Dentin PDF

Dentin By dr: Sally Sakr  Dentin Dentin is the hard dental tissue that forms the main bulk of the tooth. It is covered by enamel in the crown and by cementum in the root. Physical properties of dentin Dentin is light yellow in colour and reflect light less th...

Dentin By dr: Sally Sakr  Dentin Dentin is the hard dental tissue that forms the main bulk of the tooth. It is covered by enamel in the crown and by cementum in the root. Physical properties of dentin Dentin is light yellow in colour and reflect light less than enamel. Dentin is slightly harder than bone and cementum but softer than enamel. Dentin has a high degree of elasticity to support brittle enamel. Dentin is a permeable hard tissue. Chemical composition of dentin Dentin is first deposited as a layer of unmineralized matrix called predentin that varies in thickness from (10 to 50 µm) and lines its innermost (pulpal) portion. Predentin consists principally of collagen and noncollagenous components. Chemical composition of dentin Mature dentin is made up of inorganic organic water approximately 70% inorganic material, 20% organic material, water and 10% water by weight. 10% organ Its inorganic component consists ic of hydroxyapatite in the form of 20% small plates. inorg anic The organic component is about 30% 70% collagen (mainly type I with small amounts of types III and V) with phospholipids, growth factors and  Dentinogenesis Odontoblastic differentiation: At the bell stage, the IEE induces proliferation of undifferentiated cells of dental papilla into daughter cells. A daughter cell influenced by the epithelial cells differentiates into an odontoblast. Another daughter cell, not exposed to this epithelial influence, persists as a sub-odontoblast cell “remain  Odontoblastic differenti Differentiated odontoblasts consist of two parts ; cell body and odontoblastic process separated by junctional complexes (cell web). Cell body contains synthetic cell organelles (RER, Golgi complex, secretory granules). Odontoblastic process contains secretory granules, mitochondria, microfilaments and microtubules.  Presecretory ameloblast Odontoblast Low-magnification view of odontoblasts examining the section in the scanning electron microscope showing terminal cell web  Odontoblastic differentia Presecretory ameloblast Odontoblast  Odontoblastic differentia Presecretory ameloblast Odontoblast Formation of Primary dentin: The primary dentin refers to the dentin that is formed until the root is completed (dentin formed during tooth development). Types of primary dentin: 1. Mantal dentin. 2. Circumpulpal dentin.  1. Formation of Primary dentin: amelodentinal junction a. Mantle dentin ` The first formed dentin near ADJ is called mantle dentin. It is formed by differentiated odontoblasts after their production of the ground substance of the dental papilla. It is consisted of large diameter collagen fibers (type III collagen) called Von Korff's Mantle dentin formation fibres. Von Korff's fibres  b. Circum-pulpal dentin It constitutes the bulk of the dentin. It is formed of thin diameter type I collagen fibres. These fibres run parallel to ADJ and perpendicular to odontoblastic process. Circumpulpal dentin formation  Mantal dentin Circumpulpal dentin A. Enamel B. Dentino-enamel junction C. Mantle dentin D. Circumpulpal dentin E. predentin Circumpulpal dentin  Mechanism of dentin mineralization 1. Matrix vesicle: Occurs in mantal dentin. The matrix vesicles bud from the tip of the odontoblastic process forming hydroxyapatite crystals. These crystals grow rapidly leading to vesicle rupture with release of the hydroxyapatite crystal into the extracellular matrix. “vesicle budding deposition of crystals  crystal growth  fusion between the globules   Matrix vesicle mineralization: Budding of Rupture of Mineralization matrix matrix vesicles of the mantle vesicles dentin 2.Collagen Phosphophoryn complex: Occur in late mantal and circumpulpal dentin. Initiated by Phosphophoryn which is non collagenous protein adheres to Collagen to act as a nucleator to attract hydroxyapatite crystals. The negative charge on the Phosphophoryn creates a template for hydroxyapatite deposition. Collagen -phosphoryn complex Phosphophoryn which is non collagenous protein adheres to Collagen to act as a nucleator to attract hydroxyapatite crystals Function of non-collagenous matrix proteins: Act as a promoters or inhibitors for mineralization. Regulate mineral deposition. prevent the premature “early” mineralization of the organic matrix.  