Terminology and distribution of dentin.

Low-magnification micrographs illustrating the formation of the first layer of (mantle) dentin (D) in the rat incisor. A to C, Differentiated odontoblasts are tall columnar cells tightly grouped in a palisade arrangement. Their nucleus (N) is situated basally, the Golgi complex (G) occupies much of the supranuclear compartment, and their body is inclined with respect to that of the ameloblasts (Am). B, A concentration of large-diameter collagen fibrils (arrows) can be seen in the forming predentin (PD) matrix near the surface of the ameloblasts. C, As this matrix mineralizes, the fibrils become incorporated in the mantle dentin (D). BV, Blood vessel; E, enamel; Od, odontoblasts.

Freeze-fracture preparations showing the interface between forming mantle (A) predentin and (B) dentin, and ameloblasts at an early time during tooth formation. A, The presence of abundant, well-defined matrix vesicles (mv) in the extracellular matrix indicates that mineralization has not yet started. B, Odontoblast processes (Odp) can establish contact (arrows) with ameloblasts, an event believed to be one of the various mechanisms of epithelial-mesenchymal interaction during tooth development. sg, Secretory granule.

A, Tertiary (reparative) dentin containing only a few sparse irregular tubules. B, At higher magnification, some cellular inclusions can be seen.Figure 8-5 Early dentin formation during early bell stage of tooth development. From the apex of the tooth, dentin formation spreads down the slopes of the cusp.

Odontoblast differentiation. The undifferentiated ectomesenchymal cell (A) of the dental papilla divides (B), with its mitotic spindle perpendicular to the basement membrane. A daughter cell (C), influenced by the epithelial cell (D), differentiates into an odontoblast (E). Another daughter cell (F), not exposed to this epithelial influence, persists as a subodontoblast cell (G). This cell has been exposed to all the determinants necessary for odontoblast formation except the last.

Tertiary dentin with a regular tubular pattern and no cellular inclusions. This dentin probably was deposited slowly in response to a mild stimulus.

Electron micrograph showing the characteristic deposition of first collagen fibers to form coronal mantle predentin. Large-diameter collagen fibers (Collagen) intermingle with aperiodic fibrils (arrows) associated with the basal lamina supporting the dental epithelium.

Transmission electron microscope images. A, The odontoblast process (Odp) is the portion of the cell that extends above the cell web (cw). Numerous typical, elongated secretory granules (sg), occasional multivesicular bodies (mvb), and microfilaments (mf) are found in the process. The small collagen fibrils (Coll) making the bulk of predentin run perpendicularly to processes and therefore appear as dotlike structures in a plane passing longitudinally along odontoblasts. Bundles of larger-diameter collagen fibrils, von Korff’s fibers, run parallel to the odontoblast processes and extend deep between the cell bodies. B, At higher magnification, a von Korff’s fiber extending between two odontoblasts shows the typical fibrillar collagen periodicity. m, Mitochondria; rER, rough endoplasmic reticulum.

Electron micrograph of initial dentin formation in a human tooth germ at the early bell stage. A, Collagen fibrils of the first-formed dentin matrix can be seen, along with the basal lamina supporting ameloblasts. Intermingled between the collagen fibrils are matrix vesicles in which initial mineralization of the dentin matrix occurs. B to D show the occurrence and growth of apatite crystals in these vesicles.

Ground section showing the S-shaped primary curvature of the dentinal tubules in the crown and their straight course in the root.

Scanning electron microscope preparations of predentin (A and B) and dentin (C and D). A and B, Although no dentinal tubules (dt) occur in predentin, each odontoblast process (Odp) is surrounded by intertwined collagen fibrils (Coll) that outline the future dentinal tubule. As visible in cross-sectional (A) and longitudinal (B) profile, the fibrils run circumferentially and perpendicular to the process. C, In healthy dentin each tubule is occupied by a process or its ramifications. D, The dentinal tubule is delimited by a layer of peritubular dentin (arrowheads) that is poor in collagen and more mineralized than the rest of the dentin. The dentin between tubules is referred to as intertubular dentin (iD).

Odontoblast processes (Odp) run in canalicules called dentinal tubules (arrowheads). Images from scanning electron microscope (A), light microscope (B), and transmission electron microscope (C).

