Tissue of the teeth Dentin-Pulp Complex Dr Jamal Naim PhD in Orthodontics Dentin-Pulp Complex

Introduction Dentin and pulp are related embryologically, histologically and functionally. Dentin is a hard connective tissue and the Pulp is a soft one. Dentin forms the bulk of the tooth. It is covered by cementum at the root portion and by enamel at the crown portion.

Properties of dentin Bonelike yellowish in color Elastic, less hard than enamel, but more than cementum Less radio-opaque than enamel, but more than cementum 3-10 mm thick

Compositions of dentin organic substance 30-25% from its weight About 90% collagen fibers About 10% ground substance inorganic substance 70-75% from its weight Hydroxyapatite crystallites

Life cycle of odontoblasts There are only 3 stages in the life cycle of odontoblasts: Differentiating stage Formation stage Quiescent stage

Life cycle of odontoblasts Differentiating stage: Before Differentiation, the inner dental epithelium is separated from the dental papilla by the thin basement membrane. The undifferentiated peripheral cells are spindle and separated by great amount of ground substance

Life cycle of odontoblasts

Differentiating stage Preameloblast Basement membrane Undifferentiated cell

Life cycle of odontoblasts Differentiating stage: In the late bell stage, under the inductive influence of the inner dental epithelium, the peripheral ectomesenchymal cells differentiate into preodontoblasts.

In the late bell stage the UMC differentiate to preodontoblasts

Differentiating stage Ameloblast Basement membrane preodontoblast Undifferentiated cell

Late Bell stage/differentiating stage for odontoblasts

Life cycle of odontoblasts They assume to a columnar shape and aligned as a single row along the basement membrane. Several projections arise from the upper part of the cells.

Life cycle of odontoblasts The nuclei become basally oriented. The cells grow in length to become columnar (40u) Now the fully differentiated odontoblasts begin their work.

Life cycle of odontoblasts Formative stage: Concentration of the cell organelles, granular components and globular elements Production of the dentin matrix The odontoblasts retreat from the basement membrane

Life cycle of odontoblasts Formative stage: Leaving a single process which become enclosed in the dentinal tubule (Tomes fiber). With successive deposition of dentin, tubule and process grow in length.

Life cycle of odontoblasts Differentiating stage/ Begin of formative stage predentin odontoblast Undifferentiated cell

Mitochondrion RER Formative stage Nucleus predentin Formative stage

Formative stage Dentin

Life cycle of odontoblasts Quiescent stage: Actively secreting odontoblasts decrease slightly in size. The odontoblastic process stop to elongate In this stage the odontoblasts produce only secondary dentin.

Life cycle of odontoblasts Quiescent stage: Odontoblasts decrease in size and function The dentin formation is reduced They produce now secondary and tertiary dentin

Dentinogenesis Matrix Formation (forming predentin) Maturation Collagen fibers Ground substance Maturation (mineralization) Hydroxyapatite crystallites

Dentinogenesis Formation of predentin (dentin matrix): The first indication of forming predentin is the development of the KORFF FIBERS. They are bundles of fibrils among the odontoblasts. They are perpendicular to the basement membrane and attached to it. This layer is main part of the MANTLE DENTIN

Basement membrane MANTLE DENTIN TOMES FIBER Korffs fibers are perpendicular to the basement membrane TOMES FIBER

Dentinogenesis The korffs fibers fade gradually and smaller fibrils form a network in the dentin subsequent to the mantle dentin, the circumpulpal dentin. The odontoblasts form the main components of the dentin matrix: the collagen fibers and the mucopolysaccharides.

Basement membrane MANTLE DENTIN CIRCUMPULPAL DENTIN TOMES FIBER fibers are parallel to the DEJ TOMES FIBER

Dentinogenesis Maturation of predentin: It occurs parallel to matrix formation It begins at the tip of the crown It proceeds in a rhythmic pattern to gradually complete cervically. The first layer of predentin begins its maturation in a globular pattern (matrix vesicle), where small centers of calcification spread concentrically until they fuse together.

Dentinogenesis If somewhere those globules do not fuse together, areas of uncalcified dentin are known as interglobular dentin. The maturation goes then in linear or occasionally globular pattern. The mineralization begins by crystal deposition in form of fine plates of hydroxyapatite on the surface of the collagen fibrils. The long axes of the crystals are paralleling to the fibrils.

