labial adj. Relating to the lips. The labial surface of a tooth is the surface adjacent to the lips. See also TOOTH SURFACES.

labial bar n. See BAR.

labial bow n. A component of a removable *orthodontic appliance consisting of an *archwire, usually made of stainless steel or nickel titanium, which extends across the anterior teeth to guide orthodontic tooth movement and to provide anterior retention. Acrylic resin may be added to provide additional retention.

labial commissure The corner of the mouth where the *lips meet at the outer edges of the mouth.

labial frenulum (fraenum) See FRENULUM.

labial glands n. A large number of small secretory glands resembling salivary glands in structure located between the mucosa and muscles of the lips. They are small and circular in form and have ducts opening into the mouth on the surface of the mucosa.

labial mucosa The *epithelial surface lining on the inner aspect of the *lips within the oral cavity. See also MUCOSA.

labioplasty n. See CHEILOPLASTY.

labiotenaculum n. An instrument used for holding the lips during a surgical procedure.

labioversion n. Deviation of an anterior tooth toward the lips from the normal line of occlusion.

labrale inferior n. A point where the boundary of the lower lip and the skin is intersected in the median sagittal plane; it is the lowest point of the lower lip.

labrale superior n. A point where the boundary of the upper lip and the skin is intersected in the median sagittal plane; it is the uppermost point of the upper lip.

labrette (labret) n. An ornamental device, usually a stud, ring, or bar, inserted into a perforation in the lip. A lowbret is located as low as possible in the lower lip. A Madonna is a labrette placed in the upper lip. See also ORAL PIERCING.

lacebacks pl. n. Metal ligatures tied from the molars to the canines under the main archwire of an orthodontic appliance. They help to maintain the arch length and prevent the lower incisors from proclining as the canines upright. They can be used on one side only (unilaterally) to help centreline correction.

lacrimal adj. Relating to tears. The lacrimal glands are *exocrine glands which secrete fluid across the surface of the eye and drain via the lacrimal ducts into the nasal cavity. They are situated in the lacrimal fossae in the upper lateral part of each eye socket.

lacrimation n. Relating to the production of tears.

lactic acid n. The chemical produced by bacterial action on *carbohydrate food residues in the mouth. It can result in acid *demineralization of the teeth leading to *caries. Because of its high acidity (low pH) it is an important food preservative. During strenuous exercise pyruvic acid is converted to lactic acid, which may accumulate in the muscles and cause cramp.

Lactobacillus n. A genus of *Gram-positive anaerobic or *facultatively anaerobic bacteria (e.g. Lactobacillus acidophilus) capable of converting *lactose and other simple sugars (*monosaccharides) into *lactic acid. Lactobacilli have long been regarded as the main microbiological agent of dental caries; however, studies have shown that lactobacilli colonized carious lesions after their initial formation and that they were not prevalent in dental plaque during lesion formation. Lactobacilli multiply in an acid environment and their numbers in saliva are therefore related to sugar consumption and have been used as a *caries test.

Further Reading: Ireland, R. Clinical Textbook of Dental Hygiene and Therapy Chapter 4: dental caries and pulpitis. Blackwell Munksgaard. 2006:75–81.

lactose n. A complex sugar (*disaccharide) with one unit each of *glucose and *galactose, found in milk. It is broken down by the enzyme lactase to glucose and galactose.

lacuna n. A small cavity such as is found in compact *bone. See also HOWSHIP’S LACUNA.

lambda n. An anatomical landmark at the junction of the sagittal and lamboid sutures of the parietal and occipital bones.

lamella n. A thin layer or membrane such as the concentric layers of calcified matrix found around a *Haversian canal in *bone. See also ENAMEL.

lamina n. A thin membrane or layer of tissue. The lamina dura is a dense thin layer of cortical bone forming the wall of the *alveolus next to the tooth; radiographically it appears as a white line next to the dark line of the *periodontal ligament. The loss of lamina dura on a radiograph may be an indication of associated disease. The lamina propria is a highly vascular loose *connective tissue layer underneath the mucosal *epithelium.

lance v. To open by cutting or piercing, usually with a scalpel or *lancet. It is undertaken to establish drainage, such as when lancing an *abscess (boil).

lancet n. A surgical knife with a sharp point and a broad double-edged blade used for puncturing and making small incisions.

lancinating adj. Describing a sharp stabbing or cutting pain.

Langer curette n. See CURETTE.

Langerhans cell histiocytosis [P. Langerhans (1847–88), German physician and anatomist] A spectrum of disease characterized by accumulations of histiocytes and eosinophils. A localized form occurs in adults (eosinophilic granuloma) and may affect the jaws, causing bone destruction and loosening of teeth. Lesions occurring in children are more extensive and aggressive.

Langerhans cells [P. Langerhans (1847–88), German physician and anatomist] 1. The cells of the *pancreas that produce insulin. 2. Antigen-presenting dendritic cells (*macrophages) found in epithelium and epidermis.

laniary adj. Tearing or lacerating; of or relating to a pointed conical tooth such as a canine.

