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DICTIONARY OF TERMS IN ORAL PHYSIOLOGY

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This Dictionary is designed to assist students studying Oral Physiology. It accompanies the textbook Applied Oral Physiology.
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A
Abductors - muscle taking a limb or the jaw away from the body.
Acetyl choline - Aneurotransmitter substance found at all cholinergic synapses including those of motoneurones at the neuromuscular junction.
Acini - the secreting units of a gland. Each acinus is a sack-like structure, lined by secreting cells. The sack opens out into a tubule.
Acute necrotising ulcerative gingivitis -abbreviated to ANUG- a painful and destructive infection of the gingiva caused by a shift in the normal balance of bacteria in the gingival sulcus, in which fusobacteria and spirochaetes become dominant.
Adapt- to modify in response to change. When used in regard to evolution, it means that some structure or behaviour of an organism may over time, appear to change in response toa new threat or opportunity in the environment. The bacterium which causes tuberculosis has developed certain strains which have adapted to the antibiotics used to treat the disease which is now becoming more difficult to treat.
Adductors - muscle bringing a limb or the jaw towards the body.
Adhesion - to form a chemical bond of attachment between two surfaces (see Ligand and lectin).
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Adrenalin - see epinephrine.
Aerobic respiration -a type of respiration which requires oxygen and in which glucose is broken down to release energy in a series of steps. The end products are carbon dioxide and water. Step 1;glucose is broken down to pyruvic acid in the cell cytoplasm with the release of 4 hydrogen atoms. Step 2; pyruvic acid is oxidised to acetylcoenzyme A (acetyl CoA), with the release of 4 further hydrogen atoms. Step 3; In the KREB cycle, 16 atoms of hydrogen are released. At all stages the hydrogen atoms are used to form the high energy molecule adenosine triphospate (ATP) via the electron transport system . See also Anaerobic respiration .
Affected dentine - dentine which has been demineralised by acids in advance of invading caries bacteria. A distinction is made between affected dentine and infected dentine, because affected dentine is able to remineralise and should not be removed during cavity preparation.
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Aggregate - clumps or collections of small particles or bacteria .
Alkaline phosphatase - an enzyme which removes phosphate groups from organic compounds at an alkaline pH. It is found in high concentrations in matrix vesicles which are about to form new bone mineral. Alkaline phosphatase activity is a good indicator of bone formation.
Alveolar bone - bone which develops around the roots of the teeth to hold them firmly in place. See gomphosis. If the teeth are extracted, the alveolar bone resorbs away. Alveolar bone consists of both trabecula and cortical types of bone.
Ameloblasts- cells which differentiate from ectoderm and secrete enamel during tooth development.
Amino acids - building blocks of proteins containing a carboxyl group (COOH) and an amino group(NH2) both attached to the same carbon atom . The difference between the 20 common amino acids lies in the nature of a side chain the "R" group. Each amino acid, has a code of three adjacent nucleotides on the DNA molecule. Amino acids are joined together by peptide bonds to form polypeptides and proteins.
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Amorphous calcium phosphate - a non crystalline form of apatite which may form as much as30% of bone mineral.
Amygdala- part of the limbic system, which seems to provide the emotional assessment of a new sensation with the memory of a similar sensation.
Anaerobic respiration - the first step in the production of ATP is to break down glucose. This process of glycolysis is a 10 step series of reactions leading finally to the smaller molecule pyruvate. The energy derived from this process is a hydrogen ion and an electron, which are both placed onto the carrier molecule as nicotinamide adenine dinucleotide (NADH+). As the pyruvate and NAD H+ are produced they could move into the mitochondria, for the nextstage of aerobic respiration, provided oxygen is available. If there is no oxygen, NAD H H+ is used in a process of substrate phosphorylation to form ATP. But the pyruvate builds up. It is then converted to lactic acid and removed to the liver. If lactic acid is not removed fast enough it causes muscle weakness and pain. Anaerobic glycolysis does not produce a high yield of energy. There are still high energy bonds remaining in the pyruvate and there is no benefit from the large yield of ATP made possible by the electron transport system in the mitochondria Top
Angiogenesis - the development of blood vessels - a key event in embryology and healing.
Ankylosis - bony fusion of the two surfaces of a joint to each other, which prevents movement. Ankylosis of the tooth root to its bony socket may causes root resorption.
Antibacterial - inhibiting the growth of bacteria.
Antibodies -are proteins called immunoglobulins which circulate in the blood and body fluids. They bind specifically to antigens that have induced them. Antibodies are able to inactivate bacterial toxins, viruses and help phagocytes to engulf whole bacteria. They have a vital role to play in the bodies immune response to foreign proteins. Top
Antigens - proteins, usually foreign, which cause the bodies defense system to produce an antibody. Antigens may be food proteins, bacteria ,viruses or protozoa or cells from another individual(transplant).
Antrum - a hollow cave or SINUS, inside the maxillary bone which is lined by respiratory epithelium.
Apatites- a family of calcium phosphate salts which are found in hard tissues like bone, teeth and shells.
Apoptosis - death of a cell which is programmed by a set of specific genes. Apoptosis of chondrocytes allows osteoblasts to attach to their calcified matrix, and the epithelial cells forming webs between the fingers to die.
Articular - one of the bones which together with the quadrate bones and the dentary, made/make up a reptile's jaw. In mammals the quadrate bone is incorporated into the middle ear as the malleus.
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Artificial mouth - a laboratory device for keeping bacteria growing in a controlled environment It allows for observing bacteria and their growth under different experimental conditions.
Ascorbic acid - or Vitamin C is a dietary requirement for the proper formation of collagen. Deficiency causes scurvy.
ATP - adenosine triphosphate - ATP is a convenient packet of energy used by both animals and plant cells. The energy in ATP is stored in its three negatively charged phosphate groups which are held close together, in spite of their repulsion for each other. This energy, multiplied many hundreds of thousand of times, for each cell is able to move our muscles, transport molecules across membranes and power all the cells other energy requirements. Once the energy has been used the ATP molecule now only has two phosphate groups. It needs energy now from either aerobic or anaerobic respiration to charge it up again, a process known as phosphorylation. Large stores of ATP are not kept as it is highly reactive. The long term storage of energy in animals is in carbon rich molecules, such as glycogen or fatty acids. In plants energy is stored as starch. Top
Attachment, see epithelial-attachment
Autocrine ;cell messengers which areproduced by the cell itself and regulate the expression of genes .
Autonomic nervous system - controls routine body functions such as gut activity, respiration, blood pressure and heart rate. There are two main divisions the sympathetic nervous system and the parasympathetic system.
Axon - the extension of a nerve cell, as a thin tube which may be as long a metre or a few short microns in length. The axon, like the cell body is able to depolarise and carry impulses along its length. The impulses from one axon to another nerve cell are transmitted at a synapse. Axons may be myelinated or unmeyelinated, and they may vary in diameter. Thicker, myelinated axons transmit impulses faster than thins unmeyelinated axons.
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B
Basal lamina - a term used to describe the different layers which make up the basement membrane. These different layers of the basement membrane, the lamina lucida and lamina densa are only visible with electron microscopy. Into the lamina dense collagen fibres of the lamina propria are anchored. And on the epithelial side are anchored bundles of tonofilaments from the hemi-desmosomes which anchor the basal epithelial cells to the basement membrane.
Basement membrane - a thin sheet of proteins held together by type IV collagen. On this sheet epithelial cells attach with hemi-desmosomes. All epithelia, whether simple cuboidal cells such as found in the salivary glands, or endothelial cells lining capillaries or thick stratified squamous epithelia of the skin, are all anchored to a basement membrane.
Benign- not harmful. In the sense of tumours, not malignant. When referring to parasites, quite harmless.
Biofilm - a layer of microorganisms on a surface which is kept constantly wet. Dental plaque is an oral biofilm Top
Biosurfactants - products of bacteria which increase the hydrophilic nature of a surface so as to allow for better adhesion.
Blood clotting - one of three key processes in haemostasis, the prevention of blood loss. After three minutes of rupture of a small blood vessel, the entire cut is filled with a blood clot. After an hour, the clot has retracted inside the vessel making the plug even more effective. Within a few more hours, fibroblasts have moved into the clot, followed by capillary -forming endothelial cells. Within 10 days the clot is replaced by fibrous scar tissue. Clotting takes place in three steps. 1. In response to damage to the blood vessel prothrombin activator is formed. 2 this activator converts prothrombin into thrombin. 3.The thrombin acts as an enzyme converting fibrinogen into fibrin threads which adhere to the damaged walls of the blood vessel, trap platelets, blood cells and plasma to form a clot.
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Blood groups - blood cells from different people do not always have the same cell surface antigens. A transfusions of blood whose antigens do not match the recipient evokes an immune response and the donor cells are broken down. Two of the common blood groups are the A,B,O group and the Rh group. The blood group antigens are glycoproteins or glycolipids.
Bolus - a piece of food which is being chewed to break it down into small pieces.
Bone membrane - a theoretical membrane separating the fluid surrounding bone crystals from the fluid of the surrounding connective tissue. The membrane would be formed by the endosteum.
Bone morphogenic proteins (BMP) - part of the cytokine family of transforming growth factors. BMP have a powerful ability to cause differentiation of stem cells into osteoblasts and to initiate bone formation.
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Bradykinin - one of several substances, all known as kinins, which cause vasodilation and increased capillary permeability, both events associated with inflammation.
Buffers - chemical which are able to keep the pH of a solution within a normal range, neither acid nor alkali. Salivary buffers are important in reducing the progress of caries by neutralising plaque acids.
Buttress- an arch shaped support, used by builders of bridges and churches in the days before steel.
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C
Calcium-binding proteins - proteins which have the ability to store calcium ions and to bind onto calcium in the hydroxyapatite of the enamel surface.
Calculus - a hard deposit of calcified plaque which is found around the neck of the tooth. When it is above the free gingival margin (supra-gingival) it is white and chalky. When it is below (sub-gingival) it is dark and hard.
