Dentin Lecture Notes PDF

Dentin is a mesodermal derivative.(D. papilla) Forms the main bulk of the tooth. Determines the morphology 0f the tooth ☻In crown it is covered by enamel ☻In root it is covered by cementum - Vital tissue  Physical Characteristics  Yellowish.  Elastic.  Hard ( less than enamel but mo...

Dentin is a mesodermal derivative.(D. papilla) Forms the main bulk of the tooth. Determines the morphology 0f the tooth ☻In crown it is covered by enamel ☻In root it is covered by cementum - Vital tissue  Physical Characteristics  Yellowish.  Elastic.  Hard ( less than enamel but more than cementum and bone).  By X-ray : more radiolucent than enamel and more radio-opaque than cementum.  Thickness varies from 3-10 mm.  Permeable. Due to tubular pattern.  Chemical Characters Of Dentin 70-75% inorganic 30-25% organic material material Collagen Hydroxyapatite crystals type I inclusions of insoluble proteins glycoproteins and lipids  Ground section  Decalcified section (inorganic part) (Organic part)  Structure 1. Dental tubules. 2. Odontoblastic processes.  Dentinal Tubules - S-shape - Start at right angle from pulpal surface. - In the root, incisal edge and cusp there are almost straight. Ground Section Of D. Ts. Straight At the cusp tip or (incisal edge) At cervical area S shape Secondary curvatures Mid portion of root and Straight apically  Dentinal Tubules - Tubules are thicker near the pulp. - Diameter: 2-4 um near the pulp. 1 um at their outer end. - The ratio in no. per unit area 4:1. -The buccal and lingual walls have more tubules than the mesial and distal walls.  Dentinal Tubules Odontoblasts Dentin Predentin Terminal branches curvatures Sec.  Dentinal Tubules  - Have lateral branches (canaliculi), 1 um in diameter, at right angle to the tubule.  - Have terminal branches – more in root dentin than in coronal dentin. - No. of D.T. per square mm : 50,000 – 90,000 near the pulp. - More tubules in the crown than in the root. - More tubules in molar than incisor.  Dentinal Tubules branching Mantle D DEJ Odontoblastic process Preodontoblastic Circumpulpal D space Peritubular dentin Intertubular dentin Predentin Odontoblasts - Some terminal braches extend into the enamel as enamel spindles. Others may remain short in dentinal tubules. - Occasionally a process splits into 2 equally thick branches.  Odontoblasts And Dentinal Tubules Mantle D DEJ Odontoblastic process Preodontoblastic Circumpulpal D space Peritubular dentin Intertubular dentin Predentin Odontoblasts Histological Structure Of Dentin Dentinal tubules Dentin Predentin Odontoblasts T.S. In Dentinal Tubules Odontoblastic process (Tomes’ fiber) Peri- odontoblastic Ground section space Scanning microscope Neumann’s sheath Decalcified section  The dentinal tubules contain  odontoblastic processes  dentinal fluid.  organic sheath called lamina limitans.  Odontoblastic Processes (Tome’s fibers) - Are cytoplasmic extension occupying the D.T. - Contains - microfilaments, vesicles and ribosomes rich in RER and mitochondria. hydrolytic enzymes - thicker near the cell body,3-4m, and taper to 1mm further into the D.  Incremental Lines Of Dentin Incremental lines Neonatal line of von Ebner Contour line of Owen  ncremental lines of von Ebner: rhythmic deposition of dentin, un at right angles to DT.  Counter lines of Owen: accentuated hypomineralized line  result from secondary curvatures  counter line is found between primary and secondary dentin.  Mineralizing lines:  Neonatal lines:  seen in ground sections  hypocalcified line the  represent variations in  prenatal from postnatal D. mineralization  not regular as von Ebner lines.  have jagged appearance  lie at angle to the von Ebner line  Dentino-enamel junction  scalloped,  prevents the shearing of enamel during function.   the basal lamina separating the enamel and dentin is called membrana proformativa during early tooth development  Types Of Dentin Mantle dentin Sec. Circum- Dentin Ir D pulpal Predentin dentin Sec. Odonto RD Primary blasts dentin Secondary Predentin dentin  Peritubular (intratubular) Dentin - Forms the wall of the D.T. - sheath of Neuman - hypermineralized, 44 nm wide causes reduction in the size of tubular lumen. Intertubular Dentin - Forms the main body of the D. - Less mineralized.  Predentin - Is the first formed dentin (not mineralized). - Located adjacent to the pulp tissue. - thickness: 10-40 um. - Mineralized to become D. and new layer of predentin form circumpulpally.  Primary dentin Prior to root completion.  