Dictionary of Dentistry
A
a- (an-) Prefix denoting absence of, lacking, without; e.g. atoxic (not poisonous), abacterial (without bacteria).
abapical adj. Opposite to or directly away from the *apex.
abarticulation n. The displacement or *dislocation of a bone from its normal position (e.g. the *temporomandibular joint).
Abbé–Estlander operation (also known as a cross-flap) [R. Abbé (1851–1928), American surgeon; J. A. Estlander (1831–81), Finnish surgeon] A full thickness flap of tissue taken from the middle portion of usually the lower lip and transferred to the upper lip below the nose in order to correct inadequate lip length and fullness caused by surgical excision or growth deficiency. The flap is attached by means of a pedicle to maintain the blood supply. See also GRAFT.
ABCDE approach The method of assessment of critically ill patients and those suffering from cardiorespiratory arrest. A = Airway, B = Breathing, C = Circulation, D = Disability, E = Exposure. It provides an aide-memoire for providing assessment in an appropriate chronological sequence.
The Resuscitation Council (UK): Medical emergencies and resuscitation.
abdomen n. (adj. abdominal) That part of the body cavity below the chest and separated from it by the diaphragm. It contains a number of organs including the stomach, liver, kidneys, spleen, pancreas, and intestines.
abdominal thrust See HEIMLICH MANOEUVRE.
abduction n. Movement away from the midline; e.g. the lateral rectus muscle is an abductor of the eye.
aberrant adj. Deviating from the normal. Usually applied to a blood vessel or nerve that fails to follow its normal course.
abfraction n. The loss of tooth structure in the *cervical region of the *crown of a tooth. Some research studies suggest that this is owing to flexural forces applying an excessive biomechanical loading to one or more *cusps of the tooth, resulting in stress concentration. 
Further Reading: Bartlett D. W., Shah P. A critical review of non-carious cervical (wear) lesions and the role of abfraction, erosion, and abrasion. J Dent Res 2006;85:306–12.
Rees J. S. The biomechanics of abfraction. J of Engineering in Medicine 2006;220:69–80.
ablation n. The removal or excision of a piece of tissue, usually by surgery. Surface ablation of the skin may be carried out by chemicals or *laser.
abrasion n. 1. The non-bacterial loss of tooth tissue due to frictional wear by extrinsic agents. Common causes are *toothbrushing, particularly with abrasive pastes, pipe smoking, and pencil chewing. The lesions produced by toothbrush abrasion are typically wedge-shaped and are most commonly associated with the labial and buccal surfaces of the premolars, canines, and incisors of the permanent dentition. Similar causes can result in gingival abrasion with loss or damage to the gingival tissues. 2. A minor wound in which the surface of the skin or mucous membrane is worn away by frictional trauma. See also TOOTH WEAR. 
Further Reading: Bartlett D. W., Shah P. A critical review of non-carious cervical (wear) lesions and the role of abfraction, erosion, and abrasion. J Dent Res 2006;85:306–12.
abrasive n. A material used to smooth or roughen a softer material by mechanical wear. It may be delivered in a high pressure stream of air (*air abrasion) or by adhesion to strips, discs, wheels, or points. An abrasive strip (finishing strip) consists of a piece of linen, acetate, or thin metal of varying width coated on one or both sides with abrasive grit of differing textures. It is used for smoothing and contouring the proximal surfaces of restorations.
abscess n. A localized accumulation of *pus in a cavity caused by tissue breakdown as a result of infection or foreign materials. It is a tissue defence reaction to prevent the spread of infection to other parts of the body. An abscess may be described as acute when there has been a rapid onset frequently associated with pain, or chronic when it has developed over a longer period of time and is usually painless. A gingival abscess (gumboil) is associated with the free gingival margin (see GINGIVA) of a tooth. These are frequently caused by foreign bodies, or food impaction: they may be associated with a non-vital primary tooth and be asymptomatic. A periapical abscess is associated with the root apex of a tooth and the surrounding bone and is a sequel of pulpal infection. A lateral periodontal abscess involves the *periodontal attachment tissues and usually arises from an established *periodontal pocket. It may occur because of an increase in virulent organisms, a compromised immune response, or reduced drainage from the periodontal pocket. The last may occur following root debridement with superficial tissue healing and residual infection in the periodontal pocket. A pericoronal abscess is related to the flap of gum (*operculum) overlying a partially erupted tooth, most commonly the third molar. Treatment is by establishing drainage and addressing the cause.
