Dentin Structure (Oral Biology I, BDS 123) Fall 2024 PDF

Course Title: Oral Biology I Course Code: BDS 123 Topic of Lecture: Dentin structure.. Lecturer: Prof Samah Mehanny F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e F a l l 2 0 2 4...

Course Title: Oral Biology I Course Code: BDS 123 Topic of Lecture: Dentin structure.. Lecturer: Prof Samah Mehanny F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e F a l l 2 0 2 4 Prepared by Samah Mehanny Prepared by Samah Mehanny Dentin forms the main bulk of the tooth -In the crown, it is covered by enamel -In the root, it is covered by cementum Prepared by Samah Mehanny  Physical Properties 1-Yellowish in color. Remember that Hunter Schreger bands explain the fact that enamel in spite of being a translucent structure, doesn’t entirely reflect the yellowish color of dentin. Some of the light rays pass through the wavy coursed enamel rods and others are reflected giving the natural appearance of the tooth. If the enamel rods passed in a straight course, the teeth would clearly reflect the dentin color that gives an unaccepted esthetic appearance. Prepared by Samah Mehanny 2- Dentin is an elastic vital tissue. -Presence of collagen fibers and smaller hydroxyapatite crystals provide the dentin its elastic quality that prevents fracture of the overlying enamel. -Dentin is considered a vital tissue due to presence of dentinal tubules with its content (odontoblastic processes and dentinal lymph) 3-Thickness varies from 3-10 mm. Prepared by Samah Mehanny 4- Regarding Hardness (it is softer than enamel but harder than cementum and bone). Thus by X-ray, it takes greyish shade. It is more radiolucent than enamel (darker) and more radio-opaque than cementum. Prepared by Samah Mehanny  Chemical properties of dentin 70-75% inorganic 30-25% organic material material Collagen Hydroxyapatite type I Phosphorylated crystals proteins Glycoproteins and lipids (Inactive matrix-metalloproteinase MMPs) Prepared by Samah Mehanny Role of matrix-metalloproteinase in dentin (adult dentin and during dentinogenesis) The MMPs present in the dentin are produced by odontoblasts during secretion of the dentin matrix and are suggested to be involved in dentin formation. Prepared by Samah Mehanny After mineralization of the collagen matrix, the inactive forms of MMPs remain trapped within the calcified matrix but are mostly concentrated in the predentin and at the DEJ. Prepared by Samah Mehanny  Active MMPs Inactive MMPs (after dentin formation (dentinogenesis) and mineralization) Acidic medium Activation to this enzyme occurs if the pH decreases as in case of caries or during acid etch application. The consequences of MMPs activation are; Spread of caries especially at DEJ. Weakening to the hybrid layer that affects the durability of the restoration. Prepared by Samah Mehanny  Types Of Dentin Mantle dentin Primary Sec. dentin Circum- Ir D Sec. pulpal dentin dentin Sec. RD Predentin Prepared by Samah Mehanny Primary dentin : dentin which is formed to produce the typical form of the tooth. Secondary dentin: represent the continuing deposition of dentin by odontoblast after root formation has been completed Prepared by Samah Mehanny Histological Structure Of Dentin Odontoblastic process Dentinal tubules Dentin Predentin Odontoblasts Prepared by Samah Mehanny Prepared by Samah Mehanny  1-Odontoblasts and Dentinal Tubules Mantle D DEJ Odontoblastic process (Tome’s fiber) Circumpulpal D Preodontoblastic space (containing dentinal lymph) Peritubular dentin (highly mineralized) Intertubular Predentin dentin Odontoblasts Prepared by Samah Mehanny  D.E.J Peri - Odontoblastic odontoblastic process= space !!! → Tome’s fiber dentinal fluids Dentinal tubules Peri- tubular dentin. Enamel Prepared by Samah Mehanny spindle Dentin is a vital hard tissue consists of; Cells and Intercellular substance. Cells: the odontoblasts are not located inside its calcified ground substance but are aligned on its pulpal surface. A long process (odontoblastic process or Tomes’ fiber) extends from the distal end of these cells and traverses the whole thickness of dentin till the DEJ and just before the DCJ. Prepared by Samah Mehanny The odontoblastic processes run inside a fine tubules called the Dentinal tubules. Dentinal tubules: are the unit structure of the dentin. Dentinal tubules are built up by peritubular dentin and are separated from each other by intertubular dentin. Prepared by Samah Mehanny  The unit structure of dentin is dentinal tubules Number per unit area Pulpal side : peripheral layer 4 : 1 Diameter D.T. taper from pulpal surface outwards Closely packed near the pulp than in the peripheral layer Prepared by