Structure of Teeth.pdf

3 Structure of Teeth CHAPTER Chapter Outline • Enamel – Composition – Structure – Thickness – Color – Strength – Structure Present in Enamel – Functions of Enamel – Clinical Significance of Enamel • Dentin – Composition – Color – Thickness – Hardness – Clinical Considerations of Dentin • Dental...

3 Structure of Teeth CHAPTER Chapter Outline • Enamel – Composition – Structure – Thickness – Color – Strength – Structure Present in Enamel – Functions of Enamel – Clinical Significance of Enamel • Dentin – Composition – Color – Thickness – Hardness – Clinical Considerations of Dentin • Dental Pulp – Histology of Dental Pulp – Structural or Cellular Elements – Extracellular Components – Anatomy of Dental Pulp – Functions of Pulp – Age Changes in Pulp • Periradicular Tissue – Cementum – Periodontal Ligament – Alveolar Bone Good knowledge of dental anatomy, histology, physiology and occlusion is the foundation stone of operative dentistry. In other words, thorough knowledge of morphology, dental anatomy, histology, is essential to get optimal results of operative dentistry. Though the dental tissues are passive, the occurrence of caries can only be understood when the structure of the teeth is understood. The teeth consist of enamel, dentin, pulp and cementum (Fig. 3.1). ENAMEL Tooth enamel is the hardest and most highly mineralized substance of the body which covers the crown of the tooth. It is the normally visible dental tissue of a tooth which is mainly responsible for color, esthetics, texture and translucency of the tooth. One of the main goal in operative dentistry is preservation of enamel. So today’s dentistry mainly revolves around simulating natural enamel in its color, esthetics, contours and translucency by replacing with synthetic restorative materials. Although enamel can serve lifelong, but it is more susceptible to caries, attrition (physical forces) and Figure 3.1: Enamel, dentin, pulp and supporting structures fracture due to its structural make up, i.e. mineralized crystalline structure and rigidity. One of the interesting features of enamel is that it cannot repair itself. So, loss in 19 Structure of Teeth enamel surface can be compensated only by restorative treatment. Composition It is highly mineralized structure which mainly contains inorganic contents in the form of crystalline structure. Main inorganic content in the enamel is hydroxyapatite. In addition to inorganic content, it also contains a small portion of organic matrix along with small amount of water which is present in intercrystalline spaces. Composition  Inorganic content (by volume)  Hydroxyapatite—90 to 92 percent  Other minerals and trace elements—3 to 5 percent  Organic content (by volume)  Proteins and lipids—1 to 2 percent  Water—4 percent. Structure Enamel is mainly composed of millions of enamel rods or prisms as well as sheaths and a cementing inter-rod substance. Each rod has a head and tail. The head is directed occlusally and the tail is directed cervically. The rod is formed of number of hydroxyapatite crystals which vary in size, shape and number. Each rod formed of about 300 unit crystal length and 40 units wide and 20 unit thick in three-dimensional hexagon. In transverse sections, enamel rods appear as hexagonal and occasionally round or oval. Rods may also resemble fish scales. The diameter of rods increases from dentino-enamel junction towards the outer surface of enamel in a ratio of 1:2. The rods or the prisms run in an alternating coarse of clockwise and anticlockwise direction (twisting course). Initially there is wavy coarse in one-third of enamel thickness adjacent to DEJ, then the coarse becomes more straight in the remaining thickness. Enamel rods are arranged in such planes so as to resist the maximum masticatory forces. Rods are oriented at prependicular to the dentinoenamel junction. Towards the incisal edge these become increasingly oblique and are almost vertical at the cusp tips. In the cervical region, there is difference in the direction of the enamel rods of deciduous and permanent teeth (Fig. 3.2). Clinical Significance The cervical enamel rods of deciduous teeth are inclined incisally or occlusally, while in permanent teeth they are inclined apically clinical significance of derections of rods. Figure 3.2: Direction of enamel rods in deciduous and permanent teeth This change in direction of enamel rods should be kept in mind during tooth preparation so as to avoid unsupported enamel rods. Structure  Composed of millions of rods or prisms of enamel rod increases from dentin enamel junction towards outer surface of enamel in 1:2  Enamel rods lie perpendicular to dentino-enamel junction  In cervical region, direction of enamel rod is incisally/occlusally in deciduous while in permanent, it is apically.  