Dentine Histology PDF

HISTOLOGY OF DENTINE BY DR. R AMSTERDAM  Introduction  Dentin is a living, sensitive tissue not normally exposed to the oral environment.  It provides bulk and general form of the tooth. It is a hard tissue with tubules all throughout it.  Root dentin is...

HISTOLOGY OF DENTINE BY DR. R AMSTERDAM  Introduction  Dentin is a living, sensitive tissue not normally exposed to the oral environment.  It provides bulk and general form of the tooth. It is a hard tissue with tubules all throughout it.  Root dentin is covered by cementum, and crown dentin is covered by enamel.  Dentin is composed primarily of an organic matrix of collagen fibers and the mineral hydroxyapatite.  It is classified as primary, secondary, or tertiary on the basis of the time of its development and the histologic characteristics of the tissue.  Physical Properties  Dentin, which forms the bulk of the tooth, is yellowish in contrast to the whiter enamel.  It appears darker if a root canal procedure has been performed.  Dentin is composed of 70% inorganic hydroxyapatite crystals, 20% organic collagen fibers with small amounts of other proteins, and 10% water by weight.  Dentin is softer then enamel, although it is slightly harder than bone or cementum.  More radiolucent than enamel but much more dense or radiopaque than pulp. The radiolucency is due to the lack of mineral compared to enamel.  Dentin is resilient or slightly elastic, and this allows the impact of mastication to occur without fracturing the brittle overlying enamel.  Classification of Dentine  Primary Dentine – From formation to eruption; Major component of a tooth; Composed of mantle and circumpulpal Dentine, separated by zone of Globular Dentine  Secondary Dentine – After eruption, throughout life  Tertiary Dentine / Reparative / Response Dentine – Response to irritation and aggression  Primary Dentine  Primary dentin constitutes the bulk of dentin in crowns and roots of teeth.  It is characterized by the continuity of tubules from pulp to dentinoenamel junction and by incremental lines that indicate a daily rhythmic deposition pattern of approximately 4 mm of dentin  Mantle dentine is the first primary dentin formed ( prior to tooth eruption). It is deposited first at the dentino-enamel junction and extends approximately 150 mm from the junction pulpward to the zone of interglobular or globular dentin.  Normal circumpulpal dentine directly underlies mantle and globular dentin and comprises the bulk of the tooth’s primary dentin. It may be 6 to 8 mm thick in the crown and a little thinner in the roots.  Globular dentine contains hypomineralized areas between the globules, termed interglobular spaces- which are less mineralized areas between the globules.  Secondary Dentine  Forms internally to primary dentin of the crown and root.  It develops after the crown has come into clinical occlusal function and the roots are nearly completed.  This dentin is deposited more slowly than primary dentin, and its incremental lines are only about 1.0 to 1.5 mm apart.  The tubules of primary and secondary dentine are generally continuous unless the deposition of secondary dentin is uneven.  Tertiary Dentine  It is also referred to as Reactionary/Response and Reparative dentine.  It results from pulpal stimulation and forms only at the site of odontoblastic activation.- attrition, abrasion, caries, or restorative procedures, this dentin is deposited underlying only those stimulated areas.  It may be deposited rapidly, in which case the resulting dentin appears irregular with sparse and twisted tubules and possible cell inclusions or it can be formed slowly because of fewer stimuli, the dentin appears more regular, much like primary or secondary dentin.  Reparative dentin at times resembles bone more than dentin and is then termed osteodentin. It can also appear as a combination of several types  Loss of tubular contents results in dead tracts (black streaks) that indicate air in the tubules.  Below the dead tract area in is sclerosed dentin, which protects the pulp from bacteria or bacterial products in the tubules underlying the restoration.  Tubular Characteristics  Dentine is deposited and created by cells which are called ODONTOBLASTS.- hence dentine possesses vitality.  As dentin is formed by odontoblasts, space is provided for the lengthening process of the odontoblast that moves pulpward from the dentinoenamel junction (DEJ).  The odontoblastic process then forms an S curve, which extends to the pulp. As the process elongates, it branches, and its secondary processes appear at nearly right angles to the main process and are contained within canaliculi located perpendicular to the dentinal tubule.  The lateral branches of the odontoblastic processes are seen throughout dentin, crown, and root. These lateral branches are termed canaliculi, secondary branches, or microtubules and are less than 1 mm in diameter.  Some of these lateral branches lead to an adjacent dentinal tubule, and some appear to terminate in the intertubular matrix.  Each of these secondary tubules contains branches of the odontoblastic process that contact the adjacent odontoblasts allowing intercellular communication through gap junctions.  