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Candidiasis - an infection caused by Candida albicans, a normal commensal of the mouth; also called "thrush";
Capsule - a fibrous casing surrounding an organ or gland; also a coating for some bacteria which protects them, from the bodies immune system. It is only the variety of Pneumococcus sp. which has a capsule which is able to pass the immune barrier and cause pneumonia
Caries - the demineralisation, and breakdown of tooth structure by plaque acids.
Cariogenic - likely to cause caries. Sugar is cariogenic because it supports the growth of plaque
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Carious plaque - types of plaque which are associated with caries .
Carnivorous - an animal whose diet consists of animal tissue.
CEJ - see cemento-enamel junction.
Cell junctions - sites on the cell membrane where cells attach to neighbouring cells. There are three main types. 1. adhering junctions, which anchor cells to each other to resist separation. They may form a belt of adhesions between cells (as between muscle cells) or spot attachments like desmosomes which hold epithelial cells together. 2. tight junctions have no space between the membranes and allow no leakage between cells. They are found between cells of a secreting glands and between endothelial cells of blood vessels to prevent fluid leaking out. 3. gap junctions are channels which allow transfer of small molecules like ions, sugars and amino acids, between cells.
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Cemento-enamel junction- the junction between the enamel covering the crown of the tooth and the cementum covering its root. Often referred to as the CEJ.
Cementoblasts - cells of mesenchyme origin, induced by proteins from cells of ectodermal origin, to form a layer of cementum around the roots of teeth.
Cementum - a thin layer of bone-like material covering the roots of teeth and sometimes the enamel surface, containing both extrinsic and intrinsic fibres.
Central nervous system - the brain and spinal cord. The nerves which leave the spinal cord and brain comprise the peripheral nervous system.
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Chemotaxis - the movement of cells in response to chemical messengers. The movement of neutrophils and macrophages into damaged tissues is brought about by signals released by damaged tissues, and bacterial products.. The term applies to the movement of any organism attracted by a specific chemical, which may be a suitable nutrient.
Cholinergice - cell receptors specific for the neurotransmitter acetyl choline. Cholinergic receptors are found at neuromuscular junctions of muscle fibres and at all the synaptic junctions of the parasympathetic nervous system. They are also found at the pre- ganglionic synapse of the sympathetic nervous system.
Chondroitin sulphate - the major glycosaminoglycan of cartilage , the other being keratan sulphate.
Chromosomes - structures in the nucleus of a cell which appear visible during cell division. Each chromosome (humans have 24) is a tightly coiled string of DNA wound round a protein.
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Clearance - the removal by swallowing, of substance in the mouth. Clearance is dependent on the completeness of swallowing and the rate of flow of saliva.
Clones - a family of cells, or organisms, which are all identical to a single parent. They are produced by asexual reproduction. When a B lymphocytes has recognised a foreign antigen, it provides millions of identical daughter cells in order to produce the specific antibodies in large quantities.
Clotting - see blood clotting
Code - the code of nucleotides is written in "words" of three letters using an"alphabet" of four "letters". These four components of the code are adenine, thymine, cytosine, and guanine.
Collagen - the most common protein found in the body. It has a fibrous structure and makes up the main organic component of bone and dentine, and the fibres of tendons and ligaments.
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Collagenase - an enzyme produced by fibroblasts which breaks down collagen fibres. The fibroblast recycles the component amino acids, and secretes new collagen fibres. This process of remodelling occurs throughout life. Osteoclasts also secrete collagenases in order to remove bone matrix. Several bacteria are able to secrete collagenases and are thus able to break down and penetrate through collagen fibres in the periodontal ligament.
Colonies - communities of organisms which have taken up residence in a habitat .
Competency - the ability of a cell to respond to messengers which could cause it to differentiate into a more specialised cell. Some cells, like pericytes remain competent throughout life, whereas others, such as the oral epithelium, are only able to form an tooth bud during the 12th to 16th week of foetal development.
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Composite - a material made from two or more different types of material which contribute different properties. For example bone is a combination of a resilient fibres of collagen in a brittle matrix (hydroxyapatite).
Compressive strength - ability to withstand a crushing force.
Condylar process - the vertical extension of the mandible which ends in the condyle head, the moveable part of the temporomandibular joint.
Connective tissue - one of the four main types of collections of cells (tissues) which consists of cells in a matrix of ground substance and fibres. Some connective tissues support structures like blood vessels and glands. Others are more structural, like bone, tendons and cartilage.
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Contralateral - the opposite side as distinct from ipsilateral. Often used to refer to the teeth, joint or muscles on the opposite side from the chewing side.
Coronoid process - the vertical extension of the mandible anterior to the condyle to which the temporal muscle attaches.
Cortical-bone - the outer layer of bone which is dense and made up of lamellae.
Covalent bond - a strong bond between atoms formed by sharing outer electrons. When an atom has 8 outer electrons it is stable. Those which naturally have 8, like neon and argon gasses are quite unreactive. The carbon atom has 4 outer electrons and therefore needs 4 extra electrons to be stable. Four hydrogen atoms make a good partnership for carbon,(CH4, C2 H6 ... etc) hence hydrocarbons,(saturated with hydrogen atoms) are quite stable, insoluble and unreactive. One oxygen atom (outer shell has 6 electrons) and two hydrogen atoms (H2O) also makes a stable arrangement, although not as stable as the hydrocarbon, family as the water molecule is a little unbalanced, providing hydrogen bonds and other unusual properties of biological importance, such as its ability to hold other molecules in a solution.
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Cusps - peaks or raised areas of a tooth which usually fit into a fossa on the opposing tooth.
Cytokines -chemical messengers that allow neighbouring cells to communicate with each other. They are paracrine messages as distinct from endochrine or hormonal messengers. There are several main families of cytokines including growth factors , neurotransmitters, , lymphokines and many others. The method of communication involves detection of the chemical message, a ligand , by receptor proteins (for example an integrin on the cell membrane of the receiving cell. The result of the message is a shift in the level of gene expression or the expression of new genes and altered cell behaviour. Cytokines are complex as they sometimes inhibit and/or facilitate the actions of each other.
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Cytoplasm - the contents of the cell, not including thenucleus.
Cytoskeleton - a system of fine filaments which cross the cell in all directions, helping toand keep or change its shape. There are three main types of filaments; in order of decreasing size they are, microtubules, microfilaments and intermediate filaments.
Cytotoxins - products released by bacteria which are toxic to other living cells.
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D
Darwinian medicine - an approach to the treatment of infective diseases which takes account of the co-evolution between the host and its parasite.
Deciduous - from the Latin "falling" it applies both to trees which lose their leaves in winter and teeth which are lost to make way for the permanent set.
Demineralisation - reduction in amount of mineral in tissue. This reduction occurs when the crystals of apatite are dissolved, usually in an acid environment.
Dental abscess- an abscess around the apex of a tooth due to spread of infection from the pulp .
Dental papilla - the condensation of dental mesenchyme which provides the stem cells from which ondontoblasts, cementoblasts and osteoblasts will form the pulp-dentine, cementum and alveolar bone of the tooth socket.
Dentary - one of several bone which together made up the lower jaw in early reptiles. During evolution the other bones, the articular and quadrate bones, became part of the inner ear, and the dentary became the single the mandible of mammals.
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Dentine - a hard material like bone which forms the root and inner core of the crown of teeth. Unlike bone, dentine has fine tubules which contain the elongated process of odontoblasts, the dentine forming cells.
Dentine-pulp - a term used to describe the unity between dentine and pulp, and to view it as one integrated tissue.
Depolarisation - all cells have a slight difference in electrical potential between the inside and outside of the cell membrane. This difference is called a membrane potential and is due to a greater number of sodium ions (positively charged) outside the cell than inside. This imbalance is maintained by a membrane pump which pushes sodium ions out of the cell. Another pump also pushes potassium ions into the cell so there should be no difference in the balance of positive ions. But the potassium ions leak back out again, so there is always a potential difference across the membrane. Nerve cells have the ability to depolarise or reverse the membrane potential so that the inside is positive and outside negative. This reversal is short lived and is soon corrected, but it is long enough to influence the adjacent parts of the membrane and to be carried, like a wave, all the way along a nerve axon to the next nerve where it reaches a synapse The reversal is caused by a sudden opening of cell membrane gates which allow a flood of sodium ions into the cell. This flood causes the inside to become positive, but the gates are soon shut and potassium gates opened, which allows potassium ions to flood out and restore the membrane potential. This can all happen several times in one second, but after a while there is no flood, and the sodium pump has to get to work to build up enough pressure for the depolarisation to work again.
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Dermatan sulphate - a glycosaminoglycan found in skin, tendon, blood vessel and heart valves.
Desmosomes -one of the types of cell junctions by which cells join or communicate with each other. Desmosomes consist of a round plaque of protein, desmoplakin on the cell membrane. Into the plaque are attached fine filamanents which are part of the cell's cytoskeleton. So the plaque is attached to the skeleton of the cell. Where the filaments enter the plaque the are so dense as to be visible with a light microscope. They are then called tonofilaments. The plaque of one cell adheres to the plaque of another. This system of joining cells is designed to resist mechanical separation, so we see desmosomes joining epithelial cells which hold tightly to each other. If epithelium is processed for histology, some shrinkage occurs and the epithelial cells separate from each other, except where the desmosomes hold them together. The pulled out tags of cell membrane give these cells a star-like shape, and so they are called the stellate cells.
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Desquamation - the detachment of cells from the surface of an epithelium.
Dextrans - polysaccharides made by bacteria. They have a slimy consistency and contribute to the sticky nature of plaque.
Differentiate - change in the pattern of genes expressed by a cell resulting in altered function, from a more primitive parent cell to a more specialised group of daughter cells.
Diphyodont - only two sets of teeth, one deciduous and one permanent (from "di" = two,"phyo+ = generation and "dont" =teeth). See also polyphyodont
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Displacement - of a tooth refers to its movement within the confines of the tooth socket. A tooth can be displaced more easily when forced in a lateral direction than when forced into the socket. Continual or frequent displacement of a tooth may lead to it repositioning itself in the socket.
