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King Saud University Riyadh Saudi Arabia Dr. Gihan Gawish Assistant Professor Gihan Gawish.Dr Gihan Gawish.Dr Connective tissue Derived from mesoderm Connective tissue functions not only as a mechanical support for other tissues But also as an avenue for communication and transport among other tissues. Blood vessels and nerves travel through connective tissue. Gihan Gawish.Dr Components of Connective Tissue Connective tissue consists of embedded in an extracellular matrix. cells The matrix, in turn, consists of fibers and ground substance. Gihan Gawish.Dr Connective tissue cell types – Fibroblasts (which secrete the fibers and ground substance of the extracellular matrix). – Adipocytes (which store fat). – Mast cells (which trigger inflammation). Gihan Gawish.Dr – Macrophages (which ingest and remove foreign material or damaged cells). – lymphocytes, monocytes, and neutrophils, which are all involved in immune defense and inflammation. Gihan Gawish.Dr Types of the extracellular fibers of connective tissue Collagen fibers confer main tensile strength, and are the stuff of scars. Collagen is produced by fibroblast. Elastic fibers confer elasticity. Reticular fibers (really, a special form of collagen III) provide a delicate supporting framework for loose cells. Gihan Gawish.Dr Ground substance It is the background material within which all other connective tissue elements are embedded. In ordinary connective tissue, It consists mainly of water whose major role is to provide a route for communication and transport (by diffusion) between tissues. This water is stabilized by a complex of glycosaminoglycans (GAGs), proteoglycans, and glycoproteins, all of which comprise only a small fraction of the weight of the ground substance. Gihan Gawish.Dr Ground substance may be highly modified in the special forms of connective tissue In blood, the ground substance is fluid (plasma). In bone, the ground substance includes minerals by deposition of calcium salts. In cartilage, the ground substance is much more solid than in ordinary connective tissue but still retains more resiliency than bone . Gihan Gawish.Dr Classification of connective tissue depending on the proportion of various cellular and extracellular components Dense connective tissue (Regular, Irregular and Elastic). Loose connective tissue (Areolar, Adipose and Reticular). Cartilage (Hyaline, Fibrocartilage and Elastic). Other (Bone, Blood and Lymphatics) Gihan Gawish.Dr Dense connective tissue Also called dense fibrous tissue, has collagen (collagen type I) fibers as its main matrix element. Dense regular connective tissue has collagen fibers that are bundled in a parallel fashion. It forms strong, rope-like structures such as tendons and ligaments. Tendons attach skeletal muscles to bones; ligaments connect bones to bones at joints. Ligaments are more stretchy and contain more elastic fibers than tendons. Gihan Gawish.Dr Dense irregular connective tissue has fibers that are not arranged in parallel bundles as in dense regular connective tissue. also make up the large portion of the skin (dermis) Elastic connective tissue is primarily composed of elastin fibres, giving them great elasticity. It appears in the walls of the aorta. Gihan Gawish.Dr loose connective tissue It is a pliable, mesh-like tissue with a fluid matrix and functions to cushion and protect body organs. It has fibroblasts that are widely dispersed; they are irregular branching cells that secrete strong fibrous protein and proteoglycans as an extracellular matrix. The cells of this type of tissue are generally separated by quite some distance by a gel-like gelatinous substance primarily made up of collagenous and elastic fibers. Gihan Gawish.Dr Areolar connective tissue serves as a reservoir of water and salts for surrounding tissues. Almost all cells obtain their nutrients from and release their wastes into areolar connective tissue. It is found beneath the dermis layer and is also underneath the epithelial tissue of all the body systems that have external openings. It is also a component of mucus membranes found in the digestive, respiratory, reproductive, and urinary systems. It also surrounds the blood vessels and nerves Gihan Gawish.Dr Adipose tissue contains adipocytes, used for cushioning, thermal insulation, lubrication (primarily in the pericardium) and energy storage Reticular connective