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Eclipse - Oral Physiology Biology Dictionary
Category: Health and Medicine > Oral Physiology
Date & country: 18/09/2007, UK
Words: 391


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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.