Dentin PDF

Dentin By Dr. Asmaa Ahmed Foad Dentin: ▪ is the yellowish tissue that makes up the bulk of all teeth. ▪ It is harder than bone but softer than enamel and consists mainly of apatite crystals of calcium and phosphate ▪ Sensitive to pain, pressure, an...

Dentin By Dr. Asmaa Ahmed Foad Dentin: ▪ is the yellowish tissue that makes up the bulk of all teeth. ▪ It is harder than bone but softer than enamel and consists mainly of apatite crystals of calcium and phosphate ▪ Sensitive to pain, pressure, and temperature Physical properties Colour Young age light yellow With advancing age becomes darker Consistency Elastic and resilient Harder than bone but softer than enamel  Chemical properties BY WEIGHT 70% INORGANIC CONTENT 20% ORGANIC CONTENT 10% WATER  Histologic structure of dentin Odontoblasts Are present in the pulp and are arranged in a layer lining the pulpal surface of dentin. Each cell gives out a long thin process which enters a hollow tube-like structure within the dentin called as “dentinal tubule” Dentinal tubules :Traverse throughout the thickness of dentin Follows a gentle curvature in the crown which resembles “S shape” Starting from the pulpal surface the first convexity of the curvature is towards the root Curvature is less prominent in the root portion Dentinal tubules The tubules are perpendicular to the dentinoenamel junction and the dentino-cemental junction Near the root tips and incisal edges, the tubules are almost straight Surface area of dentin is greater at enamel surface than pulpal surface dentinal tubules are further apart at enamel surface of dentin: Tubules are larger in diameter at the pulpal end (3-4µm) as compared to enamel end (1µm) COURSE: Primary curvature: Straight course: in incisal and occlusal thirds & dentin of root S shape course: in the rest of dentin which results from crowding of odontoblasts as they move from DEJ (larger side) towards pulp (smaller side) during Dentinogenesis. Secondary curvature: Dentinal tubules shows minor spiral like kinks (curvatures) along their length of their primary curvature  The diameter near the pulp is 4 microns and at the outer surface is 1 microns No. of tubules per unit area at the pulpal surface is about 4 times that of enamel surface More tubules per unit area in the crown portion as compared to root Lateral branches of dentinal tubules are called “canaliculi” or “microtubules” (1µm in diameter) Few dentinal tubules extend through the DEJ into enamel called enamel spindles Contents of dentinal tubules 1- odontoblastic process 2- extracellular fluid, tissue changes in dentin occurs in this fluid. 3- afferent nerve endings Odontoblastic process contains: 1- numerous organelles in predentin area: mitochondria, RER, lysosomes, microtubules, intermediate filaments. 2- organelles are few in odontoblastic process present in mineralized dentin. Odontoblastic process Odontoblastic process gives off fine branches along its course which are contained in lateral extensions of dentinal tubules These lateral branches unite along their course with those of adjacent processes At the outer dentin surface the odontoblastic process and dentinal tubules usually terminates by dividing into two main branches which unite with terminal branches of neighboring processes to form plexus beneath DEJ. In crown some of terminal branches of odontoblastic processes cross DEJ and terminate in enamel as enamel spindles In root many dentinal tubules end in Tome’s granular layer Peritubular dentin(intratubular dentin) Dentin that immediately surrounds the dentinal tubules Highly mineralized contain 40% minerals more than intertubular dentin mineralization reaches 90%. as it faces pulpal tissue fluid inside the tubules (dental lymph). Lost in transverse demineralized sections and odontoblastic processes appear surrounded by empty space. transverse ground sections, it appears as shining ring surrounds black dots (odontoblastic process spaces) Inter-tubular dentin The main bulk of primary dentin present between dentinal tubules. Less mineralized than peritubular dentin About one half of the volume is organic matrix made up of collagen fibers oriented around the dentinal tubules Hydroxyapatite crystals (0.1µm in length) are present with long axis parallel to collagen fibers Appears in transverse demineralized sections between dentinal tubule spaces as it is less mineralized and contain more organic matrix. Appears darker than peritubular dentin. Types of dentin Predentin 2µm - 6µm wide layer of unmineralized dentin matrix located adjacent to pulp tissue First formed dentin (dentin matrix) Thickness depends on the activity of odontoblasts 1-PRIMARY DENTIN Dentin formed before root completion (dentin formed during tooth development which is divided into: 1- Mantle dentin 2-Circumpulpal dentin Mantle dentin : First formed dentin in the crown ❑ Seen just below the DEJ, 20µm in thickness ❑ Organic matrix is formed by collagen fibrils arranged