Samah Mehanny Dentinal tubules Prepared by Samah Mehanny  Branches Lateral Terminal branches branches The od. Processes may extend into the enamel giving rise to the Enamel spindle (pain receptor). This could explain the highest sensitivity at the DEJ Prepared by Samah Mehanny Course of dentinal tubules At the cusp tip Straight or (incisal edge) At cervical area S shape Mid portion of root and apically Straight Prepared by Samah Mehanny  Causes of S shape curvature It results from the crowding of and path followed by the odontoblasts during their recession toward the pulp. This may slow the rate of caries propagation in this area where thinner enamel thickness compared with occlusal /incisal enamel is exist. Prepared by Samah Mehanny  T.S. In Dentinal Tubules 1- Microscopic picture Odontoblastic process (Tomes’ fiber) Preodontoblastic space Prepared by Samah Mehanny  Space of Rounded light hallo odontoblastic (peritubular dentin) processes Prepared by Samah Mehanny  T.S. In Dentinal Tubules 2- Ground section 3- Decalcified section Odontoblastic processes appear shrunken surrounded by a ring- shaped space due to the break down of the delicate matrix of the peritubular dentin (due to its high mineral content its matrix is delicate). Prepared by Samah Mehanny Odontoblastic process (responsible for the dentin vitality): It exists in the dentinal tubule and follows it in the course, number, diameter, and branches. The lateral branches originate at a right angle to their processes, many of them end blindly while others unite with other branches of adjacent processes. They contain all cell organelles, especially in the area of predentin. Microtubules and intermediate filaments run longitudinally through the process. Prepared by Samah Mehanny  Peritubular dentin It is a highly calcified dentin. The mineral content is greater than 90%. In contrast, the inter-tubular dentin has a mineral content of 70%. It is deposited on the internal walls of the dentinal tubules. It plays a significant role as it keeps the patency of the dentinal tubules thus maintains the odontoblastic processes vital and unmineralized. Prepared by Samah Mehanny  Intertubular dentin Dentin located between the dentinal tubules. Represent the primary secretory product of odontoblasts. It forms the greater surface area than the dentinal tubules especially toward the dentin peripheries. Prepared by Samah Mehanny  Inter tubular D. Inter tubular D. Inter tubular D. Prepared by Samah Mehanny Prepared by Samah Mehanny  Clinical implication of Dentinal tubules - They are the reason of dentin permeability, providing a pathway for the caries invasion. - Infected dentin shows the dentinal tubules packed with microorganisms. - Drugs and chemicals present in a variety of dental restorative materials can also diffuse through the dentin and create pulpal injury. Prepared by Samah Mehanny Dentin is a permeable hard tissue with its tubules extending from the dentino-enamel junction to the pulp. Therefore, in cavity preparation, sealing of dentinal tubules is a mandatory for effective restorative dentistry. Prepared by Samah Mehanny Dentin bonding system: Difficulties that faces dentin bonding are: Dentin contains water. Presence of smear layer after dentin exposure, that is formed of a superficial layer that covers the canal wall and is loosely attached and a deeper layer that occludes the dentinal tubules and strongly adheres to the canal wall and hinder proper attachment of the restoration. Prepared by Samah Mehanny kindly figure out what’s meant by hybrid layer. Prepared by Samah Mehanny Prepared by Samah Mehanny Inter-tubular dentin (hybrid layer) vs peritubular dentin (resin tags) regarding dentin bonding system: Resin tags were the main source of bond between resin-based restorations and dentin. However, stresses induced at their depth weaken the bond and affect the durability of the restoration in return. On the other hand, Inter-tubular dentin performs wider surface areas than the dentinal tubules thus dentin bond relies more on this dentin forming a hybrid layer.  