DNA - Deoxyribosenucleic acid - a complex nucleic acid molecule which is used by cells to store genetic material as genes which control the structure of proteins and hence influencing all enzyme reactions. DNA is coiled in a single closed loop in procaryotes, but coiled round other proteins to form a chromosome, and stored in the nucleus of eucaryotes
Duct - a tube which carries a secretion onto the surface of skin or mucosa.
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E
Ecological balance - astable balance in the numbers of each species in an ecosystem .In the ecosystem of the mouth this balance is brought about by competition and cooperation between the different organism and the hosts defences which tend to control population size.
Ecosystem - a stable environment in which live a large number of different forms of life, each affecting the other. Example are a forest, desert, tidal area, soil, oral cavity, gut.
Ectoderm - the outer of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The ectoderm will form the epidermis of the skin and the nervous system. The other two layers are the mesoderm and the endoderm.
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Ectomesenchyme - a name given to dental MESENCHYME which reflects its partly ectodermal origin.
Eicosanoids - are a class of hormones which are all made from phospholipids. They include prostaglandins, thromboxanes, and leucotriens.
Elastic fibres -are long, thin, ribbons-like fibres, sometimes even sheet-like. They are composed of a central core of elastin, a rubbery protein, surrounded by glycoprotein microfilaments. Elastin is found all over the body but particularly in the walls of blood vessels and in our vocal chords.
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Electron - the negatively charged elements of an atom which circle the nucleus. If an electron is lost the atom becomes a relatively positively charged ion. It has been ionised .
Electron Transport System- Hydrogen ions produced during the 3 preparatory steps of aerobic respiration are carried by nicotinamide adenine dinucleotide (NAD). The hydrogen ion plus one electron form NADH, which is taken to the electron transport system. This transport system is run by a series of 5 molecules. The first, removes the two electrons from NADH,( one comes from the hydrogen atom, leaving behind a hydrogen ion). These two electrons, bounce from the first molecule in the transport system to the second, third, forth and then last one, cytochrome oxidase, which finally places the electrons onto oxygen gas O2. The electron rich oxygen atoms are attractive to the hydrogen ions and they combine to form water. (Oxygen in the process of aerobic respiration acts therefore as an electron acceptor). In the process of bouncing "downhill" the electrons have released sufficient energy to power up a small battery. This battery has been made by pumping hydrogen ions out of the inner membrane of the mitochondria. The collection of hydrogen ions outside, piles up and their electrical pressure mounts. They want to get back across the membrane, and are allowed, one at a time to pass back through the enzyme ATP synthase. This enzyme sits like a water wheel in the cell membrane, turned by the passage of hydrogen ions. Its turning wheel builds an ATP molecule in every turn. The wheel may be going at about 200 revolutions per second, powering the synthesis of an ATP molecule with each turn. ATP formed in this way takes a while but can be sustained to fuel the body during aerobic exercise. When the demand for power exceeds this rate, the cells have to rely on anaerobic respiration.
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Electrostatic - a force generated by differences in electric charge of two particles.
Enamel prisms - rod-like bundles of hydroxyapatie crystals which are orientated at right angles to the tooth surface. Each prism can be traced from the outside of the enamel all the way to the dentine junction.
Enamel - the outer layer hard layer which covers the dentine around the crown of a tooth. Enamel consists of closely packed crystals of hydroxyapatite with very little organic material. A recognisable unit of structure in enamel is the enamel prism.
Enameloid - a type of enamel found in fish and reptiles in which the enamel prisms are haphazardly arranged; in contrast enamel prism are parallel to each other and orientated at right angle to the tooth surface.
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Endocrine glands - the secretion passes into the blood stream, like insulin, epinephrine.
Endoderm - the inner of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The endoderm will form the gut system and its associated organs. The other two layers are the mesoderm and the ectoderm.
Endoplasmic reticulum - a system of inner cell membranes which is continuous with the nuclear membrane. It transports products of cell synthesis to the golgi apparatus. Described as rough endoplasmic reticulum when there are many ribosomes attached.
Endorphins - a neuropeptide which has specific binding sites on nerve cells called opiate receptors. When the receptor is activated by endorphins or morphine it reduces the excitability of the post synaptic cell. Peptide receptors are also found on lymphocytes which suggest an association between neuropeptides and the regulation of the immune response.
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Endosteum - a layer of bone forming cells, osteoblasts which covers the entire surface of the internal aspect of cortical and spongy bone, separating it from the surrounding connective tissue. see also bone membrane.
Endothelial cells - the epithelial cells of the endothelium which lines blood vessels. The cells are flattened into a pavement stone shape and are usually two or three layers thick.
Endotoxins - the contents and cell wallsof dead bacteria which may be toxic to the host.
Enkephalins - similar in structure and action to endorphins.
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Environment - describes the surroundings in which organisms live. Some physical features of an environment are fairly stable, like trees, rivers, mountains, houses, soil, teeth. Some physical features are changeable, like wind, water, light, pH, food supply. Others features are less predictable, such as the balance in the community of collaborators, competitors and parasites. All forms of life including bacteria in the mouth, have an environment, which has an important influence on their survival. Successful organisms manage to exploit their environment to the best advantage or to adapt to it, perhaps only after several generations, if it becomes a serious challenge to the species.
Enzyme - a protein that controls and helps a chemical reaction to take place, but is not used up in the process. Usually each enzyme is specific for a particular step in a reaction. Enzymes are sensitive to their environment, especially to excessive temperature or pH.
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Epidermal growth factor - a cytokine that stimulates epithelial cell proliferation.
Epinephrine - a neurotransmitter substance found at all adrenergic synapses (nor epinephrine or epinephrine). It is the most common neurotransmitter in the nervous system, in particular at ganglion cells of the sympathetic nervous system.
Epitaxy - the initiation of crystalformation in a saturated solution by providing a template against which crystal can form. There are specific sites on collagen molecules which appear to function as templates against which hydroxyapatite crystals form.
Epithelial attachment- the cuff of junctional epithelium which joins the gingival sulcus epithelium to the enamel of the tooth. Apical migration of the epithelium down onto the cementum may occur due to ageing or periodontal disease. Loss of attachment produces a periodontal pocket and a new habitat for anaerobic oral bacteria.
Epithelium - a layer of cells which forms alining for a tube or the covering for an organ or the whole body.
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Eucaryote - a cell in which the genetic material is confined to the nucleus, in distinction to a procaryote in which the genetic material is dispersed throughout the cell. Other distinctions of eucarytoic cells are the presence of organelles such as the golgi apparatus, endoplasmic reticulum, lysosomes and mitochondria
Exocrine glands - the secretion passes intoa duct like sweat, saliva and mucous.
Extinct - a plant or animal species may entirely cease to exist. Recent examples are the dodo, a large flightless bird which used to live as recently as two hundred years ago, on the island of Mauritius. There are today many species of birds, flowers, fish, insects, large mammals, including certain types of whale, which are threatened with extinction, most as a result of human activity. Happily, the smallpox virus is about to become extinct
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Extra cellular matrix - the supporting surrounding material of a cell including ground substance and fibres.
Extrinsic fibres - refers to those fibres of cementum which are continuous with periodontal ligament fibres. Extrinsic fibres have been trapped in cementum during its formation in order to anchor them. see also intrinsic fibres, and sharpey's fibres.
Exudate - the fluid plasma which leaks out of blood vessels due to an increase in capillary permeability. The increased permeability, is caused by histamine, and bradykinin, which are released in response to tissue damage. The formation of an exudate is the first step in the process of inflammation.
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F
Fatty acids - long straight chains of carbon and hydrogen ending with an acid group at one end. Saturated fatty acids have no capacity to absorb more hydrogen atoms. Animal fats are mostly of this type and are considered less healthy as they end to accumulate in the linings of arteries.
Feedback - a system of control, where work being done is modified by the product. For example the blood pressure is maintained by the strength of the heart beat and the muscle tone of the arterioles. In the walls of the large arteries are receptors sensitive to the degree of stretch in the muscle wall. As the blood pressure increases, the wall are stretched, and the receptor sends signals via the brain to the sympathetic nervous system back to the heart and blood vessels, causing decreased pumping effort and more relaxed muscle tone in the arteries. In chemical reactions the accumulated product slows down the rate of production. For example if the oxygen level of the body falls, the rate of respiration.increases to restore the levels to normal. These control system are thus circular; what is produced returns to control the further production. They are examples of negative feedback, and are common in maintaining stability or homeostasis. Positive feedback is less common as it tends to be unstable. An example is the release by platelets of thrompotaxin. When the levels of thrombotaxin are high, they do not inhibit further production as occurs in a negative feedback system but actually stimulate more platelets to produce more thrombotaxin and so on until there is an explosive increase in the number of sticky platelets. This is useful in an emergency to stop bleeding, but very dangerous when a clot forms inside a blood vessel.
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Fibre - a long thin string-like structure constructed of smaller fibrils and even smaller microfibrils. Examples are collagen, elastic and keratin fibres. Collagen fibres are arranged parallel to each other in a tendon, to give it great resistance to tension (pulling).
Fibrinogen - a large soluble protein found in blood which is converted into fibrin during blood clotting.
Fibroblasts - cell of connective tissue which form both the intercellular matrix and fibres.
Fibronectin - a glycoprotein which is found in the extracellular matrix and is important for the attachments, and therefore the movement of cells.
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Filamentous - long, thin, hair-like.
Fluorapatite- an apatite crystal in which fluoride has replaced hydroxyl ions.
Fluorosis - mottling of the teeth caused by an excess of fluoride in the drinking water. A fluorosis index recognises 4 stages of severity.
Foramina - the plural of foramen, which is a hole, for example Foramen Ovale.
Fossils - dead plant or animal remains whichhave become infused with minerals over many millions of years and are now hard and rock -like. The original shape of the animal or plant may be very well preserved.
