Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Chapter 8 Dentin Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin: Learning Objectives After reading this chapter, the student will be able to: Describe the various types of dentin and the structures they contain. Describe the dental process that lies in the dental tubules. Discuss the relationship of the enamel to the dentin at their junction. Key terms are important to the understanding of the information in this chapter. Please review and become familiar with them. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Dentin Physical properties Dentin classification Predentin Tubular and intertubular relations Incremental lines Granular layer Odontoblastic cell processes Dentinoenamel junction Permeability Repair process Dentin classificationprimary, secondary, and reparative or tertiary dentin. Tubular and intertubular relations: Primary and secondary tubules, intratubular or peritubular dentin, and intertubular dentin. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Dentin Dentin is a living, sensitive tissue. It is composed primarily of an organic matrix of collagen fibers and the mineral hydroxyapatite. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin: Physical Properties Forms bulk of tooth Yellowish in color Composed of 70% inorganic hydroxyapatite crystals, 20% organic fibers, with small amounts of other proteins and 10% water Softer than enamel Harder than bone or cementum Resilient Radiographically, dentin appears more radiolucent than enamel but more radiopaque than pulp. The resilient or elastic nature of dentin allows the impact of mastication to occur without fracturing the brittle overlying enamel. This resilience is partly the result of the presence of tubules throughout the matrix. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin Classification Primary dentin forms the body of the tooth. Mantle Circumpulpal dentin Secondary dentin forms only after tooth eruption. Narrow band that borders the pulp Tertiary or reparative dentin forms only in response to trauma to the pulp. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin Classification: Primary Dentin Mantle dentin is deposited first at the dentinoenamel junction (DEJ). Normal circumpulpal dentin underlies mantle and globular dentin. Mantle dentin extends approximately 150 µm from the DEJ toward the pulp to the zone of interglobular or globular dentin. Circumpulpal dentin comprises the bulk of the tooth’s primary dentin. It may be 6 to 8 mm thick in the tooth crown and thinner in the tooth roots. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin Classification: Structural Differences Mantle dentin is composed of large collagen fibers. Circumpulpal dentin fibers are tenfold smaller than those in mantle dentin. Mantle dentin is slightly less mineralized and contains fewer defects than circumpulpal dentin. Zones of dentin have structural differences. Mantle dentin fibers may be 0.1 to 0.2 µm in diameter, compared with circumpulpal dentinal matrix fibers of 50 to 200 nm in diameter. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin Classification: Structural Differences Globular dentin usually exists only in the tooth crown, but can extend into the root. Such a zone of dentinal matrix is not completely mineralized, and the area of globular calcospherites has not fused correctly. Globular dentin contains hypomineralized areas between the globules, termed interglobular spaces, which are not true spaces. Interglobular spaces are less mineralized areas between the calcified globules. Dentinal tubules run through the interglobular spaces, indicating a defect in mineralization, not a defect in matrix formation. Interglobular dentin is noticeable with vitamin D deficiency, which affects mineralization of teeth and bones. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin Classification: Secondary Dentin Forms internally to primary dentin Develops after crown is in clinical occlusal function and roots near completion Deposited slowly, perhaps to prevent pulp obliteration Deposition of secondary dentin may be uneven, as is the case with molar teeth. More secondary dentin is deposited on the roof and floor of the coronal pulp chamber than on the lateral walls. Why? This is to protect pulpal horns as occlusal function occurs. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin Classification: Tertiary Dentin Results from pulpal stimulation Attrition Abrasion Caries Restorative procedures Forms only at site of odontoblastic activation Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentin Classification: Tertiary Dentin A, Normal dentin. B, Decrease in number of tubules. C, Cell inclusionsodontoblasts, fibroblasts, blood cells. D, Irregular and twisted tubules. E, Combinations of types. Tertiary dentin resembles bone more than dentin and is thus termed osteodentin. Reactionary or response dentin: Term used when original odontoblasts function in deposition. Reparative dentin: Term used when newly recruited odontoblasts begin depositing dentin, which occurs in a more severe injury. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Predentin A band of newly formed, unmineralized matrix of dentin at the pulpal border Predentin is evidence that dentin forms in two stages: 1. Organic matrix is deposited. 2. Inorganic mineral substance is added. During primary dentin formation, 4 µm of predentin is deposited and calcified each day. After occlusion and function, this activity decreases to 1.0 to 1.5 µm per day. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Tubular and Intertubular Relations: Primary and Secondary Tubules Odontoblast process in the dentinal tubule and extending from the DEJ above to the pulp below. What are canaliculi? What is contained within canaliculi? What gives the dentin vitality? What is the surface area ratio of the DEJ to the pulpal surface? How does this surface area ratio affect tubules? What is the significance of secondary tubules? Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Intratubular or Peritubular Dentin A hypermineralized collar or dental matrix that immediately surrounds the tubules Present in tubules throughout dentin, except near the pulp Missing from dentinal tubules in interglobular dentin Interglobular dentin is an area of deficient mineralization like the area of predentin, which is also not calcified. In some areas, the hypermineralized intratubular dentin completely fills the tubules, such as in the area near the DEJ overlying the pulp horns. Hypermineralized intratubular dentin also is found in the peripheral tubules of the root near the cementum. These are areas of very small tubules and areas in which external stimulation might have a role. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Sclerotic Dentin This is the term for dentin with tubules that are completely obliterated. Increases in amount with age Believed to be mechanism to protect pulp Pulp permeability eliminated in areas of sclerotic dentin Sclerotic dentin is found in areas of attrition, abrasion, fracture, and caries. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Intertubular Dentin The body of dentin that comprises the crown and root Consists of organic matric fibers and inorganic crystals of hydroxyapatite Less highly calcified than intratubular dentin Changes little throughout life Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Incremental Lines, Imbrication Lines, or Lines of von Ebner Lines indicating a hesitation in deposit of matrix activity Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Neonatal Line This line reflects the abrupt change in environment that occurs at or near birth. Which dentin has fewer defects? Answer: Prenatal dentin. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Granular Layer of Tomes Result of a coalescing and looping of the terminal portions of the dentinal tubules. It is possible that the odontoblast is initially disoriented as it begins dentin formation. It turns at right angles to the root surface and proceeds pulpward, causing the dentinal matrix in this area to be defective. This disorientation of the odontoblasts could be due to the initial incomplete information transmitted by the inner root sheath cells, resulting in the granular layer. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Odontoblastic Cell Processes Cytoplasmic extensions of the cell body positioned at the pulp-dentin border These processes extend to the DEJ. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Odontoblastic Cell Processes In some cases, these processes extend into the enamel for a short distance as enamel spindles. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Odontoblastic Cell Processes The odontoblastic processes are largest in diameter near the pulp (3 to 4 µm) and taper to 1 µm near the DEJ. During development, these processes were divided near the DEJ into branched processes but as the odontoblast matured, the processes were retracted and formed a single main process. Along the odontoblastic process, lateral branches arise at nearly right angles to the main odontoblastic process, extend into the intertubular dentin, and contact adjacent odontoblast processes. They form gap junctions and sometimes extend into adjacent dentinal tubules. Within the odontoblastic process are microtubules, small filaments, occasional mitochondria, and microvesicles. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Odontoblastic Cell Processes Loss of the odontoblastic process usually results in the appearance of dead tracts in dentin. In the dentin underlying an area of attrition or a carious lesion, odontoblasts may die and processes disintegrate, producing a group of open tubules that contain debris and spaces. If these tubules are open to overlying caries, bacteria can enter them and migrate to the pulp, causing inflammation. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Dentinoenamel Junction The junction between dentin and enamel is scalloped to enhance contact and adherence of the two structurally different tissues. Scalloping is accentuated in the cusps where incisal or occlusal contact is greatest. The DEJ also is characterized by enamel spindles and fine branching of the terminal dentinal tubules in the mantle dentin. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Permeability Size of tubules at the pulp border (C) compared with those in the floor of the cavity (B and D) and at the DEJ (A). Deposition of reparative dentin underlies invading caries. Tubules are cone-shaped and permit increased permeability from the cavity wall or floor to the pulp. Branching tubules increases the permeability. Also, because the peritubular dentin is more highly calcified than the intertubular, the etching of a cavity causes an increase in the diameter of the tubule. The only feature that protects the pulp is that it has higher osmotic pressure than the area of the DEJ. Fluid is constantly being forced outward by this increased pressure of the pulp. Bacteria can percolate down the dentinal tubules to the pulp. Tubules of dentin are blocked by the production of a smear layer on the floor or walls of the cavity preparation. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Repair Process Changes in dentin are caused by: Odontoblastic degeneration Formation of dead tracts Calcification of tubules, leading to sclerosis Tertiary or reparative dentin formation After death and degeneration of odontoblast, dead tracts appear, sclerosis may occur, and further reparative dentin secreted by replacement odontoblast in the pulp forms. Dentin is laid down throughout life. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Repair Process Pulp in the first molar appears normal, with no sign of sclerotic dentin or dead tracts. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Questions and Considerations Which type of dentin comprises the greater part of the crown and root? What factors affect permeability of the dentin? Why are newly restored teeth sensitive for a period of time? What is sclerotic dentin? Review and check for student understanding. Copyright © 2014 by Mosby, an imprint of Elsevier Inc.