Lec. 7 Dr. Ali H.Murad DENTIN It a hard vital tissue, surrounds the pulp & underlies the enamel on the crown & the cementum on the roots of the teeth. Physical properties: 1-Dentin is pale yellow in color, becoming darker with age. 2-it is harder than bone & cementum, but softer & less brittle than enamel. 3-The specific gravity of dentin is 2.1 g/ml 4-Dentin is resilient or slightly elastic. 5- The dentin is permeable, because it s traversed by tubules. Chemical composition: 1-Dentin consists 35% organic material & water, & 65% inorganic material. 2- The organic substance consists of collagenous fibrils & a ground substance of mucopolysaccharides. 3- The inorganic component consists of hydroxyapatite 4- Dentin also contains small amounts of phosphate, carbonates, & sulphates. Dentin classification 1-Primary dentin: A- Mantle dentin: is the 1 st primary dentin formed at the D.E.J., & extends pulpward to the zone of interglobular dentin. 20 µm in thickness, 1
less mineralized than circumpulpal dentin, and mainly composed of Von Korff s fibers. B- Circumpulpal dentin: directly underlies mantle dentin & comprises the bulk of the tooth s primary dentin & may be 6-8 mm thick in the crown & little thinner in the roots. 2-Secondary dentin: Forms internally to primary dentin of the crown & root. It develops after the crown has come into clinical occlusal function & the roots are nearly completed. This dentin is deposited more slowly than primary dentin, in which the brain signals the dentin to slow the role of the production. This keeps the pulp from being obliterated by the previous rapid rate of dentin formation. 2
3-Tertiary dentin (Reparative Dentin) Result from pulpal stimulation & form only at the site of odontoblastic activation. Whether the formation is due to attrition, abrasion, caries, or restoration, this dentin is deposited underlying only those stimulated areas. It may be deposited rapidly, in which the resulting dentin appears irregular with sparse & twisted tubules. Odontoblasts, fibroblasts, & blood cells have been found in this type of dentin. In contrast, if it is formed slowly because of fewer stimuli, the dentin appears more regular, much like primary or secondary dentin. Reparative dentin resembles bone more than dentin & is then termed osteodentin. Structures of dentin: 1-Dentinal tubules: The course of dentinal tubules resembles a letter S in shape. Starting at right angles from the pulpal surface, the first convexity of this doubly curved course is directed toward the apex of the tooth. These tubules end perpendicular to the D.E.J., & D.C.J., Near the root tip & along the incisal edges & cusps, the tubules are almost straight. 3
2-Peritubular dentin: Is the dentin that immediately surrounds the dentinal tubules. This dentin forms the walls of the tubules. It is highly mineralized (90%), by it s growth, it constricts the dentinal tubules to a diameter of 1µm near the DEJ. 3-Intertubular dentin: It forms the main body of dentin; it is located between the dentinal tubules. Although it is highly mineralized, it likes bone & cementum & about ½ of its volume is organic matrix, especially collagen fibers. 4- Predentin: Is located adjacent to the pulp tissue & is 2-6 µm wide. It is the 1 st formed dentin & is not mineralized. 4
5-Odontoblast process: These are the cytoplasmic extensions of the odontoblasts. The odontoblast cells reside in the peripheral pulp at the pulp-predentin border & their processes extend into the dentinal tubules. The processes are largest in diameter near the pulp & taper further into the dentin. The odontoblast processes divide near the DEJ, & may extend into enamel in the enamel spindles. 6-Incremental lines: A- incremental lines of Von Ebner: Appear as fine striations in dentin, they run at right angles to the dentinal tubules. These lines reflect the daily rhythmic, recurrent deposition These lines decrease after a tooth reaches functional occlusion 5
B- Contour lines of Owen: Some of the incremental lines occasionally are accentuated because of disturbances in the matrix & mineralization process. C- Neonatal line: It is a line that separates between the prenatal & postnatal dentin 7- Interglobular dentin: Sometimes mineralization of dentin begins in small globular areas, that fail to coalesce into a homogenous mass. These results in zones of hypomineralization between the globules, these zones are known as globular dentin or interglobular spaces. This type of dentin forms in the crowns of teeth in the circumpulpal dentin just below the mantle dentin. 8- Granular layer: In dry ground sections of the root dentin, a zone adjacent to the cementum appears granular known as Tome s granular layer This zone increases slightly in amount from the CEJ, to the root apex & is believed to be caused by a coalescing & looping of the terminal portions of the dentinal tubules. 6
Innervations of Dentin: Dentinal tubules contain numerous nerve endings in the predentin & inner dentin (intratubular nerves) no further than 100-150 µm from the pulp. Most of these small nerve endings are located in the coronal zone, especially in the pulp horns. The nerves & their terminals are found in close association with the odontoblast process. It is believed that most of these are terminal processes of the myelinated nerve fibers of the dental pulp. 7