Immunocytochemical preparations of reparative dentin for (A) bone sialoprotein (BSP) and (B) osteopontin (OPN). Reparative dentin is poor in collagen and enriched in noncollagenous matrix proteins such as bone sialoprotein and osteopontin. A, Reparative dentin begins formation as globular masses (asterisks) among collagen fibrils (Coll). B, These globules grow and fuse to form larger masses of mineralized matrix. The cells associated with reparative dentin have a general fibroblastic appearance, a well-developed Golgi complex (G), and abundant rough endoplasmic reticulum (rER). N, Nucleus.

Electron micrograph illustrating initial root dentinogenesis. The first collagen fibers of the matrix are aligned parallel to the basal lamina supporting the root sheath cells. The circled area outlines a junctional complex. The discontinuity in the basal lamina is notable.

Initial root dentin formation. Epithelial cells of the root sheath have initiated differentiation of odontoblasts that are about to begin the formation of root dentin. Inset, Higher magnification of the milieu in which root dentin matrix will first form.

The morphologic changes of the peripheral capillaries and odontoblasts in the process of dentinogenesis. CL, Capillary; PD, predentin.

Dentinal tubule branching. A, Light microscope cross section of dentin stained with silver nitrate showing the extensive fine branching network of the tubular compartment. B, Scanning electron micrograph showing dentinal tubules that accommodate branches of various sizes. C, A microbranch (arrow) extends from a larger dentinal tubule through the peritubular dentin. A thin layer of peritubular dentin also borders the microbranch.

Terminal branching of dentinal tubules is more profuse in root dentin (A) than in coronal dentin (B). C, Scanning electron micrograph showing branching.Figure 8-25 Caries of dentin. Transmission electron micrographs showing the natural pathway created for microorganisms by the dentinal tubules in longitudinal section (A) and in cross section (B). C, The microorganisms absorb stain, and in light microscope sections the tubules of carious dentin are seen as dark streaks.

Longitudinal ground section of the granular layer of Tomes.

Ground section across the root of a tooth. The granular layer of Tomes is visible just beneath the cementum.

Sclerosis of the dentinal tubule, which occurs in different ways. A, The tubule is filled with an even deposition of mineral, which has been interpreted as a spread of peritubular dentin. However, at B, tubular occlusion has occurred in a similar way, although no peritubular dentin is recognizable. At C, diffuse mineralization is occurring in the presence of a viable odontoblast process (Odp). At D, mineralization occurs within the odontoblast process and around collagen fibrils deposited within the tubule. ID, Intertubular dentin; PT, peritubular dentin; S, sclerotic dentin.

A, Pattern of incremental line deposition in dentin. B, Tooth section of a person who received tetracycline intermittently. The drug has been incorporated at successive dentin-forming fronts, mimicking incremental line patterns.

Ground section, approximately 100 µm thick, of an old tooth. The section has been placed over a pattern, which can be seen through the apical translucent sclerotic dentin.

Interglobular dentin. A, Ground section. B, Demineralized section stained with hematoxylin-eosin. C, Demineralized section stained with silver nitrate. The spherical borders of the interglobular areas indicate the failure of calcospherite fusion. In B the staining of nonmineralized matrix is lighter and in C is darker. Dentinal tubules pass through the interglobular dentin, but no peritubular dentin is present in these areas. Silver nitrate staining reveals numerous smaller tubules into which run the branches of the odontoblast process.

Peritubular dentin seen in ground section by (A) light microscopy and (B) scanning electron microscopy. The dark central spots are empty dentinal tubules surrounded by a well-defined collar of peritubular dentin

Immunocytochemical preparation illustrating an accumulation of dentin sialoprotein (DSP) around odontoblast processes (Odp) in certain regions of the rat incisor. Less collagen is present in these areas corresponding to the position of peritubular dentin (pD). The matrix between these areas is the intertubular dentin (iD) and constitutes the bulk of the dentin.

Cells bordering pulp. rER, Rough endoplasmic reticulum.

