O
objective structured clinical examination (OSCE) A method of assessment in which the candidate is required to attend a series of stations and undertake a clinical exercise at each station within a defined period of time.
obligate adj. Restricted to a particular set of environmental conditions without which an organism cannot survive e.g. an obligate anaerobe can only grow under anaerobic conditions.
oblique lateral radiograph An extra-oral radiograph that can be taken using a dental x-ray set which will allow visualization of the posterior teeth, angle, ramus, and condyle of the mandible and posterior maxilla. See also BIMOLAR RADIOGRAPH.
observational study n. Where the study is non-experimental and current behaviour is observed without intervention. No attempt is made to affect the outcome.
obtund v. To diminish or blunt sensitivity or pain.
obtundent n. An agent or drug that has the property of reducing or relieving pain.
obturation n. 1. The act of closing, obstructing, or occluding. 2. The process of filling the root canal system with an inert material following complete extirpation of the pulpal tissue. Research currently indicates that obturation beyond the radiographic apex of the root results in a poorer prognosis.
obturator n. A prosthesis used to close or cover a defect in the palate and restore the occlusion. The defect may be consequent upon the removal of a tumour or be congenital, as in a *cleft palate. An obturator is usually made of resin or a rubberized material and may be hollow to reduce the weight.
Further Reading Walter J. Obturators for acquired palatal defects. Dent Update 2005;32(5):277–80, 283–4.
occipital bone n. The bone forming the back and part of the base of the cranium.
occipital triangle An anatomical description of a region of the neck. It is bounded posteriorly by the trapezius muscle, anteriorly by the sternocleidomastoid muscle, and inferiorly by the omohyoid muscle.
occiput n. The most posterior part of the skull.
occlude v. To close or shut. In dentistry it describes bringing the opposing jaws together to bring the teeth into contact.
occluding paper n. Inked paper or ribbon (usually blue or red) placed between natural or artificial teeth to record tooth contacts. See also WAX.
occlusal adj. Relating to the chewing or grinding surfaces of the molar or premolar teeth. See also TOOTH SURFACES.
occlusal adjustment The selective grinding of the occluding (contacting) surfaces of the teeth in order to remove premature contacts or occlusal interferences and to establish maximum masticatory efficiency. It is also undertaken to eliminate *occlusal trauma and abnormal muscle tension, to aid the stabilization of orthodontic therapy, to aid periodontal therapy, and following complex restorative treatment. It has been used to eliminate *temporomandibular joint problems, although the evidence to support this is controversial. See also BALANCED OCCLUSION.
Further Reading Fricton J. Current evidence providing clarity in management of temporomandibular disorders: summary of a systematic review of randomized clinical trials for intra-oral appliances and occlusal therapies. J Evid Based Dent Pract 2006;6(1):48–52.
Milosevic A. Occlusion: 2. Occlusal splints, analysis and adjustment. Dent Update 2003;30(8):416–22.
occlusal analysis The study of the relationship of the occlusal surfaces of opposing teeth. It may be undertaken in the mouth or by the use of articulated study casts.
occlusal classification See INCISOR RELATIONSHIP; MOLAR RELATIONSHIP.
occlusal contact The point at which the occluding surfaces of one or more opposing posterior teeth meet. A deflective occlusal contact is a condition in which the tooth contacts divert the mandible from a normal path of closure; it may occur in the natural or artificial dentition. An interceptive occlusal contact is an interference with the normal movement of the mandible on initial tooth contact.
occlusal contouring The modification of the occlusal tooth *morphology to achieve a harmonious *occlusion and to protect the periodontal tissues.
occlusal curvature See CURVE OF MONSON; CURVE OF SPEE.
occlusal embrasure See EMBRASURE.
occlusal equilibration See EQUILIBRATION.
occlusal form See FORM.
occlusal guard See OCCLUSAL SPLINT.
occlusal indicator wax See WAX.
occlusal interference A condition that occurs when any tooth contact inhibits the remaining occluding tooth surfaces from achieving stable and harmonious contacts.