The ABCDE approach: the method of assessing critically ill patients
absolute risk reduction (ARR) See RISK DIFFERENCE.
absorbable gelatin(e) sponge n. A material applied topically to aid *haemostasis, usually following a dental extraction. It provides a structure for clot formation.
absorbent adj. Describing a material capable of taking up other substances by suction e.g. an absorbent paper point.
absorption n. The passage of one substance to another by penetration or solution. For example, the passage of liquids into the mucosa, skin, or dental materials.
absorption layer n. An amorphous zone on the dentine surface into which adhesive agents can flow. See also HYBRID LAYER.
abuse v. and n. Inappropriate use or treatment of materials, techniques, persons, programmes, or language. See also CHILD ABUSE.
abut v. To touch or border upon. To have a common boundary.
abutment n. A tooth, tooth root, or implant used to support a fixed or removable *prosthesis (bridge or partial denture). It may provide either the terminal support for a prosthesis or additional intermediate support (pier abutment). In implant dentistry, healing abutments are designed to allow peri-implant soft tissues to heal; they may be screwed into the implant at the time of implant insertion or several months later; they are usually made of titanium. Restorative implant abutments are designed to attach the restoration to the implant and can compensate for soft tissue contour or implant position, angle, or depth.
acanthion n. The tip of the anterior *nasal spine of the maxillary bone.
acantholysis n. The breakdown of epidermal or epithelial cells due to a loss of intercellular substance. It is often seen in conditions such as *pemphigus vulgaris, where it is caused by autoantibodies, but may also occur in other conditions.
acanthosis n. (adj. acanthotic) An increase in the number of cells within the prickle cell layer (the middle part) of the *epithelium.
accelerator n. A substance that speeds up a chemical reaction, such as the addition of *plaster of Paris to *mineral trioxide aggregate. Heat may also act as an accelerator in speeding up the setting reaction of an impression or restorative material. See also CATALYST.
access n. An approach or pathway, either natural or prepared, to view, instrument, or treat an area of interest. An access cavity is prepared in a tooth to identify root canal entrances in the pulp chamber or to enable the instrumentation and removal of carious tissue.
accessory adj. Additional, supplementary, subsidiary to the main thing. An accessory root canal is a branch of the principal root canal frequently occurring in the apical third of the root.
Access to Health Records Act 1990 (in Britain) A British act of parliament that established legislation for controlling a patient’s access to their written clinical health records. This act has largely been replaced by the *Data Protection Act 1998.
accidental extraction n. See TOOTH EXTRACTION.
accident book A book used to record all accidents to staff, patients, and visitors in a dental practice or clinic. Entries should include the time, date, and nature of the accident, where it took place, who was involved, and what action was taken. The accident record does not have to be in book format, and may for example be stored as a file, written log, or electronic record.
Health and Safety Executive guidance details.
accreditation n. A process of formal recognition by a professional external body whereby an educational establishment or programme meets certain agreed quality standards.
accredited prior learning (APL) n. Credit given for previously gained skills or knowledge.
accretion n. An accumulation of material such as *calculus, *plaque, or dental cement on tooth surfaces.
accretion lines n. Lines visible in microscopic sections of *enamel marking successive layers of added material.
acellular n. Describing any tissue or part of a tissue that does not contain cells.
acesulfame-potassium (ace-K, acesulfame-K) n. A calorie-free artificial sweetener known in Europe under the additive code E950. It is 150–200 times sweeter than *sucrose. It is used in many foods, including cakes and low-calorie drinks. It is not metabolized or stored in the body and after ingestion is rapidly excreted unchanged.
acetate strip n. A clear plastic strip of celluloid acetate used as a *matrix band for tooth-coloured restorations in anterior teeth, to restore the contour of the proximal surface.
acetone n. A colourless liquid ketone used as a solvent in some dental restorative *primer materials. Primers with high acetone content can cause significant erosion of calcium hydroxide lining materials.
acetylsalicylic acid n. See ASPIRIN.
ache n. A dull persistent pain.
acheilia n. Congenital absence of the lips.
achlorhydria n. An absence of hydrochloric acid in the stomach. It may not be associated with disease.
achondroplasia n. A genetic disorder in which the bones of the arms and legs fail to grow to normal size, due to a defect in both cartilage and bone, resulting in dwarfism. It can result in delayed exfoliation of the primary teeth.
aciclovir (acyclovir) n. An antiviral drug that acts by inhibiting DNA synthesis in cells infected with the *herpes virus. It can be applied to the lips as a cream in the treatment of herpes labialis (cold sores), or can be used systemically for severe infections or in the immunocompromised patient. Trade name: Zovirax.
