development in tissue adjacent to concave tip of the folded inner enamel epithilium.(it is the site where cuspal development begins.

• Root dentin forms at a slightly later stage of development.

• requires the proliferation of epitilial cells ( hertwig’s epithelial root sheath) from the cervical loop of enamel organ around growing pulp to initiate the differentiation of root odontoblast.

Pattern of dentin formation

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• Many genes are implicated in dentinogenesis, the newer ones being

– MAP1B for odontoblast differentiation, and– PHEX for dentin mineralization

Genetic regulation of dentinogenesis

Kaneko T, Arayatrakoollikit U, Yamanaka Y, Ito T, Okiji T. Immunohistochemical and gene expression analysis of stem-cell-associated markers in rat dental pulp. Cell and

tissue research. 2013 ; 351 (3): 425-432.

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• Color :Pale yellow in deciduous teeth ,Yellow in

permanent dentition.Light passes through thin, highly mineralized

enamel and is reflected by underlying dentin.

Thicker or hypomineralized enamel does not permit light to pass through readily.

• Thickness of dentin:Range: 3-10mmRatio of thickness in primary and permanent

teeth is 1:2

Physical properties of dentin

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• Hardness:Dentin is softer than enamel but more hard

than bone or cementum. Hardness of dentin is one fifth (1/5th ) that of

enamel; near the DEJ it is three times greater than near the pulp.

• The compressive strength of dentin is 217-300 MPa which is much higher than enamel.

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• Modulus of elasticity of dentin is 1.67x 10⁶ PSI.

• Tensile strength of dentin is approx. 40MPa , which is less than cortical bone and approx one half (1/2) that of enamel.

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• Extend through entire thickness of dentin from DEJ to pulp.

• ‘S’-shaped path from the outer surface of the dentin to the perimeter of the pulp in coronal dentin.

• Less pronounced in root dentin in the cervical third and in incisal edges and cusps .

• Straight in deciduous teeth.

Histology of dentinDentinal tubule:

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• Diameter of dentinal tubules : – Larger in diameter near pulp - 3 to 4µm, and

smaller at the DEJ- 1µm.

• Number of Dentinal tubules : – At the pulpal surface of dentin the number

/sq mm varies between 50,000 & 90,000.– At DEJ : 8000- 15,000

• More tubules per unit area in the crown than in the root.

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• The dentin that immediately surrounds the dentinal tubules is termed peritubular dentin.

• This dentin forms the walls of the tubules.

• It is highly mineralized (about 9% more) than intertubular dentin.– The formation of

intratubular dentin is a slow continuing process causing reduction in size of lumen.

Peritubular dentin/ intratubular dentin:

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• The main body of dentin is composed of intertubular dentin.

• It is located between the dental tubules more specifically, between the zones of peritubular dentin.

• About one half of its volume is organic matrix, specifically collagen fibers which are randomly oriented around the dentinal tubules.

Inter-tubular dentin:

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• It is term used to describe areas of unmineralized or hypo mineralized dentin where globular zones of mineralization (calcospherites) have failed to fuse into a homogenous mass within mature dentin.

• These areas are prevelent especially in person which has had a deficiency in vit D or exposure to high level of fluoride at the time of dentin formation.

Inter globular dentin:

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• When root dentin is viewed under transmitted light in ground section , a granular- appearing area, the granular layer of Tomes, can be seen just below the surface of the dentin where the root is covered by cementum.

• Caused by a coalescing and looping of the terminal branches of the dentinal tubules. These areas remain unmineralized.

Granular layer of TOMES:

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• Incremental lines of von Ebner appear as fine lines or striationsion.

• A that reflect rhythmic dentin deposition are more distinctly visualized in this demineralized section.

• B is devoid of such lines. This is a characteristic of mantle dentin.

• C that reflects the spherule-

like mineralization pattern of

dentin.

Incremental/Imbrication Lines of von Ebner

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Dentinoenamel junction:• Unique bond between two

very dissimilar materials.

• It is scalloped or pitted or wavy in outline, with the crest of the waves penetrating towards the enamel.

• Function- prevention of delamination.

Dentinal junction

Shimizu D, Macho A. functional significance of microstructral detail of the primate dentino-enamel junction: A possible example of exaptation. J Hum Evol.

2007;52 :103-111.

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Dentino-cemental junction:• There is a smooth line

junction between the dentin and cementum in permanent teeth.

• The cemento-dentinal junction in deciduous teeth is sometimes scalloped.

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• In human teeth three types of dentin can be recognized–– Primary dentin– Secondary dentin– Tertiary dentin

Types of dentin

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Primary Dentin-

• Formed prior to the eruption of the teeth and root completion.

• Major bulk of dentin.

• It is composed of Mantle dentin and Circumpulpal dentin.

• Completed 2-3 years after tooth eruption for permanent teeth and 18 months for deciduous teeth.

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Mantle Dentin-

• The first-formed dentin in the crown underlying the DEJ.

• Large collagen fibrils perpendicular to DEJ (0.1-0.2µm in diameter) : argyrophilic or silver-stained and called von Korffs fibers.

• 4% less mineralized than circumpulpal dentin.

Circumpulpal Dentin-

• Forms bulk of the tooth.

• Formed prior to root completion.

• Smaller collagen fibrils (0.05µm in diameter); more closely packed together.

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Secondary dentin-• Formed after completion of root formation.

• Continuing, but much slower deposition of dentin.

• Narrow band of dentin bordering the pulp.

• Contains fewer tubules than primary dentin.

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• Greater deposition of secondary dentin on the roof and floor of the pulp chamber leads to an asymmetric reduction in size and shape of the chamber and the pulp horns.

• The tubules of secondary dentin undergo sclerosis more readily than primary dentin.

