X-rays, Dental: From 1 Different Sources
See dental X-rays.
Also known as Röntgen rays, these were discovered in 1895 by Wilhelm Conrad Röntgen. Their use for diagnostic imaging (radiology) and for cancer therapy (see RADIOTHERAPY) is now an integral part of medicine. Many other forms of diagnostic imaging have been developed in recent years, sometimes also loosely called ‘radiology’. Similarly the use of chemotherapeutic agents in cancer has led to the term oncology which may be applied to the treatment of cancer by both drugs and X-rays.
The rays are part of the electro-magnetic spectrum; their wavelengths are between 10?9 and 10? 13 metres; in behaviour and energy they are identical to the gamma rays emitted by radioactive isotopes. Diagnostic X-rays are generated in an evacuated tube containing an anode and cathode. Electrons striking the anode cause emission of X-rays of varying energy; the energy is largely dependent on the potential di?erence (kilovoltage) between anode and cathode. The altered tissue penetration at di?erent kilovoltages is used in radiographing di?erent regions, for example in breast radiography (25–40 kV) or chest radiography (120–150 kV). Most diagnostic examinations use kilovoltages between 60 and 120. The energy of X-rays enables them to pass through body tissues unless they make contact with the constituent atoms. Tissue attenuation varies with atomic structure, so that air-containing organs such as the lung o?er little attenuation, while material such as bone, with abundant calcium, will absorb the majority of incident X-rays. This results in an emerging X-ray pattern which corresponds to the structures in the region examined.
Radiography The recording of the resulting images is achieved in several ways, mostly depending on the use of materials which ?uoresce in response to X-rays. CONTRAST X-RAYS Many body organs are not shown by simple X-ray studies. This led to the development of contrast materials which make particular organs or structures wholly or partly opaque to X-rays. Thus, barium-sulphate preparations are largely used for examining the gastrointestinal tract: for example, barium swallow, barium meal, barium follow-through (or enteroclysis) and barium enema. Water-soluble iodine-containing contrast agents that ionise in solution have been developed for a range of other studies.
More recently a series of improved contrast molecules, chie?y non-ionising, has been developed, with fewer side-effects. They can, for example, safely be introduced into the spinal theca for myeloradiculography – contrast X-rays of the spinal cord. Using these agents, it is possible to show many organs and structures mostly by direct introduction, for example via a catheter (see CATHETERS). In urography, however, contrast medium injected intravenously is excreted by the kidneys which are outlined, together with ureters and bladder. A number of other more specialised contrast agents exist: for example, for cholecystography – radiological assessment of the gall-bladder. The use of contrast and the attendant techniques has greatly widened the range of radiology. IMAGE INTENSIFICATION The relative insensitivity of ?uorescent materials when used for observation of moving organs – for example, the oesophagus – has been overcome by the use of image intensi?cation. A faint ?uorographic image produced by X-rays leads to electron emission from a photo-cathode. By applying a high potential di?erence, the electrons are accelerated across an evacuated tube and are focused on to a small ?uorescent screen, giving a bright image. This is viewed by a TV camera and the image shown on a monitor and sometimes recorded on videotape or cine. TOMOGRAPHY X-ray images are two-dimensional representations of three-dimensional objects. Tomography (Greek tomos
– a slice) began with X-ray imaging produced by the linked movement of the X-ray tube and the cassette pivoting about a selected plane in the body: over- and underlying structures are blurred out, giving a more detailed image of a particular plane.
In 1975 Godfrey Houns?eld introduced COMPUTED TOMOGRAPHY (CT). This involves
(i) movement of an X-ray tube around the patient, with a narrow fan beam of X-rays; (ii) the corresponding use of sensitive detectors on the opposite side of the patient; (iii) computer analysis of the detector readings at each point on the rotation, with calculation of relative tissue attenuation at each point in the cross-sectional plant. This invention has enormously increased the ability to discriminate tissue composition, even without the use of contrast.
The tomographic e?ect – imaging of a particular plane – is achieved in many of the newer forms of imaging: ULTRASOUND, magnetic resonance imaging (see MRI) and some forms of nuclear medicine, in particular positron emission tomography (PET SCANNING). An alternative term for the production of images of a given plane is cross-sectional imaging.