occlusal morphology See MORPHOLOGY.
occlusal neurosis See BRUXISM.
occlusal pattern The shape or form of the occlusal surface of a tooth or teeth which may or may not conform to that of the natural anatomical form.
occlusal plane An imaginary surface that theoretically touches the tips of the cusps of the posterior teeth and the incisal tips of the anterior teeth.
occlusal radiograph An intra-oral radiograph placed with the film between occluded teeth. It may be taken to show the upper anterior teeth (standard upper occlusal) or posterior teeth (upper oblique occlusal) or the mandibular teeth (lower true occlusal, lower 45° occlusal or lower oblique occlusal) 
occlusal record A means of recording the relationship between the occlusal surfaces of the maxillary and mandibular teeth. It allows the accurate articulation of laboratory plaster casts. It is usually created from a syringable *impression material or a *wax that is initially softened and hardens at mouth temperature.
Further Reading Shargill I., Ashley M. Good night, squashbite: a ‘how to’ paper on better wax occlusal records. Dent Update 2006;33:626–31.
occlusal rest A rigid, usually metal, extension of a removable partial denture which rests on the occlusal surface of a posterior tooth for the support of a prosthesis. The occlusal rest is usually accommodated in a shallow prepared depression on the occlusal surface (occlusal rest seat) which allows the normal occlusal morphology of the tooth to be maintained.
occlusal rim The wax occlusal extension of a denture base used to establish jaw and tooth relationships during the construction of a complete or partial denture. Also known as bite block, bite rim, *bite plate, or occlusal record block.
occlusal splint (occlusal guard) A fabricated appliance, usually made from laboratory-processed acrylic resin, designed to cover the occlusal tooth surfaces and modify the occlusal contacts with the opposing dentition. The occlusal surface of the splint is flat without indentations so that the mandible is not guided into any predetermined position. An occlusal splint can have many functions, including to prevent tooth surface loss, to manage mandibular dysfunction, to create space to restore worn anterior teeth, to provide pre-restorative stabilization, and to protect the teeth and new restorations from destructive *parafunction.
Further Reading Capp N. J. Part 3: Occlusion and splint therapy. Br Dent J 1999;186:217–22.
DuPont J. S. Jr, Brown C. E. Occlusal splints from the beginning to the present. Cranio. 2006;24(2):141–5.
occlusal table The total occlusal or grinding surface of the molars and premolars, including the *cusps, marginal *ridges, fossae, and grooves.
occlusal traumatism Abnormal occlusal contacts resulting in damage to the periodontium (periodontal *traumatism) or other supporting structures. Occlusal trauma has been investigated in relation to the progression of *periodontal disease. Studies do not support the role of occlusal trauma in the healthy, plaque-free dentition; there is evidence to suggest that occlusal trauma may be a risk factor for disease progression in the periodontium with established periodontitis. Diagnostic features include tooth mobility, tooth migration, discomfort on chewing or tooth percussion, muscle tenderness, excessive occlusal wear facets, chipped teeth, *fremitus, and radiographically visible widening of the periodontal ligament space.
occlusal vertical dimension (OVD) The vertical dimension, usually recorded from two fixed anatomical points, when the teeth (natural or artificial) or *occlusal rims are in contact. An increase in occlusal vertical dimension may occur as a result of a modification to the occlusal rims, tooth form or position, or denture rebasing or relining. A decrease in occlusal vertical dimension may result from attrition or drifting of the teeth, or the resorption of the alveolar ridges in edentulous patients.
occlusion n. 1. The relation of the upper and lower teeth when they are in contact. 2. The act of closing or the state of being closed. Balanced occlusion is the harmonious relationship between the upper and lower teeth of a natural or artificial dentition within the normal functional range of mandibular movement. It may be achieved entirely intra-orally or with the aid of an *articulator. Centric occlusion is the relationship of the mandible to the maxilla when the teeth are in maximum occlusal contact, irrespective of the position or alignment of the mandibular condyle. Functional occlusion refers to tooth contacts made within the functional range of the opposing teeth and is independent of aesthetics. Lingualized occlusion is where the maxillary teeth on a denture are placed buccally to the crest of the ridge so that occlusion only occurs between the palatal cusps of the upper teeth and the central fossae of the lower teeth, except for the first premolars where the situation is reversed. This occlusion has one upper tooth only contacting with its lower counterpart and not contacting any other tooth.