Diameter Thickness The thickness of enamel varies in different areas of the same tooth and from one type of tooth to another type of tooth. The average thickness of enamel at the incisal edges of incisors is 2 mm; at the cusp of premolar and molar it ranges from 2.3 to 3.0 mm. Thickness of enamel decreases gradually from cusps or incisal edges to cemento-enamel junction. Thickness of enamel Tooth type tooth (incisal edges)  Premolar tooth (cusp)  Molar tooth (cusp)  Anterior Thickness 2.0 mm 2.3 to 2.5 mm 2.5 to 3.0 mm Color The color of enamel is usually gray and translucent in nature. Color of tooth mainly depends upon three factors: 1. Color of underlying dentin 2. Thickness of enamel 3. Amount of stains in enamel. The translucency of enamel is directly related to degree of mineralization and homogenicity. Anomalies occurring during developmental and mineralization stage, antibiotic usage and excess fluoride intake affect the color of tooth. 20 Textbook of Operative Dentistry Color of enamel is affected by  Color of underlying dentin of enamel  Amount of stains in enamel  Anomalies occurring during developmental and mineralization stage like antibiotic usage and excess fluoride intake affects the color.  Thickness Strength Enamel has a rigid structure. It is brittle, has a high modulus of elasticity and low tensile strength. The specific gravity of enamel is 2.8. Hardness of enamel is different in different areas of the external surface of a tooth. The hardness also decreases from outer surface of the enamel to its inner surface. Also the density of enamel increases from dentino-enamel junction to the outer surface. When compared, dentin has high compressive strength than the enamel. Significance Because of high compressive strength of dentin than enamel, the dentin acts as a cushion for enamel when masticatory forces are applied on it. For this reason, during tooth preparation, for maximal strength of underlying remaining tooth structure all enamel rods should be supported by healthy dentin base. Structure present in enamel  Gnarled enamel of Hunter-Schreger  Enamel tufts  Enamel lamellae  Enamel spindles  Striae of Retzius  Prismless layer  Dentino-enamel junction  Occlusal pits and fissures.  Bands Figure 3.3: Different structures present in enamel Bands of Hunter-Schreger Hunter-Schreger bands usually occur because of alteration of light reflection (optical phenomenon) due to changes in rod direction. This results in alternating light and dark zones under the microscope. It is best seen in longitudinal ground sections seen under reflected light. They are mainly found in the inner surface of tooth. H-S bands are composed of different contents of organic material and varied permeability. Significance: They are considered to resist and disperse the strong forces. Enamel Tufts Enamel tufts are ribbon-like structures which run from dentin to enamel. They are named so because they resemble tufts of grass. They contain greater concentration of enamel proteins. Significance: Enamel tufts are hypomineralized structure in the enamel, thus play role in spread of dental infection. Structure Present in Enamel (Fig. 3.3) Enamel Lamellae Gnarled Enamel These are leaf like defects present in enamel and may extend to DEJ. They contains organic substances. Lamellae are commonly found at the base of occlusal pits and fissures. Bodecker in 1906 was the first to describe these developmental defects of enamel which he named ‘lamellae’. These are caused by ‘imperfect calcification of enamel tissue’. Pincus suggested that if developing cusps fail to coalesce when forming a fissure, a gap in the enamel occurs. Such a gap may vary in size from a crack or lamella. There are group of irregular enamel that is more resistant to cleavage called Gnarled enamel present mostly in cervical, incisal and occlusal portion. This consists of bundles of enamel rods which interwine in an irregular manner with other group of rods, finally taking a twisted and irregular path towards the tooth surface. Significance: This part of enamel is resistant to cutting while tooth preparation. Structure of Teeth Three types of lamellae are commonly seen: 1. Type A composed of ‘poorly calcified rod segments’ 2. Type B composed of degenerated cells 3. Type C arising after eruption where the crack is filled with mucoproteins from the oral preparation Type A lamellae is confined to enamel while types B and C may extend into dentin. Significance Various studies have shown that lamellae might be the site of entry of caries. Ten Cate stated that tufts and lamellae are of no significance and do not appear to be sites of increased vulnerability to caries attack. A lamella at the base of an occlusal fissure provides an