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Fractal dimension - a dimension which is some fraction in between a line(1) and a plane(2), or a plane and a solid (3). These fractal dimensions are useful in describing the quality of natural lines and surfaces, such as coastlines, trees, vascular branching and the patterns of trabecula bone
Freeway space - the space between the teeth when the jaw is in a rest position .
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G
Gangrene - the death of tissue on a large scale. May be caused by certain bacteria which spread rapidly through tissues, or by an inadequate blood supply.
Ganglion - a collection of nerve cells usually found outside the central nervous system, from which axons arrive from the periphery and proceed to the spinal cord or brain.
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Gene cloning - a technique which uses recombinant DNA , inserted into a host cell as a plasmid which reproduces copies of itself, and hence the inserted gene, many times
Generic - belonging to the same main group. For example generic medicines are identified by the main group they fall into rather than by their trade names.
Genes - the unit of inheritance that transmits information from one cell to its daughters and hence to the next generation. A gene consists of a specific series of DNA nucleotides. Each three nucleotides is the code for an amino acid. Humans have about 200,000 genes which collectively are know as the genome.
Genetic engineering - see recombinant DNA.
Genome - the complete complement ofgenetic material in a species.
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Gingival crevice fluid - a secretion found in the gingival sulcus, formed by the cells attaching the gingival epithelium to the tooth.
Gingival sulcus - a potential space between the gingival margin and the tooth, lined by non-keratinised epithelium. The depth of the sulcus is normally between 1 and 2 mm in health.
Gingivitis - an inflammation of the gingival mucosa, due to the increase in the virulence or mass of bacteria in the gingival sulcus, or to reduced resistance of the host.
Glands - a collection of cells secreting a specific product such as insulin or sweat.
Glucocorticoids - one of the two major hormones secreted by the adrenal medulla. The most common glucocorticoid is cortisol (hydrocortisone) but they all share the common effect of increasing blood glucose concentration. They may achieve this at the cost of body protein stores, by converting amino acids into glucose. Cortisol also converts fatty acids into glucose. Any type of stress, including trauma, infection, fear, anxiety or malnutrition causes an increase in cortisol secretion. Cortisol stabilises the membrane of lysosomes, which are then unlikely to rupture, a process which stimulates inflammation. Cortisol therfore inhibits inflammation. Cells like neutrophils, are less able to protect the body from foreign proteins. Stress therefore reduces the bodies ability to cope with infection. Malnutrition not only stunts mental and physical development but also allows viral, bacterial and parasitic infections to flourish.
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Glucosamine - a glucose or galactose molecule with an amine group attached. see also glucuronic acid.
Glucose - a molecule of great importance to life as it provides a ready source of energy for both plant and animal cells. Glucose can only be formed in plants with the aid of sunlight. This process of photosynthesis sustains all animal life on earth. The glucose molecule is formed by a ring of a six carbon atoms. It is progressively broken down in a process called glycolysis during both aerobic and anaerobic respiration into ATP
Glucuronic acid- a glucose molecule with an acid carboxyl group. One of the two molecules which makes up the repeating disaccharide unit of glycosaminoglycans other molecule is a glucosamine.
Glycine - one of 20 amino acids commonly found in proteins.
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Glycogen - a polysaccharide made up of repeated glucose units. Animals make glycogen and store it in liver and muscles.
Glycolysis - the breakdown of glucose in series of metabolic steps. Energy in the form of ATP is released even if there is no oxygen available as in anaerobic respiration . In the presence of oxygen as in aerobic respiration the breakdown is more complete and yields more energy.
Glycoproteins - are proteins which have many sugar molecules attached to them. They are an important component of saliva where they provide lubrication for the teeth. They also have a wide range of other functions in connective tissues. Examples are fibronectin, osteonectin, osteopontin and interferon. Glycoproteins are also found in cell membranes where they define part of the cells identity. The four major blood groups are defined by glycoproteins on the cell membranes of red blood cells.
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Glycosaminoglycans (GAGs) - large to huge molecules of the connective tissue matrix, made up of repeating disaccharide units linked to a protein core. The disaccharide units are made of glucosamine and glucuronic acid. The position of a sulphate molecule on the glucosamine determines the type of GAG.
Golgi apparatus - a cell organelle which is part of the inner cell membrane. It collects and stores the products from the endoplasmic reticulum. It is prominent in actively secreting cells.
Gomphosis - a form of tooth attachment in which the root is help in a bony socket by a fibrous ligament.
Gonial angle - the angle made by the posterior part of the ramus and the lower border of the mandible.
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Ground substance - a jelly-like substance which surrounds cells and provides, with fibre, a supportive matrix around each cell. It consists of water and huge molecules which helps transport nutrients to cells and carries away cell products.
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H
Habitat - a location which has a suitable environment for an organism to live in. Caves are natural habitats for bats, trees for birds; oral surfaces and crevices, for some bacteria.
Haemostasis - the prevention of blood loss through a damaged vessel wall. There are three main mechanisms, vasoconstriction, formation of a platelet plug and blood clotting.
Heparin sulphate - a glycosaminoglycan which is unusual in that it is stored inside the cell (mast cells) surrounding the liver. Heparin prevents blood clotting.
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Herbivorous- an animal whose diet consists of grass, leaves, roots or other plant matter.
Heterodont- a dentition in which some of the teeth have different shapes and special functions. Form "hetero" = different) see also homodont.
Hierarchy - an order of power between individuals. A ranking of most dominant to least dominant.
Hippocampus - part of the limbic system, it seems to provide a spatial map, useful in the event of a sudden need to escape from an unpleasant sensory experience.
Hypothalamus - this small body of nerve cells controls the activity of the pituitary gland, the source of several hormones which control the activity of other hormones, including ACTH which in turn controls the level of glucocorticoid secretion. The hypothalamus also has powerful connections with the other members of the limbic system, from which nerve pathways descend to control nerves in the spinal cord. The influence of the limbic system on the hypothalamus explains the raised levels of glucocorticoids in response to emotional stress. This bridge with the peripheral nervous system, provides a link between the emotional state of a person, as influenced by the activity of the limbic system, and the excitability of neurones in the spinal cord, to in-coming pain impulses.
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Histamine - is a product of the amino acid, histidene and is released by damaged cells. Histamine causes an increase in capillary permeability and vasodilation, two vascular events which are the first stages of inflammation. Histamine is also a neurotransmitters substance, released at nerve synapses mostly in the hypothalamus.
Homeostasis - control of an organism’s internal environment. Water content, temperature, acid-base balance, level of oxygen and carbon dioxide, adequate supply of energy are some of the many factors in the organism which require monitoring and control. A common form of control is feedback.
Homodont - a dentition in which all the teeth are the same shape (from "home" = same) see also heterodont.
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Hyaluronic acid - the largest glycosaminoglycan known, it plays an important role of restricting the flow of water in tissues, particularly in synovial fluid where it acts as a lubricant..
Hydrogen bonds - a weak force holding two molecules containing hydrogen together, each of which has a covalent bond with another atom. For example, water is a molecule made up of two hydrogen atoms attached covalently to an oxygen atom. The hydrogen proton is however not completely balanced and is still attracted to the oxygen atom of a neighbouring molecule. Molecules of water are thus held together by hydrogen bonds, which accounts for the unusually high boiling point of water considering its low molecular weight. Hydrogen bonds hold protein molecules in shape by linking up various sections. When proteins are heated, these bonds collapse and the protein is physically altered, even though its chemical composition remains unchanged. When an egg is heated the white part rapidly gels, indicating a change in the shape of the protein. The process is not reversible.. so an egg cannot be uncooked.
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Hydroxyapatite - one of the apatites which is the main salt of bone and teeth.
Hydroxyl ion- a negatively charged ion of hydrogen and oxygen written as OH-.
Hyperplasia - an increase in the size of an organ due to an increase in the numbers of cells. The developing embryo increases in size due to cell division. The cells of some tissues retain the ability to divide throughout life, like the epithelium and connective tissues but muscle and nerve cells lose their ability to divide soon after birth. When hyperplasia is uncontrolled it produces a tumour which may be benign if it is well contained, not destructive and does not spread. But it may be malignant, destroys normal tissue, and spread all over the body.
Hypertrophy - an increase in the size of an organ due to an increase in the size of each cell. Muscles increase in size due to hypertrophy.
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Hypoplasia - reduced formation of a tissue during development. Enamel hypoplasia may be recognised as pits and depressions in the enamel and may be cause by fluorosis.
Hypotonic - a comparison between two solutions, indicating that one has a lower osmotic pressure, or is less salty than the other.
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I
In Vitro - experiments which are carried out in a laboratory as distinct from in vivo experiments
In Vivo -experiments which are carried out in live animals as distinct from in vitro experiments
Immunity - The body’s response to a foreign antigen, either ingested as food, or as part of a foreign organism. There are two major ways the body defends itself; one is by antibody, production, the so called humeral response, as the antibodies circulate in the blood and the fluid between cells. The other is the cellular response, as it involves the cells of the immune system, the family of leucocytes. The particular leucocyte responsible for immune specificity is the lymphocyte . In total cell mass there are as many lymphocytes as there are liver or brain cells. During development there are millions of B (from the Bone marrow) lymphocytes made, each with a different cell membrane ligand, specific for any one of millions of antigens. The lymphocytes are circulating all the time so that they can have the chance to meet up with a foreign antigen. As soon as an antigen has been recognised by one of these cells, and bound to the cell ligand, it stimulates the cell to reproduce millions of copies of itself. All the daughter cells are clones of the original cell. These B lymphocyte daughters, migrate to the site where the antibody is needed. Instead of making an antigen for the membrane these cells make large amounts of soluble antibody. They are now recognisable as plasma cells. T lymphocytes ( having spent time in the Thymus) comprises the cell mediated response to an antigen. They are of two types, Killer T cells and Helper T Cells. Most T lymphocytes are helpers and they regulate the response of the B lymphocytes . The killer T cells are however capable of recognising the foreign antigen on the surface of a cell, and then killing the entire cell. The immune response is part of a less specific defense and healing response of the body known as inflammation.