tissue is a network of reticular fibres (fine collagen, type III) that form a soft skeleton to support the lymphoid organs (lymph nodes, bone marrow, and spleen) Gihan Gawish.Dr Gihan Gawish.Dr Its mechanical properties are intermediate between bone and dense connective tissue like tendon. Gihan Gawish.Dr Cartilage composition specialized cells chondrocytes collagen fibers Ground substances Proteoglycan+ elastin fibers Cartilage is classified into three types elastic cartilage hyaline cartilage fibrocartilage Cartilage abundant articular surface of the bones, the rib cage, the ear. Gihan Gawish.Dr nose, bronchial tubes intervertebral discs Blood is traditionally classified as a specialized form of connective tissue, with no fibers, highly fluid ground substance, and mobile cells. Bone are special forms of connective tissue, made by specialized osteoblasts with uniquely solidified ground substance. Lymphoid tissue is a connective tissue with large numbers of lymphocytes that have accumulated in the tissue (lymph nodes, bone marrow, and spleen.) . Gihan Gawish.Dr Gihan Gawish.Dr Classification of connective tissue Connective tissue proper. Specialized connective tissues. Embryonic connective tissues. Gihan Gawish.Dr Gihan Gawish.Dr Collagen Collagen is the main protein of connective tissues in animals and the most abundant protein in mammals It making up about 25% of the whole-body protein content. Collagen is an inextensibile fibrous protein that is found in connective tissue. Fibrous proteins are generally water-insoluble and are found as an aggregate due to hydrophobic R group that stick out of the molecule Gihan Gawish.Dr Tough bundles of collagen called collagen fibers are a major component of the extracellular matrix that supports most tissues and gives cells structure from the outside, but collagen is also found inside certain cells. Collagen has great tensile strength, and is the main component of cartilage, ligaments, tendons, bone and teeth. Gihan Gawish.Dr It strengthens blood vessels and plays a role in tissue development. It is present in the cornea and lens of the eye in crystalline form. It is also used in cosmetic surgery and burns surgery. If collagen is partially hydrolyzed by boiling, the three tropocollagen strands separate into globular, random coils, producing gelatin, which is used in many foods, including flavoured gelatin desserts. Gihan Gawish.Dr Tropocollagen The triple-helix tropocollagen molecule is the basic unit of the collagen fiber. It Composed of about 1000 amino acids each, the individual chains of tropocollagen contain a left-handed helical structure, but are wound together with the other two chains of the fiber in a right-handed manner. Gihan Gawish.Dr Each five tropocollagens combine to form a fiber segment. It is important to realize that in an actual fiber segment the ends of the tropocollagen would be staggered. The staggered ends would permit overlap in the association of the tropocollagens in adjacent segments, and thus aid in forming a strong fiber. Gihan Gawish.Dr The tropocollagen or "collagen molecule" subunit is a rod about 300 nm long and 1.5 nm in diameter A triple helix or "super helix", a cooperative structure stabilized by numerous hydrogen bonds. Collagen's properties of rigidity and inextensibility are due to this highly ordered structure. Gihan Gawish.Dr There is some covalent cross linking within the triple helices, and a variable amount of covalent cross linking between tropocollagen helices, to form the different types of collagen found in different mature tissues Collagen's insolubility was a barrier to study until it was found that tropocollagen from young animals can be extracted because it is not yet fully cross linked. Gihan Gawish.Dr Synthesis of collagen The repeating amino acid sequence is Gly-X-Y, where X is often proline and Y is proline or hydroxyproline (a modified form of proline( or may be any of various other amino acid residues Every third residue lies near the center of the triple helix and can only be glycine, because all other amino acid side chains would be too bulky. Hydroxyproline helps to stabilize the triple helix via hydrogen bond. Gihan Gawish.Dr Glycine Proline Hydroxyproline Melting temperature of collagen This is supported by the fact that helical polymers with the repeating sequence (Pro-HypGly) are much more stable to thermal denaturation than those with the sequence (Pro-ProGly). Indeed the melting temperature of collagen from various sources is directly dependent on the hydroxyproline content. Gihan Gawish.Dr In collagen, Gly is required at every third position because the assembly of the triple helix puts this residue at the interior (axis) of the helix, where there is no space for a larger side group than glycine’s single hydrogen atom. For the same reason, the rings of the Pro and Hyp must point outward. These two amino acids thermally stabilize the triple helix Gihan Gawish.Dr Collagen is unusual not only in having modified amino acid residues, such as hydroxyproline and hydroxylysine, but also in having so many of them. Hydroxylation of proline requires ascorbic acid (vitamin C). Deficiency of vitamin C reduces hydroxyproline production, leading to weakened collagen fibers and the condition known as scurvy. Part of collagen's toughness arises from cross-links between lysine residues of adjacent chains. This cross linking reaction occurs throughout life and makes bones, skin, and tendons less elastic. Gihan Gawish.Dr Types of collagen There are 28 types of collagen. These varieties are produced by different genes, have somewhat different properties, and occur in different locations. Type I collagen forms the familiar eosinophilic collagen fibers of ordinary fibrous connective tissue (e.g., dermis, tendon, organ sheath, fascia) . Type II collagen reinforces cartilage. Type III collagen forms reticular fibers and also occurs in bone. Gihan Type IV& V forms the basement membrane. Gawish.Dr Staining The dye methyl violet may be used to stain the collagen in tissue samples. The best stain for use in differentiating collagen from other fibers is Masson's trichrome stain. Gihan Gawish.Dr Scurvy Collagen diseases commonly arise from genetic defects that affect the biosynthesis. Vitamin C deficiency causes scurvy, a serious and painful disease in which defective collagen prevents the formation of strong connective tissue. Gihan Gawish.Dr The symptoms include, dark purplish spots on skin; especially the legs, spongy gums; often leading to tooth loss, bleeding from all mucous membrane, pallor, bleeding gums, sunken eyes, opening of healed scars; separation of knitted bone fractures, nosebleeds, non-stopping diarrhea, and nail loss. Gihan Gawish.Dr In the human body, a malfunction of the immune system, called an autoimmune disease, results in an immune response in which healthy collagen fibers are systematically destroyed with inflammation of surrounding tissues. The resulting disease processes are called Lupus erythematosus, and rheumatoid arthritis, or collagen tissue disorders. Gihan Gawish.Dr Pathophysiology Normal collagen synthesis depends upon the hydroxylation of proline and lysine residues in the endoplasmic reticulum, to form hydroxyproline and hydroxylysine, respectively. Gihan Gawish.Dr Prolyl and lysyl hydroxylase, the enzymes that catalyze the hydroxylation, require ascorbic acid (vitamin C) to function correctly. With no ascorbic acid, the enzymes cannot hydroxylate proline and lysine, and so normal collagen synthesis cannot be performed. Many bacteria and viruses have virulence factors which destroy collagen or interfere with its production. Gihan Gawish.Dr Ehlers-Danlos syndrome It is a group of rare genetic disorders affecting humans and domestic animals caused by a defect in collagen synthesis. Depending on the individual mutation, the severity of the disease can vary from mild to life-threatening. There is no known cure. Treatment is supportive. Gihan Gawish.Dr Symptoms Symptoms vary widely based on which type of Ehlers Danlos Syndrome (EDS) the patient has. In each case, however, the symptoms are ultimately due to faulty or reduced amounts of collagen. For example, in the most common type of EDS, Hypermobility Type, symptoms often include unstable, flexible joints with a painful tendency to dislocate and subluxate. Gihan Gawish.Dr This is due to ligaments which are lacking proper collagen--the molecule that provides strength to ligaments--are overly stretchable. The so-called Classic EDS Type features skin that forms cigarette-paper-like scars. Another type of collagen is usually responsible for lending strength to skin (and scars). The most serious type of EDS, Vascular EDS, can result in premature death via vascular (blood vessel) and organ rupture. Gihan Gawish.Dr Individual with EDS displaying hypermobile joints