appropriate pathway for bacteria and initiate caries. Significance: Shape and nature of the dentino-enamel junction prevents tearing of enamel during functions. Occlusal Pits and Fissures Pits and fissures are formed by faulty coalescence of developmental lobes of premolars and molars (Fig. 3.4). These are commonly seen on occlusal surfaces of premolars and molars. These are formed at the junction of the developmental lobes of the enamel organs. Grooves are developed by smooth coalescence of developmental lobes. Significance: • Thickness of enamel at the base of pit and fissure is less. • Pits and fissures are the areas of food and bacteria impaction which make them caries prone (Fig. 3.5). Enamel Spindles Odontoblastic processes sometimes cross DEJ and their ends are thickened, called enamel spindles Significance: Spindles serve as pain receptors, that is why, when we cut in the enamel patient complains of pain. Striae of Retzius They appear as brownish bands in the ground sections and illustrate the incremental pattern of enamel. These represent the rest periods of ameloblast during enamel formation, therefore also called as growth circles. When these circles are incomplete at the enamel surface, they result in alternating grooves called imbrications lines of pickerills, the elevations in between are called Perikymata. Perikymata are shallow furrows where the striae of Retzius end. These are continuous around the tooth and parallel to the CEJ. Striae of Retzius are stripes that appear on enamel when viewed microscopically in cross-section. Formed from changes in diameter of ‘Tomes’ processes, these stripes demonstrate the growth of enamel, similar to the annual rings on a tree. Figure 3.4: Pits and fissures of premolars and molars Prismless Layer There is structureless layer of enamel near the cervical line and to a lesser extent on the cusp tip which is more mineralized. Dentino-enamel Junction Dentino-enamel junction is pitted/scalloped in which crests are toward enamel and shallow depressions are in dentin. This helps in better interlocking between enamel and dentin. This is a hypermineralized zone and is about 30 microns thick. Figure 3.5: Deep pits and fissures making areas favorable for food impaction 21 22 Textbook of Operative Dentistry • V-shaped grooves provide escapement of food when cusps of teeth of opposite arch occlude during mastication. Functions of Enamel • It is hardest structure of tooth which supports masticatory forces • It is mainly responsible for color, esthetics, surface texture and translucency of the tooth • It also supports the underlying dentin and pulp. Functions of enamel  Hardest structure of tooth supporting the masticatory forces  Responsible for color and esthetics  Responsible for surface texture and translucency of tooth  Supports underlying dentin and pulp. Clinical Significance of Enamel • Color: Color of the enamel varies because of following factors: – Age – Ingestion of tetracycline during the formative stages – Ingestion of fluoride – Extrinsic stains – Developmental defects of tooth. • Attrition: The change usually seen in enamel with age due to wear of occlusal surfaces and proximal contact points during mastication. Sometimes bruxism or contacts with porcelain also lead to attrition (Fig. 3.6). So, in these patients, try to avoid placing the margins of restoration in occlusal contact area or place a restorative material that wears at a same rate as enamel. • Acid etching: Acid etching is used in fissure sealants and bonding of restorative material to enamel. Acid • • • • • etching has been considered as accepted procedure for improving the bonding between resin and enamel. Acid etching causes preferential dissolution of enamel surface and helps in increasing the bonding between resin and enamel. Permeability: Enamel has been considered to be permeable to some ions and molecules. Hypomineralized areas present in the enamel are more permeable than mineralized area. So, these hypomineralized areas are more sensitive to dental caries. Defective surfaces like hypoplastic areas, pits and fissures are at more risk for dental caries Cracks present on the enamel surface sometimes lead to pulpal death and fracture of tooth. To avoid fracture of tooth and restoration, enamel walls should be supported by underlying dentin. Also the preparation walls should be made parallel to direction of enamel rods since enamel rod boundaries are natural cleavage lines through which fracture can occur. Remineralization: Remineralization is only because of enamel’s permeability to fluoride, calcium and phosphate (available from saliva or other sources). DENTIN Dentin, the most voluminous mineralized connective tissue of the tooth, forms the hard tissue portion of the dentin-pulp