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Indirect pulp cap - a dressing, usually calcium hydroxide, placed against the pulpal wall of a deep cavity, in order to encourage affected dentine to remineralise. The cavity is closed with a temporary filling material and re-opened after 6 weeks to assess the state of the pulp.
Induction - cell differentiation which is brought about by the influence of cytokines released by cells of another type.
Infected dentine- dentine which has been damaged beyond repair by caries and is infected by large numbers of caries bacteria.
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Inflammation - is a whole complex of events which occur in sequence, in response to injury. Tissue damaged by bacteria, chemicals, heat, trauma etc, release histamine and bradykinin and serotonin which cause an increase in capillary permeability and vasodilation. Both these factors contribute to the formation of a fluid exudate in the damaged tissue, which includes fibrinogen and therefore soon clots into a firm gel. This process has the effect of walling off the bacteria or toxic substances causing the damage, or at least it slows down their spread into surrounding tissues. Local macrophages, begin their phagocytic activity but their numbers are small. Damaged tissues also release interleukin, messengers which are transported all the way to the bone marrow, where millions of leucocytes are stored.. These stores now release leucocytes, mostly neutrophils into the blood. The neutrophils gather at the site of damage because the endothelial cells of the local capillary walls have become sticky to leucocytes. This stickiness is specific for leucocytes and is the work of selectins expressed on the cell membrane of the endothelial cell. The leucocytes begin to catch and roll along the endothelium until they are brought to a standstill. The increased permeability of the endothelial cells allows leucocytes to wriggle out of the capillary and migrate into the damaged area. This migration is also dependent on a process know as chemotaxis, in which cytokine messages from the damaged cells attract the leucocytes to come to their aid. After several days the battle zone is filled with dead bacteria, dead tissue cells, dead neutrophils and macrophages. This dead mass of tissue is called pus. The end of the event may be the gradual resorption of pus by fresh macrophages, or the pus, now under some pressure, may force its way somewhere else. Pus from the apex of a tooth may escape laterally through the alveolar bone and mucosa, where it is recognisable as a "gum boil".Ten days after a foreign protein is detected for the first time, the bodies immune system has mounted a more specific defense. Antibodies are produced by B lymphocytes and T lymphocytes have been alerted to the invasion.
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Insulin - an endochrine hormone produced in the spleen which controls the amount of sugar in the blood by a) transporting it into cells and promoting glycolysis b) converting it into glycogen for storage in the liver and muscles, and c) converting it into fats . Without sufficient insulin, glucose accumulates in the blood and urine and the cells of the body are starved, a condition known as diabetes. The control of insulin production is another example of a feedback system.
Insulin-like growth factor (IGF) - a cytokine that influences growth hormone activity.
Integrins are the cell surface receptor molecules which match up with parts of the matrix protein ligands to allow adhesion of the cell to the matrix. The attachment of cells to matrix proteins also influences the cells behaviour, by the expression of genes. The integrins are a family of proteins, found doing the same job on all animal cells. Their importance in maintaining the structural integrity of cells led to the name integrins.
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Intercalated ducts - ducts which carry saliva between the tubules and the striated ducts .
Interferon - a glycoprotein produced by cell s which mobilise the T lymphocytes to inhibit viruses and the growth of cancer cells.
Interleukins - a variety of compounds(about 20) that are produced by lymphocytes, macrophages, and monocytes. They regulate the cell mediated response of the immune system. Interleukin-1 is involved in the triggering of the immune response, starting acute inflammation and maintaining chronic inflammation. Interleukin-2 is produced by helper T cells and induces proliferation of immune cells, both T and B. Interleukin-3 promotes the differentiation and proliferation of stem cells of the leucocyte family.Interleukin -6 produced by various cells including tumour cells and acts as a stimulant of plasma proteins and B and T cells. Interleukin -12 is produced by a range of cells. It activates T cells and natural killer cells. It promotes the response to a range of pathogens including HIV of Interleukin-2. It appears to be one of the most promising Interleukins for the control of viral, bacterial and protozoal infections.
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Intermediate filaments - unlike microfilaments and microtubules, they are verystable. Instead of being stacked proteins, as in actin, intermediate filaments are built of interlocking proteins. A dense sheet of intermediate filaments strengthens the nucleus. Skin cells are filled with keratin, which at the last moment, just before they die. they cross link, to provide a really insoluble barrier layer of the skin. The cross linkage is between the sulphur atoms of cysteine, one of keratin's amino acids .
Interproximal wear - loss of enamel on the adjacent surfaces of teeth which is due to continual friction between the two surfaces as teeth move against each other.
Intratubular dentine - dentine formed inside the tubule by the odontoblast process in response to tooth wear, ageing or arrested caries.
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Intrinsic fibres - refers to those fibres of cementum which were laid down by cementoblasts. see also extrinsic fibres
Ionised - the loss or gain of an electron from an atom which makes it no longer neutral but an electrically charged ion. If the electron leaves the atom it becomes a positively charged ion, such when calcium or sodium becomes ionised (Ca+,Na+). If the electron is gained, the atom becomes relatively negatively charged such as when chlorine or a phosphate group of atoms lose an electron (Cl-, PO4-). Ionized atoms or groups of atoms are more reactive than when they are neutral.
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Ions - an atom or molecules which has a net electrical charge This may be caused by the temporary loss (positive ion) or gain (negative ion) of an electron. A calcium ion is written Ca+.
Ipsilateral - the same side as distinct from contralateral. Often used to refer to the teeth, joint or muscles on the same side as chewing is occurring.
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J
Junctional epithelium - the epithelium which seals the base of the gingival sulcus against the tooth.
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K
Keratan sulphate - a glycosaminoglycan found in cartilage, with chondroitin sulphate.
Keratin - a fibrous polymer which is notas strong as collagen but less soluble. It forms the strong and water-resistant properties of skin, nails, hair, horn and beaks.
Keratinised - an epithelium in which the superficial cells have lost their nuclei and become filled with intermediate filaments ofkeratin.
Keratinocytes - Cells of the epidermis which secrete the protein keratin. They become progressively flattened as they mature and are eventually are off.
Kreb cycle - the end stage of aerobic respiration. Kreb's cycle is a circular series of reactions taking place in the matrix of mitochondria in which acetyl CoA is broken down into carbon dioxide and hydrogen atoms. The hydrogen atoms are used to produce ATP via the electron transport system.
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L
Lamella-bone - the microscopic structure of cortical bone gives it the appearance of concentric or parallel plates ( from Latin, lamella, the diminutive of lamina, meaning a plate or leaf).
Lamina propria - the layer of loose connective tissue underneath the epithelium of mucosa, which provides physical and nutritional support.
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Lamina-dura - the name given to the radiographic appearance of a dense layer of bone around the tooth root. It represents the dense cortical bone lining the tooth socket.
Laminin - an adhesive molecule of connective tissue related to fibronectin andtenascin.
Langherhans cells are active in the immune response of the skin and mucous membrane. They act as sentries, detecting the presence of foreign antigens on the surface of the epithElium. They do not contain keratin and are thus sometimes called clear cells.
Lectin - a protein molecule which bindson to a specific sequence of sugars. Bacteria may use lectin attachments to bind onto each other or oral surfaces.
Leucocytes - un pigmented (white) cells of the blood. Those with granular cytoplasm are neutrophils, eosinophils and basophils. The agranulocytes are lymphocytes and monocytes.
Leucotriens- concerned with signalling between cells of the immune system and a member of the eicosanoid family of hormones.
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Ligand - a protein molecule which binds to another specific protein molecule. The forces of the bond are week and thus protein-ligand bonds depend on close fit of one molecule to the other, so as to capture as many bonding sites as possible. Ligands are specific for a particular protein. They are found on cell surfaces of microorganisms where they assist in cell adhesion. They are also sights on cell membranes onto which protein messengers attach such ascytokines (see also lectins).
Limbic system - a ring of structures around the thalamus which play a major role in pain as well as other types of behaviour. The limbic system includes the hypothalamus, hippocampus, amygdala, septum and cingulum. The limbic system plays an important role in pain at the level of motivation to avoid it. It thus operates at a slightly higher level than the reticular formation with strong connections to the thalamus and cortex.
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Lipid - - large molecules containing hydrogen and carbon which are insoluble in water. Simple lipids consist of long chains of fatty acids. Compound lipids contain phosphoric acid, sugars, nitrogenous bases or proteins, and include the phospholipids, glycolipids and lipoproteins. Steroids may also be classified as lipids.
Lubrication - helping two surfaces to slide over each other.
Lycine - one of 20 aminoacids common in proteins. It is a common amino acid of collagen and like proline must be hydroxylated by ascorbic acid in order to allow the formation of bonds which will hold the triple helix together..
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Lymphocytes - white cells involved in the immune response. B lymphocytes are so called because they mature in bone while T lymphocytes mature in the thymus. Both cells look alike until they recognise a foreign antigen. The B cell starts to make antibodies while the T lymphocytes accumulate vesicles loaded with cytotoxic agents. On contact with a foreign cell, the lymphocytes changes shape so that all it vesicles are pointed at the enemy. The release of cytotoxic agents need to be carefully controlled. One of the methods by which the enemy cell is killed is by agents which make holes in its cell membrane. Enemy cells maybe bacteria, or the bodies own cells which have ingested viruses or they may be cancer cells, or the cells of transplanted organs .
Lymphokines - a variety of cytokines released by lymphocytes which coordinate the proliferation of T and B lymphocytes. They also regulate the brain's contribution to the immune response via the hypothalamus - adrenal cortex axis.
Lysosomes - small membrane bound vesicles in the cytoplasm of cells which contain toxic enzymes. When a cell dies, these membranes rupture and the enzymes are released. They break down the cells structure, and the debris is removed. The lysosome also contains cytokines which summon inflammatory cells and stimulate inflammation. The contents of lysosomes can be released by macrophages and neutrophils both to kill bacteria and viruses, and to stimulate inflammation.