A- Mantle dentin Fibers are perpendicular  The first formed dentin to D E J (crown) layer in crown close to the DEJ  And root Fibers are parallel to basement membrane(root)  B) Circumpulpal dentin surrounds the pulp more mineralized Mantle dentin Circumpulpal dentin. The fibers are parallel to DEJ ( right or oblique angle to DT) Crowding of the cells and appearance of junctional complex  Crown Root Mantle dentin Circumpulpal dentin  Thickness: 10-20 um  Thickness: bulk of the tooth  Diameter of collagen  Diameter of collagen fibers: fibers: large (0.1-0.2 um) small (0.05um)  Direction of collagen  Direction of collagen fibers : fibers : have right angle have right or oblique angle to to DEJ and parallel to dentinal tubules (parallel to basement membrane in dentin surface) root  Ground substance: from Ground substance: from odontoblasts odontoblasts and the  Mineralization: Globular cell free zone below mantle dentin then  Mineralization: linear become mixed in the form (contains matrix remaining circumpulpal vesicles). dentin (no M V ).  Secondary Dentin  After root completion Site of formation: on the entire pulpal surface thicker on the roof and floor of the pulp chamber Dentinal tubules: - have more wavy course - They decrease in number. Line of demarcation Present and stained dark.  Interglobular Dentin  Calcification of dentin in some areas occurs in a form of globular pattern.  These globules fuses together to form homogenous substance.  Sometimes globules in some areas failed to fuse. Area of organic matrix between the globules remain uncalcified or partially mineralized. These areas bonded by the curved outlines of the adjacent globules. Tomes’ Granular Layer Tomes’ granular layer Cementum  Interglobular  Tomes’ granular dentin layer  (Size) Large  (Size) Small granular in  (Cause) Areas of appearance unmineralized or  (Cause) Areas of minute hypomineralized dentin IGD, but recent studies (sometimes present). indicate that it result from  (Site) Appear in the the looping of the terminal crown just below mantle portions of DT which is a dentin. result different orientation  (D T) Dentinal tubules of odontoblastic process cross the IGD without (always present). the peritubular dentin  (Site) Appear in the root  (IL) Follow incremental adjacent to the cementum. line pattern  (DT) Dentinal tubules do  In badly formed tooth it not cross this layer  (IL) Does not follow any  Deficiency of vitamin D or exposure to high level of fluoride. May be the cause for interglobular dentin these spaces appears black in transmitted light.  The tom’s granular layer may be  true spaces or due to  The looping of the terminal parts of the dentinal tubules.  Interglobular dentin with small size.  An interference of mineralization.  Hopewell and Smith layer - found between the tom’s granular layer and cementum. It is a structureless hyaline layer 15 nm width may be enameloid.  Innervations Of Dentin The nerve will loose its schwann caoting then pass between the High at D E J odontoblasts bodies and enter the dentinal Less sensitive tubules ( In crown and area fewer in the root ) High near the Plexus of Raschkow pulpal surface (suodontoblastic layer) Theories Of Pain Transmission Through Dentin. Direct neural Odontoblastic Fluid or stimulation transduction hydrodynamic theory theory God has not called me to be successful he has called me to be faithful  Life Cycle Of Odontoblasts 1- Differentiation of odontoblasts. Ameloblasts IDE Basement membrane Differentiate from At first become the peripheral The cells grow in length short columnar (40u) and closely dental papilla cell with many cells (UMC) packed together stubby processes  2- secretary odontoblasts Odontoblast become a protein forming and secreting cell.  R E R , Mitochondria and Golgi bodies  Ribonucleic acid and alkaline phosphatase Large open faced N Inner dental RER epith side Mitochondria Golgi Predentin bodies  3- Transitional odontoblasts  Decrease in size  Reduction in organelles  Condensation of chromatin  Vacuoles  4- Resting odontoblasts  Flat  Reduction in organelles  Condensation of chromatin  Absence of secretory granules 4- Quiescent and resting state of odontoblasts The odontoblasts decrease in size and form dentin in a slowly diminishing rate until stimulated to form reparative dentin.   Dentinogenesis  Pattern of dentin formation  begins at cusp tips and spreads down the slopes of each cusp to reach the cervical loop  The root dentin forms once the epithelial root sheath of Hertwig occurs.  The rate of coronal dentin deposition is approximately 4 µm / day,  the root dentin takes place at a slightly slower level.  Root dentin shows different orientation of collagen fibers and less phosphoryl content than the coronal dentin.  