Further Reading Davies S. Conformative, re-organized or unorganized. Dent Update 2004;31:334–45.
Davies S., Gray R. M. J. Occlusion: what is occlusion? Br Dent J 2001;191:235–41.
occupational disease A disease to which workers in specific occupations are particularly prone e.g. workers in contact with acid fumes can show evidence of acid tooth *erosion. Historically *mercury was used in the making of hats and the workers ingested the fumes; this resulted in mercury poisoning with kidney and brain damage (mad hatter syndrome).
odds n. A way of expressing the chance of an event, calculated by dividing the number of individuals in a sample who experienced the event by the number for whom it did not occur. For example, if in a sample of 100, 20 people were infected and 80 were infection free, the odds of being infected are 20/80 or 0.25.
odds ratio (OR) The odds of having the target condition or disease in the experimental group relative to the odds in favour of having the disease or condition in the *control group. The value of an odds ratio can be less than, equal to, or greater than 1. An odds ratio less than 1 indicates an inverse or negative association. The effects being measured may be adverse such as death, or desirable such as smoking cessation.
odontalgia n. (adj. odontalgic) Pain in a tooth or teeth (toothache). Phantom odontalgia is pain interpreted as toothache referred from an area or socket where a tooth has been extracted.
odontectomy n. The removal (usually surgically) of a tooth or tooth root.
odonterism n. Chattering of the teeth.
odontiasis n. See TEETHING.
odontoameloblastoma n. A very rare *odontogenic neoplasm containing dentine and enamel in the form of an odontome (*odontoma) with an epithelioid component that is similar to an *ameloblastoma in its locally aggressive behaviour.
odontoblast n. A dentine-forming cell. They are mesodermal in origin and are formed from cells at the periphery of the *dental papilla at about 17–18 weeks in utero. Odontoblasts are columnar cells that initially secrete a collagenous unmineralized matrix to form predentine; as they retreat towards the dental pulp they leave an elongated process (odontoblast process). Functionally active odontoblasts have long cell bodies, which contain a well-developed granular endoplasmic reticulum, many mitochondria, a Golgi apparatus, a nucleus, and several secretory vesicles; they secrete dentine throughout life. See also DENTINE.
odontocele n. A *cyst in the *alveolus of a tooth: a dentoalveolar cyst.
odontoclast n. A cell responsible for the resorption of *dentine and cementum. They are usually associated with the normal physiological resorption of the roots of the primary (deciduous) dentition prior to *exfoliation. Occasionally there may be pathological odontoclastic resorption of the roots of a permanent tooth.
odontoclastoma (pink spot) n. Internal tooth resorption which begins centrally within the tooth and is characterized by a pink discoloration of the crown. The resorbed tooth tissue is replaced by hyperplastic vascular tissue. See also ROOT RESORPTION.
Further Reading Tripathi A. M., Pandey R. K. Odontoclastoma. J Indian Soc Pedod Prev Dent 2006;24(Suppl):S18–S19.
odontocnesis n. An itching sensation in the gingival tissue.
odontodynia n. See TOOTHACHE.
Further Reading Hamdan M. A., Sawair F. A., Rajab L. D., Hamdan A. M., Al-Omari I. K. Regional odontodysplasia: a review of the literature and report of a case. Int J Paediatr Dent 2004;14(5):363–70.
odontogenesis (odontogeny) n. The process of tooth formation and development.
odontogenesis imperfecta n. See ODONTODYSPLASIA.
odontogenic adj. Of or relating to the formation and development of teeth or tooth tissue.
odontogenic cyst See CYST.
odontogenic tumour Any one of a group of *lesions derived from the tooth-forming apparatus. They are only found in the jaws. See also AMELOBLASTOMA; AMELOBLASTIC FIBROMA; CEMENTOBLASTOMA; MYXOMA; ODONTOMA.
