Dentin 1 PDF

Dentin Dentin ENAMEL 1 1  Dentin Dentin: 1. Dentin is the mineralized,Living, vital tissue that forms main bulk of the tooth. Covered by enamel in the crown and by...

Dentin Dentin ENAMEL 1 1  Dentin Dentin: 1. Dentin is the mineralized,Living, vital tissue that forms main bulk of the tooth. Covered by enamel in the crown and by cementum in the root. Surrounds the soft tissue of the pulp. 2. Capable of repair (unlike Enamel), by deposition of new layers by the odontoblasts lining pulpal surface. ►Physical characteristic: Color light yellowish (become darker with age). Seen through the overlying translucent enamel Hardness It is less hard than enamel, harder than cementum and bone. Harder in permanent than deciduous teeth. Resiliency it is viscoelastic (unlike enamel) subjected to slight deformation. elastic property of dentin is important for proper functioning of the tooth to provide flexibility to prevent fracture of the overlying brittle enamel. Thickness 3-10mm or even more more radiolucent than enamel, more radiopaque than cementum and bone due to Radiograph lower mineral content. Enamel is more radiopaque than dentin. Tissue with high mineral content appears more radiopaque. Permeability (Decrease with age) Due to its tubular structure. It Is permeable to certain molecules which pass: from pulp to DEJ from outer environment crossing enamel to dentin reaching pulp. 2  Dentin ►Chemical characteristic: Mature dentin composed of: 70% inorganic material, 20% organic material, 10% water by weight. Inorganic consists mainly of calcium hydroxyapatite crystals. component 70% The crystals are plate like-shape, appear needle shape in edge view. consists of fibrils embedded in an amorphous ground substance. 20% Collagenous and non-collagenous proteins Organic ❑ Collagen (90%) component 20% ❑ Lipids ❑ Proteoglycans ❑ non-collagenous proteins ►Classification of dentin According to development: 1ry dentin 2ry dentin 3ry dentin dentin formed during Formed after root Formed in response to pathologic development until root completion stimuli completion: Throughout life. In localized areas: A. Mantle (below ADJ) At the entire pulp dentin a. Reactive. B. Circumpulpal surface b. Reparative. (the rest of dentin) At very slow rate unless stimulated 3  Dentin Histological Structure Odontoblastic processes In fully formed tooth, the odontoblasts are normally found in a continuous layer of closely packed cells on the pulpal surface of dentin. Each odontoblasts gives cytoplasmic process which traverses the whole thickness of dentin in a fine tubule called Dentinal tubules. The processes are largest in diameter near the pulp (3-4µm), taper to 1µm further into dentin. Its cytoplasmic content is sparse; Near its base: (in predentin), contain strands of mitochondria.its predominant structure is microtubules and filaments. In calcified dentin, contain microtubules, microfilaments and vesicles for transport and discharge of materials into periodontoblastic space. Occasionally mitochondria, lysosomes, coated vesicle and micro- vesicle. Each processes gives off fine branches along its course called Lateral branches, originate at right angle to the dentinal tubules. These lateral branches unite along their course with those of adjacent processes. At the outer dentin surface, the tubules divide into 2 main branches called Terminal branches. These terminal branches unit with each other forming a plexus beneath the outer dentin surface near ADJ. 4  Dentin Dentinal tubules The unit structure of dentin is the dentinal tubules which are closely packed traverse the entire thickness of dentin. Dentinal tubules contain for at least part of their length the cytoplasmic processes of odontoblasts or tom's fibers (odontoblastic processes). They are closely packed towards the pulpal surface than on the outer surface because of the smaller pulpal surface of dentin. 5  Dentin 1ry curvature 2ry curvature the tubules take S shaped along its course these are the result of the spiral track taken by where first curve convex facing root ward. odontoblasts during its course from the outer dentin to In the root portion and under cusp or incisal the pulp edge, tubules take straight course. The dentinal tubule is wider (taper) at the pulpal surface than at the ADJ(4:1). Diameter of tubules are: 2.5 µmnear the pulpal surface 1.2 µm in mid root portion Diameter 900 nmnear ADJ. Each DT gives off side branches along its course called Lateral branches, originate at right angle to the dentinal tubules which unite along their course with those of adjacent processes. Branches Terminal branches: ✓ At the outer dentin surface near ADJ: the tubules divide into 2 main branches called Terminal branches which may explain increased sensitivity at this region. 