Gihan Gawish.Dr Again, another type collagen is necessary to give strength to the walls of blood vessels and the walls of hollow organs (such as the large bowel, aka colon). (It should be noted that Vascular EDS is also one of the most rare types of the disease.) For instance, many of the types feature velvety or hyperextensible skin. Gihan Gawish.Dr Collagenase Gihan Gawish.Dr Mammalian collagenases belong to a family of extracellular metalloproteinases. They are the only enzymes that can specifically cleave native collagen. They catalyze a single proteolytic cleavage in the helical collagen chains, resulting in two fragments that are subsequently accessible to less specific proteases. The action of collagenase is regarded as a 'committed step' since, without it, degradation of collagen cannot take place Gihan Gawish.Dr Gihan Gawish.Dr Mammalian collagenases occur in a variety of tissues and cells. Human skin collagenases are synthesized and secreted as proenzymes. Only after activation, the enzymes can act on their substrate, collagen. The active enzymes in turn can be readily inactivated by a variety of inhibitors The strong regulation of synthesis, secretion and activation-inactivation reflects the importance of collagenases in the metabolism of tissue matrix Gihan Gawish.Dr proteins. Cells Producing Collagenases: It has been reported that the enzymes are produced in a variety of cells, namely neutrophil granulocytes, macrophages, fibroblasts, keratinocytes and others. These cells play an essential role in the different stages of wound healing Gihan Gawish.Dr Gihan Gawish.Dr Bacterial collagenases Collagenases are enzymes that break the peptide bonds in collagen. They assist in destroying extracellular structures in pathogenesis of bacteria such as Clostridium. They are an exotoxin (a virulence factor) and help to facilitate the spread of gas gangrene. Gihan Gawish.Dr Gas gangrene Gas gangrene is a bacterial infection that produces gas within tissues in gangrene. It is a deadly form of gangrene usually caused by Clostridium bacteria (genus of Gram-positive bacteria). It is a medical emergency. Gihan Gawish.Dr These environmental bacteria may enter the muscle through a wound and go on to proliferate in necrotic tissue and secrete powerful toxins. These toxins destroy nearby tissue, generating gas at the same time. A gas composition of 5.9% hydrogen, 3.4% carbon dioxide, 74.5% nitrogen and 16.1% oxygen was reported in one clinical case Gihan Gawish.Dr Collagenase-2 Collagenase-2 is a member of a protein family called matrix metalloproteinases, a large group of enzymes that break down collagen and other components of the body's connective tissue. Gihan Gawish.Dr collagenase-2 plays a role in the development of multiple sclerosis, an autoimmune disease that causes various physical and mental symptoms, and often progresses to physical and cognitive disability. Gihan Gawish.Dr Gihan Gawish.Dr Elastin is another fibrous protein. As the name suggests, elastin is elastic. In ordinary connective tissue, elastic fibers help restore normal shape after distortion. In high enough concentrations, elastin confers a yellowish color (as in the elastic ligament) Like rubber bands, elastic fibers can deteriorate with age and exposure to sun. Gihan Gawish.Dr Locations in body Elastin serves an important function in arteries and is particularly abundant in large elastic blood vessels such as the aorta. Elastin is also very important in the lungs, elastic ligaments, the skin, the bladder, elastic cartilage, and the intervertebral disc above the sacroiliac. Gihan Gawish.Dr Composition Elastin is primarily composed of the amino acids glycine (about 30%), valine (13%), alanine(23%) & proline and hydroxyproline(10%). It is a specialized protein with a molecular weight of 64 to 66 kDa, and an irregular or random coil conformation made up of 850 amino acids. Gihan Gawish.Dr Gihan Gawish.Dr The fundamental polypeptide chain in elastin is tropoelastin (MW=70000) Elastin is made by linking many soluble tropoelastin protein molecules, in a reaction catalyzed by lysyl oxidase, to make a massive insoluble, durable cross-linked array. The amino acid responsible for these crosslinks is lysine. Gihan Gawish.Dr Cross-links in Elastin Desmosine and isodesmosine are both found in elastin. A desmosine cross-link is formed from three allysyl side chains plus one unaltered lysyl side Isodesmosine is a lysine derivative found in elastin Lysine Gihan Gawish.Dr Lysyl oxidase Allysine About 25 – 30 desmosine cross links are found / tropoelastin chain, to provide about one cross-link for every 28-34 residues Allysine Allysine Desmosine Allysine Gihan Gawish.Dr Lysine Elastin Hydrolyzed 1- Elastin can be hydrolyzed slowly by pepsine at pH 2 . 