Dentin-omae 2nd Handout

DENTIN

Dentin

The greatest part of a human tooth

Dentin, which constitutes the entire body of the tooth, is located in both the crown and the root of a tooth

Physical Properties1. Dentin is significantly softer than

enamel, but harder than bone or root cementum.

2. Dentin has a yellowish intrinsic color3. Physically, dentin is firm, resilient or

highly elastic and deformable 4. Dentin is radiographically more

radioluscent than enamel and more radioopaque than the pulp

Physical Properties

5. Dentin is positively birefingent because of the net effect of superimposing optically positive collagen fibrils and optically negative crystals

6. Dentin is also porous and permeable

Chemical PropertiesChemically by weight is:

Approximately 70% inorganic materialconsist mainly of hydroxyapatite and contains calcium and phosphorous In addition, small amount of carbonates and magnesium and varying concentrations of fluoride

20% organic material and 10% water (adsorbed on the surface of the mineral or in interstices between crystals) 10% water

Types of Dentin1. PRIMARY DENTIN (REGULAR

DENTIN or ORTHODENTIN)2. SECONDARY DENTIN3. TERTIARY DENTIN (REACTIVE,

REPARATIVE OR IRREGULAR SECONDARY DENTIN)

4. PREDENTIN OR DENTINOID

Types of Dentin1.PRIMARY DENTIN

(REGULAR DENTIN or ORTHODENTIN)

2.SECONDARY DENTIN3.TERTIARY DENTIN

(REACTIVE, REPARATIVE OR IRREGULAR SECONDARY DENTIN)

4. PREDENTIN OR DENTINOID

Primary Dentin

Dentin mostly developed before eruption containing regularly arranged dentinal tubules and all the dentin that is formed up until the conclusion of growth Most of the tooth is formed by primary dentin, which outlines the pulp cavity

Primary Dentin

Primary DentinA. Mantle Dentin

It is the outer thin layer of primary dentin (the initial dentin formed) 150 micrometers thick, running parallel with the dentino-enamel junctionConsidered the product of young, still immature odontoblasts or newly differentiated odontoblastslacks phosphophorynslightly (4%) less mineralized

B. Circumpulpal DentinIs the bulk of dentin mass between mantle dentin and the pulpal space.It is the exclusive product of functionally coordinated odontoblasts.

Secondary DentinDevelops after root formation has been completed. It was once thought that secondary dentin was formed only in response to functional stimuli, but it was found in unerupted tooth as well. Thus, secondary dentin represents the continuing, but much slower, deposition of dentin by the odontoblasts after root formation has been completed.

Secondary Dentin

Tertiary DentinAlso known as Reactive, Reparative or Irregular Secondary DentinIs formed in response to outside or noxious stimuli such as attrition, erosion, caries, cavity preparation or therapeutic intervention.

Tertiary DentinIt is the result of defensive activities of the pulp dentin complex and can have a variable, atypical structure in which dentinal tubules may be sharply reduced in number, irregularly arranged, wavy in their course or completely absent.The cells forming tertiary dentin either line its surface or are included in the dentin.This dentin is then referred to as osteodentin.

Primary Dentin

Tertiary Dentin

Secondary Dentin

Predentin or DentinoidIs unmineralized or uncalcified dentin matrix with variable thickness (10-47 micrometer) that lines the innermost (pulpal) portion of the dentin.Is thickest where active dentinogenesis is occurring and its presence is important in maintaining the integrity of dentin, since when it is absent the mineralized dentin is vulnerable to resorption of odontoclasts.It is similar to osteoid in bone.Unmineralized dentin matrix consists principally of collagen, glycoproteins & proteoglycans.

Schreger’s Line

The change from primary to secondary or tertiary dentin is marked by abrupt changes in tubular pattern. This line of directional change has been referred to as SCHREGER’S LINE.

Schreger’s Line

Schreger’s Line

Structural Elements of Dentin1.Dentinal Matrix■ Are intercellular material of dentin consists of 2

fundamental units: FORMED ELEMENTS composed of collagenic (ALPHA OR KORFF”S FIBERS) and fibrous (BETA FIBRILS) and UNFORMED ELEMENTS—ground substance (NUCOPOLYSACCHARIDES)

2.Dentinal TubulesAre regularly arranged canals or spaces lie close together and extend from the tooth pulp to the dentino-enamel junction in the crown of the tooth and to the dentinocemental junction in the root.

Dentinal tubules

The dentinal tubules are tapered structures measuring approximately 2.5 micrometers in diameter near the pulp, 1.2 micrometers in the midportion of the dentin, and 900 nm near the dentino-enamel junction.Dentinal tubules are generally thought to contain the process of odontoblast bathed in tissue fluid and to be lined by an organic sheath, the lamina limitans.

Odontoblasticprocess

Parts of Dentinal Matrix1. Peritubular Dentin or Intratubular Dentin

The dentinal matrix that covers the walls of the dentinal tubules and is very dense. It has more apatite crystals per unit volumeHighly uniformly mineralized It is roughly 44 nm wide near the pulpal end, 750 nm wide near the dentino-enamel junction, and sharply demarcated from the intertubular dentin.

2. Intertubular DentinThe dentinal matrix located between the dentinal tubules. It is the main bulk of the dentinal material. It is less densely mineralized and noticeably less radioopaquethan peritubular dentin.It represent the primary secretory product of the odontoblasts and consists of a tightly interwoven network of type I collagen fibrils (measuring between 50 and 200 nm in diameter), is which apatite crystals are deposited.