Thus Hybrid layer is formed of a hybrid of demineralized inter-tubular dentin intermingled with the resin meaning that it is neither resin nor tooth, but a hybrid of the two. However, the high collagen content in the inter- tubular dentin could be degraded by active MMPs (activated by the applied acid etch) that causes weakness in the hybrid layer and decreasing the durability of the restoration. Prepared by Samah Mehanny  Acid etch application is thus a double- edged weapon because it Demineralizes the dentin exposing the collagen fibers of the intertubular dentin (hybrid layer) allowing proper bond between the resin-based restoration and dentin. The acidity, on the other hand, activates the MMPs that degrade the collagen fibers of the hybrid layer which could weaken the bond Prepared by Samah Mehanny  To overcome the downside of high collagen content and activated MMPs, the dentin bond should contains enzymatic inhibitors to inhibit activation of MMPs. Prepared by Samah Mehanny  2- Incremental Lines Of Dentin Incremental lines Neonatal line of von Ebner Prepared by Samah Mehanny  2- Incremental Lines Of Dentin 1- Incremental lines of von Ebner They reflect variation in structure and mineralization during dentin formation. They are hypocalcified bands. They represent 5 days formation (20 microns increments) 2-Neonatal line One of the incremental lines which separates the prenatal from the postnatal dentin. It is found in deciduous teeth and first permanent molars. Prepared by Samah Mehanny  3-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. Prepared by Samah Mehanny  4-Tomes’ Granular Layer Tomes’ granular layer Cementum Prepared by Samah Mehanny The Tome’s granular layer results from looping of the terminal portion of the dentinal tubules thus the odontoblastic processes don’t extend to the cemento-dentinal junction differing from that may occur at the dentino-enamel junction (enamel spindle). Prepared by Samah Mehanny The significance of Tome’s granular layer: It may protect the pulpal tissues from any insult arising from the PDL as the covering cementum is thin and highly permeable. Prepared by Samah Mehanny  E C Interglobular dentin Tomes’ granular layer (Size) Large (Size) Small granular in appearance (Cause) Areas of unmineralized or (Cause) it results from hypomineralized looping of the terminal dentin (sometimes portions of DT (always present). present). Prepared by Samah Mehanny  E C (Site) Appear in the crown (Site) Appear in the root just below mantle dentin. adjacent to the cementum. (D T) Dentinal tubules cross (DT) Dentinal tubules do not the IGD without the cross this layer peritubular dentin (IL) Follow incremental line (IL) Does not follow any pattern incremental pattern. In badly formed tooth it appears in the root dentin Prepared by Samah Mehanny  Functional adaptation of the dentinal tubules: In the crown; The coronal dentin is well protected by enamel thus the dentinal tubules reach to the dento- enamel junction. However, their diameters are narrow at the DEJ as a sort of protection to the pulpal tissues. Narrower diameter Wider diameter Prepared by Samah Mehanny In the root; The radicular dentin is covered with thin permeable cementum thus the dentinal tubules don’t reach the surface and loop forming Tomes’ granular layer. Prepared by Samah Mehanny Innervations Of Dentin Plexus of Raschkow (sub- odontoblastic layer) The nerves will loose their schwann coating then pass between the odontoblasts bodies and enter the dentinal tubules (they are higher in the crown than in the root ) Prepared by Samah Mehanny Dentin sensitivity: High at D E J Less sensitive area High near the pulpal surface Prepared by Samah Mehanny Theories Of Pain Transmission Through Dentin. Fluid or Direct neural Odontoblastic hydrodynamic stimulation transduction theory theory Prepared by Samah Mehanny Theories Of Pain Transmission Through Dentin. Prepared by Samah Mehanny  A- Direct neural stimulation: This theory depends on the fact that dentin contains nerve endings, which respond when dentin is stimulated. Recent studies confirm the presence of these nerve endings. Prepared by Samah Mehanny  B- Odontoblastic transduction theory: This theory is explained as follows; since odontoblasts are of neural crest origin, they retain the ability to transduce and propagate an impulse. However, this is not true because there is no synapse between the cells and the nerve fibers. Prepared by Samah Mehanny C- Fluid or hydrodynamic theory: This theory involves fluid movement through the dentinal tubules which affects the nerve endings in the plexus of Raschkow. Both theories A and C are the most accepted Fluid or hydrodynamic theory explains the pulp response in case of exposed dentin accompanied with reversal pulpitis: Prepared by Samah Mehanny Hot drinks produce Cold drinks produce a weaker response a stronger response Prepared by Samah Mehanny  Explanation Cold stimulus; Contracts the dentinal fluids leading Hot stimulus; expands the to outward movement of dentinal fluids leading to the fluid as well as the inward movement thus odontoblasts. This will pushing the odontoblasts into cause pressure on the nerve the pulp, releasing the pressure endings in the tubules. on the nerves. Prepared by Samah Mehanny Prepared by Samah Mehanny