acid n. Any chemical compound which when dissolved in water produces a solution with a *pH of less than 7. An acid bath is an acid (usually hydrochloric or sulphuric) solution used to remove the oxide layer of a metal, a process known as *pickling. acidic adj. Compare ALKALINE.
acid-etch technique n. A technique for bonding resin-based materials to enamel or dentine. An acid, usually phosphoric acid, is applied in either gel or liquid form to the previously dried and isolated tooth surface for about 30 seconds. The dissolution of the mineral element of the tooth creates micro-porosities into which the subsequently applied unfilled resin can flow and provide a mechanical lock by means of resin tags. It is used to bond *fissure sealants, restorative materials, orthodontic *bands, and adhesive *bridges (prostheses).
acidogenic adj. Describing the ability to produce acid.
acidogenic theory A theory describing the cause of dental caries, first postulated by Willoughby D. Miller in 1890, which stated that non-specific bacteria in the plaque fermented refined carbohydrates to produce acid that demineralized tooth enamel.
acidosis n. A condition in which the acid–base balance in the body is characterized by an excess of acid or a deficiency of alkali. In health this is regulated by the respiratory and renal systems. Compare ALKALOSIS.
acidulated phosphate fluoride gel (APF) n. See FLUORIDE GEL.
aciduric adj. Describing the ability to tolerate exposure to pH environments lower than 7.
acinic cell tumour n. A malignant tumour of the salivary glands in which the cells typically resemble salivary acini. It is now classified by the *World Health Organization (WHO) as acinic cell carcinoma. It is most commonly seen in the *parotid gland and may produce symptoms of pain and tenderness. Tumours arising from non-epithelial tissue of the salivary glands (*sarcomas) are very rare.
acinus n. (pl. acini; adj. acinous) 1. A small sac-like dilatation surrounded by excretory cells in a compound gland such as the salivary glands. 2. (in the lung) The tissue supplied with air by one terminal bronchiole.
aclusion (disclusion) n. The condition of not having the teeth in contact with each other.
acne (acne vulgaris) n. A common skin condition occurring particularly during adolescence that affects the hair follicles and sebaceous glands in the skin. In puberty, acne occurs because of changes to hormone levels. These cause the sebaceous glands to produce increased amounts of sebum which, together with dead skin, block the hair follicles. Acne is characterized by the presence of spots ranging from blackheads and whiteheads to painful red nodules usually occuring on the face, hands, and neck. Acne during puberty normally corrects itself in time without treatment. Acne rosacea See ROSACEA.
aconite n. An alkaloid from the dried roots of the herbaceous plant Aconitum napellus used in the homeopathic treatment of dental fear or acute anxiety. It was formerly used as a *tincture for toothache. Its use is controversial in view of its low safety margin and evidence of its being a cardiotoxin.
acquired immunodeficiency syndrome (AIDS) n. See AIDS.
acrodont adj. Having tooth attachment in which the teeth are fused (*ankylosed) to the jaw bone, rather than being located in sockets within the bone. It is common in reptiles and fish.
acrodynia (pink disease) A rare severe illness of children of teething age, possibly leading to the early loss of the primary teeth and permanent tooth germs. It is characterized by pink cold clammy hands and feet, rapid pulse, raised blood pressure, stomatitis, periodontitis, and premature loss of teeth. It is thought to be caused by an allergy to mercury, which used to be a constituent of teething ointments, lotions, and powders. Since mercury-containing paediatric preparations have been banned, the disease has virtually disappeared.
acromegaly n. A chronic metabolic disorder caused by the presence of excess growth hormone. It results in gradual enlargement of body tissues, including the bones of the face (*frontal bossing), jaw, hands, feet, and skull.
acrosclerosis n. A skin disease thought to be a type of generalized *scleroderma mainly affecting the hands, face, and feet.
acrylic (polymethylmethacrylate) resin n. A thermoplastic vinyl polymer made by free radical vinyl polymerization from methyl methacrylate monomer. It was first developed in 1928 and eventually replaced *vulcanite as a material in the construction of acrylic resin complete and partial dentures. It is also used for the construction of temporary resin crowns and bridges and in the manufacture of resin teeth and removable orthodontic appliances. The material is supplied as a polymethylmethacrylate powder and a liquid monomer. To construct a denture base, the powder and liquid are mixed together to form a dough, which is packed into an appropriate mould and subjected to prolonged heat to produce the final rigid product. Acrylic resin may be polymerized at room temperature by including a chemical initiator, such as a tertiary amine, in the liquid monomer: these resins are known as self-curing or auto-curing resins. The impact strength of acrylic resin may be increased by grafting a rubber-like butadienestyrene polymer to the acrylic molecules. Acrylic resin can produce an allergic contact reaction with the soft tissues and in such cases may then be substituted with a *polyamide resin.