While the production of X-ray and other images has been largely the responsibility of radiographers, the interpretation has been principally carried out by specialist doctors called radiologists. In addition they, and interested clinicians, have developed a number of procedures, such as arteriography (see ANGIOGRAPHY), which involve manipulative access for imaging – for example, selective coronary or renal arteriography.
The use of X-rays, ultrasound or computerised tomography to control the direction and position of needles has made possible guided biopsies (see BIOPSY) – for example, of pancreatic, pulmonary or bony lesions – and therapeutic procedures such as drainage of obstructed kidneys (percutaneous nephrostomy), or of abscesses. From these has grown a whole series of therapeutic procedures such as ANGIOPLASTY, STENT insertion and renal-stone track formation. This ?eld of interventional radiology has close a?nities with MINIMALLY INVASIVE SURGERY (MIS).
Radiotherapy, or treatment by X-rays The two chief sources of the ionising radiations used in radiotherapy are the gamma rays of RADIUM and the penetrating X-rays generated by apparatus working at various voltages. For super?cial lesions, energies of around 40 kilovolts are used; but for deep-seated conditions, such as cancer of the internal organs, much higher voltages are required. X-ray machines are now in use which work at two million volts. Even higher voltages are now available through the development of the linear accelerator, which makes use of the frequency magnetron which is the basis of radar. The linear accelerator receives its name from the fact that it accelerates a beam of electrons down a straight tube, 3 metres in length, and in this process a voltage of eight million is attained. The use of these very high voltages has led to the development of a highly specialised technique which has been devised for the treatment of cancer and like diseases.
Protective measures are routinely taken to ensure that the patient’s normal tissue is not damaged during radiotherapy. The operators too have to take special precautions, including limits on the time they can work with the equipment in any one period of time.
The greatest value of radiotherapy is in the treatment of malignant disease. In many patients it can be used for the treatment of malignant growths which are not accessible to surgery, whilst in others it is used in conjunction with surgery and chemotherapy.... x-rays
See TEETH, DISORDERS OF – Caries of the teeth.... decay, dental
Decay of teeth... dental caries
See TEETH, DISORDERS OF.... dental emergencies
Short-wavelength penetrating electromagnetic rays produced by some radioactive compounds. More powerful than X-rays, they are used in certain RADIOTHERAPY treatments and to sterilise some materials.... gamma rays
A statutory body set up by the Dentists Act which maintains a register of dentists (see DENTAL SURGEON), promotes high standards of dental education, and oversees the professional conduct of dentists. Membership comprises elected and appointed dentists and appointed lay members. Like other councils responsible for registering health professionals, the General Dental Council now comes under the umbrella of the new Council for Regulatory Excellence, a statutory body. (See APPENDIX 7: STATUTORY ORGANISATIONS.)... general dental council
See DENTAL SURGEON.... general dental services
See APPENDIX 8: PROFESSIONAL ORGANISATIONS.... british dental association
A person quali?ed to carry out the scaling (removal of calculus [deposits]) from the teeth and to advise patients on how to keep their teeth and gums healthy. Hygienists usually work in a quali?ed dentist’s surgery.... dental hygienist
A dental surgeon, or dentist, is an individual trained to diagnose and treat disorders of the teeth and gums, as well as to advise on preventive measures to ensure that these areas remain healthy. Dentists qualify after a four-year course at dental school and then register with the GENERAL DENTAL COUNCIL, which is responsible for maintaining educational and professional standards. Around 25,000 dentists practise in the NHS and private sector.
Over the past four decades the ?nancial outlay on NHS dental services has been around 5 per cent of total NHS funding. This contrasts with 10 per cent during the service’s early years, when the NHS was coping with decades of ‘dental neglect’. The population’s dental health has, however, been steadily improving: in 1968 more than one-third of people had no natural teeth; by the late 1990s the proportion had fallen to 13 per cent.
Dentistry is divided into several groupings.
General dental practitioners Concerned with primary dental care, the prevention, diagnosis and treatment of diseases of the gums and teeth – for example, caries (see TEETH, DISORDERS OF). They also deal with diffculties in biting and the effects of trauma, and are aware that oral disorders may re?ect disease elsewhere in the body. They will refer to the hospital dental services, patients who require treatment that cannot be satisfactorily carried out in a primary-care setting.