Dentin Development Odontoblasts differentiation Early dentin formation  Odontoblastic process formation As more D is laid down, the At first more than one cells receed and leave single process process ( Tomes’ fiber)  Dentinogenesis 1 Matrix formation 2 Maturation (Predentin) Dental organ (mineralization) Collagen Hydroxyapatite Ground crystals Dental papilla fibers substance  1- Matrix formation  A- Mantle dentin Fibers are perpendicular  The first formed dentin to D E J layer in crown  And root Fibers are parallel to basement membrane B) Circumpulpal dentin Mantle dentin Circumpulpal dentin. The fibers are parallel to DEJ ( right or oblique angle to DT) Crowding of the cells and appearance of junctional complex  2- Mineralization Budding of matrix Rupture of matrix Mineralization of the vesicles vesicles mantle dentin Has membrane rich in alkaline Matrix phosphata vesicle se Calcium and phosphate ions undergo crystallization  Pattern Of Mineralization 1- Linear at the mantle dentin area 2- Globular in M V in Crystal matrix circumpulpal lization dentin just below mantle dentin 3- Combination in the remaining Lodgment circumpulpal Rupture of crystals dentin of the crown and root  Age Changes Of Dentin - Rate of dentin formation decrease  Thickness increase with age.  Age Changes Of Dentin  Regular secondary dentin (Mild stimulus)  Occurs on the entire pulpal surface. In multirooted teeth it is thicker on the roof and floor of pulp chamber.  The size of the pulp cavity decrease and obliteration of the pulp horns  The dentinal tubules change their direction to a more wavy course  The no of dentinal tubules are fewer  Line of demarcation (dark). Irregular Secondary Dentin (Reparative or tertiary dentin)  Severe stimulus  The dentin is formed at a localized area.  The dentinal tubules are less in number and irregular in Irregular D T arrangement.  UMC from the subodontoblastic layer will differentiate and replace the degenerated odontoblasts to form reparative dentin  Types Of Reparative Dentin Osteodentin (entrapped cells). Atubular dentin ( area without dentinal tubules) Vasodentin (entrapped b.v.)  Secondary Dentin  Regular  Irregular  Cause: Mild stimuli Severe stimulus Site of formation: Formed at the area on the entire pulpal surface of corresponding to the pulpal the tooth end of the exposed dentin. Dentinal tubules: - Have irregular or twisted - have more wavy course course - They decrease in number - They decrease in number and some areas may have no tubules (a tubular dentin). Line of demarcation Present and stained dark. May or may not present  Clinically:  The  Thelocalized area decrease of the pulp chamber of dentin height and formation obliteration of the increase the time pulp horns make taken by caries to the liability of reach the pulp pulp exposure (barrier) during cavity preparation much less likely to occur  Transparent (Sclerotic Dentin) Mild stimulus leads to changes for the dentin already present. 1- Odontoblast and its process Transparent D undergo fatty degeneration. 2- Then there will be calcification of Trasparent D dentinal tubules. First become narrow by widening of the 3- Then the DT peritubular dentin. become obliterated. The affected area have occluded dentinal, so the dentin have uniform refractive index. So this area of dentin appear translucent by transmitted light.  Dead Tracts  Severe stimulation to dentin leads to destruction of the odontoblastic process and odontoblasts. This leads to empty and wide dentinal tubules.  These areas apear black with transmitted light.  Under the dead tracts from the pulpal surface , reparative dentine will be formed.  The dead tract surrounded by sclerotic dentin.  Clinical considerations of the dentin  Exposed dentin should be sealed. When 1mm2 of dentin is exposed, about 30,000 of the living cells are damaged.  Tubular nature of dentin allows spread of caries and passage of bacteria.  Trauma can damage the pulp and cause dislodgment of odontoblasts from periphery of the pulp and their aspiration within tubules.  Dentin sensitivity of pain may not a symptom until pulp is infected.  Indirect pulp capping by application of calcium hydroxide dressing and odontoblasts form new reparative dentin.  Dentinal tubules permeability is 20% more in coronal dentin than root dentin and most permeable at area over pulp horns.  Smear layer is fluid flow during cavity preparation should be removed because it contains toxic bacterial products.  Demarcation between secandary and reparative dentin is called calciotraumatic line.  Hypersensitive dentin treated by potassium nitrate. Cement base should be placed under metallic restoration to protect the pulp by decreasing the conduction of heat.  Dentinogenesis and osteogenesis imperfecta in which there are defect in collagen in dentin. a child with dentinogenesis Imperfecta. an autosomal dominant genetic defect. A good head and a good heart are always a formidable combination.  (Nelson Mandela) Thank you