vaccination n. A means of producing immunity (*immunization) to a disease by the administration of a preparation of antigenic material (vaccine) to stimulate the formation of appropriate antibodies. Vaccination is usually given by injection and over two or three stages to reduce the potentially unpleasant side-effects.

vacuum formed appliance n. See ORTHODONTIC APPLIANCE.

vacuum mixing n. See MIXING, VACUUM.

validity n. 1. The degree to which data or the results of a study are correct. 2. The extent to which a clinical sign or test is a true indicator of the disease being tested.

vallate adj. Having a surrounding wall or rim. See also PAPILLA.

valve antiretraction A valve or device integrated into a variety of dental instruments connected to *dental unit waterlines (DUWLs). They are used in the patient’s mouth (e.g. ultrasonic scalers, turbine and conventional handpieces) to prevent back siphonage of oral fluids into DUWLs. The requirement for antiretraction devices has been emphasized by studies that demonstrated that oral fluids can be retracted into DUWLs during instrument use. The detection of oral bacterial species and other human-derived microbial pathogens and potential pathogens in dental unit water has provided convincing evidence for probable failure of antiretraction devices. Currently, best practice recommends that dental handpieces should be operated to discharge water and air for a minimum of 20–30 seconds after each patient to flush out patient material and oral fluids that may have been retracted into the handpiece air, or waterlines.

Further Reading Coleman D. C., O’Donnell M. J., Shore A. C., Swan J., Russell, R. J. The role of manufacturers in reducing biofilms in dental unit waterlines. Journal of Dentistry 2007;35:701–11.

Van Buchem’s syndrome (generalized cortical hyperostosis) An inherited skeletal *dysplasia resulting in an excessive deposition of endosteal bone throughout the skeleton. It is characterized by enlargement of the lower jaw and thickening of the long bones and the top of the skull. The face may appear swollen with some facial paralysis and deafness. There may also be widening of the bridge of the nose and angles of the mandible. The symptoms are not painful and there is no bone tenderness. It was first described by Van Buchem, a Dutch physician, in 1955. See also HYPEROSTOSIS.

vancomycin n. A glycopeptide *antibiotic used in the *prophylaxis and treatment of serious life-threatening infections caused by Gram-positive bacteria. It has been given as a prophylactic measure to patients about to receive invasive dental treatment and who are considered to be at special risk or who have a history of infective *endocarditis; however, the *National Institute for Health and Clinical Excellence (NICE) clinical guideline 64 recommends that *antibiotic prophylaxis should no longer be offered routinely for defined interventional procedures. Vancomycin is delivered by slow intravenous infusion. Trade name: Vancocin.

Vancouver citation system A referencing system which uses a number series to indicate references. Bibliographies list these in numerical order as they appear in the text. Vancouver style is so named as it is based on the work of a group, first meeting in Vancouver in 1978, which became the International Committee of Medical Journal Editors (ICMJE). See also HARVARD CITATION SYSTEM.

Van der Woude syndrome n. See LIP PITS.

vapour (US vapor) n. The gaseous form of a solid or liquid, subsequent to its change in state due to alteration in the heat or pressure of the environment or to an alteration of both.

variable 1. adj. Able to vary in quantity or magnitude. 2. n. The properties of an object which can take on different values. A continuous variable can be found at any point on a continuous scale (e.g. height). A dependent variable (response variable) is a factor whose values in different treatment conditions are compared: that is, the researcher is interested in determining if the value of the dependent variable varies when the values of another variable (the independent variable) are varied, and by how much; the independent variable is said to cause an apparent change in, or simply affect, the dependent variable. A dichotomous variable has two categories (e.g. gender: male and female). A discrete variable can be found only at fixed points and is expressed in whole units or mutually exclusive categories (e.g. numbers of teeth). Interval data is measured on a scale of which the intervals are equal. Nominal variables classify *data into categories (e.g. male, female). Ordinal variables rank data according to degree; they indicate only that one data point is ranked higher or lower than another. A predictor variable tries to predict values of another variable (the outcome variable). A quantitative variable takes a numerical value e.g. DMF score; a qualitative variable takes a non-numerical value or defines a characteristic e.g. sex (M or F).

variance n. (in statistics) A measure of variability. See also ANALYSIS OF VARIANCE.

varicella n. See CHICKENPOX.

varicosities n. Enlarged and superficial veins or other blood vessels. They increase with age and are common underneath the tongue.

varnish, cavity See CAVITY VARNISH.

varnish, fluoride See FLUORIDE VARNISH.

vascular adj. Relating to or supplied with blood vessels.

vasoconstrictor n. An agent that causes constriction of blood vessels which reduces local blood flow to an area, and temporarily raises blood pressure. Vasoconstrictors such as *adrenaline (epinephrine) and *felypressin may be added to dental local analgesic agents to prolong their effectiveness. They also reduce local haemorrhage, which can be helpful during surgical procedures. Intravenous deposition should be avoided as *hypertension may occur. Vasoconstrictors have a rapid effect on mucous membranes and may be used to relieve nasal congestion. Compare VASODILATOR.

vasodentine n. A modified form of *dentine, with branching blood vessels but lacking dentinal tubules, such as is found in marine fishes of the cod family.

vasodilator n. An agent that causes widening of the blood vessels and therefore an increase in blood flow. Vasodilators are used to lower the blood pressure in cases of *hypertension. *Glyceryl trinitrate (GTN) increases the blood flow to the heart and is used to relieve or prevent *angina. Compare VASOCONSTRICTOR.

vasomotor adj. Controlling the muscular walls of blood vessels creating either expansion or contraction and therefore modifying their diameter. A vasomotor nerve is any nerve, usually belonging to the *autonomic nervous system, that controls the passage of blood through blood vessels by its action on the muscular walls or its action on the heartbeat.

vasopressin (anti-diuretic hormone, ADH) n. A hormone secreted by the *pituitary gland that causes constriction of the blood vessels and increases the reabsorption of water by the kidneys.

vasovagal attack Excessive activity of the vagus nerve resulting in a slowing of the heart and a drop in blood pressure which leads to fainting (*syncope).

vault, palatal n. 1. The arched form of the maxillary palate. 2. The form of a denture adapted to the maxillary palate.

Veau’s cleft classification See CLEFT CLASSIFICATION.

Veau’s operation [V. Veau, (1871–1949), French surgeon] A surgical technique for the repair of a cleft palate which includes dissection and suturing of the nasal mucosa.

vegetation n. A mesh of *fibrin and *platelets that can form on the surface of heart valves in patients suffering from infective *endocarditis; it can trap micro-organisms present in the bloodstream.

vehicle n. Any substance, usually a liquid, that acts as the medium in which a drug is administered.

Veillonella n. A genus of non-motile, *Gram-negative bacterial diplococci that are part of the normal flora of the mouth and the intestinal and respiratory tracts. Veillonella species have been isolated from plaque and have the ability to use lactic acid produced by other bacterial species to generate energy for growth. Veillonella alcalescens has been isolated from the flora of periodontal pockets and may be associated with the periodontal disease process.

vein n. (adj. venous) A blood vessel conveying blood towards the heart. Only the pulmonary veins carry oxygenated blood. Small veins (venules

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