Maturation of dentin MANTLE DENTIN CIRCUMPULPAL DENTIN Mineralized MD Matrix vesicle Rupture of the MV and begin of mineralization Maturation of dentin

Maturation of dentin Matrix vesicle Begin of Crystallization Matrix vesicle Crystal lodgment Rupture of the MV and begin of mineralization Maturation of dentin

Types of dentin Primary (physiological formed) dentin Secondary (physiological formed) dentin Tertiary (reparative, irregular secondary) dentin

Enamel Mantle dentin Circumpulpal dentin Tertiary (irregular secondary) dentin regular secondary dentin

Primary dentin All of dentin formed before root formation has been completed is Primary dentin. Physiological formed primary Dentin is composed of: Mantle dentin & Circumpulpal dentin

Histological structure of dentin Odontoblasts & their process Dentinal tubules (canals) Peritubular dentin Intertubular dentin Interglobular dentin tome's granular layer

Circumpulpal dentin Pulp Pulp predentin Odontoblasts layer

Oral Histology, 5th edition, A R Ten Cate Odontoblasts & their process ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl Oral Histology, 5th edition, A R Ten Cate

Odontoblasts & their process Odontoblasts are specialized in dentin forming (primary, secondary or tertiary). arranged in a well defined layer Adjacent to the pulpal end of dentin. Every cell has one process (tomes fiber) that traverse dentin to reach the D.E.J and the C.D.J. Adjacent to enamel and cement the odontoblastic process ends by formation of several terminal branches.

Odontoblasts & their process It is about 5000 µm long. The process is about (4-5 µm) thick. It becomes smaller in predentin (1-3 µm) and more smaller in mineralized dentin (0.5-2.0 µm). They have several smaller branches (terminal branches), that fuse with the adjacent processes terminal branches.

Dentin Predentin odontoblasts

Dentinal Tubules

DEJ terminal branches Odontoblastic processes

Dentinal tubules They are s-shaped in the crown-dentin and more straight in the root-dentin. They have lateral branches (canaliculi) enclosing the terminal branches. The density of the tubules is higher at the pulpal end of dentin (64000 DT/mm2) than at the D.E.J (16000 DT/mm2).

Dentinal tubules The diameter of the DT at the D.E.J. is smaller than at the pulpal end of dentin. The density decreases also from coronal toward apical dentin.

S-shaped Dentinal tubules

Dentinal Tubules periodontoblastic space Odontoblastic process (tomes fiber)

Peritubular dentin It is the layer of dentin surrounding the dentin tubules It is highly mineralized more homogenous than intertubular dentin It has less than 20% of its volume an organic matrix, so it has higher x-ray opacity than intertubular dentin Its thickness varies according to age (thicker in old dentin) and location.

Peritubular dentin (Neumann sheath)

Intertubular dentin It is the sum of dentin between the dentin tubules It is less mineralized and less homogeneous than PTD It has more than 50% of its volume an organic matrix, so it has less x-ray opacity than peritubular dentin The collagen fibrils surround the tubule and form a network between them

Peritubular dentin (Neumann sheath) Intertubular dentin Peritubular dentin (Neumann sheath) Odontoblastic process (tomes fiber)

Mantle dentin Circumpulpal dentin

Mantle dentin It is the first formed layer of dentin and is about 30 µm thick. It is less mineralized than circumpulpal dentin The difference between it and CPD in ground sections is the direction of the collagen (korff´s) fibrils. They are rectangular to the dentino-enamel or cemento-enamel junction It hasn’t growth lines (von Ebner lines) like CPD

Mantle dentin In ground section D.E.J. and C.D.J appears as scalloped line. There is more irregularity in the cusp and crown area. Cement Enamel Dentin Dentin D.E.J. and C.D.J

Incremental lines of von Ebner Like the lines of Retzius in enamel, the incremental lines of von Ebner show the growth pattern and the daily deposition of dentin. They are hypomineralized lines of dentin and corresponds the rest of odontoblasts. The distance between them varies from 3-20 µm. They run in rectangular direction to the dentin tubules

Contourline of Owen If any thing (disease, fever etc.) disturbs the dentin development, the lines of von Ebner are wider and less mineralized. They are called then contourlines of Owen. The best known contour lines of Owen is the neonatal line. It corresponds the first weeks of a baby life, because of the change of nutrition.

Owen contourlines

neonatal line

Interglobular dentin The mineralization of dentin runs in globular pattern If the globules doesn’t fuse completely together, the hypomineralized dentin among them is known interglobular dentin. Those areas follow the course of the von Ebner lines. The tubules in those areas hasn’t peritubular dentin

Tome's granular layer Black spaces in the ground section adjacent to the CDJ, so only in the root mantle dentin They are also hypomineralized areas of dentin, but smaller the interglobular dentin They doesn’t follow the lines of von Ebner.

Tome's granular layer cementum Granular layer of Tomes Dentin (with tubules) ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Granular Layer of Tomes dentin enamel cementum

Areas of hypo-mineralized dentin Areas of hypo-mineralized dentin Interglobular dentin Tome's granular layer Size: large Size: small Areas of hypo-mineralized dentin Areas of hypo-mineralized dentin In crown and root dentin Only in mantle root dentin Follows incremental lines Doesn’t follow incremental lines

Age and functional changes Physiologic regular secondary dentin Pathologic irregular secondary dentin Transparent (sclerotic) dentin

Physiologic regular secondary dentin Primary D Secondary D

Physiologic regular secondary dentin This is the type of dentin formed under Physiologic conditions after complete root formation. It is deposited continuously as long as the pulp is vital. It is formed at a lower rate and is separated by a darkly stained line from primary dentin It has less number of tubules. It occurs in the entire pulpal surface. Higher deposition at the roof and floor of the pulp chamber.