Actinobacillus actinomycetem comitans A carbon dioxide-requiring (capnophilic), microaerophilic, *Gram-negative rod-shaped bacterium associated with chronic periodontitis. Toxins released by these bacteria produce an inflammatory response in the gingival tissues with a consequent increase in gingival crevicular fluid flow. Virulence factors include collagenese, endotoxin, IgA proteases making it capable of evading normal host response and destroying connective tissue and bone.
Actinomyces n. A genus of non-spore forming Gram-positive bacteria that can be *anaerobic or facultatively anaerobic. Individual bacterial cells tend to be rod-shaped, whereas bacteria in colonies form branched networks of hyphae-like fungi. Several Actinomyces species are opportunistic pathogens of humans, especially in the oral cavity, and can be isolated from plaque. See also ACTINOMYCOSIS.
actinomycosis n. An uncommon bacterial disease of humans generally caused by A. israelii and A. gerencseriae and species of propionibacteria. The disease is characterized by painful abscesses in the oral cavity, lungs, or digestive tract. Treatment is by antibiotic therapy.
action potential n. The electrical signal that rapidly propagates along the *axon of nerve cells as well as over the surface of some muscle and glandular cells. It is due to a change in membrane electrical potential caused by a change in flow of ions across the membrane, in turn due to voltage-activated ion channels.
actisite n. A trade name for a polyvinyl acetate fibre impregnated with *tetracycline used as a form of *chemotherapy to provide a *topical antibiotic for the treatment of periodontal disease. The impregnated fibres are packed into the gingival pocket and retained for about 10 days by means of a *cyanoacrylate adhesive.
active adj. (v. activate) Describing an orthodontic appliance which has been adjusted to provide an effective force on a tooth, teeth, or jaw. Compare PASSIVE.
active metabolite n. An agent produced following metabolism of a drug, which has its own therapeutic effect (e.g. salicylate from aspirin).
acupressure n. The pressure applied by hands, elbows, or fingers to acupuncture points on various parts of the body as an alternative to using needles (*acupuncture).
acupuncture n. The insertion of a solid needle into any part of the human body for the purpose of disease prevention, therapy, or maintenance of health. It is a form of traditional Chinese medicine used by some dental practitioners to relieve symptoms of pain, nausea, dental anxiety, and the gag reflex. It is based on the theory of energy pathways that run through the body (the *meridian system). Needles are used to stimulate the nerves in skin or muscle to increase the release of endorphin and serotonin (neuro-endocrine theory). Electro-acupuncture uses a device to pass a small electrical current across acupuncture points. 
Further Reading: Thayer M. L. T. The use of acupuncture in dentistry. Dent Update 2007;34:244–50.
The British Medical Acupuncture Society website.
acute adj. 1. Describing a condition of rapid onset, severe symptoms, and brief duration, e.g. acute pulpitis. Compare CHRONIC. 2. Describing any intense symptom such as acute toothache or acute inflammation.
acute ulcerative gingivitis n. See GINGIVITIS, NECROTIZING.
Adams crib n. See CRIB.
Adams pliers n. See PLIERS.
adaptation n. 1. The close approximation of a prosthetic appliance to the oral tissues. 2. The adjustment of a band or restorative material to closely approximate against a tooth surface. 3. The process by which a sense organ shows a progressively diminishing response to continuous or repetitive stimulation. 4. The alteration that an organism gradually undergoes to adjust to a changing environment.
Adcortyl in orabase See TRIAMCINOLONE ACETONIDE.
addiction n. Psychological and bodily dependence, on a substance or practice, which is beyond voluntary control. Treatment is aimed at gradual withdrawal of the substance or behaviour and eventually complete abstention.