Immunocytochemical preparations for bone sialoprotein (BSP) and osteocalcin (OC, inset). Round granules (arrowheads) are immunoreactive for these two matrix proteins, suggesting that a secretory granule population may exist, distinct from the elongated collagen-containing ones, that may be responsible for the transport and secretion of noncollagenous dentin matrix proteins. A cell web (cw) is associated with the apical junctions and separates the odontoblast body from the process (Odp). m, Mitochondria; PD, predentin.

A and B illustrate two views of cross-cut odontoblast processes at the level of predentin, close to the cell body. The processes are surrounded by collagen fibrils (Coll) and contain elongated and round secretory granules (sg), coated pits (cp), and vesicles (cv) suggestive of intense pinocytotic activity along the cell membrane. B is at a higher magnification than A.

Freeze-fracture (A) and scanning electron microscope (B) preparations illustrating the odontoblast process (Odp) near its point of emergence from the cell body. The process is surrounded by the collagen fibrils (Coll) of predentin (PD). The fibrils are intimately associated with the process and in certain areas they imprint the membrane (arrowheads). Od, Odontoblast.

Electron micrographs of the odontoblast process. A, The process is an arborizing cell extension that extends above the apical junctional complex (jc) into predentin and dentin. Numerous collagen-containing secretory granules are found in the process, particularly near its base where the surrounding collagen fibrils (Coll) are packed less densely. The fibrils become thicker and more compact toward the dentin. B, A process at the predentin-dentin junction. A bundle of larger collagen fibrils, von Korff’s fibers, runs parallel to the process.

A, Scanning electron micrograph of a cross-fractured odontoblast at the level of the Golgi apparatus (Golgi). Rough endoplasmic reticulum (rER) surrounds the Golgi apparatus. B, Transmission electron micrograph. Golgi saccules exhibit cylindrical (cd) and spherical (sd) distentions in which the collagen molecule is assembled. m, Mitochondria; mvb, multivesicular body.

Cytochemical preparations for a Golgi-associated phosphatase using a light (A) and electron (B) microscope, illustrating the position and extent of this protein-synthesizing organelle in the supranuclear compartment. B, Reaction product is found selectively in the intermediate saccules of the Golgi complex. BV, Blood vessel; m, mitochondria; N, nucleus; Odp, odontoblast process.

A, Low-magnification view of odontoblasts taken by examining the section in the scanning electron microscope. These tall, bowling pin–shaped cells border the pulp and form a tight layer against predentin. Despite the presence of nuclei (N) at different levels, there is only one layer of odontoblasts that extends cell processes (Odp) across predentin into dentin. Blood vessels (BV) are present among the cells. B, A large portion of the supranuclear compartment is occupied by an extensive Golgi apparatus (Golgi) surrounded by abundant rough endoplasmic reticulum (rER) profiles. cw, Cell web; m, mitochondria.

Dead tracts in a ground section of dentin. A, Under incident illumination the tracts appear white because light is reflected. B, Under transmitted illumination the tracts appear dark because air in them refracts the light.

Difference in pulp volume between halves of a young tooth (A) and an old tooth (B).Figure 8-66 Dystrophic calcification in the center of the pulp chamber. Inset, Dystrophic calcification beginning in a vessel wall.

Nerve at the predentin-dentin (PD, D) junction demonstrated by staining for nerve growth factor receptor in a tangential section. Its extensive ramification is notable.

Nerve fibril arising from the plexus of Raschkow is shown passing between the odontoblasts and looping within the predentin.

Electron micrograph of pulpal horn dentin seen in cross section. Many of the tubules contain a process and multiple fine neural elements.

Free (false) pulp stones in an aged dental pulp.

A, Changes in the dental papilla associated with initiation of dentin formation. B, The panels labeled a to d are higher magnifications as the corresponding areas in A. a, An acellular zone (*) separates the undifferentiated cells of the dental papilla (preodontoblasts, pOd) from the differentiating inner dental epithelium (ameloblasts, Am). b to d, The preodontoblasts develop into tall and polarized odontoblasts (Od) with the nucleus away from the matrix they deposit at the interface with ameloblasts. The matrix first accumulates as an unmineralized layer, predentin (PD), which gradually mineralizes to form mantle dentin (D). SI, Stratum intermedium; SR, stellate reticulum.