perpendicular to the DEJ ❑ Collagen fibers are termed von Korf’s fibers, they are large and thick ❑ Globular mechanism of calcification Circumpulpal dentin : Remaining portion of primary dentin which forms the bulk of the tooth ❑ Collagen fibrils are much smaller in diameter (0.05µm) and are more closely packed together and parrellel DEJ ❑ May be slightly more mineralized than mantle dentin ❑ linear mechanism of calcification and mixed below mantle dentin Secondary Dentin Develops after root formation Slower rate of deposition Tubules are less regular There is a line between primary and secondary dentin called line of demarcation Tertiary Dentin 1- Reactionary Dentin is the secretion of a tertiary dentine matrix by surviving odontoblast cells in response to an appropriate stimulus. 2- Reparative dentin: formed by UMC IN SUB ODONTOBLASTIC LAYER Hypocalcified Structures of Dentin - Incremental lines of dentin A- Incremental lines of Von Ebner The daily deposition of dentin matrix is approximately 4 μm But the changes in collagen fiber direction every 5 days are exaggerated and form an accentuated band called Incremental lines of Von Ebner. So, Incremental lines of Von Ebner are alternative bands show the rhythmic deposition of dentin matrix every 5 days. The distance between them is about 20 μm. In longitudinal sections they appear parallel to each other under the cusp tip or incisal edge.  In cross section, they appear as concentric rings parallel to each other and to ADJ. b- Contour lines of Owen Dark accentuated von Ebner band due to deficiency in mineralization during dentin development. Best seen in longitudinal ground section and usually in the root. c- Neonatal line: An accentuated line of von Ebner separates prenatal from postnatal dentin. It is found in all deciduous teeth and first permanent molars. It is produced by the disturbance in nutrition and the abrupt change in the environmental conditions of the child at birth. D- Interglobular dentin ❑Unmineralized or hypomineralized areas of dentin where pattern of dentin mineralization is globular in nature. ❑Found In circumpulpal dentin just below mantle dentin in crown ❑Large star shaped areas appear black under transmitted light in ground sections ❑Incomplete fusion of dentin globules in circumpulpal dentin just below mantle dentin ❑odontoblastic processes pass uninterrupted in these areas as it is defect in mineralization and not in matrix formation ❑Interglobular dentin follow incremental pattern of dentin formation E- Tomes granular layer ❑ granular thin layer of dentin adjacent to cementum (constant feature of root dentin). ❑ Below CDJ This layer increase slightly in amount from CEJ to root apex ❑ Small black dots seen under transmitted light in ground sections only. They are true spaces and not hypo mineralized areas. ❑ Dentinal tubules don’t cross this layer. ❑ This layer doesn’t follow any incremental pattern of dentin formation Causes They may represent smaller areas of interglobular dentin than those found in the crown. Looping of the terminal ends of the D. tubules due to different orientation of odontoblast processes during initial dentin formation. Special arrangement of collagen fibers and matrix proteins between D. and cementum. F- Dentino cemental junction (DCJ): It is smooth and difficult to determine the boundary between the dentin and cementum. It is marked Tomes, granular layer. G- Dentino enamel junction (DEJ): Scalloped, with convexities facing dentin. It is a very tight junction due to: Interdigitation of crystals of dentin and enamel. Interdigitation of collagen fibers (with its HA crystals) of dentin with the enamel calcification. Dentin Sensitivity Dentin is extremely sensitive to many stimuli (cold air, cavity preparation, heat, electric stimuli…) The most sensitive part of dentin is located at DEJ. There is a nerve plexus located in the sub-odontoblastic layer (beneath odontoblast) in the pulp called the plexus of Raschkow. Theories of Pain Transmission Through Dentin: 1- Direct neural stimulation theory 2- Odontoblastic transduction theory 3- hydrodynamic theory 1- Direct neural stimulation intratubular nerve endings is located between odontoblasts and may extend not more than 100-150 μ in the D.T. So, there are no nerve fibers endings in the outer dentin layer at DEJ which is the most sensitive area in the dentin. It postulates that nerve endings in dentin are responsible for pain when dentin is stimulated. But against this theory: The application of topical anesthesia to the exposed dentin surface doesn't remove the sensitivity. Recently, it was found that intratubular nerve endings and Plexus of Raschkow don't establish themselves till sometime after the tooth has erupted and the newly erupted teeth are sensitive. 