Addison’s disease [Thomas Addison (1793–1860), English physician] Hypo-secretion of the adrenal glands characterized by symptoms of tiredness, weakness, weight loss, and thirst. An early oral sign is blue-black pigmentation usually of the gingivae or mucous membrane of the cheek but may involve other parts of the mouth and face. An acute infection or severe adrenal hypofunction can precipitate an Addisonian crisis manifested by low blood pressure and collapse. Treatment is by replacement hormone therapy.
addition curing See POLYMERIZATION.
adduction n. The movement towards the midline of the body.
adenitis n. Inflammation of a gland or lymph node.
adenocarcinoma n. See CARCINOMA.
adenofibroma n. A tumour consisting of fibrous tissue and containing glandular structures.
adenoid n. Lymphatic tissue covered by ciliated epithelium situated on the posterior wall of the *nasopharynx (pharyngeal tonsils). They function as part of the body’s immune system and form part of the ring of lymphatic tissue known as *Waldeyer’s ring.
adenoid cystic carcinoma n. A *malignant salivary gland *neoplasm which is more common in the minor glands than the major. It has a characteristic ‘Swiss cheese’ pattern arrangement of the epithelial cells and spreads widely along nerves. Patients present with slow growing swelling with pain and ulceration. Treatment is wide local excision.
adenolymphoma n. (Warthin’s tumour) [A. S. Warthin (1866–1931), American pathologist] A benign cystic tumour that occurs exclusively in the *parotid gland. It contains epithelial and lymphoid tissue and accounts for about 5% of all parotid tumours. It is frequently bilateral (affects both glands). See also ADENOMA.
adenoma n. A benign epithelial tumour of glandular origin. A pleomorphic adenoma is a benign tumour of *salivary glands and is the most common tumour of the *parotid gland. It has a variable histological appearance in terms of the proportions and arrangements of epithelial cells and connective tissue stroma and is usually enveloped by a fibrous capsule. It may grow to a large size and treatment is by surgical excision. Recurrence is rare. Longstanding tumours may become malignant. Other types of adenoma arising in the salivary glands are basal cell adenoma and canalicular adenoma.
adenomatoid odontogenic tumour n. A benign *odontogenic tumour that is often associated with the crown of an unerupted tooth, particularly the upper canines. It is composed of odontogenic epithelium and mesenchyme and characterized by *ameloblast-like cells that form ducts and tubules. Calcification is common. It is treated by excision and does not usually recur.
adenosine triphosphate (ATP) n. A nucleotide which provides the energy to drive sodium (sodium pump) out of the nerve cell as part of the repolarization phase following nerve stimulation. It stores energy in muscles which is released on hydrolysis to adenosine diphosphate (ADP).
adhesion n. 1. The sticking of two surfaces together (e.g. an orthodontic *bracket to tooth enamel, or a denture to the roof of the mouth). Adhesive systems in restorative dentistry permit the bonding to dentine and enamel using an *acid-etch technique. 2. The tissue that provides the pathological joining of two normally separate surfaces. 3. The healing process by which the edges of a wound are united. This may be primary with minimal *granulation tissue or secondary when the edges are joined by granulation tissue. See also WOUND.
adipose adj. Fatty or pertaining to fat. Adipose tissue is connective tissue with a predominance of fat cells which serves as an insulating layer and an energy store.
adipsia n. The inability to drink or the avoidance of drinking. It is the extreme form of an abnormally diminished thirst (hypodipsia) and is usually caused by damage to the thirst centre in the anterior hypothalamus.
adjudication n. (US) A part of a dental peer review process in which a peer review committee expresses a non-binding opinion of a dispute brought before it.
adjuvant n. A pharmacological or immunological agent which is added to modify the effectiveness of the main ingredient (e.g. an adjuvant drug used to enhance the pain relief provided by another drug). Adjuvant therapy is additional treatment supporting primary treatment such as radiation therapy following surgery for the removal of a malignant lesion.
adnexa pl. n. Accessory or adjoining anatomical parts or appendages to an organ.
adolescence n. The stage of development from *puberty to adulthood. Puberty in girls starts usually at the age of 10 years and in boys at about 12 years. The behaviour and identity of an adult usually starts at about the age of 19 years.
adrenal crisis Acute adrenocortical insufficiency characterized by headache, nausea, vomiting, rapid weak *pulse, circulatory collapse, and coma. It may occur in response to the additional stress of dental treatment in patients with adrenal suppression or who are being treated with cortisone therapy. Treatment is by intravenous or intramuscular *hydrocortisone and *oxygen.
adrenal glands The two *endocrine glands situated above each kidney. The outer part (adrenal cortex) produces corticosteroid hormones e.g. cortisone and hydrocortisone and the inner part (adrenal medulla) produces epinephrine (*adrenaline) and norepinephrine (*noradrenaline).