2- The pancreas secretes a zymogene called proelastase trypsin elastase Elastase capable of hydrolyzed alanine and valine Gihan Gawish.Dr Gihan Gawish.Dr 1. Hyaluronan It is one of the chief components of the extracellular matrix, contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumors. Gihan Gawish.Dr Hyaluronan (also called hyaluronic acid or hyaluronate) is a non-sulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. glycosaminoglycans are long unbranched polysaccharides consisting of a repeating disaccharide unit. Gihan Gawish.Dr The repeating disaccharide unit of hyaluronan Gihan Gawish.Dr The average 70 kg (154 lbs) man has roughly 15 grams of hyaluronan in his body, one-third of which is turned over (degraded and synthesized) every day. Hyaluronic acid is also a component of the group A streptococcal extracellular capsule and is believed to play a role in virulence Gihan Gawish.Dr Functions of Hyaluronic acid Hyaluronan is an important component of articular cartilage, where it is present as a coat around each cell (chondrocyte). Hyaluronan is also a major component of skin, where it is involved in tissue repair. Gihan Gawish.Dr hyaluronan also contributes to tissue hydrodynamics, movement and proliferation of cells, and participates in a number of cell surface receptor;CD44. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. High concentrations of hyaluronan in the brains of young rats, and reduced concentrations in the brains of adult rats suggest that hyaluronan plays an important role in brain development. Gihan Gawish.Dr 2.Chondroitin sulfate Chondroitin sulfate is a sulfated glycosaminoglycan (GAG) composed of a chain of alternating sugars (Nacetylgalactosamine and glucuronic acid). Chondroitin-4sulfate: R1 = H; R2 = SO3H; R3 = H. Chondroitin-6sulfate: R1 = SO3H; R2, R3 = H. Gihan Gawish.Dr It is usually found attached to proteins as part of a Proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities. Chondroitin sulfate is an important structural component of cartilage and provides much of its resistance to compression. Along with glucosamine, chondroitin sulfate has become a widely used dietary supplement for treatment of osteoarthritis Gihan Gawish.Dr 3. Heparin Heparin, a highly-sulfated glycosaminoglycan. Native heparin is a polymer with a molecular weight ranging from 3 kDa to 50 kDa, although the average molecular weight of most commercial heparin preparations is in the range of 12 kDa to 15 kDa. Gihan Gawish.Dr Heparin structure Heparin is a member of the glycosaminoglycan family of carbohydrates (which includes the closely-related molecule heparan sulfate) and consists of a variablysulfated repeating disaccharide unit. Gihan Gawish.Dr Most of the amino groups of glucoseamine carry an N- sulphate group, a small fraction carry n-acetyl group A heptasaccharide fragment of heparin Gihan Gawish.Dr Gihan Gawish.Dr Composition Cartilage is a type of dense connective tissue. It is composed chondrocytes of specialized cells called that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers. Cartilage is classified in three types, which differ in the relative amounts of these three main components. Gihan Gawish.Dr Occurrence Cartilage is found in many places in the body including the articular surface of the bones, the rib cage, the ear, the nose, the bronchial tubes and the intervertebral discs. Its mechanical properties are intermediate between bone and dense connective tissue like tendon. Gihan Gawish.Dr Types of cartilage 1. Hyaline cartilage It is a rather hard, translucent material rich in collagen and proteoglycan. It covers the end of bones to form the smooth articular surface of joints. It is also found in the nose, the larynx and between the ribs and the sternum. Bones grow via a hyaline cartilage intermediate, a process called endochondral ossification. Gihan Gawish.Dr 2. Elastic cartilage It contains large amounts of elastic fibers (elastin) scattered throughout the matrix. It is stiff yet elastic, and is important to prevent tubular structures from collapsing. Elastic cartilage is