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M
Macrophages - cells derived from monocytes which have the ability to phagocytose foreign particles and dead tissue and to move through tissue, or to remain fixed in one place. There are many macrophages in the spleen where they remove dead red blood cells from the circulation.
Major salivary glands - are three large glands on each side of the face; the parotid, submandibular and submaxillary.
Malleus - one of the three bones of the inner ear. The others are the stapes and the incus.
Mastication - the process of preparing food for swallowing and digestion by chewing it.
Matrix - comes from the Latin word "mater"meaning mother. It is a structure which encloses or holds something within it. Cells are held or enclosed in a matrix of fibres, water and large molecules called the ground substance .
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Matrix vesicles. - small bubble-like structures containing calcium-binding phospholipids and alkaline phosphatase. Crystals of hydroxyapatite from inside the vesicle which ruptures and releasing crystals into the surrounding osteoid or predentine so as to start mineralising it.
Mechano-receptors- sensory receptors which respond when mechanically deformed by pressure, tension, vibration or touch.
Mesenchyme - dental mesenchyme is tissue derived from the mesoderm of the embryo and which has been infiltrated and highly influenced by migrating cells from theneural crest.
Mesial drift - a gradual movement of all the posterior teeth in a mesial direction. It occurs only if there has been interproximal wear between the teeth. The drift is not a passive one however, as it has been shown that during chewing, the bite force has a a mesial component.
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Mesial - towards the midline.
Mesoderm - the middle of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The mesoderm will form the muscles, blood system, connective tissue, including bone and dentine, the kidneys and the dermis of the skin. The other two layers are the ectoderm and theendoderm.
Messenger RNA - a ribose nucleic acid acid which caries the DNA code in matching nucleotides, from the nucleus to the ribosome of the cell.
Metabolise - to obtain energy by breaking down a molecule into smaller components, as in respiration or to store energy by building a more complex molecule out of smaller components. It always takes place in a number of stages, controlled by enzymes. Each step in the process follows a predictable "metabolic" pathway for that reaction.
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Microbiology - the study of the microscopic forms of life.
Microfilaments - are the smallest filaments of the cytoskeleton. The filaments are made of hundreds of actin molecules, stacked in a line. They can be quickly broken down or extended. Actin filamanents give the cell its shape and help to change it. When cells move, in embryology and repair, or just during the continual patrol of lymphocytes, they must hold on to something in order to crawl. The filaments serve to anchor one part of the cell, via fibronectin to the cell matrix, so the rest of the cell can pull itself towards the anchor. Lymphocytes move and scavenge by sticking out arms and feet to help them crawl and engulf foreign particles. Muscle cells change their shape by using stacks of actin filaments as a ladder on which myosin climbs.
Micron - 1000th part of a millimetre.
Microorganisms - single celled animals which may range from the very small viruses, through bacteria and fungi to almost visible protozoa.
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Microtubules - are the largest filament in the cytoskeleton. They are the hollow tubes along which cell products are conducted long distances. The system is not unlike a railway network around the cell, sometimes involving long distances. For example, neurones transport out neurotransmitter substances along the axons to distant synapses, inside microtubules.
Minor salivary glands - are microscopic glands under the surface of the oral mucosa. They are found throughout the lining mucosa of the mouth including the tongue.
Mitochondria - a cell organelle found in eucaryotic cells which produces ATP as a product of the kreb cycle and the electron transport system Cells requiring large amounts of energy, such as secreting odontoblasts, have large numbers of mitochondria. Mitochondria are self replicating and contain their own DNA for this purpose.
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Mitosis- the division of a cell into two daughter cells, each of which is identical.
Mitotic activity - the rate of mitosis, and hence cell division. The mitotic activity of basal cells in an epithelium must match the rate of desquamation.
Molecules - a combination of atoms joined together in fixed proportions.
Monocytes - remain in the blood only a short time before they migrate into the tissues particularly where dead tissue must be removed, where they are calledmacrophages.
Morphogenesis - the process in which tissue shapes and organ structures are developed during embryology.
Morphogenic fieled - an environment in which the shape or pattern of a developing organ is determined.
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Motoneurone - nerve cells with their cell bodies in the brain stem or spinal cord, which transmit impulses along their axons to effector organs, including endocrine, exocrine glands and muscles fibres. The axons of most motoneurones have many branches, each of which ends at a neuromuscular junction. The group of muscle cells innervated by one motoneurone is called a motor unit .
Mucoperiosteum - a type of oral mucosa which has a fibrous lamina propria , no submucosa, and is attached to the underlying periosteum of bone. The attached gingiva is a mucoperiosteum.
Mucous - a secretion which is viscous and slimy due to the presence ofglycoproteins .
Mutation - a change in the order of nucleotide bases on a gene, which alters the configuration of the protein produced, and thus may alter the behaviour of the cell. A mutation may cause a cell to die, or become cancerous. Mutations in bacteria and viruses help them to evade detection by their hosts.
Myelin - the fatty covering of myelinated nerves which appears white to the naked eye. The parts of the brain and spinal cord, in which myelinated nerves run, has therefore been called the "white" matter as distinct from the "grey" matter composed of nerve cells. Myelin also contains about 20 % of proteins whose prime role is to mediate adhesion between adjacent Schwann cells. These cell membrane glycoproteins are also members of the immunoglobulin family of cell surface proteins. Defects in the these surface proteins may cause them to act as antigens to the immune system. The disease multiple sclerosis is caused by antibodies to the myelin proteins, which results in inflammation and loss of myelin.
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Myelinated - nerves axons which are completely wrapped in a sheath of myelin by schwann cells. One cell wraps about a millimetre of nerve axon. Myelinated nerve axons carry impulses faster then unmeyelinated nerves as the impulse jumps across the myelin sheath of each adjacent Schwann cell to that of the next
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N
Nerve growth factor- a cytokine that promotes the growth and repair of sensory nerves and maintenance of sympathetic nerves.
Neural crest cells - cells derived from the ectoderm layer in the embryo. This layer folds to form a neural tube which will later become the spinal cord of the animal. Cells from the crest of this fold, leave the ectoderm and migrate into the mesoderm layer. These neural crest cells are thus of ectomesenchymal origin. They migrate to form the dental mesenchyme, supportive cells of the nervous system, the adrenal cortex and melanocytes of the skin.
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Neuromuscular junction the synapse between the axon terminal of a motoneurone and a skeletal muscle fibre. The release at this synapse of the neurotransmitter substance, acetyl choline causes the muscle to contract.
Neuropeptides - compounds which have extremely potent affect to excite or depress nerve cells, in very low concentration . In this regard they are distinctly different from neurotransmitters. They include substances such as prostaglandins, substance P , endorphins and enkephalins. Neuropeptides also have receptors on lymphocytes and thus influence the immune response.
Neurotransmitters - chemicals which are secreted into a synapse in order to transmit an electrical nerve impulse from a nerve axon of one cell to the cell body of another nerve cell. They bind to receptors on nerve cells and are produced rapidly in high concentrations at nerve synapses. In these respects they differ from neuropeptides. There are many different neurotransmitter substances. They include acetyl choline, epinephrine, histamine, serotonin GABA and glutamate.
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Neutrophils - members of the family of white blood cells which are involved in non-specific phagocytosis of bacteria and foreign material. Neutrophils are also called polymorphonuclear leucocytes (PMN) because of their multi-lobed nucleus. Neutrophils also release toxic enzymes, stored safely in their cytoplasm as lysosomes and released in the presence of foreign proteins. These toxic enzymes may do more harm to the host tissues than the bacteria they were released to kill.
Niche - an opportunity which can be exploited in order to make a living or survive in an ecosystem.
Noma - a highly destructive and usually fatal infection of the teeth and jaws which is a progression of ANUG Only found in malnourished children. - also called cancrum oris.
Nucleic acids - occur as chains of nucleotides, either asDNA (two chains) or RNA(one chain) and make up the genetic material of a cell.
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Nucleotides - are made up of three components, a pentose sugar (ribose or deoxyribose), a phosphate group and an organic base which may either be a purine ( adenine or guanine) or a pyrimidine ( cytosine thymine or uracil).This basic structure is found in many important cell molecules such as in ADP, ATP and coenzymes. Nucleotides also form the subunits from which nucleic acids (DNA and RNA)are built.
Nucleus a cell organelle which contains the chromosomes whose genes control the structure of proteins within the cell. The nucleus is also a term used to refer to the mass of nerve cell bodies connected by tracts of nerve fibres, which occur in the brain.
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O
Occlusal wear - loss of enamel on the biting surface of the teeth due to the abrasive action of chewing natural unprocessed food.
Odontoblast process - the extension of the cytoplasm of an odontoblast which remains surrounded by dentine during tooth formation. The process is still an active part of the cell and contributes to the production of intratubular dentine in response to ageing, tooth wear or arrested caries.
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Odontoblasts- cells lining the dental pulp, derived from the dental papilla wich form the dentine of the tooth crown and root. New odontoblasts may become differentiated from less specialised pericytes in the pulp.
Occlusal interference - contact between opposing teeth during chewing, which prevents the other teeth touching. In extreme lateral and protrusive positions of the jaw, this would happen in most dentitions and be of no concern. When occlusal interference occurs close to the area of maximum tooth contact, it may be troublesome.
Oncogenes - genes which have the capacity if expressed to cause tumour formation.
Organelle - a structures within a cell which has a specific structure or function, such as thenucleus, endoplasmic reticulum, golgi apparatus, lysosomes and mitochondria.. Cell organelles are a feature of eucaryotic cells.
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Osmotic pressure - Water tends to move towards dense concentrations of ions. Sugar solutions on the surface of exposed dentine cause water to be drawn out of the dentinal tubules causing which distorts the odontoblast causing pain.
Osseous integration - a term used to describe the desired adhesion between an implant and the bone which holds it in place.
Osteoblasts - cells which differentiate from pericytes and secrete both the matrix and mineral of bone.
