14: Dental Imaging

CHAPTER 14 Dental Imaging

Radiation hazards

X-rays are a type of ionising radiation. Thus, while radiography can be essential for diagnosis and treatment planning, it involves exposure of patients and, potentially, staff to ionising radiation. The problem with ionising radiation is that it can damage DNA, causing mutations that may possibly lead to cancer. Ionising radiations, particularly X-rays, are also a potential hazard to body organs and tissues where cells are proliferating rapidly (e.g. in the fetus or a young child, or in the gonads and bone marrow). Here ionising radiation has the capacity not only to induce malignant tumours (this is called an oncogenic effect) but also to damage reproductive tissues (teratogenic effect).

Therefore, since there is always a slight risk from excessive exposure to radiation, the benefit of it must always outweigh the risk to the patient. These advantages and disadvantages must be discussed with the patient and the patient must give informed consent. Women should always inform their clinician if there is any possibility that they are pregnant. Exposure to ionising radiation in pregnant women must be kept to the absolute minimum and X-rays taken only when absolutely essential: benefit must well exceed any possible harm.

We are all constantly exposed to normal background ionising radiation arising from the earth (especially in areas where the rocks emit radon gas – in UK this is mainly in mountainous areas). People are also exposed to radiation when travelling by air. So diagnostic X-rays produce radiation in addition to this background radiation. As such the dose of X-rays that a person receives while undergoing basic dental radiography (intra-oral X-rays and panoramic radiography) is quite low, probably equivalent to only a few days of background radiation. However, it might still increase the risk of salivary gland and thyroid tumours. Having a CT scan means much higher exposures.

In the past, ionising radiation was also a serious occupational hazard to radiographers and clinical dental staff. Some clinicians even developed radiation-induced dermatitis or cancer of their hands from holding X-ray films in the patients’ mouths during radiography. Having one’s hand in the X-ray beam gives about 4000 times the exposure compared with that received 2 m away from the X-ray tube (the recommended ‘safe’ distance). Therefore this practice is illegal now, and there have been tremendous improvements in technology and techniques resulting in greater ionising radiation safety. Specific precautions to take in dental radiography are discussed later in this chapter.

Types of dental radiograph

Dental radiographs are taken to aid:

Dental radiographs can be taken with the film held within the mouth (intra-orally) or extra-orally – when the film is outside the mouth.

Intra-oral Radiographs

For these radiographs, the X-ray films commonly used are called the periapical, bitewing and occlusal films (Figure 14.1), all of which are small enough to be partially inserted into the mouth. Intra-oral radiographs are taken to detect dental pathology including small carious lesions. They can be useful in the diagnosis of:

Extra-oral Radiographs

Extra-oral radiography means using large films to visualise the skull, jaws, temporomandibular joints and sinuses. These films are used with intensifying screens in a cassette (Figure 14.1).

Examples of the use of intra- and extra-oral radiographs in dentistry are given in Table 14.1.

TABLE 14.1 Examples of the More Common Dental Radiographs and Their Main Uses

Area to be Examined Radiographic Film Used Often Used for
Whole of the mandible and the maxilla DPT (dental panoramic tomograph; Figure 14.2) Presence and position of teeth; jaw fractures
A single tooth or three to four teeth plus the supporting bone Periapical film (Figure 14.3): size varies from 35 × 22 mm to 40.5 × 30.5 mm Assessing the periapical area, for root canal treatment and to assess root fractures
Molar/premolar region Bitewing (horizontal) (Figure 14.4): size varies from 35 × 22 mm to 54 × 27 mm Caries detection interproximally
Bitewing (vertical) Periodontitis
Maxillary incisor/canine region Anterior occlusal (Figure 14.5): size is about 57 × 76 mm Impacted canines; super- numerary teeth; palatal cysts; salivary duct stones
Third molars Oblique lateral, or DPT, or periapical Inspecting unerupted or impacted third molars
Sinuses DPT or occipito-mental radiograph Sinusitis, root in sinus

Other types of imaging used in dentistry

Processing radiographs

Digital X-rays need no processing (see below). Otherwise, the radiographic film has several components apart from the actual celluloid film coated with emulsion (Table 14.2).

TABLE 14.2 Components of Radiographic Film, their Function and Disposal

Intra-oral X-ray Film Packet Component Function Dispose into Waste Marked
Plastic envelope Protects the film from moisture and light Clinical
Black paper Protects the film from light Domestic
Celluloid film Produces the radiograph Domestic
Lead foil Prevents radiation that has not been absorbed by the film passing on into the patient Special

X-ray processing can be automated or manual. X-ray film processing takes place in the dark, using an automated processor, or a locked darkroom with light for illumination compatible with the red or orange filter. The solutions must be at normal room temperature (18–22 °C)

The manual steps are as follows:

Faults in Radiograph Exposure and/or Processing

Faults in radiograph exposure and/or processing are shown in Table 14.3 and the accompanying figures.

TABLE 14.3 Radiographic Film Faults

Film Appears Reasons Comments
Faint or blank Under-developed, under-exposed, not fixed Low temperature; wrong developing time; wrong strength of developer. See Figure 14.6A
Dark Over-developed or over-exposed High temperature; wrong developing time; wrong strength of developer. See Figure 14.6B
Foggy Exposed to light before developing or old film  
Fading Under-fixed  
Black />

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Jan 8, 2015 | Posted by in Dental Nursing and Assisting | Comments Off on 14: Dental Imaging
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