found in the pinna of the ear, in tubular structures such as the auditory (Eustachian) tubes and in the epiglottis. Gihan Gawish.Dr 3. Fibrocartilage It is the most common form of cartilage by weight. It is characterized by a dense network of Type I collagen. It is a white, very tough material that provides high tensile strength and support. It contains more collagen and less proteoglycan than hyaline cartilage. Thus, its properties are closer to those of tendon than hyaline cartilage. It is present in areas most subject to frequent stress like intervertebral discs, the symphysis pubis and the attachments of certain tendons and Gihan Gawish.Dr ligaments. Section through the head of the femur Gihan Gawish.Dr Composition The primary tissue of bone, osseous tissue, is a relatively hard and lightweight composite material, Osseous tissue formed mostly of calcium phosphate in the chemical arrangement termed calcium hydroxylapatite Ca5(PO4)3(OH) (this is the osseous tissue that gives bones their rigidity). It has relatively high compressive strength but poor tensile strength, meaning it resists pushing forces well, but not pulling forces. Gihan Gawish.Dr While bone is essentially brittle, it does have a significant degree of elasticity, contributed chiefly by collagen. All bones consist of living cells embedded in the mineralized organic matrix that makes up the osseous tissue. Gihan Gawish.Dr Molecular structure of bones 1. Matrix The matrix is the major constituent of bone, surrounding the cells. It has inorganic and organic parts. Gihan Gawish.Dr 1-1 Inorganic The inorganic is mainly crystalline mineral salts and calcium, which is present in the form of hydroxyapatite. The matrix is initially laid down as unmineralised osteoid (manufactured by osteoblasts). Mineralization involves osteoblasts secreting vesicles containing alkaline phosphatase. The vesicles then rupture and act as a centre for crystals to grow on. Gihan Gawish.Dr 1-2 Organic The organic part of matrix is mainly composed of Type I collagen. The organic part is also composed of various growth factors, the functions of which are not fully known. These factors present include glycosaminoglycans, osteocalcin, osteonectin, bone sialo protein and Cell Attachment Factor. Gihan Gawish.Dr Bones act as reserves of minerals important for the body, most notably calcium and phosphorus Calcium balance The process of bone resorption by the osteoclasts releases stored calcium into the systemic circulation and is an important process in regulating calcium balance. As bone formation actively fixes circulating calcium in its mineral form, removing it from the bloodstream, resorption actively unfixes it thereby increasing circulating calcium levels. These processes occur in tandem at site-specific locations. Gihan Gawish.Dr The role of bone in calcium metabolism Although calcium flow to and from the bone is neutral, about 5 mmol is turned over a day. Bone serves as an important storage point for calcium, as it contains 99% of the total body calcium. Calcium release from bone is regulated by parathyroid hormone. Calcitonin stimulates incorporation of calcium in bone, although this process is largely independent of calcitonin. Gihan Gawish.Dr Major Mediators of Calcium and Phosphate Balance Parathyroid hormone (PTH) Calcitriol (active form of vitamin D3) Gihan Gawish.Dr Role of PTH Stimulates renal reabsorption of calcium Inhibits renal reabsorption of phosphate Stimulates bone resorption Inhibits bone formation and mineralization Stimulates synthesis of calcitriol Net effect of PTH Gihan Gawish.Dr ↑ serum calcium ↓ serum phosphate Regulation of PTH Low serum [Ca+2] Increased PTH secretion High serum [Ca+2] Decreased PTH secretion Gihan Gawish.Dr Role of Calcitriol Stimulates GI absorption of both calcium and phosphate Stimulates renal reabsorption of both calcium and phosphate Stimulates bone resorption Net effect of calcitriol Gihan Gawish.Dr ↑ serum calcium ↑ serum phosphate Overview of Calcium-Phosphate Regulation Gihan Gawish.Dr Overview of Calcium Balance Gihan Gawish.Dr Overview of Phosphate Balance Gihan Gawish.Dr Gihan Gawish.Dr PERIODONTIUM Cementum Pulp cavity Enamel Dentin Gingiva PDL Alveolar bone Cementum Sharpey's fibers Attachment organ Periodontal ligament Root canal Alveolar bone Apical foramen Gihan Gawish.Dr Alveolar vessels & nerves Structure: The basic tissues that make up the vertebrate tooth are