Osteocalcin - a calcium binding protein, synthesised by the osteoblast and secreted into the matrix at the time of bone mineralisation. Mice bread without the osteocalcin gene develop heavy bones suggesting that osteocalcin is a negative regulator of bone formation
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Osteoclast - a multi-nucleate cellcapable of removing both the organic and mineral component of bone. Osteoclasts activity is controlled by nearby osteoblasts.
Osteoid - the extracellular matrix inwhich bone forms. It is high in collagen and other bone proteins but lacks any crystal formation.
Osteonectin - a bone glycoprotein which has the property of binding to both collagen fibres and the hydroxyapatite crystals, and thus may be important in initiating bone mineralisation by acting as a template for nucleation. Osteonectin is also produced by endothelial cells and plateletes and is able to bindfibrinogen.
Osteopontin - an adhesive glycoprotein related to sialoproteins, which is secreted by osteoclasts to assist in their adhesion to the bone surface. After bone resorption it may then act as a signal to stimulate osteoblast activity
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Osteoporosis - a reduction in bone mass which occurs commonly in post menopausal females, but also in older men. It is due to a reduction in the activity of the ovaries and a decreased secretion of oestrogen. Bone formation and bone healing are not affected but more bone is resorbed by osteoclasts than is replaced. Lack of exercise is also a factor in bone loss.
Oxytalin fibres - are related to elastic fibres, though they have a smaller core of elastin. They are found in the periodontal ligament and in the epidermis of thin skin, but not in the oral mucosa.
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P
Paracrine - cell messengers also called cytokines which are locally acting, produced by neighbouring cells or the extracellular matrix, as distinct from as distinct from endochrine or hormonal messengers.

Parakeratinised - an epithelium in which the superficial cells have not lost their nuclei , but have become filled with keratin. see also keratinised
Parasympathetic - part of the autonomic nervous system concerned with maintaining routine functions. Always acts as a balance to activity of the sympathetic nervous system.
Pathogenic - able to cause disease.
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Pellicle - a thin layer of salivary proteins which forms on the surface of enamel.
Peptide bonds - a covalent bond made between the carbon atom of the carboxyl group of one amino acid and the nitrogen atom from the amine group of another. In the process a molecule of water is removed. Peptide bonds allow chains of amino acids to form polypeptides and proteins When peptide bonds are broken apart they need water to reform the amino acids. This process is known as hydrolysis, and occurs during cooking and in digestion. .
Periaquaductal grey - is an integrative centre for inputs form the autonomic nervous system, the limbic system and from sensory and motor pathways. It has an inhibitory affect on pain transmission due to descending connections through the raphe nucleus along the corticospinal tract to the cells of the dorsal horn.
Pericytes- small cells lying next to the endothelial cells of capillaries which have the capacity to differentiate into osteoblasts.
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Periodontal pocket - loss of epithelial attachment to the tooth, producing an increase in gingival sulcus depth beyond the normal 1-2 mm.
Periosteum - a connective tissue layer containing osteoblasts on the external aspect of all bones. see alsoendosteum.
Peritubular dentine - see intratubular dentine
pH - a measure of how acid or alkali a solution is. As the pH gets lower, the solution is more acid. At a pH of 7 the solution is neither acid nor alkali. pH is the inverse of the logarithm of the concentration of hydrogen ions.
Phagocytosis - the ingestion of small particles, bacteria or viruses into the cell, by engulfing it in a vacuole .
Phosphate - a salt in which the negatively charged part is a phosphorus molecule joined to four oxygen molecules as PO4.
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Phospho-proteins - proteins which contain available phosphate groups.
Phospholipids - are the most common lipids in our cell membranes. The head group contains a phosphate and is readily soluble in water. Phospholipids are also found inmatrix vesicles, and they provide the first step in the synthesis of prostaglandins
Planktonic - a form of life style in which an organisms floats freely in a fluid without significant attachment or association with other living forms.
Plaque is a film of bacteria in a matrix of salivary and bacterial polymers. It can be called a biofilm as it has a complex population of organisms which when mature, reach an ecological balance with one another.
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Plasma - the fluid part of blood, containing proteins and salts, from which the blood cells have been removed. see alsoserum.
Plasmid- a circular piece of DNA found in the cell cytoplasm of bacteria which is able to reproduce itself independently of it host. Plasmids may transmit a resistance to antibiotics from one bacteria to another. They are of great importance in techniques using for recombinant DNA.
Platelet- derived growth factor - a cytokine found especially in platelets. It stimulates cell proliferation and encourages wound healing.
Platelets - are small colourless discs of cytoplasm found in blood. When platelets come into contact with a damaged vessels surface they change in several important ways. They begin to swell, their shape becomes irregular with protruding processes, they become sticky and they release an enzyme which causes the formation of thromboxane, one of the precursors of thrombin . Thromboxane also activates nearby platelets, thus starting a positive feedback which rapidly increases the mass of sticky platelets which form a platelet plug. This process accounts for daily damage to capillary walls. Damage on a larger scale requires other mechanism for haemostasis. Platelets also release serotonin which acts as a powerful vasoconstrictor
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Polymers-large molecules made up of many joined units of a more simple molecule. Examples are polysaccharides and polypeptides .
Polypeptides; -chains of amino acids joined by peptide bonds . They are not the size of proteins, but may be biologically very active. Some hormones are peptides, such as insulin which has 51 amino-acid residues. Peptides may also be powerful neurotransmitter substances.
Polyphyodont - continuous replacement of teeth with many generations (from "poly" =many; "phylo" = generation and "dont" =teeth). See also diphyodont
Polysaccharides - long molecules made of chains of sugars linked together. Examples are starch, glycogen and dextrans.
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Predentine - the extracellular matrix produced by odontoblasts, which becomes mineralised to form dentine. Similar in structure to osteoid .
Procaryote - a cell in which the genetic material is dispersed throughout the cell in distinction to a eucaryote which has a nucleus and other organelles. Bacteria and blue-green algae are procaryotes
Prognathic- a prominent lower jaw which may bring the lower teeth ahead of the upper teeth
Proline- one of 20 amino acids common in proteins. It is a common amino acid of collagen and like lycine must be hydroxylated by ascorbic acid in order to allow the formation of hydrogen bonds which will hold the triple helix together.
Proline-rich proteins - a group of proteins in saliva which have the ability to bind to calcium. They provide the protective layer of pellicle on the tooth surfaces by binding to the calcium in enamel. They also bind onto microorganism, providing a link between organism and the tooth surface. Proline rich proteins help to de-toxify tanins, which are potentially poisonous plant substances found in tea, and unripe fruit.
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Prostaglandins - are members of a class of hormones known as the eicosanoids. They are released by cells which have been damaged and have a powerful ability to sensitise nerve endings causing tenderness to the damaged area, and to cause vasoconstriction by contracting the smooth muscle of arterioles. They belong to a group of compounds which have a similar effect on nervous tissue, known asneuropeptides.
Proteins - usually very large molecules, from 10,000 to 200,000 amino acids, which form the structural component of a cell'smatrix. and cytoskeleton. All enzymes are proteins.
Proton - the positively charged elements of the nucleus of an atom. A hydrogen atom without its electron amounts to a single proton charge.
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Pulp - the dental pulp is a connective tissue trapped inside the fully formed tooth with just one entry and exit for nerves and vessels, at the apex of the root. The characteristic cell of the pulp, is the odontoblast, which lines the walls of the pulp chamber and is able to form dentine throughout life.
Pulpitis - inflammation of the dental pulp caused by irritation from chemical, physical or bacterial injury, usually transmitted to the pulp via the dentine. It is important for the clinical management of the tooth, to decide whether the pulpitis is reversible, that is will it resolve if the irritation is removed, or whether it has been damaged beyond its capacity to repair.
Pyrophosphate - inhibitors of mineralisation, they may offer up phospate ions in the presence of alkaline phosphatase. Crystals of calcium pyrophosphates are found in abnormal calcification of soft tissue, such as the disc of the TM Joint.
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Q
Quadrate - one of the bones which together with the articular bones and the dentary, made/make up a reptile's jaw. In mammals the quadrate bone is incorporated into the middle ear as the incus.
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Ramus - the vertical part of the mandible which supports the coronoid and the condylar processes.
Recombinant DNA - is DNA from a plasmid into which has been inserted a foreign gene. The plasmid is then introduced into a host cell, often the bacterium E.coli. The host cell may then express the foreign gene and secrete the desired protein. This process, commonly known as genetic engineering, has been used to great effect in synthesising proteins such as insulin and interferon.
Reduced enamel epithelium - (REE) the epithelium produced by the combination of the external and internal enamel epithelium. The REE remains covering the enamel crown until the tooth erupts when it fuses with the oral epithelium. The REE remaining on the enamel surface becomes the junctional epithelium.
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Refined carbohydrates - natural carbohydrates from which other bulk such as fibres have been removed. Granulated sugar is a refined form of sugar cane.
Remineralisation - the replacement of mineral salts lost by de-mineralisation of a solid salt.
Remodelling - of bone refers to the constant removal by osteoclasts and rebuilding by osteoblasts The mass of bone can be controlled constantly by altering the balance between removal and rebuilding. The shape of a bone can also be altered by removing in one place and building somewhere else, without necessarily changing the total mass of a bone mass.
Repositioning - of a tooth refers to its movement within the entire dentition which involves the remodelling of the tooth socket. Repositioning of teeth occurs naturally due to continued eruption and mesial (or distal) drift.
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Rest Position - a position the jaw adopts when at rest with the lips lightly together.
Reticular fibres - are fine type III collagen fibres forming a net-like supporting framework or reticulum. They are found around small blood vessels, nerve cells, muscle fibres and in particular beneath epithelial membranes as part of thebasal lamina.
Reticular formation - in the central core of the medulla, it consists of several structures, including the periaquaductal grey. The reticular formation integrates information from many sources and influences sensory motor and autonomic activity. It is involved in aversive drive (behaviour which is an instinctive turning away from the unpleasant).