adrenaline (epinephrine) n. A hormone secreted by the medulla of the adrenal gland. It is a directly acting sympathetomimetic amine with both alpha and beta adrenergic activity and stimulates the heart, blood vessels, and respiratory system. Adrenaline may be injected in the treatment of *cardiac arrest (intravenously) or *anaphylactic shock (intramuscularly). In the dose used in cardiopulmonary resuscitation (CPR), it stimulates alpha 1 and alpha 2 receptors, causing vasoconstriction, and thereby increasing systemic vascular resistance during CPR and causing a relative increase in cerebral and coronary *perfusion. In the beating heart, adrenaline acts on beta 1 receptors to increase the heart rate and force of myocardial contraction. It is added as a *vasoconstrictor in dental local analgesic solutions to prolong the action of the analgesic.
adrenal shock n. See ADDISON’S DISEASE.
adsorption n. The adhesion of a gas, liquid or dissolved substance onto the surface of a solid material or body.
adult dental health survey A review carried out in the UK and many EU states and countries worldwide every ten years since 1968, to provide information on the current state of adults’ teeth and oral health in the four countries of the UK and to measure changes in oral health since the previous survey. The specific aims of the survey are to establish the condition of the natural teeth and supporting tissues; to investigate dental experiences, attitudes, and knowledge; dental care and oral hygiene; to establish the state and use made of dentures worn in conjunction with natural teeth; to identify those people who have lost all of their natural teeth and investigate their use of dentures; and to monitor the extent to which oral health targets set by government are being met. See also CHILDREN’S DENTAL HEALTH SURVEY.
Summary of the 1998 survey on the government’s Office of National Statistics site.
adumbration n. Sketchy or lack of sharp-edge definition of an image on a radiographic film.
advanced life support (ALS) Medical care provided by trained personnel to assess a patient’s condition, administer drugs, defibrillate, and provide advanced airway management prior to transfer to a hospital. See also BASIC LIFE SUPPORT.
The Resuscitation Council (UK) information on advanced life support.
adventitia (tunica adventitia) n. 1. The outer coat of the wall of an artery or vein. 2. The outer covering of various organs.
adventitious adj. Describing something occurring in an unexpected location.
adverse effect An abnormal or harmful event for which the causal relation between the drug or intervention and the event is at least a reasonable possibility. It can be applied to all interventions, unlike an adverse drug reaction which is applied only to drugs. Adverse effects are indicated usually by pathological changes, illness, or even death.
aerobic adj. 1. Living or occurring only in the presence of oxygen. 2. Cellular respiration by which carbohydrates are completely oxidized by atmospheric oxygen to achieve maximum energy production.
aerodontalgia n. See BARODONTALGIA.
aerodontia n. The science of the effect of either increased or reduced atmospheric pressure on the teeth.
aerosol n. A suspension of very small solid or liquid particles that range in size up to 50μm diameter in air or gas: they may be suspended in passive air for several days. Aerosol sprays are used for the delivery of some drugs (e.g. Ventolin for the treatment of asthma). Aerosols are a possible hazard when using high speed turbines and ultrasonic scalers because of the potential spread of infected material.
Further Reading: Day C. J., Sandy J. R., Ireland A. J. Aerosols and splatter in dentistry—A neglected menace. Dent Update 2006;33:601–6.
aetiology (US etiology) n. 1. The study of the causes of disease. 2. The cause of a disease.
afferent adj. 1. Conducting information inwards. 2. Designating the part of the peripheral nervous system which transmits impulses from organs or tissues to the central nervous system, i.e. any sensory nerve or neurone. 3. Describing blood vessels that feed a capilliary network. 4. Designating lymphatic vessels that enter a lymph node. Compare EFFERENT.
agar (agar-agar) n. A vegetable polysaccharide gel made from seaweed extract (Gelidium cartilagineum, Gracilaria confervoides, and related red algae) and used as a sterile, solid, bacterial culture medium (agar plate) contained in a *Petri dish. Agar is the principal ingredient of reversible *hydrocolloid impression material.
agate n. A hard gemstone used in the construction of spatula blades. They are used for mixing tooth-coloured materials because of their resistance to abrasion and their ability not to cause discoloration of the material, unlike some metallic spatulas.
age change An alteration in the form or function of a tissue or organ over a period of time. Age changes which take place in the oral soft tissues include a decrease in the thickness of the mucosa, a reduction in taste bud function, and an increase in the number of *sebaceous glands; there is an increase in the incidence of mucosal disease such as *oral cancer, *lichen planus, and *candida. The dental hard tissue changes include a reduced permeability of the enamel, a reduced rate of secondary dentine formation, and a progressive occlusion of the dentinal tubules with calcified material. See also GERODONTOLOGY.
