- What is a typical dose from a dental radiological procedure?
- Can I take measures to promote a good radiation protection practice in dentistry?
- What are the most important features of intraoral examinations that contribute to dose
reduction?
- What are the most important features of panoramic and cephalometric dental equipment that
contribute to dose reduction?
- How does a digital image receptor affect patient dose in dental radiology?
- Should patients and carers wear lead apron and personal protective devices during a dental
radiographic procedure?
- What are the recommendations and safety measures for children undergoing dental
radiography
Mean values from various national surveys are in the following ranges: i) 1-8 mGy in terms of entrance surface air
kerma for intraoral radiography; ii) 3-7 mGyΦΌcm2 in terms of kerma-area product for
panoramic radiography; and iii) 1-7 mGy in terms of entrance surface air kerma for cephalometric radiography [UNSCEAR 2000] . Effective doses are: i) intraoral dental X ray imaging procedure 1–8 μSv; ii) panoramic
examination 4-30 μSv; and iii) cephalometric examinations 2-3 μSv. Thus the doses from intraoral and
cephalometric dental radiological procedures are lower, usually less than one day of natural background radiation.
Doses for panoramic procedures are more variable, but even at the high end of the range are equivalent to a few days of
natural background radiation which is similar to that of a chest radiograph [EC-RP 136].
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The short answer is YES. Avoiding unnecessary dental X ray procedures is the most effective way to reduce dose in
dental radiology. There must be a clear clinical benefit to each patient undergoing an X ray procedure. Routine dental
X ray examination for all patients is not justified. For more details on referral criteria please see [EC-RP 136]. In addition, the patient dose for each X ray examination should be optimized so that it is As
Low As Reasonably Achievable (ALARA) and consistent with producing the required image quality. It is important that the
equipment is subject to formal acceptance testing, routine quality control, undergoes proper maintenance, and has all
standard dose reduction features.
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Many actions can be taken, such as:
- Rectangular collimation which approximates the size and shape of the receptor reduces dose significantly in
comparison to circular collimation; a dose reduction exceeding 60 % can be achieved in dental radiology by using
rectangular collimation.
- The fastest available film consistent with achieving satisfactory diagnostic results should be used. E-speed and
F-speed films reduce dose more than 50% compared with D-speed films.
- Digital detectors have the potential for further dose reduction, even compared with F-speed film, provided the
repeat rate and use of higher exposure factors than necessary are controlled.
- Using tube voltage in the range 60 to 70kV.
- The X ray tube filtration should be sufficient to reduce entrance skin dose to the patient consistent with
producing satisfactory image quality.
- A position indication device which ensures a minimum focus-to-skin distance of 20 cm should be attached to the tube
head (eg. by use of a long collimator/cone as opposed to a short conical one).
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These features are:
- Only the fastest screen-film combinations (at least 400) that are compatible with imaging requirements should be
used for panoramic and cephalometric imaging.
- The X ray beam for cephalometric imaging should be collimated to the area of clinical interest.
- The inclusion of wedge filters in cephalometric equipment reduces exposure to the soft-tissue facial profile and
allows optimal imaging, while the provision of asymmetric collimation allows the exposed area to be confined to the
area of clinical interest.
- Modern panoramic systems also allow the field to be limited to the area of clinical interest, thereby offering a
significant potential for dose reduction. If available, limitation of field size to the area required for diagnosis
should be used for panoramic radiography.
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- Two types of digital system are used in intraoral, panoramic and cephalometric imaging. One involves imaging
sensors based on charge-couple devices (CCD) and another uses photo-stimulable storage phosphor (PSP) plates.
- Radiographic technique for digital imaging should be adjusted for the minimum patient doses required to provide the
required image quality for each examination type.
- Intraoral digital radiography offers a potential for significant dose reduction; some studies report that,
depending on the diagnostic task, a lower exposure may be used when density and contrast is adjusted using the software
features [EC-RP 136]. This is one of the benefits of digital radiography where image quality
can be optimised after the image has been taken.
- Although digital radiography offers possibility of significant dose reduction, it can, in practice, lead to
increased patient dose. This can arise from, for example: using an image quality higher than is necessary; use of
unduly long exposure times; retakes by staff (e.g. due to bad positioning) that may go undetected; and lack of concern
for collimation. Furthermore, due to smaller sensor size, more than one exposure may be required to cover the
anatomical area imaged using a single conventional film.
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With well designed and optimised equipment and procedures there is no need for routine use of lead aprons for the
patient in dental radiology. Lead aprons may provide some protection in the case of the vertex occlusal examination,
and may be prudent in the case of vertex occlusal examinations in a patient who is, or may be, pregnant. On the
other hand, the use of a lead apron may reassure patients that every effort is being made to ensure their safety, and
may reduce the amount of time that needs to be taken to reassure them. Certainly a lead apron should be provided
for any patient who requests one. It may also be advisable to consider using them on a cautionary basis where
equipment and/or technique have not been verified by a radiation protection specialist, and where they will not
otherwise interfere with the examination. Thyroid collars should be used in the few examinations where the
thyroid may be in the main beam.
Lead aprons should be provided for a person who is required to support a patient during the radiographic procedure
(i.e., a comforter or carer). Assisting adults should be positioned so that all parts of their body are out of the main
beam.
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Many actions are similar to those recommended in adult procedures. Please refer to Qn. 4 and
Qn. 5 for details ».
Although radiation exposure arising from dental radiology is low, a child may undergo many repeated procedures
during childhood and adolescence. Therefore, the accumulated effect of the radiation exposure should be taken into
consideration. The salivary and the thyroid glands are among the organs at risk in dental radiology. The
salivaries are often within the primary beam, while the thyroid receives dose mainly due to scattered radiation [LOOE,
H.K., et al., Radiation exposure to children in intraoral dental radiology, Rad. Prot. Dosim. 121 (2006)
461-465]. Since the thyroid is one of the most radiosensitive organs in children, it may be necessary to consider
shielding it from time to time; useful guidance in this regard is available in [EC-RP 136].
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References
- UNITED
NATIONS Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation, UNSCEAR
Report Volume 1, United Nations, New York (2000).
- EUROPEAN COMMISSION, European
Guidelines on Radiation Protection in Dental Radiology, RP 136, Luxembourg (2004).