2- Odontoblastic transduction theory: The odontoblasts are supposed to be of neural crest origin. So, this theory postulates that: the odontoblasts are a receptor cell that transmits excitation to the adjacent nerve plexus. But against this theory: There is no synaptic relation between the odontoblasts and the underlying nerve plexus. Also, there are no neurotransmitter vesicles was observed in the odontoblasts or their processes adjacent to nerve endings. 3- Hydrodynamic theory: When dentin is first exposed, small droplets of fluid can be seen on the cavity floor. When cavities are dried, with air or cotton, a greater loss of fluid is induced, leading to more movement and more pain. The increased sensitivity at the DEJ is explained by the profuse branching of tubules in this region (increase in loss of fluid). This theory also explains why local anesthetics applied on exposed dentin fail to block sensitivity. The hydrodynamic mechanism depends on fluid movement through the dentinal tubules. This theory proposes that fluid movement through the tubules distorts the local pulpal environment and is sensed by the free nerve endings in the plexus of Raschkow. This theory is the most accepted one as it explains most of experimental data:  Dentinogenesis Dentin formation occurs in two steps: 1- matrix formation (predentin): uncalcified organic matrix of dentin 2- mineralization which doesn’t begin until wide band of predentin (10-20 microns) is formed Linear Globular mixed  Life cycle of odontoblasts 1- Differentiation of preodontoblasts: Odontoblasts differentiate from undifferentiated mesenchymal cells of dental papilla under the influence of inner enamel epithelium U.M.C divide giving two cells, one of them remians undifferentiated and the other differentiated into odontoblasts Differentiated odontoblasts are short cells with several short processes arising from distal end of the cell 2- secretory odontoblasts  After differentiation, odontoblasts increase in length and become columnar cells (40 ϻ in length and 7 ϻ in width),  They become densely packed together and connected with each other by junctional complex  Now, odontoblast become a protein forming cell:  large open-faced nucleus  Abundant cytoplasm  large number of mitochondria, rough endoplasmic reticulum and Golgi apparatus  Presence of secretory granules  Ribonucleic acid  alkaline phosphatase enzyme  At first, odontoblasts start to secret dentin matrix (predentin) around the area directly adjacent to the IEE then begin to recede away from the basement membrane.  As the matrix is formed, odontoblasts move toward the pulp pushing several short stubby processes into the formed extracellular matrix.  One of these processes may penetrate the enamel matrix and become enamel spindle  The 1st layer of predentin is calcified forming mantle dentin (1st layer of dentin).  By formation of 1st layer of dentin, odontoblasts begin to recede away (pulpal), to form circumpulpal dentin, leaving behind only one odontoblastic process (Tome’s fibre) which is embedded in dentin matrix while the others disappear. 3- Quiscent state odontoblasts (resting odontoblasts) After complete root formation odontoblasts enter resting stage, they produce secondary dentin through out life Reduction in height, organelles and number of odontoblasts with age will take place with increased number of lysosomes and phagosomes 1- Matrix formation (predentin):  A- Mantle dentin  It is the first layer of the formed dentin in crown and root.  Its thickness is about 10-20 μm.  The ground substance is the product of odontoblasts in addition to preexisting ground substance of dental papilla.  The first layer of collagen fibers matrix is Von Korff’s fiber. Which is thick type III collagen fibers (0.1- 0.2μm) perpendicular to DEJ.  They originate deep in the odontoblasts and fan out in the structureless ground substance immediately below the epithelium.  In The root, collagen fibers are arranged parallel to CDJ.  Mineralization: Globular calcification  B- Circumpulpal dentin:  It is the remaining primary dentin which forms the main bulk of the tooth.  At this stage odontoblasts enlarge in size and connect each other by junctional complexes. Its ground substance is  collagen fibers: type I collagen fibers.  diameter: smaller (0.05um)  Direction: have right or oblique angle to dentinal tubules (parallel to dentin surface)  Mineralization: Globular below mantle dentin then become mixed in the remaining circumpulpal dentin.  Slightly more mineralized than mantle dentin. 2- Mineralization: Mineralization starts after formation of 10- 20 μm band of predentin at the Mineralization front. Odontoblasts bud off small matrix vesicles from their plasma membrane into the extracellular matrix. These vesicles are rich in calcium and phosphate ions and contain alkaline phosphatase enzyme. These matrix vesicles provide a special environment in which the first hydroxyapatite crystals can form. Once the first crystal forms in the vesicle, it grows rapidly and ruptures through the vesicle wall to spread as clusters of crystallites then fuse with adjacent one to form the fully mineralized matrix. Types of D. mineralization 1- globular calcification: appear in the mineralization front beneath DEJ (after a band of 10-20 μm of predentin is formed). Deposition of crystals starts at several areas of the matrix at the same time. By continuous calcification, globular masses (small spherical areas or Calcospherits) develop. These globules enlarge in size to coalesce with each other to form a single mineralized mass. Mainly appears in mantle dentin and occasionally in circumpulpal D. below mantle dentin. 