Dentinal Tubule Intratubular Dentin

IntertubularDentin

Inter-globular Dentin

Dentin separating the mantle dentin and circumpulpaldentin is hypo-mineralized and is called inter-globular dentin

Dentinal tubulesDentinal tubules

Interglobular dentin

Contents of Dentinal Tubules1.ODONTOBLASTIC PROCESS (TOME’S FIBER,

DENTINAL FIBER)■ The odontoblasts lie on the inner surface of

dentin and on the periphery of the pulp 2.PERIODONTOBLASTIC SPACE

Is seen between the cytoplasmic membrane of the odontoblastic process and the wall of the dentinal tubule. This space contains tissue fluid—DENTINAL FLUID and organic structural elements such as collagen fibrils and peritubular dentin matrix and plays a role in the physiologic maintenance of dentin

3. INTRATUBULAR NERVEStudies indicate that nonmyelinated nerve fibers of the trigeminal nerve extend into predentin and into a zone of circumpulpal dentin up to 0.2 mm from the pulpIn occlusal dentin, specially over the pulp horns, approximately every other tubule contains a nerve fiber. Nerve fibers are fewer in dentin forming the wall of the pulp chamber, still fewer in cervical dentinIn addition to the above contents indicates the presence of proteoglycans, tenascin, serum albumin, alpha-2 HS, and transferrin and type V collagen, clearly a complex mixture.

Periodontoblastic space

Odontolastic process

Intratubular Nerve

Theories of Dentin Sensitivity

1. TRANSDUCTION THEORYThe odontoblastic process mediates the transmission of stimuli from the periphery of the dentin to the nerve ending near the pulp

2. DIRECT CONDUCTION THEORY The nerve endings near the pulp are stimulated directly

Theories of Dentin Sensitivity

3.HYDRODYNAMIC THEORY OF BRANNSTROMSuggests that transmission of stimuli is added by a movement of fluid within the dentinal tubules or odontoblastic process

Structural Characteristics of Dentin

1. INTERGLOBULAR DENTINIs the area of structural defect where unmineralizedor hypomineralizeddentin result from the failure of globules of calcospherites (or globular zones of mineralization) to fuse into a homogenous mass within mature dentin.

1. Interglobular Dentin

These areas are especially prevalent in human teeth in which there has been a deficiency in Vit. D or exposure to high levels of fluoride at the time of dentinogenesis.Interglobular dentin are unmineralized spots, irregular in shape most frequently seen in circumpulpal dentin just below the mantle dentin inside the dentino-enamel junction, where the pattern of mineralization is largely globular.

INTERGLOBULAR DENTIN

2. Granular Layer of TomesA structural defect that comprise uncalcified parts of the ground substance with numerous , closely packed, tiny areas of hypomineralizeddentin, which appear as dark (black) granules in ground section and nonmineralized

2. Granular Layer of TomesIt is once thought that its granular appearance was associated with minute hypomineralized areas of interglobular dentin, but in fact, they are true spaces.Seen just below the surface of the dentin where the root is covered by cementum.Granular layer of Tomes is believed due to coalescing and looping of the terminal portions of the dentinal tubules. It is possible that odontoblast is initially disoriented, turns until oriented at right angles to the root sheath, and then proceeds in an orderly fashion, leaving a straight tubule behind. This looping is also related to the lower rate of dentin formation in root dentin

3. Incremental Lines of Von Ebner

Is the phasic or increment of dentin formation at the daily rate approximately 4 micrometers.

4. Contour Lines of OwenIs the result in an accentuation of the growth lines in dentin, which are widened, and distinctly hypomineralizedThey occur at irregular intervals and in variable numbers. Their width is a measure of the duration of the disturbance that caused them.

NEONATAL LINErepresents an accentuated growth line that occurs regularly in deciduous teeth and near occlusalsurfaces of permanent first molars

Age Changes in Dentin

1. Sclerotic Dentin or Transparent Dentin

Is the morphologic change in dentin which includes thickening of the peritubulardentin and complete obliteration of the dentinal tubules.Increased with age and is most common in the apical third of the root and in the crown midway between the dentinoenamel junction and the surface of the pulp.

Dentinal sclerosis occurs both as a physiologic aging process and as a defense reactionThe age related increase in the amount of sclerotic dentin is at first confined to the mesial and distal tooth surface in the root region. It begins apically and peripherally among the dentino-enamel junction and with advancing age, increases in intensity and spreads toward the crown and pulp.

Sclerotic Dentin or Transparent Dentin

Independent of age, dentin can also become sclerotic in locally affected areas as a reaction to abrasion, attrition, caries, cavity preparation and application of corticosteroids and filling materials.

Sclerotic Dentin or Transparent Dentin

The reaction to pathologic stimuli can result in complete obliteration of more than 90% of the dentinal tubules fulfilling the defense reaction of sclerotic dentin

2. Dead TractsDentinal tubules are emptied either by complete refraction of the odontoblasticprocesses from the tubule or through the death of odontoblasts

2. Dead TractsThese are not seen clinically, only microscopicallyDentinal tubules are sealed off so that in ground section appear in transmitted light as blackDisintegration may result from attrition, erosion, abrasion, caries and odontoblastic crowding.

The end