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Retinoic acid - a product of retinol(Vitamin A) which binds onto cell membranes and controls cell division and differentiation through gene expression.
Ribosomes - - structures in the cytoplasm of cells which attach onto messenger RNA . At the ribosome, the code of nucleotides on the mRNA is translated into a series of aminoacids.
RNA - Ribosenucleic acid - seenucleic acids .
Root resorption - resorption of cementum and underlying root dentine by osteoclasts. Temporary zones of root resorption may occur during orthodontic tooth repositioning. More extensive and irreversible root resorption may occur if the root becomes ankylosed .
Rugae - raised ridges of epithelium, each with its core of lamina propria, found on the anterior wall of the hard palate.
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S
Saturated solutions - Salts such as the apatites do not readily become ionized and dissolve in water. When no more ions can dissolve the solution is said to be saturated. The concentration of ions in a saturated solution, its solubility product, is constant for each salt, at a neutral pH . If the solution becomes more acidic, more ions can dissolve from the solid. Saliva is a super saturated solution of calcium phosphate.
Schwann cells - members of a family of nerve-supporting (neuroglial) cells. The Schwann cell has an extensive cytoplasm which allows it to wrap a myelin sheath around nerve axons.
Sclerotic - hardened, as in sclerotic dentine, which is hardened by intratubular dentine in response to tooth wear, ageing and arrested caries.
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Secondary caries - caries which has occurred after a primary lesion has been restored. It is most commonly due to failure of the restoration at its margins, which have broken down and allowed a leak to develop between the restoration and the wall of the cavity. Caries bacteria which have been left behind during cavity preparation are unable to produce secondary caries if the margins of the restoration have achieved a proper seal against the tooth.
Septa - the thin plate of bone between the roots of teeth ( Latin septum = a wall). Also the fibrous walls which separate sections of a gland. Septa separate sections of an orange or grapefruit.
Serotonin - ( 5 Hydroxytryptamine) is present throughout the body, especially in blood platelets and in the intestines. Its release from blood platelets contributes to the pain, vasoconstriction and inflammation after injury. In nervous tissue it functions as a neurotransmitter, mainly in the midbrain in clusters of cells called the raphe, and in the medulla. The fibres of these cells connect with the forebrain, cerebellum and spinal cord. It therefore exerts a strong influence over arousal, sensory perception, emotion and thought. Drugs which slow down the removal of serotonin can reduce depression and pain.
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Serous - a watery secretion which resembles serum.
Serum - the fluid component of blood from which the clotting protein fibrinogen has been removed.
Sesamoid bone - a small bone which appears at the age of thirteen, adjacent to the carpo-metacarpal joint of the thumb and is of use in determining the skeletal age of a child.
Sharpey's fibres. - are collagen fibres which have been trapped in bone or cementum in order to anchor them. see also extrinsic fibres.
Sialoproteins - a family of adhesion molecules which include osteopontin. Bone sialoprotein is formed by cells lining the root surface and influences cementoblast differentiation which encourages mineralisation. Dentine sialoprotein appears to inhibit mineralisation. Osteoclasts adhere both to bone sialoprotein and osteopontin.
Sinus - a curved out hollow space in side the skull which is lined by respiratory epithelium and drains into the back of the throat. For example, maxillary s., ethmoid, s., sphenoids.
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Solubility-product - a value found by multiplying the concentration of positive IONS by the concentration of negative ions in a solution of a salt, hence [Ca]+ x [P04]- = Ksp(solubility product). The value for Ksp is constant when the solution of ions is saturated and in balance with its solid crystalline form. Acid helps increase the solubility of a weakly soluble salt.
Sphenomandibular ligament - a ligament which joins the lingula of the mandible to the spine of the sphenoid bone.
Spongy-bone - the bone beneath the cortical bone which has been thinned out by bone remodelling to form a spongy inner core. Also called cancellous (lace-like) bone.
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Stem cells - cells from which a number of more Stimulated saliva - saliva which has been stimulated by chewing.
Stippled - a pattern which is made of small dots. Gingiva has a stippled appearance due to small depressions caused by the attachment of clumps of fibres in the lamina propria to the basement membrane of the epithelium..
Striated ducts - ducts which carry saliva from the intercalated ducts to a series of main collecting ducts. Striated duct cells are actively involved in secretion and absorption. Their striated appearance is due to the many long folds of the cell membrane.
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Submucosa - a layer beneath the lamina propria of mucosa, which is loose and elastic. It may contain large blood vessels, nerves, glands and lymphatic tissue.
Substance P - a neuropeptide with a particularly powerful ability to excite a post synaptic cell. When substance P is released into a synapse of a sensory neurone it causes severe pain.
Sulcus - see Gingival sulcus.
Super-saturated solutions - When a solution is saturated and still more ions are added, they cannot be held in solution but precipitate as a solid deposit. The proline-rich proteins of saliva are capable of binding calcium. They hold a store of calcium ions which allows saliva to carry more ions in solution than is theoretically possible. Saliva is thus a super-saturated solution of calcium phosphate.
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Symbiosis - a mutually beneficial inter-relationship between two organisms, for example between bees and flowers (pollen carrying in return for nectar).
Sympathetic nerves - the sympathetic nervous system is one of he two main divisions of the autonomic nervous system. Sympathetic nerves make synapses at ganglia close to the spinal cord and have long post -ganglionic axons which, in general place the body on a state of alert. Always acts as a balance to activity of the parasympathetic nervous system.
Synapse - the point at which one nerve cell connects with another. The nerve impulse is transmitted by the release of chemical neurotransmitter substances from the pre-synaptic cell membrane. The neurotransmitter substance diffuses across the synaptic cleft to the post-synaptic membrane which it depolarises. When the post-synaptic cell is sufficiently excited by a number of incoming impulses and enough neurotransmitter substance, it discharges an electrical impulse along its axon membrane to the next neurone.
Synovial fluid - the lubricating fluid containing glycosaminoglycans which is held in the capsule of a synovial joint.
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T
Template - an outline form which can be used to make many identical copies without being used itself. Metal templates can be used placed over a piece of clothing material, which is then cut according to the shape of the template. Many pieces can be made from the same template, and they will all be the right shape for that part of the garment. Molecular templates can guide the formation of crystals by providing a shape which is characteristic of, for example anapatite crystal. The role of templates in crystal formation is calledepitaxy .
Temporomandibular joint - the joint between the condyle of the mandible and the glenoid fossa of the temporal bone. The joint is divided into an upper and lower compartment by a fibrous disc and surrounded by a capsule.
Tenascin - an adhesive molecule of connective tissue related to fibronectin andlaminin .
Thalamus - the major co-ordinating centre or sensory information in the brain.
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Threshold - the minimum level of a signal(sound. pressure, pain) which is detectable.
Thrombin - the final chain in the series of blood clotting forms fibrin from fibrinogen. Thrombin is formed from prothrombin by a prothrombin activator, itself the end of a series of reactions. This cascade of events may begin two ways. One, is the release of tissue factors from damaged vessels. The other, is the activation of factors in blood platelets which are altered by coming into contact with collagen or an artificial surface.
Thromboxanes - concerned with platelet clotting and a member of the eicosanoid family of hormones.
Topical - in a local area. e.g application of medication to the affected part only.
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Trabecula-bone -a description of the radiographic appearance of spongy bone. Radiographs provide an unusual opportunity to see condensations within spongy bone. These condensations form lines, or beams with are orientated so as to give the best support to loads tending to crush or fracture the bone.( the Latin word for a wooden beam was trabes, a small beam was a trabecula)
Transcription- a process which leads to the copying of a gene's code, from a section of DNA, onto a strand of messenger RNA and which eventually leads to the synthesis of the peptide or protein which that gene codes for.
Transforming growth factor- TGF a superfamily of cytokines secreted by a variety of cells (monocytes, T cells, platelets, fibroblasts). The family include bone morphogenic proteins, which stimulate angiogenesis, fibroblast proliferation and inhibit T cell proliferation.
Tropocollagen - the precursor to the collagen molecule secreted by the cell. The removal of terminal peptides on the tropocollagen allows each molecule to join end to end with another to make a collagen fibril.
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Tubule - a small tube leading into a duct,or as in dentinal tubules.
Turnover - the replacement of cells by mitosis which keeps pace with cell loss, as in epithelia and blood cells. Also refers to the continual replacement of connective tissues like bone and fibrous tissue.
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Vaccine - a planned exposure to an antigen in order that memory B lymphocytes can retain a memory for it. In practice the organism carrying the antigen is either killed or modified so that it does not cause the disease. When encountered again, the antigen is recognised and there will be a rapid production of antibodies. For example smallpox, polio, measles. Influenza vaccines are less effective as new strains of the virus are always occurring which do not have recognisable antigens.
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Vacuole- a sac-like structure within a cell lined by cell membrane, containing material ingested by phagocytosis.
Vasoconstriction - a reduction in the diameter of small arteries (arterioles) which is caused by constriction of the smooth muscle fibres in the wall of the arteriole. Vasoconstriction is an important method of increasing the blood pressure. In local areas of damage it prevents blood loss by haemostasis. Local vasoconstriction can be caused by nerve impulses to the smooth muscle from the sympathetic nervous system, by locally released prostaglandins, serotonin and Epinephrine.
Vasodilation - an increase reduction in the diameter of small arteries (arterioles) which is caused by relaxation of the smooth muscle fibres in the wall of the arteriole. While vasoconstriction prevents blood loss in damaged tissues, vasodilation follows in order to allow the blood flow to slow down and clotting factors and leucotrines to seep into the damaged tissue. Local vasodilation can be caused by nerve impulses to the smooth muscle from the parasympathetic nervous system, and by locally released bradykinins.
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Visco-elastic - a property of a material which combines elasticity and viscosity. The suspension of a car and the periodontal ligament of the tooth are examples of visco-elastic support. Elasticity refers to the return of a material to its original shape after being stretched or compressed. Viscosity is the resistance of a fluid to flowing fast.
Viscous - a liquid which has a high viscosity, or resistance to flow.
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