Most routine dental prevention and treatment is carried out in general dental practitioners’ surgeries, where the dentists also supervise the work of hygienists and dental auxiliaries. Appliances, such as dentures, crowns, bridges and orthodontic appliances are constructed by dental technicians working in dental laboratories.
There are around 18,800 dentists providing general dental services in the UK. These practitioners are free to accept or reject any potential patient and to practise where they wish. Those dentists treating patients under an NHS contract (a mixture of capitation fees and items of service payments) can also treat patients privately (for an appropriate fee). Some dentists opt for full-time private practice, and their numbers are increasing in the wake of changes in 1990 in the contracts of NHS general dental practitioners.
Community dental practitioner Part of the public-health team and largely concerned with monitoring dental health and treating the young and the handicapped.
In the hospitals and dental schools are those who are involved in only one of the specialities.
Around 2,800 dentists work in NHS hospitals and 1,900 in the NHS’s community services. In some parts of the UK, people wanting NHS treatment are having diffculties ?nding dentists willing to provide such care.
Restorative dentist Concerned with the repair of teeth damaged by trauma and caries, and the replacement of missing teeth.
Orthodontist Correction of jaws and teeth which are misaligned or irregular. This is done with appliances which may be removable or ?xed to the teeth which are then moved with springs or elastics.... dental surgeon
See: TEETH DECAY, TEETH EXTRACTION, ALOE VERA. DEOBSTRUENT. That which clears obstruction by dilating natural passages of the body. Usually of the intestines (Ispaghula seeds) or colon (Buckbean). ... dental problems
The wearing away of tooth enamel, often accompanied by the erosion of dentine (the layer beneath the enamel) and cementum (the bonelike tissue that covers the tooth root), usually through too-vigorous brushing. Abraded areas are often sensitive to cold or hot food or drink, and a desensitizing toothpaste and/or protection with a bonding (see bonding, dental) agent or filling may be needed.... abrasion, dental
The movement of teeth by using either fixed or removable orthodontic appliances (braces) to correct malocclusion (incorrect bite).... alignment, dental
The bony cavity or socket supporting each tooth in the jaw.... alveolus, dental
A material, consisting of an alloy of mercury with other metals, that is used as fillings for teeth (see filling, dental).... amalgam, dental
See orthodontic appliances.... brace, dental
False teeth that are attached to natural teeth on either side of a gap left by a missing tooth or teeth. (See also denture.)... bridge, dental
The deposition of calcium salts in developing teeth. Primary teeth begin to calcify in a fetus at between 3 and 6 months gestation; calcification of permanent teeth (other than the wisdom teeth) begins between birth and 4 years. Abnormal calcification occurs in amelogenesis imperfecta, an inherited disorder of the enamel (see hypoplasia, enamel), and can also result from the absorption of high levels of fluoride (see fluorosis).... calcification, dental
A hard, crust-like deposit (also known as tartar) found on the crowns and roots of the teeth. Calculus forms when mineral salts in saliva are deposited in existing plaque. Supragingival calculus is a yellowish or white deposit that forms above the gum margin, on the crowns of teeth near the openings of salivary gland ducts. Subgingival calculus forms below the gum margin and is brown or black. Toxins in calculus cause gum inflammation (see gingivitis), which may progress to destruction of the supporting tissues (see periodontitis). Calculus is removed by professional scaling. Attention to oral hygiene reduces recurrence.... calculus, dental
See crown, dental.... capping, dental
A hole in a tooth, commonly caused by dental caries (see caries, dental).... cavity, dental
See overcrowding, dental.... crowding, dental
A protrusion on the grinding surface of a tooth.... cusp, dental
The hard outer layer of a tooth that covers and protects the inner structures.... enamel, dental
The process of replacing a chipped or decayed area of tooth with an inactive material. Dental filling is also used to describe the restorative material itself. Amalgam, a hard-wearing mixture of silver, mercury, and other metals is generally used for back teeth. If a front tooth is chipped, a bonding technique (see bonding, dental) may be used, in which plastic or porcelain tooth-coloured material is attached to the surface of the tooth.... filling, dental