A description of mandibular cysts and odontogenic tumours on the emedicine website.
odontogeny n. See ODONTOGENESIS.
odontoid adj. Shaped like a tooth.
odontology n. The scientific study of the structure and diseases of teeth. See also DENTISTRY.
odontolysis n. Tooth resorption. See also ROOT RESORPTION.
odontoma (odontome) n. A relatively common *benign *odontogenic malformation (*hamartoma) composed of dental hard tissues. Two types are recognized: a complex odontoma consists of a disorganized mixture of enamel, dentine, and cementum; a compound odontoma contains a more organized mixture of dental tissues often arranged to form miniature tooth-like structures surrounded by a fibrous sac. They often present in young patients and may cause a delay in or an abnormal path of eruption of permanent teeth. Treatment is by surgical removal.
odontome n. See ODONTOMA.
odontometry n. The application of measurements and statistics in the study of the face, jaws, and teeth.
odontonomy n. The nomenclature of dental structures and tissues.
odontophobia n. An intense, abnormal, or illogical fear of teeth, usually applied to dentistry in general.
odontoplasty (enameloplasty, prophylactic odontotomy) n. The selective recontouring or reshaping of the morphological anomalies of the tooth surface, such as occlusal fissures, by removal of small amounts of enamel to change the surface, length, or shape of a tooth. This procedure has been adopted to reduce *plaque retention but has been largely replaced by the more conservative approach of using *fissure sealants.
odontoprisis n. The grinding together of the teeth. See BRUXISM.
odontorrhagia n. Profuse bleeding from the socket after the extraction of a tooth.
odontoscope n. 1. A device which contains a plane or magnifying dental mirror used for the examination of the teeth and oral tissues. 2. An optical device, similar to closed circuit television, that projects an image of the oral cavity onto a monitor to make multiple viewing possible.
odontoscopy n. The use of an *odontoscope for the examination of the oral cavity. It is used for the intimate examination of tooth structures such as to study the markings of the cutting edges of the tooth surfaces, used like fingerprints, as a method of forensic identification.
odontoseisis n. Looseness of a tooth or teeth.
odontotomy n. The act or procedure of cutting into the crown of a tooth. *Odontoplasty (prophylactic odontotomy) may be undertaken to improve plaque control.
odynophobia n. A morbid fear of pain.
oedema (US edema; adj. oedematous, US edematous) n. An accumulation of fluid in the body tissues which occurs during inflammation. Angioneurotic oedema is characterized by painless spontaneous swelling of the lips, cheeks, tongue, eyelids, soft palate, *pharynx, and *glottis due to increased permeability of the capillaries, often as a result of *allergy to food or drugs.
oesophagus (US esophagus) n. A muscular tube that extends from the *pharynx to the stomach, forming part of the digestive tract. It is about 25–30cm long and is the narrowest part of the gastrointestinal tract; it is lined with stratified squamous (non-keratinizing) *epithelium, becoming columnar at the stomach. Mucous glands are present in the mucosa and submucosa.
oil of cloves An essential oil from the clove plant. It contains the active ingredient *eugenol which has *analgesic properties and is included in some temporary tooth dressing materials. It can be irritant if applied topically to mucous membranes.
ointment n. A greasy substance which may or may not contain medication for use as a lubricant or as a topical application to the skin or mucous membrane.
olfaction n. (adj. olfactory) 1. The sense of smell. 2. The process of smelling. Specialized receptors are present in the mucous membrane (olfactory epithelium) lining the posterior part of the nasal cavity; these are stimulated by odorants (volatile chemical compounds) which send electrical signals via the olfactory nerve to the olfactory cortex of the brain.
oligodontia n. A condition in which one or more teeth are congenitally missing (partial *anodontia).
-ology See -LOGY.
-oma Suffix denoting a tumour e.g. lymphoma (of the lymph nodes).
omoclavicular triangle (subclavian triangle) n
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