complex, whereas the dental pulp is the living, soft connective tissue that retains the vitality of dentin. Enamel covers the dentin in crown portion while cementum covers the dentin in root portion. Dentin contains closely packed dentinal tubules in which the dentinal fluid and the cytoplasmic processes of the odontoblasts, are located. Hence, dentin and bone are considered as vital tissues because both contain living protoplasm. Dentin is type of specialized connective tissue which is mesodermal in origin, formed from dental papilla. The unity of dentin-pulp is responsible for dentin formation and protection of the tooth. Composition Dentin contains 70 percent inorganic hydroxyapatite crystals and the rest is organic substance and water making it more resilient than enamel. The organic components consist primarily of collagen type 1. Composition (by weight)  Inorganic material 70 percent material 20 percent  Water 10 percent  Organic Figure 3.6: Attrition of teeth 23 Structure of Teeth Color Structure of dentin The color of dentin is slightly darker than enamel and is generally light yellowish in young individuals while it becomes darker with age. On constant exposure to oral fluids and other irritants, the color becomes light brown or black (Fig. 3.7). Thickness Dentin thickness is usually more on the cuspal heights and incisal edges and less in the cervical areas of tooth. It is around 3 to 3.5 mm on the coronal surface. With advancing age and various irritants, the thickness of secondary and tertiary dentin increases. Hardness The hardness of dentin is one-fifth that of enamel. Hardness is not the same in all its thickness. Its hardness at the DEJ is 3 times more than that near the pulp so it is important to keep the depth of preparation near the DEJ. Hardness of dentin also increases with advancing age due to mineralization. Compressive hardness is about 266 MPa. The modulus of elasticity is about 1.67 × 106 Psi. As the modulus of elasticity of dentin is low, so it indicates dentin is flexible in nature. The flexibility of dentin provides support or cushion to the brittle enamel. The tensile strength of dentin is 40 to 60 MPa. It is approximately one-half of that of enamel. Hardness of dentin  1/5th of enamel  Compressive hardness is 266 Mpa  Tensile strength—40 to 60 Mpa  Hardness increases with age. Figure 3.7: Dark colored dentin because of irritants  Dentinal tubules  Predentin  Peritubular dentin  Intertubular dentin  Primary dentin  Mantle  Circumpulpal  Secondary dentin  Reparative dentin  Sclerotic dentin. Dentinal Tubules (Table 3.1) • The dentinal tubules follow a gentle ‘S’ shaped curve in the tooth crown and are straighter in the incisal edges, cusps and root areas • The ends of the tubules are perpendicular to dentinoenamel and dentino-cemental junctions (Fig. 3.8) • The dentinal tubules have lateral branches throughout the dentin, which are termed as canaliculi or microtubules • Each dentinal tubule is lined with a layer of peritubular dentin, which is much more mineralized than the surrounding intertubular dentin • Number of dentinal tubules increase from 15,00020,000/mm2 at DEJ to 45,000-65,000/mm2 toward the pulp Table 3.1: Dentinal tubules Pulp DEJ Diameter 2–3 µm 0.5–0.9 µm Numbers 45,000–65,000/mm2 15,000–20,000/mm2 Figure 3.8: Course of dentinal tubules 24 Textbook of Operative Dentistry • Dentinal tubules may extend from the odontoblastic layer to the dentino-enamel junction and give high permeability to the dentin. In addition to an odontoblast process, the tubule contains dentinal fluid, a complex mixture of proteins such as albumin, transferrin, tenascin and proteoglycans. Predentin • The predentin is 10 to 30 µm unmineralized zone between the mineralized dentin and odontoblasts. • This layer of dentin, lie very close to the pulp tissue which is just next to cell bodies of odotoblasts. It is first formed dentin and is not mineralized. Peritubular Dentin (Fig. 3.9) This dentinal layer usually lines the dentinal tubules and is more mineralized than intertubular dentin and predentin. Intertubular Dentin (Fig. 3.9) • This dentin is present between the tubules which is less mineralized than peritubular dentin • Intertubular dentin determines the elasticity of the dental matrix. Primary Dentin This type of dentin is formed before root completion, gives initial shape of the tooth. It continues to grow till 3 years after tooth eruption. Figure 3.9: Pattern of intertubular and peritubular dentin • Mantle dentin: At the outermost layer of the primary dentin, just under the enamel, a narrow zone called mantle dentin exists. It is formed as a result of initial mineralization reaction by newly differentiated odonto blasts. In other words, it is first formed dentin in the crown underlying