Low-power photomicrograph of the dentin-pulp complex of a premolar tooth. Primary and secondary dentin are present in this tooth. The amount of secondary dentin deposition varies, more having occurred on the right than on the left. The cell-free zone (of Weil) beneath the odontoblast layer is clearly visible, as is the cell-rich zone.

Dentin innervation demonstrated by immunocytochemical staining of nerve growth factor receptor (NGFR). NGFR is present in some of the dentinal tubules.

Plexus of Raschkow in a silver-stained demineralized section. The ascending nerve trunks branch to form this plexus, which is situated beneath the odontoblast layer.

Light microscopic appearance of fibroblasts in the dental pulp.

Photomicrographs of a tooth showing the general pattern of distribution of nerves and vessels in the root canal (A) and in the pulp chamber (B).

Lymphatic vessels (arrows) in the dental pulp.

Electron micrographs of an arteriovenous shunt in dental pulp. Such a shunt is characterized by a lining of cuboid endothelial cells (A) that contrasts with the flattened endothelial lining cells of venules (B).

Resin cast of the vasculature of a canine molar. On the right, the peripheral vasculature can be seen. On the left, this vaculature has been removed to show the central pulp vessels and their peripheral ramifications.

Dendritic cells in the odontoblast layer.

Nerves in radicular pulp. Side branches are directed to the dentine, and a plexus of Raschkow is absent.

Electron micrograph of a cross section of pulp showing a mixture of myelinated and nonmyelinated nerves.

Dystrophic calcification in the center of the pulp chamber. Inset, Dystrophic calcification beginning in a vessel wall.

Decreased pulp volume with age. The pulp has been reduced considerably by the continued deposition of dentin on the pulp chamber floor.

Association between immunocompetent cell (IC), vascular (V), and neural elements (N).

Undemineralized section of the mature dentin-pulp complex. The vascularity of the pulp is evident. The cell-free zone of Weil can be clearly seen beneath the odontoblast layer.

Tooth section stained to demonstrate the nerves of the pulp. Note the plexus beneath the odontoblast layer.

Ectopic calcification. Illustrated here is a “free” pulp stone; it is not attached to dentin. Note the concentric layering of its matrix, which reflects a phasic growth pattern.

Primary dentin. Odontoblasts border the pulp chamber and line the predentin surface. Below the odontoblasts is a cell-free zone followed by a cell-rich zone.

Pulp stone (false). Note the concentric layers of matrix and the absence of cells. Its proximity to dentin surface suggests that it may eventually become embedded in it (attached pulp stone).

Odontoblast differentiation and initial dentin formation. An acellular zone separates the undifferentiated cells of the dental papilla from the differentiating ameloblasts. The preodontoblasts gradually develop into tall and polarized cells with their nucleus away from the matrix; they deposit at the interface with ameloblasts.

Histologic preparation illustrating the transformation of predentin into mineralized dentin along a linear mineralization front (arrows).

Globular mineralization results in an irregular mineralization front (arrows) at the predentin-dentin interface.

Odontoblasts have apical processes that remain in the matrix they form.

Silver-stained section illustrating the globular nature of the mineralization front.

Interglobular dentin represents unmineralized matrix regions resulting from imperfect globular mineralization.

The junction between primary and secondary dentin is characterized by a change in the direction of dentinal tubules (arrowheads).

Higher magnification of the acellular zone separating differentiating odontoblasts and ameloblasts.

Ground section of dentin showing the dentinal tubules in which the odontoblast processes run.

The first secretory products of odontoblasts accumulate as an unmineralized layer, predentin, that gradually mineralizes to form mantle dentin.

Thicker fibers of collagen (arrowheads) originate from between odontoblasts and extend into the forming mantle predentin. These fibers are referred to as von Korff’s fibers.

Mineralization foci appear in the initial matrix deposited by odontoblasts. These foci eventually grow and coalesce to form the mantle dentin.

Primary dentin. Odontoblasts border the pulp chamber and line the predentin surface. Below the odontoblasts is a cell-free zone followed by a cell-rich zone.

Reference: Nanci A.: Ten Cate's Oral Histology: Development, Structure, and Function, 6th Edition, 2003, Mosby.