Physiologic regular secondary dentin Reparative D CPD CPD

Physiologic regular secondary dentin The size of the pulp cavity decreases and obliteration of the pulp horns The course of the dentin canals is more irregular

Pathologic irregular secondary dentin It is also known as tertiary or reparative dentin This type of dentin is formed as a protection for the pulp against severe stimulus (pathological conditions or irritations), such as Attrition Caries Preparations It is formed at a localized area (e.g. pulp horn) Some UMC in the subodontoblastic layer differentiate to new odontoblast to form dentin.

Pathologic irregular secondary dentin The number of the tubules is reduced. Tertiary dentin has frequently twisted tubules Some areas doesn’t contain tubules Reparative dentin is separated from other types by a darkly stained line.

Pathologic irregular secondary dentin Tertiary dentin

Types of reparative dentin Osteodentin: The odontoblasts (cells) are included in the formed dentin

Types of reparative dentin Atubular dentin: areas without tubules

Types of reparative dentin Vasodentin: entrapped blood vessels

Types of secondary dentin irregular Cause: severe stimuli, severe attrition, erosion, deep caries, Site of formation: located (eg pulp horn) Tubules: wavy and twisted course, decrease in number or atubular Regular Cause: mild stimuli (slow attrition, slowly progressing caries) Site of formation: entire pulpal surface (thicker on pulp roof and floor) Tubules: wavy course, decrease in number

Types of secondary dentin Regular Line of demarcation: stain dark Clinically: The increase of the dentin thickness and the closure of the pulp horns make it much less possible to expose the pulp chamber during preparation. Irregular Line of demarcation: stain dark Clinically: Functions as a barrier for against caries.

Transparent (Sclerotic) dentin Sclerotic dentin can be seen as physiological change (elderly dentin) or pathological change (caries, attrition, deep fillings, ) in primary or secondary dentin. Partial or complete obliteration of the dentin tubules, at first thickining of peritubular dentin, then complete obliteration of the tubules with intertubular d. Higher mineralized, harder and denser than normal dentin Appears light in transmitted light and dark in reflected light.

Transparent (Sclerotic) dentin Young dentin Adult dentin Sclerotic dentin

Transparent (Sclerotic) dentin

Dead tracts Severe stimulation to dentin leads to destruction or disintegration of the odontoblastic process and odontoblasts. The dentin tubules are empty and filled with air. Most often in areas of narrow pulp horns due to odontoblastic crowding. In ground section they appear black. Often surrounds with sclerotic dentin.

Dead tracts

Dead tracts

Dead tracts

Vitality and sensitivity of dentin Vitality of dentin is its ability to react following physiological or pathological stimuli. Forming secondary or tertiary dentin, feeling pain are signs of being vital. Several theories have been cited to explain the mechanism involved in dentinal sensitivity & vitality: The transducer theory, the conduction theory, the modulation theory the Brännström's hydrodynamic theory.

The transducer theory The transducer theory contend that the odontoblast and its process are capable to mediate neural impulse in the same way as nerve cells. Contra: But investigations have proved that no pain is experienced in exposed dentin by application of substance known to bare nerve endings. The measurement of membrane potential of the odontoblasts shows clearly that this potential is very low to contribute in the pain excitation.

The transducer theory

The conduction theory The conduction theory (intratubular innervation theory) contend that dentin is richly innervated and those nerves mediate the impulse to the brain. Some new studies show that predentin and the first layer of circumpulpal dentin (0.2mm) is innervated with nerve fiber from the raschkows plexus. The fibers run parallel ro the tomes fiber in the dentin tubules. The density of those fiber is much higher in the coronal dentin than cervical dentin. Root dentin doesn’t include such fibers.

The conduction theory

The conduction theory Some authors contend that those fibers end at the DEJ, but can not be seen in histological slides. Contra: It is uncapable to explain the higher sensitivity at the cemento-enamel junction than that felt at other areas.

The conduction theory

The hydrodynamic theory The “hydrodynamic theory”, developed in the 1960’s is the widely accepted physiopathological theory of Dentin Sensitivity. Temperature, physical osmotic changes or electrical and chemical stimuli and dehydration are the most pain-inducing stimuli. According to this theory, those stimuli increase centrifugal fluid flow within the dentinal tubules, giving rise to a pressure change throughout the entire dentine.

The hydrodynamic theory The movement stimulates intradentinal nerve receptors sensitive to pressure (BARORECEPTORS), which leads to the transmission of the stimuli . This simulation generates pain.

The hydrodynamic theory Berman describes this reaction as: “The coefficient of thermal expansion of the tubule fluid is about ten times that of the tubule wall.  Therefore, heat applied to dentin will result in expansion of the fluid and cold will result in contraction of the fluid, both creating an excitation of the 'mechano-receptor'.”

Vitality and sensitivity of dentin