ageusia n. Total loss of the ability to taste sweet, sour, salty, or bitter substances. It has many causes including neurological damage particularly affecting the lingual and hypoglossal nerves. The loss of taste may only be partial (*hypogeusia).
agglutination n. Clumping together often as a result of infection, antibodies, or inflammation (e.g. red blood cells or bacteria).
aggressive periodontitis n. See PERIODONTITIS, AGGRESSIVE.
aglossia n. The congenital absence of the tongue.
agnathia n. The total failure of development of the mandible or maxilla.
agomphious adj. The condition of being toothless (*edentulous). See also ANODONTIA.
agonist n. 1. A muscle whose contraction causes movement of part of the body at the same time as another muscle (*antagonist) relaxes. 2. A drug that acts at a cell receptor site and mimics the action of the body’s natural *neurotransmitters.
agranulocytosis n. An acute blood disorder in which there is a severe deficiency in *granulocytes. It can be caused by drugs, chemicals, or *neoplasia. Oral signs are necrotic ulcers of the gingivae, tongue, and buccal mucosa.
AIDS (acquired immunodeficiency syndrome) n. A disease caused by the human immunodeficiency virus (*HIV). The syndrome was first identified in Los Angeles in 1981. AIDS is essentially a sexually transmitted disease although transmission can also be via infected blood, blood products, or breast milk. The virus may also be present in saliva. The virus can only survive for a few minutes outside the body and must enter the bloodstream to cause infection. High standards of clinical practice are required by all clinical dental health workers in order to avoid inadvertent infection via blood or body fluids from HIV positive people. See also KAPOSI’S SARCOMA.
air abrasion A method of delivering an abrasive material, usually aluminium oxide, under high pressure. The average particle size is 27.5 microns and the nozzle tip exit pressure commonly employed ranges between 60 and 120 pounds per square inch. It is a non-rotary technique used to cut small cavities in enamel, dentine or to remove surface accretions or stain. The nozzle tip is usually placed less than 1mm from the tooth surface to minimize the cone-shaped particle scatter. It is an alternative in some situations to using the *air turbine for cavity preparation.
Further Reading: Banerjee A., Watson T. F. Air abrasion: Its uses and abuse. Dent Update 2002;29:340–46.
WebMD page providing an overview of restorative dentistry using air abrasion.
air block n. A material, such as petroleum jelly, applied to the surface of a resin composite restoration prior to curing. It acts as a barrier to oxygen which is a polymerization inhibitor. See also OXYGEN INHIBITION LAYER.
air embolism n. A bubble of air present in the tissues. It may occur in an artery, vein, or tissue space as a result of surgery, injury, or injection.
air syringe n. An instrument for delivering compressed air to a given location for the purpose of removing fluids or loose particles.
air turbine handpiece n. A handpiece with a turbine powered by compressed air. Used with diamond or tungsten carbide burs and a water coolant spray to dissipate the heat produced when removing enamel, dentine, or other hard materials. See also HANDPIECE.
airway n. 1. The passageway allowing air to pass into and out of the lungs. 2. A device to facilitate free passage of air to the lungs when the patient is unconscious. Oropharyngeal airways are made in a range of sizes from newborn to large adult. The airways are rigid curved plastic tubes with a reinforced flange. They are inserted in the mouth in the inverted position and rotated 180° as the tip passes into the *oropharynx. Nasopharyngeal airways are an alternative if the patient is not deeply unconscious and should be inserted via the nostril, following lubrication, with a twisting action into the oropharynx. 
airway obstruction See CHOKING.
akinesia n. An inability to move or a difficulty in beginning or maintaining a body motion. It is a symptom of *Parkinson’s disease.
ala n. (pl. alae) A wing-like structure such as the ala of the crista galli, part of the projection from the cribriform plate of the ethmoid bone, the ala of the vomer, and the alar part of the nasalis muscle. The alar cartilage is the U-shaped structure on the lateral aspect of the external naris (nostril) which forms the tip of the nose.
ala-tragal line A line from the lower border of the ala of the nose to the upper border of the *tragus of the ear. It is used as a reference line in orthodontics, radiography, and the construction of complete dentures. Also known as Camper’s line [P. Camper (1722–89), Dutch anatomist].
Ala-tragal line
Albers–Schönberg disease See OSTEOPETROSIS.