Pattern Of Mineralization 1- Linear at the circumpulpal dentin area just below mantle dentin 2- Globular in mantle dentin 3. Combination in the remaining circumpulpal dentin of the crown and root Linear Globular  Mantle dentin Circumpulpal dentin Thickness 10-20 um (near bulk of the tooth ADJ) Diameter of large (0.1-0.2 um) small (0.05um) collagen fibers Direction have right angle have right or oblique of collagen to DEJ and angle to dentinal fibers parallel to tubules (parallel to basement membrane DEJ) in root. Mineralizat globular form linear below mantle ion (contains matrix dentin then become vesicles). mixed in the remaining circumpulpal dentin Structures of dentin Dentinal tubules: It is the main structure of dentin. They traverse the dentin and contained the odontoblastic process. They form a network for the diffusion of nutrients Course of the dentinal tubules: Coronal dentin It has different course in different parts of the tooth: They are straight in the cusp Cervica l region. dentin S-shape in cervical part of Radicula crown and root (primary r dentin curvature). Dentinal tubules by scanning electron microscope  Contents of dentinal tubules 1. Odontoblastic process. 2. They also contain afferent nerve terminals in the areas near the pulp. 3. Within the dentinal tubules there is a peri-odontoblastic space which filled with extracellular dentinal fluid or dental lymph. Transmission electron micrograph of pulpal dentin seen in cross section. Some of the tubules contain an  lamina limitans: The dentinal tubules have an inner organic lining termed the lamina limitans. This is described as a thin organic membrane, high in glycosaminoglycan (GAG). It is important in the regulation or inhibition of calcification of dentinal tubules.  Secondary Curvature The dentinal tubules show numerous small secondary curves on their course?? Due to the spiral track taken by the odontoblast process (Tome’s fibres) in its course from the outer dentine surface to the pulp.  Lateral and terminal branches The dentinal tubules have lateral branches throughout dentin, which are termed canaliculi or microtubules by which they form a profuse anastomosing canalicular system. At the outer dentine surface, the odontoblastic processes and the Lateral and terminal branches Peritubular Dentin “intratubular dentin” This dentinal layer usually lines the dentinal tubules and is more mineralized than inter-tubular dentin and predentin. Peritubular dentin is present throughout dentin, except in the tubules near the pulp  Intertubular Dentin This dentin is present between the tubules which are less mineralized than peritubular dentin. It determines the elasticity of the dental matrix. It represents the primary secretory product of the odontoblasts and consists of a tightly interwoven Interglobular dentin Area of unmineralized dentin formed due to lack of fusion (coalescence) between calcospheroite or “globules”. Interglobu It appears as black lar dentin space in ground section and light pink in decalcified section.  Interglobular dentin Dentinal tubules pass through the interglobular dentin, with no peritubular dentin present in these areas. Causes: Vitamin D deficiency. Exposure to high level of chloride at the time of dentin formation.  Granular layer of Tomes Cross ground Longitudinal section of root ground section of When root dentin is dentin root dentin viewed under transmitted light in ground sections, a granular- appearing area can be seen just below the surface of the dentin where the root is covered by cementum, called  Incremental lines of dentin incremental A. Incremental line of Von lines at right Ebner: angles to the dentinal They appear as a dark tubules fine lines or striation in the dentin. They run at right angles to the dentinal tubules and correspond to the incremental lines in enamel or bone. These lines reflect the daily rhythmic deposition of dentin. Histological section showing fine incremental deposition “Von Ebner”  b. Contour line of Owen “incremental line of Owen” Occurs occasionally and represent disturbance in mineralization. Demonstrated in longitudinal ground section. Cause: Periods of illness or inadequate nutrition.  c. Neonatal line Found in deciduous teeth and first permanent molars and separate the prenatal dentin to postnatal dentin. This line reflects the sudden changes in Neonatal line of enamel the environment that occurs at birth Prenatal ”zone of hypocalcification”. dentin Neonatal The quality of dentin matrix formed line of dentin before birth “prenatal” is usually better that that formed after birth “postnatal”. The neonatal lines are not seen in the Postnatal roots because radicular dentin is formed dentin after birth.