Larsen syndrome [L. J. Larsen (1914–), American orthopaedic surgeon] A rare autosomal dominant genetic condition characterized by cleft palate, flattened nasal bridge and facial features, prominent forehead, multiple congenital dislocations, and deformities of the hands and feet.

laryngopharynx (hypopharynx) n. The third part of the pharynx extending from the oropharyngeal isthmus and the hyoid bone to the lower border of the cricoid cartilage.

laryngoscope n. An instrument consisting of a handle, curved blade, and a light used to examine the upper respiratory tract and the larynx or to aid the insertion of a tube into the trachea (endotracheal tube).

laryngospasm n. Spasmodic contraction of the larynx. It sometimes occurs during the induction phase of general anaesthesia.

larynx n. (adj. laryngeal) A cartilaginous organ located above the *trachea and below the *oropharynx. It serves as part of the air passage from the pharynx to the lungs and as a *sphincter preventing food from entering the airway; it has a pair of vocal folds responsible for voice production (*phonation).

laser n. A device which produces a high-energy light source. The word laser is an acronym for ‘light amplification by stimulated emission of radiation’. Lasers are used for surgery because of the ability to use them in small areas without causing damage to surrounding structures. Argon lasers emit a blue-green light and are used for polymerizing resin composite. Carbon dioxide (CO2) lasers use carbon dioxide gas, which is readily absorbed by soft tissues because of the high cellular water content, causing surface cell vaporization to a depth of about 0.1mm. They operate at a wave band of 10600nm. Because the beam from a CO2 laser is invisible, a second laser beam, based on the elements helium and neon, adds a visible red beam, so that the laser beam can be accurately focused. CO2 lasers are used for gingival surgery, *fraenectomy, *biopsies, and the removal of benign or malignant soft tissue lesions. Erbium:yttrium aluminium-garnet (erbium: YAG) lasers have also been used for periapical surgery and the removal of hard tissue such as tooth enamel and dentine as an alternative method of cavity preparation, but access can be difficult and the cutting speed is slow; excessive heat generation can cause pulpal damage. Neodymium:YAG lasers penetrate more deeply than CO2 lasers and utilize a jet of cool water or air to minimize possible heat damage; they operate at a wave band of 1064nm; these lasers may be used for soft tissue surgery but they can cause excessive damage to thin tissues. Holmium:yttrium aluminium-garnet (holmium: YAG) lasers have been used experimentally for the removal of the cartilaginous disc in the *temporomandibular joint.

Further Reading Sulieman M.An overview of the use of lasers in general dental practice: 2. Laser wavelengths, soft and hard tissue clinical applications. Dent Update 2005;32(5):286–8, 291–4, 296.

latent adj. Describing a condition that is present but not yet active or causing symptoms.

latent period 1. The very short interval between the time that a nerve impulse reaches a muscle fibre and the time the fibre starts to contract. 2. An alternative description for *incubation period.

lateral adj. Situated or occurring at the side of an organ or tissue.

lateral cephalogram An extra-oral radiograph which provides a standardized reproducible image of the lateral skull. It is a widely used diagnostic tool in orthodontics as it allows the antero-posterior and vertical relationships of the teeth, jaws, and soft tissues to be assessed. It is taken using a *cephalostat.

lateral deviation 1. An asymmetry of the face when viewed from the front. 2. A movement of the mandible to one side on opening or during forward thrusting due to a condition of the *temporomandibular joint, *muscles of mastication, or the teeth.

lateral excursion The sideways movement of the mandible from a centric position.

lateral nasal processes n. Soft tissue protrusions formed from the *fronto-nasal process at about 5 weeks of intrauterine life.

lateral oblique radiograph n. See OBLIQUE LATERAL RADIOGRAPH.

lateral repositioned flap (graft) See FLAP.

latero- A prefix denoting at the side of or towards the side.

lateroalveolism n. A condition in which the *alveolar process is shifted laterally on the base of the jaw. Compare MESIOALVEOLISM.

laterogenia n. A condition in which the chin prominence is shifted to one side in relation to the normal mandible.

lateromaxillism n. A condition in which the base of the *maxilla has shifted laterally but is of normal size and width. The most common cause is trauma.

laterotrusion n. The sideways movement of the mandible produced by the *muscles of mastication.

latex n. A milky fluid derived from the rubber tree and used for the manufacture of gloves, tubes, etc.

latex allergy A *hypersensitivity to natural latex characterized by skin irritation and inflammation (*dermatitis), itchy eyes, nasal irritation; in severe cases it can result in *anaphylaxis. Latex products include gloves, *dental dam, prophylactic polishing cups, and the bungs in local anaesthetic cartridges. Latex allergy has become more common and presents a significant hazard in dentistry. See also LATEX DERMATITIS.

latex dermatitis A skin inflammation in response to a *hypersensitivity to latex. Irritant contact dermatitis is a common non-allergic reaction to chemicals present in latex products, especially gloves; this is reduced by the use of powder-free gloves. Allergic contact dermatitis is an allergic reaction to specific proteins present in the natural latex.

Further Reading Vozza I., Ranghi G., Quaranta A. Allergy and desensitization to latex. Clinical study on 50 dentistry subjects. Minerva Stomatol 2005;54(4):237–45.

lathe n. A machine tool with a rotating shaft to which may be attached various cutting instruments, grinding stones, and polishing wheels. It is used for grinding and polishing dental appliances.

lathe-cut amalgam alloy See AMALGAM.

lavage n. Washing out or irrigating a body cavity with water or a medicated solution.

lead apron

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