Odontoblastic Processes  Odontoblastic cell processes are cytoplasmic extensions of the cell body that are positioned at the pulp–dentin border junction.  They also extend into the enamel for a short distance as enamel spindles. The odontoblastic processes are largest in diameter near the pulp (3 to 4 mm) and taper to 1 mm near the dentinoenamel junction.  Along the odontoblastic process, lateral branches arise at nearly right angles to the main odontoblastic process, extend into the intertubular dentin, and where they contact adjacent odontoblast processes and form gap junctions.  Peritubular/intratubular dentine  The dentin that immediately surrounds the dentinal tubules is termed peritubular dentin.  This dentin forms the walls of the tubules in all but the dentin near the pulp  It is more highly mineralized (about 9%) than the dentin present between the tubules which is called intertubular dentin.  Between the odontoblastic process and the peritubular dentin there is a space known as periodontoblastic space. This space contains the dentinal fluid.  The normal flow of the fluid is outwards from the pulp. The dentinal fluid has a higher K and a lower Na content.  This fluid movement allows for sensation to be felt. Click to add text  Intertubular dentine  It is located between the dentinal tubules or, more specifically, between the zones of peritubular dentin.  ½ of its volume is organic matrix, specifically collagen fibers, which are randomly oriented around the dentinal tubules  The fibrils range from 0.5 to 0.2 µm in diameter and exhibit cross banding at 64 µm intervals, which is typical for collagen  Hydroxyapatite crystals, which average 0.1 µm in length, are formed along the fibers with their long axes oriented parallel to the collagen fibers Incremental Lines/Von Ebner . This hesitation in dentine formation results in an alteration of the matrix known as incremental lines, imbrication lines, or lines of Von Ebner. Contour lines of Owen  During development of dentin, variations in the metabolism of the organism cause variations in the amount of organic material deposited in the dentin, just as occurs in the enamel.  Changes in the coloration of the dentin are called contour lines of Owen.  The first dentin that is laid down (at the DEJ) forms the mantle layer while subsequent dentin forms the circumpulpal layer. In the crown of tooth, dentinal tubules from S-shaped primary curves.  Interglobular dentine  Sometimes mineralization of dentin begins in small globular areas that fail to coalesce into a homogeneous mass leading to zones of hypomineralization between the globules.  These zones are known as globular dentin or interglobular spaces.  This dentin forms in the crowns of teeth in the circumpulpal dentin just below the mantle dentin, and it follows the incremental pattern  The dentinal tubules pass uninterruptedly through interglobular dentin, thus demonstrating defect of mineralization and not of matrix formation.  Interglobular dentin occurs most frequently in the cervical and middle thirds followed by intercuspal and coronal third in the crown.  In roots, the highest occurrence is seen in the cervical third followed by the middle third  Granular Layer  A granular-appearing layer of dentin is seen underlying the cementum that covers the root.  This layer is known as the granular layer or granular layer of Tomes.  This zone increases slightly in width, proceeding from the cementoenamel junction to the root apex. The zone is believed to be the result of a coalescing and looping of the terminal portions of the dentinal tubules.  The Tomes' granular layer is caused by a coalescing and looping of the terminal portions of the dentinal tubules.  This can be as a result of the odontoblasts turning on themselves during early dentin formation.  These areas remain unmineralized, like interglobular dentin.  The cause of development of this zone is probably similar to the branching and beveling of the tubules at the dentinoenamel junction.  Tomes’ granular layer and interglobular dentin have similarities in their formation, they differ in their mineral content.  Among the hypomineralized areas, Tomes’ granular layer showed highest concentrations of calcium and phosphorus, while interglobular dentin showed a higher content of sulfur.  Dentino-enamel Junction  This is the scalloped junction between dentin and enamel, termed the dentinoenamel junction  Enamel spindles and fine branching of the terminal dentinal tubules in the mantle dentin in addition to scalloping are distinctive characterisitcs of DEJ  Dentine Permeability  Dentinal tubules become occluded by growth of peritubular dentin or by reprecipitation of minerals from demineralized areas of dental caries.  Exposed dentinal surface becomes hypermineralized.  Dentin permeability depends upon the patency of dentinal tubules.  Reduction in dentin permeability would lessen the sensitivity of dentin.  As you get closer to the pulp, dentin permeability increases since the number and diameter of the tubules are more per unit area towards pulp than towards periphery.  The outward flow of dentinal fluid and the odontoblasts act as barriers for entry of bacteria or their toxins