A post, surgically embedded in the jaw for the attachment of a dental prosthesis (an artificial tooth). Titanium or synthetic materials may be used. A dental implant is fitted under local anaesthesia. A hole is drilled in the jaw and a post inserted. Several months later, an attachment that protrudes from the gum is screwed into the post; a few weeks after that, the prosthesis is fitted.... implant, dental
The deposition of calcium crystals and other mineral salts in developing teeth. (See calcification, dental.)... mineralization, dental
The soft tissue containing blood vessels and nerves in the middle of each tooth (see teeth).... pulp, dental
Replacement of a tooth in its socket after an accident so that it can become reattached to supporting tissues. The front teeth are most commonly involved. The tooth needs to be reimplanted soon after the accident and is maintained with a splint (see splinting, dental) while it heals. Healing may take several weeks.... reimplantation, dental
The reconstruction of part of a damaged tooth. Restoration also refers to the material or substitute part used to rebuild the tooth. Small repairs are usually made by filling the tooth. For extensive repairs, a dental inlay or a crown may be used. Chipped front teeth may be repaired by bonding (see bonding, dental).... restoration, dental
Removal of dental calculi (see calcuus, dental) from the teeth to prevent or treat periodontal disease.... scaling, dental
Plastic coatings that are applied to the chewing surfaces of the back teeth to help prevent decay.... sealants, dental
The mechanical joining of several teeth to hold them firmly in place while an injury heals or while periodontal disease is treated.... splinting, dental
See implants, dental.... titanium dental implants
a reclinable chair on which a patient lies for dental treatment. Electric switches change the position of the patient, and the chair is frequently attached to the *dental unit.... dental chair
a fine thread, usually of nylon, used to clean the surfaces between teeth. A thicker version is known as dental tape. It may be waxed to help the user slide it past the tooth contacts.... dental floss
a piece of dental equipment (high-speed or low-speed) for holding a dental *bur or *file. It is made of corrosion-resistant materials to allow sterilization. See drill.... dental handpiece
see implant.... dental implant
either of two nerves that supply the teeth; they are branches of the trigeminal nerve. The inferior dental nerve supplies the lower teeth and for most of its length exists as a single large bundle; thus anaesthesia of it has a widespread effect (see inferior dental block). The superior dental nerve, which supplies the upper teeth, breaks into separate branches at some distance from the teeth and it is possible to anaesthetize these individually with less widespread effect for the patient.... dental nerve
any of several professionals supporting a dentist, formerly referred to as dental auxiliaries and professionals complementary to dentistry. A dental hygienist performs scaling and instruction in oral hygiene. A dental nurse helps the dentist at the chairside by preparing materials, passing instruments, and aspirating fluids from the patient’s mouth. A dental technician constructs dentures, crowns, and orthodontic appliances in the laboratory for the dentist. A clinical dental technician provides dentures directly to patients. A dental therapist performs non-complex treatment under the prescription of a dentist. In the UK dental care professionals are required to be statutorily registered with the General Dental Council (GDC).... dental care professional
see dental care professional.... dental nurse
(DPT) a special form of tomogram (see tomography) that provides a picture of all the teeth of both jaws on one film. Newer equipment can produce three-dimensional images of part of the jaw.... dental pantomogram
a major fixed piece of dental equipment to which are attached the dental drills, aspirator, compressed air syringe, and ultrasonic scaler. It is frequently integral with the *dental chair.... dental unit
(inferior alveolar nerve block) a type of injection to anaesthetize the inferior *dental nerve. Inferior dental block is routinely performed to allow dental procedures to be carried out on the lower teeth on one side of the mouth.... inferior dental block
a bony canal in the *mandible on each side. It carries the inferior *dental nerve and vessels and for part of its length its outline is visible on a radiograph.... inferior dental canal
invisible short-wavelength radiation beyond the violet end of the visible spectrum. Sunlight contains ultraviolet rays, which are responsible for the production of both suntan and – on overexposure – *sunburn. The dust and gases of the earth’s atmosphere absorb most of the ultraviolet radiation in sunlight (see ozone). If this did not happen, the intense ultraviolet radiation from the sun would be lethal to living organisms.... ultraviolet rays
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