Albright syndrome See DYSPLASIA.
alcohol n. Compounds with a hydroxyl (OH) group attached to a carbon atom. Alcoholic beverages contain ethyl alcohol (ethanol) which has the formula C2H5OH. It has a depressant effect on the central nervous system. Ethyl alcohol potentiates the effects of carcinogens (e.g. cigarette smoke), by increasing the permeability of the oral mucosa and it is therefore a risk factor for oral carcinoma. Excessive alcohol consumption over a short period of time (binge drinking) can lead to acetaldehyde accumulation in the oral mucosa which is thought to be a carcinogenic factor. Alcohol consumption during pregnancy can have a detrimental effect on foetal development. A frequent high intake of alcohol can lead to physical deterioration and mental impairment (alcohol abuse). Prolonged alcohol consumption can lead to cirrhosis of the liver, enteritis, and heart damage. A mental or physical desire to consume alcohol can lead to alcohol dependence (alcoholism), which is characterized by a strong craving, anxiety, and tremor, and a reliance on the intake of alcohol despite adverse physical, mental, and social consequences. Support groups are available, such as Alcoholics Anonymous for sufferers from alcoholism and Al-Anon for friends and families of alcoholics.
Alcoholics Anonymous website.
Al-Anon website.
-algia Suffix denoting pain e.g. neuralgia (pain in a nerve).
alginate n. Any salt of alginic acid (e.g. sodium alginate, calcium alginate). Alginate impression material is a mixture of sodium, potassium, and triethanolamine alginate, calcium sulphate (gypsum), and a filler (65–75%) such as diatomaceous earth which, when mixed with water, forms calcium alginate, an irreversible hydrocolloid. Trisodium phosphate is added (1–3%) to control the setting time. Alginate is used for primary impressions for complete and partial dentures and for the construction of study casts. Because of its dimensional instability it is not a suitable material for crown or bridge preparations.
align v. 1. To set prosthetic teeth up in the line of the dental arch. 2. To orthodontically bring teeth into the normal arch position. This is usually achieved by the use of flexible nickel or stainless steel *archwires attached to a *fixed appliance.
alignment (of tooth) n. The location of the tooth relative to the supporting alveolar *bone and adjacent and opposing teeth.
alimentary tract n. The digestive passage extending from the mouth to the anus. Each region is specialized to undertake mechanical breakdown (in the mouth), chemical digestion and absorption (in the stomach and small intestine), and faeces formation and water absorption (in the colon and rectum).
alkaline adj. Describes any chemical compound which, when dissolved in water, produces a solution having a pH greater than 7. See also ACID.
alkalosis n. A condition in which the acid-base balance in the body is characterized by an excess of alkali or a deficiency of acid. In health this is regulated by the respiratory and renal systems. Compare ACIDOSIS.
allergen n. (adj. allergenic) A substance capable of inducing hypersensitivity or an allergic reaction e.g. *latex.
allodynia n. Pain due to a stimulus that does not normally provoke pain. This is exemplified by non-painful stimulation such as touch, gentle pressure, cold, or gentle joint movement producing symptoms of pain. Compare HYPERALGESIA.
allograft n. See GRAFT.
allopathy n. Treatment of disease by the use of medicines or drugs that oppose the presenting symptoms.
alloplasty n. (adj. alloplastic) A surgical procedure utilizing a synthetic material, i.e. a material not from the human body.
alloy n. A mixture, either in solution or compound, of two or more metals. *Gold, *palladium, *titanium, *nickel-chrome, and nickel metal–ceramic alloys may be used in the construction of bridges and crown restorations. Copper is added to gold to reduce the density and melting point and increase the strength and hardness; however, the corrosion resistance is reduced. The addition of silver to gold increases the hardness and strength but also increases porosity and the degree of tarnish. Zinc or indium are added as scavengers to prevent the oxidation of other metals during melting and casting. A eutectic alloy has a melting point which is lower than that of any of the individual metals of which it is constituted. See also AMALGAM.
Further Reading: Brown D. Alloys for metal-ceramic restorations. Dent Update 2005;32:583–6.
alumina n. Aluminium oxide (SiO2), a component of dental *porcelain. Also used as an abrasive material.
aluminium n. A silvery white metallic element. It is used as a filter in x-ray machines to block x-rays over a certain wavelength. It is also added to some dental waxes to modify the hardening properties. Aluminium chloride hexahydrate is a powerful antiperspirant used in the treatment of excessive sweating.
alveolalgia n. See ALVEOLITIS.
alveolar adj. Pertaining to an alveolus.
alveolar bone n. See BONE.
alveolar crest n
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