2- Linear calcification: By decreasing the rate of Dentinogenesis, the hydroxyapatite crystals spread along the mineralization front more regularly. So, it is called linear pattern. 3- Mixed calcification: Linear and globular calcification appears in circumpulpal D. as globular calcification appears beneath mantle dentin and Linear one appears more pulpal.  Age Changes of Dentin Secondary dentin Is the dentin which is formed after root formation is completed Its formation is slower in rate than 1ry dentin Its dentinal tubules are less regular 1-Regular (physiologic) secondary dentin It is a normal physiological process due to aging. Its formation starts after the root formation has been completed and continues for life. Is characterized by a slower rate of deposition. Separated from 1ry dentin by line of demarcation due to abrupt change in the direction of the dentinal tubules. Its deposition increases eventually on the (pulp recession). Usually, its DTs are filled with calcified materials to decrease the D. permeability to protect the pulp.  2- Irregular (tertiary) secondary dentin Called tertiary, irregular secondary, irritation, reparative or reactive dentin. is laid down in response to irritation or damage to the overlying dentin and/or enamel. May be separated from 1ry D. by line of demarcation or not. This D. is localized opposed to the area of irritation only as it is formed by the cells which are affected by the stimulus. If the D. is formed by the pre-existing odontoblasts, it is called reactionary dentin. If the D. is formed by the newly differentiated odontoblast-like cells, it is called reparative dentin. Its quality and quantity depend on the severity and duration of the stimulus: In mild stimulus, DTs may be continuous with DTs of regular D. In moderate stimulus, they may be spares in number and less arranged. In sever stimulus: They may appear as calcific barrier without dentinal tubules at all (a tubular dentin). The odontoblasts may be entrapped in the D. matrix during Dentinogenesis (osteodentin) Blood vessels may be entrapped in the D. matrix during Dentinogenesis (Vaso dentin) Sclerotic Dentin [Transparent dentin] It develops due to mild stimulus or normal physiological process due to aging. Is the occlusion of the dentinal tubules by calcified material resulting in a glass transparent appearance? most common in the apical third of the root and in the crown midway between the pulp It appears in the ground section: by transmitted light it appears translucent With reflected light it appears black It is a protective response to prolong the vitality of the tooth: decrease the permeability of dentin. decrease the sensitivity of dentin. increase the resistance to caries. Occlusion of the tubules is usually due to continuous deposition of intratubular dentin. And may also occur in other ways: - deposition of mineral within the tubule without any dentin formation - diffuse mineralization that occurs while a viable odontoblast process is still present. - mineralization of the process itself and tubular contents, including intratubular collagen fibrils. Dead tracts [Opaque dentin] Caused by sever stimulus to the tubules such as erosion, deep caries or sever attrition. When dentin is damaged, odontoblastic processes die or retract leaving empty dentinal tubules. So, dead tract is a dentinal tubule devoid of a vital odontoblastic process due to cell death. It is usually located in the coronal dentin. It appears dark in transmitted light and white in reflected light due to the presence of air. Usually, it is bound by sclerotic dentin. Sometimes the empty tubules are obliterated by minerals from the pulpal side so, it is called blind tract. Areas of growth Metric Current value Previous quarter Change (%) Revenue $2,500,000 2,200,000 +14% Operating expenses $1,200,000 $1,400,000 -14% Net profit $1,000,000 $800,000 +25% Operating margin 40% 36% +4% Cash reserves $5,000,000 $4,500,000 +11% Innovative Solutions Future initiatives 1. Product enhancement. Introduce regular updates and features to enhance product offerings. 2. Technology integration. Explore emerging technologies Green supply chain for potential integration into our operations. Reduced carbon footprint 3. Collaborative partnerships. Foster collaborations with tech innovators and industry leaders to drive innovation. Waste reduction Water conservation Thank you Dr. Laura Meglar [email protected] www.example.com