Dentin

• Dentin-Pulp Complex


  The soft connective tissue that occupies the central portion of the tooth (dental pulp) and the bonelike matrix characterized by multiple closely packed dentinal tubules that traverse its entire thickness and contain the cytoplasmic extensions of odontoblasts (dentin)
• Dentin


  • Bonelike matrix 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
  • Cell bodies of the odontoblasts are aligned along the inner aspect of the dentin, against a layer of predentin, where they also form the peripheral boundary of the dental pulp
• Dental pulp


  • Soft connective tissue that occupies the central portion of the tooth
  • Space it occupies is the pulp cavity, which is divided into a coronal portion (pulp chamber) and a radicular portion (root canal)
  • Pulp chamber conforms to the general shape of the anatomic crown and extends into pulp horns under the cusps
  • Root canal (or root canal system) terminates at the apical foramen, where the pulp and periodontal ligament meet and the main nerves and vessels enter and leave the tooth
  • Connections between the pulp and the periodontal tissues may occur along the lateral surface of the root through the lateral canals
• Predentin


  Unmineralized matrix that lines the innermost (pulpal) portion of dentin, consisting principally of collagen and similar to osteoid in bone
• Dentinogenesis


  The process of dentin formation
• Collagen type I in dentin

  • Acts as a scaffold that accommodates a large proportion of the mineral in the holes and pores of fibrils
  • Non-collagenous matrix proteins regulate mineral deposition and can act as inhibitors, promoters, and/or stabilizers
• Mantle dentin


  The outer layer of primary dentin, near enamel or cementum, that differs from the rest of the primary dentin in the way it is mineralized and in the structural interrelation between the collagenous and non-collagenous matrix components
• Primary dentin


  • Most of the tooth is formed by primary dentin, which outlines the pulp chamber and is referred to as circumpulpal dentin
• Secondary dentin


  • Develops after root formation has been completed and represents the continuing, but much slower, deposition of dentin by odontoblasts
  • Has a tubular structure that, though less regular, is for the most part continuous with that of the primary dentin
  • Ratio of mineral to organic material is the same as for primary dentin
  • Not deposited evenly around the periphery of the pulp chamber, especially in molar teeth, leading to an asymmetrical reduction in its size and shape
• Tertiary dentin


  • Produced in reaction to various stimuli, such as attrition, caries, or a restorative dental procedure
  • Unlike primary or secondary dentin that forms along the entire pulp-dentin border, tertiary dentin is produced only by those cells directly affected by the stimulus
  • Quality (architecture) and quantity of tertiary dentin produced are related to the cellular response initiated, which depends on the intensity and duration of the stimulus
  • May have tubules continuous with those of secondary dentin, tubules sparse in number and irregularly arranged, or no tubules at all
  • Cells forming tertiary dentin line its surface or become included in the dentin (osteodentin)
  • Subclassified as reactionary (deposited by preexisting odontoblasts) or reparative (deposited by newly differentiated odontoblast-like cells)
• Pattern of dentin formation

  1. Dentin formation begins at the bell stage of tooth development in the papillary tissue adjacent to the concave tip of folded inner enamel epithelium, the site where cusp development begins

  2. From that point, dentin formation spreads down the cusp slope as far as the cervical loop of the enamel organ, and the dentin thickens until all the coronal dentin is formed

  3. Root dentin forms at a slightly later stage of development and requires the proliferation of epithelial cells (Hertwig's epithelial root sheath) from the cervical loop of the enamel organ around the growing pulp to initiate the differentiation of root odontoblasts

  4. Completion of root dentin formation does not occur in the deciduous tooth until about 18 months after it erupts and in the permanent tooth until 2 to 3 years after it erupts
• Dentinogenesis


  1. Dentin is formed by cells called odontoblasts that differentiate from ectomesenchymal cells of the dental papilla following an organizing influence that emanates from the inner enamel epithelium

  2. Dental papilla is the formative organ of dentin and eventually becomes the pulp of the tooth, a change in terminology generally associated with the moment dentin formation begins
• Odontoblast differentiation


  1. Differentiation of odontoblasts from the dental papilla in normal development is brought about by the expression of signaling molecules and growth factors in the cells of the inner enamel epithelium

  2. Ectomesenchymal cells adjoining the acellular zone rapidly enlarge and elongate to become preodontoblasts first and then odontoblasts as their cytoplasm increases in volume to contain increasing amounts of protein-synthesizing organelles

  3. Acellular zone between the dental papilla and the inner enamel epithelium gradually is eliminated as the odontoblasts differentiate and increase in size and occupy this zone
• Formation of mantle dentin


  1. First sign of dentin formation is the appearance of distinct, large-diameter collagen fibrils (von Korff's fibers) consisting of collagen type III associated with fibronectin, originating deep among the odontoblasts and extending toward the inner enamel epithelium

  2. As the odontoblasts continue to increase in size, they also produce smaller collagen type I fibrils that orient themselves parallel to the future dentino-enamel junction

  3. Coincident with this deposition of collagen, the plasma membrane of odontoblasts adjacent to the differentiating ameloblasts extends stubby processes into the forming extracellular matrix

  4. Odontoblast also buds off a number of small, membrane-bound vesicles known as matrix vesicles, which come to lie superficially near the basal lamina