• This process tends to reduce the overall permeability of the dentin and thereby to protect the pulp.

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Tertiary dentin-

• Tertiary dentin is also known as Reactive, Reparative or Irregular secondary dentin.

• It is the dentin that is formed in response to abnormal stimuli such as attrition, abrasion, erosion, trauma, moderate dentinal caries and restorative materials.

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• Usually appears as a localized dentin deposit on the wall of the pulp cavity immediately subjacent to the area on the tooth that has received the injury (dentin deposits underneath the affected tubules).

• Types of tertiary dentin:Reactionary dentinReparative dentin

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Reactionary dentin:• When the original odontoblasts that made

secondary dentin are responsible for focal tertiary dentin formation.

• Rate of formation of dentin is increased.

• Tubules remain continuous with the secondary dentin.

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Reparative dentin:

• If the provoking stimulus causes destruction of the original odontoblasts, the newly differentiated odontoblast -like cells secrete less tubular, more irregular dentin called Reparative dentin.

• Here, tubules are usually not continuous with those of secondary dentin.

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• Nerve fibers were shown to accompany 30-70% odontoblastic process, and these are reffered to as intratubular nerves.

• Nerve and their terminal are found in close association with odontoblast process withih tubules

• It is believed that most of these are terminal processes of mylinated nere fibers of dental pulp.

Innervation of dentin:

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• 3 basic theories of pain conduction through dentin are:

• Direct neural stimulation: by which the nerve in dentin get stimulated.

• Transduction theory: which presumes that the odontoblast process is primary structure excited by the stimulus and that impulse is transmittes to the nerve endings in inner dentin.

Theories of pain transmission through dentin

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• Hydrodynamic theory: various stimuli affect fluid movement in dentinal tubule.

• This fluid movement , either inward/ outward stimulates pain mechanism in tubules by mechanical distribution of nerves closely associated with the odontoblast and its process.

• Thus these endings may act as mechanoreceptors as they are affeced by mechanical displacement of tubular fluid.

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• Dead tracts and blind tract:

• When dentin is damaged, odontoblastic processes die or retract leaving empty dentinal tubules. These areas with empty dentinal tubules are called dead tracts.

• With time these tracts can become completely filled with mineral. This region is called blind tracts.

Age and functional changes:

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• Longitudinal ground section of permanent teeth dentin showed DT following an “S”-shaped curve, where as in primary DT follow a straight curve.

• Density of innervation is less in primary teeth as compare to the permanent teeth.

Primary dentin and permanent dentin

Chowdhary N ,Subba Reddy VV. Dentin comparison in primary and permanent molars under transmitted and polarised light microscopy: An in vitro study. J Indian Soc Pedod Prev Dent. 2010; vol 28(3) : 167-172

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• Primary tooth showing incremental lines at an angle to the dentinal tubules, whereas permanent tooth showing incremental lines at right angles to the dentinal tubules

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• Infected dentin: Superficial layer which is soft and leathery in consistency and dark brown in color.– It has a high concentration of bacteria and

collagen is irreversibly denatured .– It is not remineralizable and must be

removed

• Affected dentin: Deeper layer which is hard in consistency and light brown in color. – It does not contain bacteria and is

reversibly denatured. Therefore this layer preserved

Infected dentin & affected dentin

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• Whenever dentin has been cut or abraded, a thin altered layer is created on the surface.

• Composed of denatured collagen, hydroxyapatite and other cutting debris.

• Serves as a bandage over the cut dentinal surface because it occludes many of dentinal tubules with debris called smear plugs.

• Clinical significance :

Smear layer

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• The fundamental principle of adhesion to tooth substrate is based upon an exchange process by which inorganic tooth material is exchanged for synthetic resin.

• This process involves 2 phases1. Etching of tooth surface,2. Hybridization phase

• Clinical relevance of etching time on dentin demineralization:

Dentin bonding system

Perdigấo J, Lopes M. The effect of etching time on dentin demineralization. Quintessence int.2001 ; 32:19-26.

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Clinical implications:

• Dental caries

• Dentin hypersentivity

• Dentinogenesis imperfecta

• Dentin dysplasia

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• Dentin is a living tissue. It is covered by enamel in crown portion and by cementum in root portion.

• It will become sensitive if covering of either enamel or cementum will lost due to any reason.

• So, all efforts should be made during restorative procedures to preserve as much healthy dentinal tissue as possible.

Conclusion

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• Chowdhary N ,Subba Reddy VV. Dentin comparison in primary and permanent molars under transmitted and polarised light microscopy: An in vitro study. J Indian Soc Pedod Prev Dent. 2010; vol 28(3) : 167-172

• Kaneko T, Arayatrakoollikit U, Yamanaka Y, Ito T, Okiji T. Immunohistochemical and gene expression analysis of stem-cell-associated markers in rat dental pulp. Cell and tissue research. 2013 ; 351 (3): 425-432.

• Shimizu D, Macho A. functional significance of microstructral detail of the primate dentino-enamel junction: A possible example of exaptation. J Hum Evol. 2007;52 :103-111.

• http://docbds.blogspot.in/2012/05/removing-of-any-remaining-infected.html

References

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• Gallagher R, Balooch M, Balooch G, Wilson R, Marshall S, Marshall G. Coupled nanomechanical and Raman microspectroscopic investigation od human third molar dentinoenamel junction. J Dent Biomech. 2010;1:1-4.

• Perdigấo J, Lopes M. The effect of etching time on dentin demineralization. Quintessence int.2001 ; 32:19-26.

• Nanci A. Tencate’s Oral histology. 8th ed. 2013

• Kumar GS. Orban’s oral histology and embryology. 12th ed. India: Elsevier, 2009

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