the dentino-enamel junction. • Circumpulpal dentin: It forms the remaining primary dentin and is more mineralized than mantle dentin. This dentin outlines the pulp chamber and therefore it may be referred to as circumpulpal dentin. It is formed before root completion. Secondary Dentin • Secondary dentin is formed after completion of root formation Difference between Enamel and Dentin Color Sound Hardness Reflectance Enamel Dentin Whitish blue or white gray Sharp, high pitched sound on moving fine explorer tip Hardest structure of the tooth More shiny surface and reflective to light than dentin Yellowish white or slightly darker than enamel Dull or low pitched sound on moving fine explorer tip Softer than enamel Dull and reflects less light than enamel Difference between Primary, Secondary and Reparative/Tertiary Dentin Secondary Formed after root completion Orientation of tubules Rate of formation Primary Dentin formed before root completion Usually formed by primary odontoblasts Found in all areas of dentin Regular Rapid Permeability More Less Definition Type of cells Location Formed by primary odontoblasts It is not uniform, mainly present over roof and floor of pulp chamber Irregular Slow Tertiary Formed as a response to any external stimuli such as dental caries, attrition and trauma Secondary odontoblasts or undifferentiated mesenchymal cells of pulps Localized to only area of external stimulus Atubular Rapid between 1.5 and 3.5 µm/day depending on the stimuli Least 25 Structure of Teeth • In this, the direction of tubules is more asymmetrical and complicated as compared to primary dentin. Secondary dentin forms at a slower rate than primary dentin. Reparative Dentin/Tertiary Dentin • Tertiary dentin;s frequently formed in response to external stimuli such as dental caries, attrition and trauma • If the injury is severe and causes odontoblast cell death, odontoblast like cells synthesize specific reparative dentin just beneath the site of injury to protect pulp tissue • The secondary odontoblasts which produce reparative dentin are developed from undifferentiating mesenchymal cells of pulp • Unlike physiological dentin, reparative dentin is irregular, with cellular inclusions • The tubular pattern of the reparative dentin ranges from a irregular to an atubular nature • Reparative dentin matrix matric is less permeable, this prevents the diffusion of noxious agents from the tubules. Sclerotic Dentin • It occurs due to aging or chronic and mild irritation (such as slowly advancing caries) which causes a change in the composition of the primary dentin • In sclerotic dentin, peritubular dentin becomes wider due to deposition of calcified materials, which progress from enamel to pulp • This area becomes harder, denser, less sensitive and more protective of pulp against irritations. black when ground sections of dentin are viewed under transmitted light. These are called dead tracts due to appearance of black under transmitted light. Functions of dentin  Provide strength to the tooth  Offers protection of pulp  Provides flexibility to the tooth  Affects the color of enamel  Defensive in action (initiating pulpal defence mechanism). Clinical Considerations of Dentin • As dentin is known to provide strength and rigidity to the tooth, care should be taken during tooth preparation • Tooth preparations should be done under constant air water spray to avoid build up of heat formation which, in further, damages dental pulp • Dentinal tubules are composed of odontoblastic processes and dentinal fluid. The dehydration of dentin by air blasts causes outward fluid movement and stimulates the mechanoreceptor of the odontoblast, resulting in dentinal sensitivity (Fig. 3.10) • Dentin should always be protected by liners, bases or dentin bonding agents • When tooth is cut, considerable quantities of cutting debris made up of small particles of mineralized collagen matrix are formed. This forms a layer on enamel of dentin called smear layer for bonding of restorative materials to tooth structure, this smear layer has to be removed or modified. This can be done by etching or conditioning. Types of Sclerotic Dentin Physiologic sclerotic dentin: Sclerotic dentin occurs due to aging. Reactive sclerotic dentin: Reactive sclerotic dentin occurs due to irritants. Eburnated dentin: It is type of reactive sclerotic dentin which is formed due to destruction by slow caries process or mild chronic irritation and results in hard, darkened cleanable surface on outward portion of reactive dentin. Dead Tracts • This type of dentin usually results due to moderate type of stimuli such as moderate rate caries or attrition • In this case, both affected and associated odontoblasts die, resulting in empty dental tubules which appear Figure 