enamel, dentin, cementum, and pulp Gihan Gawish.Dr 1.Enamel Enamel is the hardest tissue in the body because of the very high concentration, about 96%, of mineral salts. The remaining 4% is water and organic matter. The protein is in embryonic enamel is a fibrous protein characterized by a very high proline content and presence of hydroxyproline that is laid down and calcified. Gihan Gawish.Dr The enamel has no nerve supply, although it is nourished to a very slight degree from the dentin it surrounds. The fine, microscopic hexagonal crystallites rods (prisms) of apatite which make up the enamel are held together by a cementing substance. Gihan Gawish.Dr 2.Dentin Dentin, a very bonelike tissue, makes up the bulk of a tooth, consisting of 1. 70% of such inorganic material as calcium and phosphorus , 2. and 30% of water and organic matter, principally collagen. The rich nerve supply makes dentin a highly sensitive tissue. Gihan Gawish.Dr 3. Cementum Cement is a calcified tissue, a type of modified bone less hard than dentin 1. It is approximately 45% inorganic material (mainly hydroxyapatite), 2. 33% organic material (mainly collagen) 3. and 22% water. Gihan Gawish.Dr Cementum is excreted by cementoblasts The principal role of cementum is to serve as a medium by which the periodontal ligaments can attach to the tooth for stability. Gihan Gawish.Dr Role of Cementum 1) It covers and protects the root dentin (covers the opening of dentinal tubules) 2) It provides attachment of the periodontal fibers 3) It reverses tooth resorption Gihan Gawish.Dr Cementum simulates bone Organic fibrous framework, ground substance, crystal type, development Cellular component Incremental lines (also known as “resting” lines; they are produced by continuous but phasic, deposition of cementum) Gihan Gawish.Dr Differences between cementum and bone • Not vascularized – a reason for it being resistant to resorption •More resistant to resorption compared to bone •Lacks neural component – so no pain • 70% of bone is made by inorganic salts (cementum only 45-50%) Gihan Gawish.Dr 4. Pulp The dental pulp is the central part of the tooth filled with soft connective tissue. This tissue contains blood vessels and nerves that along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin Other cells in the pulp include fibroblasts, preodontoblasts, macrophages and T lymphocytes The pulp is commonly called "the nerve" of the tooth. Gihan Gawish.Dr Dental caries Tooth decay, which is also called dental cavities or dental caries, is the destruction of the outer surface (enamel) of a tooth. Decay results from the action of bacteria that live in plaque, which is a sticky, whitish film formed by a protein in saliva (mucin) and sugary substances in the mouth. The plaque bacteria sticking to tooth enamel use the sugar and starch from food particles in the mouth to produce acid. Gihan Gawish.Dr The transitions from sound tooth structure to caries-affected tooth structure to cariesinfected tooth structure. Plaque with refined carbohydrate Sound tooth structure Demineralization Remineralization Removal of plaque, saliva, fluoride, reduced carbohydrates Gihan Gawish.Dr Carious tooth (affected) Demineralization Carious tooth (infected) Irreversible destruction requiring restorative dentistry to replace lost structures The most effective and least expensive means of rendering the tooth less susceptible to the caries attack is through fluoridation ,either by systemic means such as water fluoridation, or by topical application of fluoride to the tooth surfaces. Water fluoridation (approximately 1 part per million) by itself reduces the incidence of caries by 50–60%. Topical fluoridation can be instituted by many means, ranging from professional applications in the dental office to self-applied fluoride in the form of toothpastes, mouth rinses, and gels Gihan Gawish.Dr It is believed that fluoride, when incorporated into the mineral phase of enamel and the other hard tissues, results in a better crystalline structure that is less susceptible to acid dissolution. Alternatively, the anticaries effect of fluoride may be due to its ability to inhibit demineralization and promote remineralization . Gihan Gawish.Dr Florid has antimicrobial activity which inhibits the enzymatic production of glucosyl transferase Glucose glucosyltransferaseextra cellular polysaccharides polysaccharides increases bacterial adhesion Gihan Gawish.Dr