6  Dentin Effect of DTs profuse branching ???? Make dentin permeable which may provide a pathway for the invasion of caries. ❑DTs are filled with tissue fluid and occupied for part of their length by the odontoblastic processes. ❑In the adult tissue, the extent of the processes in DT varies. Inter-tubular dentin Dentin located between the dentinal tubules is called inter-tubular dentin It consists of tightly interwoven network of type I collagen fibrils in which the apatite crystals are deposited. The fibrils are arranged in randomly roughly right angle to the dentinal tubules. It forms the main bulk of dentin. Peri-tubular dentin (intra-tubular dentin) Highly calcified matrix that immediately surrounds the dentinal tubules. It is shown to be hyper mineralized with little collagen fibrils. Transverse ground section: peri-tubular dentin appears as translucent rings around odontoblastic processes spaces with inter-tubular dentin in between. 7  Dentin →Periodontoblastic space It is the space exists between the wall of the tubules and odontoblastic processes. This space contains “tissue fluid”, dentinal lymph. It considered important because tissue change occur in it. Cytoplasmic vacuoles discharged from odontoblastic processto this space. “tissue fluid” within the pulp and dentinal lymph continued into dentin through this space. Inter-globular dentin These are areas of hypomineralized dentin where globular zones of mineralization failed to fuse into homogenous mass within mature dentin so areas of organic matrix between globules will remain uncalcified bounded by curved outlines of adjacent globules. Location: ✓ It is seen most frequently in circumpulpal dentin just below mantle dentin ✓ in crown next to ADJ where pattern of mineralization is largely globular. ✓ Its incidence increase with vit D deficiency and increased fluorine intake during dentinogenesis. Because it is defect in mineralization (not of matrix formation) so: ✓ dentinal tubules pass uninterrupted through interglobular dentin ✓ no peri-tubular dentin exists. ✓ In dried ground section, it is called interglobular dentin spaces. 8  Dentin Granular Layer of Tomes It is a constant feature of root dentin immediately adjacent to cementum. It appears granular and best seen in ground section as black granules. It was thought to be associated with minute hypomineralized areas of interglobular dentin but differ in: 1- They are smaller. 2- They don’t follow any incremental pattern. 3. Dentinal tubule doesn’t cross it. 4. It may represent section through looped terminal portion of dentinal tubules. 5. Interference with mineralization. Remember Interglobular dentin Tomes' granular layer Size ✓ Large ✓ Small granular in appearance Cause ✓ Areas of unmineralized or ✓ it results from the looping of the terminal hypomineralized dentin (sometimes portions of DT which is a result different present). orientation of odontoblastic process (always present) Site ✓ Appear in the crown just below mantle ✓ Appear in the root adjacent to the cementum. ✓ dentin. IL ✓ Follow incremental line pattern ✓ Does not follow any incremental pattern. ✓ In badly formed tooth it appears in the root 9  Dentin Interglobular dentin Incremental lines of dentin a. Incremental lines of Von-Ebner: They reflect normal rhythmic linear pattern of dentin deposition of daily 4- 8 microns in crown, much less in root. These incremental lines at run at right angles to the dentinal tubules in an inward and root ward direction. b. Contour line of Owen: It is more accentuated incremental lines of von Ebner (Exaggerated contour lines), resulted from disturbance in matrix mineralization process. It is easily seen in longitudinal ground section. ❑ Reasons for its formation: ✓ Represent normal physiologic alterations mineralization, in the pattern of which occur at less frequent intervals. c. Neonatal line: ✓ Result from the changes in physiology (nutritional, hormonal, etc.) at birth. ✓ Seen in the primary teeth and the first permanent molars. ✓ The dentin nearer the ADJ was formed prior to birth, and the dentin nearer to the pulp was formed after birth. 10  Dentin Dentin Junctions a- Dentino-enamel junction: Previously described in enamel. b- Dentino-cemental junction: It is usually smooth in permanent teeth, but scalloped in deciduous teeth. It is often difficult to be seen, it is masked by the granular layer of tomes. 11