3.10: Fluid movement in dentinal tubules resulting in dentin hypersensitivity 26 Textbook of Operative Dentistry • Etching of dentin causes removal of smear layer and etching of intertubular and peritubular dentin for micromechanical bonding. • Restoration should be well adapted to the preparation walls so as to prevent microleakage and thus damage to underlying dentin/pulp. DENTAL PULP The dental pulp is soft tissue of mesenchymal origin located in the center of the tooth. It consists of specialized cells, odontoblasts arranged peripherally in direct contact with dentin matrix. This close relationship between odontoblasts and dentin is known as ‘Pulp – dentin complex’. The pulp is connective tissue system composed of cells, ground substances, fibers, interstitial fluid, odontoblasts, fibroblasts and other cellular components. Pulp is actually a microcirculatory system consists of arterioles and venules as the largest vascular component. Due to lack of true collateral circulation, pulp is dependent upon few arterioles entering through the foramen. Due to presence of the specialized cells, i.e. odontoblasts as well as other cells which can differentiate into hard tissue secreting cells. The pulp retains its ability to form dentin throughout the life. This enables the vital pulp to partially compensate for loss of enamel or dentin occurring with age. Histology of Dental Pulp Basically the pulp is divided into the central and the peripheral region. The central region of both coronal and radicular pulp contains nerves and blood vessels. The peripheral region contains the following zones (Fig. 3.11): • Odontoblastic layer • Cell free zone of Weil • Cell rich zone. Odontoblastic Layer Odontoblasts consist of cell bodies and their cytoplasmic processes. The odontoblastic cell bodies form the odontoblastic zone whereas the odontoblastic processes are located within predentin matrix. Capillaries, nerve fibers and dendritic cells may be found around the odontoblasts in this zone. Figure 3.11: Different zones of dental pulp Cell Rich Zone This zone lies next to subodontoblastic layer. It contains fibroblasts, undifferentiated cells which maintain number of odontoblasts by proliferation and differentiation. Contents of pulp  Cells Odontoblasts Fibroblasts  Undifferentiated mesenchymal cells  Defense cells Macrophages Plasma cells Mast cells  Matrix  Collagen fibers Types I and II  Ground Glycosaminoglycans Substance Glycoproteins Water  Blood vessels Arterioles, venules, capillaries  Lymphatics Draining to submandibular, submental and deep cervical nodes  Nerves Subodontoblastic plexus of Rashkow sensory afferent from Vth nerve and superior cervical ganglion   Cell Free Zone of Weil Structural or Cellular Elements Central to odontoblasts is subodontoblastic layer, termed as cell free zone of Weil. It contains plexuses of capillaries and fibers ramification of small nerve. • They are first type of cells encountered as pulp is approached from dentin. Odontoblasts Structure of Teeth • The number of odontoblasts range from 59,000 to 76,000/mm2 in coronal dentin with lesser number in root dentin. • In the crown of the fully developed tooth, the cell bodies of odontoblasts are columnar and measure approximately 500 µm in height, whereas in the midportion of the pulp, they are more cuboid and in apical part, more flattened. • Ultrastructure of the odontoblast shows (Fig. 3.12) large nucleus which may contain up to 4 nucleoli. Nucleus is situated at basal end. Golgibodies is located centrally. Mitochondria, rough endoplasmic reticulum (RER), ribosome are also distributed throughout the cell body. • Odontoblasts synthesize mainly type I collagen, proteoglycans. They also secrete sialoproteins, alkaline phosphatase, phosphophoryn (phosphoprotein involved in extracellular mineralizations). • Irritated odontoblast secretes collagen, amorphous material and large crystals into tubule lumen which result in dentin permeability to irritating substance. Fibroblasts • The cells found in greatest numbers in the pulp are fibroblasts. • These are particularly numerous in the coronal portion of the pulp, where they form the cell-rich zone. • These are spindle shaped cells which secrete extracellular components like collagen and ground substance (Fig. 3.13). • They also eliminate excess collagen by action of lysosomal enzymes. Undifferentiated Mesenchymal Cells Undifferentiated mesenchymal cells are descendants of undifferentiated cells of dental papilla which can dedifferentiate and then redifferentiate into many cells types. Defence Cells (Fig. 3.14) • Histiocytes and macrophages: They originate from undifferentiated mesenchymal cells or monocytes. They appear as large oval or spindle shaped cells which are involved in the elimination