7

Radiography

Besides a clinical examination, projection dental radiography is the most frequently used diagnostic tool in dentistry. Its uses range from detecting caries to more elaborate findings such as gross pathologies of the jaws. Cone beam computed tomography (CBCT, discussed in Chapter 8), is the latest radiology tool, offering enhanced and sophisticated visualisation of dentomaxillofacial anatomy.

X-Ray Tube

The production of X-rays has changed very little since they were discovered by Röntgen in 1895. X-rays are produced when electrons are accelerated to strike a metal target. A contemporary dental X-ray tube for producing radiation is housed in a casing and has an appropriate sized collimator to restrict the emitted beam. The typical setting for intra-oral dental radiography is 60 kVp, 7 mA, with varying distance of 15–32 cm. The exposure time is selected according to tooth, age and the physical build of the individual.

Radiation Safety and Precautions

X-rays are part of the electromagnetic spectrum classified as ionising radiation, which are potentially hazardous for living organisms, causing irreversible ailments such as cancer, sterilisation and gene mutation. The aims of radiation safety are:

• Justification for its use, i.e. risks vs benefit;
• Optimisation of protection using the lowest possible dosage, e.g. for a periapical exposure the limit is 2.3 mGy;
• Limitation of exposure by conforming to recommended limits as specified by law. In the UK, Ionising Radiation Medical Exposure Regulations 2000 guidelines must be observed for all types of radiographic examination.

Radiation protection is for the operator, patient, ambient environment and third parties (other patients and staff members in the practice). Precautions include regular equipment testing and maintenance,

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