  5. Odontoblast then develops a cell process, the odontoblast process or Tomes' fiber, which is left behind in the forming dentin matrix as the odontoblast moves away toward the pulp
• Control of mineralization


  1. Mineralization is achieved by continuous deposition of mineral, initially in the matrix vesicle and then at the mineralization front

  2. Calcium channels of the L type have been demonstrated in the basal plasma membrane of the odontoblast, and alkaline phosphatase activity and calcium adenosinetriphosphatase activity at the distal end of the cell are consistent with a cellular implication in the transport and release of mineral ions into the forming dentin layer
• Patterns of mineralization


  1. Globular (or calospheric) calcification involves the deposition of crystals in several discrete areas of matrix by heterogeneous capture in collagen, with continued crystal growth and fusion to form a single calcified mass (best seen in mantle dentin region)

  2. In circumpulpal dentin the mineralization front can progress in a globular or linear pattern, with the size of the globules depending on the rate of dentin deposition (larger globules where deposition is fastest, more uniform linear pattern where deposition is slower)
• Formation of root dentin

  1. The epithelial cells of Hertwig's root sheath initiate the differentiation of odontoblasts that form root dentin

  2. The outermost layer of root dentin, the equivalent of mantle dentin in the crown, shows differences in collagen fiber orientation and organization, in part because the collagen fibers from cementum blend with those of dentin
• Secondary and tertiary dentinogenesis

  1. Secondary dentin is deposited after root formation is completed, is formed by the same odontoblasts that formed primary dentin, and is laid down as a continuation of the primary dentin

  2. Tertiary dentin is deposited at specific sites in response to injury by damaged odontoblasts or replacement cells from pulp, with the rate of deposition depending on the degree of injury (more severe injury leads to more rapid deposition)
• Histology of dentin


  • Dentinal tubules, peritubular and intertubular dentin, areas of deficient calcification (interglobular dentin), incremental growth lines, and the granular layer of Tomes in the root portion
  • Odontoblast processes run in canaliculi that traverse the dentin layer and are referred to as dentinal tubules, forming a network for the diffusion of nutrients throughout dentin
  • Dentinal tubules follow an S-shaped path from the outer surface of the dentin to the perimeter of the pulp in coronal dentin, with the curvature least pronounced beneath the incisal edges and cusps
• Dentin deposition rate


  The more severe the injury, the more rapid the rate of dentin deposition
• Cells often become trapped in the newly formed dentin matrix, and the tubular pattern becomes grossly distorted
• Structural features of dentin

  • Dentinal tubules
  • Peritubular dentin
  • Intertubular dentin
  • Interglobular dentin
  • Incremental growth lines
  • Granular layer of Tomes
• Dentinal tubules


  Canaliculi that traverse the dentin layer, containing odontoblast processes
• Dentinal tubules


  • Extend through the entire thickness of the dentin
  • Form a network for the diffusion of nutrients throughout dentin
  • Follow an S-shaped path in coronal dentin
  • Run a straight course in root dentin
  • Taper, being larger near the pulp and thinner at the dentinoenamel junction
  • Have a significant reduction in average density in radicular dentin compared to cervical dentin
  • Branch extensively, creating a profuse anastomosing canalicular system
• Peritubular dentin


  A collar of more highly calcified matrix that delimits the dentinal tubules
• Sclerotic dentin


  Dentinal tubules that have become occluded with calcified material, causing the dentin to appear glassy and translucent
• Intertubular dentin


  The dentin located between the dentinal tubules, consisting of a tightly interwoven network of type I collagen fibrils with apatite crystals deposited in the ground substance
• Interglobular dentin


  Areas of unmineralized or hypomineralized dentin where globular zones of mineralization (calcospherites) have failed to fuse
• Incremental growth lines


  Minute changes in collagen fiber orientation that mark the normal rhythmic, linear pattern of dentin deposition
• Granular layer of Tomes

  A granular-appearing area just below the surface of root dentin, related to a special arrangement of collagen and noncollagenous matrix proteins at the interface between dentin and cementum
• Zones of the dental pulp

  • Odontoblastic zone
  • Cell-free zone of Weil
  • Cell-rich zone
  • Pulp core
• Odontoblasts


  Cells that form a layer lining the periphery of the pulp and have a process extending into the dentin
• Odontoblasts


  • Appear in a palisade pattern in the crown of the mature tooth
  • Vary in morphology from an active synthetic phase to a quiescent phase
  • Cannot undergo further cell division after differentiation
• Fibroblasts


  The most numerous cells in the pulp, responsible for forming and maintaining the pulp matrix
• Undifferentiated ectomesenchymal cells


  The pool from which connective tissue cells of the pulp are derived, able to give rise to odontoblasts and fibroblasts
• Inflammatory cells


  T lymphocytes, leukocytes, and antigen-presenting dendritic cells found in the pulp, involved in immunosurveillance
• Pulp matrix


  The extracellular compartment of the pulp, consisting of collagen fibers (primarily type I and III) and ground substance (glycosaminoglycans, glycoproteins, and water)
• Dentin is a mineralized connective tissue composed of hydroxyapatite crystals, collagen fibers, and water.
• Odontoblasts have long cytoplasmic processes that extend into the predentin matrix.
• Odontoblast processes extend into the tubules to form the cell body.