of dead cells, debris, bacteria and foreign bodies, etc. • Polymorphonuclear leukocytes: Most common form of leukocyte is neutrophil, though it is not present in healthy pulp. They are major cell type in micro abscesses formation and are effective at destroying and phagocytising bacteria and dead cells. • Lymphocytes: In normal pulps, mainly T-lymphocytes are found. They are associated with injury and resultant immune response. • Mast cells: On stimulation, degranulation of mast cells release histamine which causes vasodilatation, increased vessel permeability and thus allowing fluids and leukocytes to escape. Extracellular Components The extracellular components include fibers and the ground substance of pulp: Fibers The fibers are principally type I and type III collagen. Collagen is synthesized and secreted by odontoblasts and fibroblasts. Ground Substance It is a structureless mass with gel like consistency forming bulk of pulp. Figure 3.12: Odontoblasts Figure 3.13: Histology of pulp showing fibroblasts 27 28 Textbook of Operative Dentistry Figure 3.14: Cells taking part in defence of pulp Components of ground substance are: • Glycosaminoglycans • Glycoproteins • Water. Functions of ground substance: • Forms the bulk of the pulp. • Supports the cells. • Acts as medium for transport of nutrients from the vasculature to the cells and of metabolites from the cells to the vasculature. Anatomy of Dental Pulp Pulp lies in the center of tooth and shapes itself to miniature form of tooth. This space is called pulp cavity which is divided into pulp chamber and root canal (Fig. 3.15). Pulp Chamber It reflects the external form of enamel at the time of eruption, but anatomy is less sharply defined. The roof of pulp chamber consists of dentin covering the pulp chamber occlusally. Figure 3.15: Pulp cavity The apical foramen is an aperture at or near the apex of a root through which nerves and blood vessels of the pulp enter or leave the pulp cavity. Functions of Pulp The pulp lives for dentin and the dentin lives by the grace of the pulp. Root Canal It is that portion of pulp preparation which extends from canal orifice to the apical foramen. The shape of root canal varies with size, shape, number of the roots in different teeth. Basic functions of pulp  Formation of dentin  Nutrition of dentin  Innervation of tooth  Defense of tooth. 29 Structure of Teeth Formation of Dentin PERIRADICULAR TISSUE It is primary function of pulp both in sequence and importance. Odontoblasts are differentiated from the dental papilla adjacent to the basement membrane of enamel organ which later deposits dentin. Pulp primarily helps in: • Synthesis and secretion of organic matrix • Initial transport of inorganic components to newly formed matrix • Creates an environment favorable for matrix mineralization. Periradicular tissue consists of cementum, periodontal ligament and alveolar bone (Fig. 3.18). Nutrition of Dentin Nutrients exchange across capillaries into the pulp interstitial fluid, which in turn travels into the dentin through the network of tubules created by the odontoblasts to contain their processes. Cementum Cementum can be defined as hard, avascular connective tissue that covers the roots of the teeth. It is light yellow in color and can be differentiated from enamel by its lack of luster and darker hue. It is very permeable to dyes and chemical agents, from the pulp canal and the external root surface. Cementum consists of approximately 45 to 50 percent inorganic matter and 50 to 55 percent organic matter and water by weight. It is softer than dentin. Sharpey’s fibers, Innervation of Tooth Through the nervous system, pulp transmits sensations mediated through enamel or dentin to the higher nerve centers. Pulp transmits pain, also senses temperature and touch. Defense of Tooth Odontoblasts form dentin in response to injury particularly when original dentin thickness has been compromised as in caries, attrition, trauma or restorative procedure. Age Changes in Pulp Pulp like other connective tissues, undergoes changes with time. Pulp can show changes in appearance (morphogenic) and in function (physiologic). Figure 3.16: Reduced volume of pulp cavity because of secondary dentin deposition Morphologic Changes • Continued deposition of intratubular dentin-reduction in tubule diameter • Reduction in pulp volume due to increase in secondary dentin deposition (Fig. 3.16) • Presence of dystrophic calcification and pulp stones (Fig. 3.17) • Decrease in sensitivity • Reduction in number of blood vessels. Physiologic Changes • Decrease in dentin permeability provides protected environment for pulp-reduced effect of irritants • Possibility of reduced ability of pulp to react to irritants and repair itself. Figure 3.17: Pulp stones