Medical knowledge | Dentistry » Paul Abbott - Are dental radiographs safe

C O N T I N U I N G E D U C AT I O N Australian Dental Journal 2000;45:(3):208-213 Are dental radiographs safe? Paul Abbott* Abstract Dental patients are often aware that radiation has the potential to harm them but they do not usually understand how or why and what potential harmful effects may arise from dental radiographs. The potential for undesirable effects must be balanced against the benefits obtained from radiographs. Dentists should address the concerns of patients who question the need for radiographs and allow them to make an informed decision. Data are available that relate radiation exposure levels from medical and dental radiographs to normal background exposure levels and allow comparisons with everyday risks in life. Recognized radiation authorities publish guidelines to help dentists with their use of radiographs, although, due to the time lag associated with testing and the publication of results, some of the published data may not always be entirely relevant to

currently used X-ray machines and techniques. Dentists also have professional obligations not only to limit the use of radiographs to potentially beneficial situations but also to take good quality diagnostic radiographs, to limit the doses used, to use good radiation safety measures and to use modern equipment to achieve the best possible films. Radiographs must then be properly developed and viewed under appropriate conditions to gain the maximum possible diagnostic information from each exposure. Key words: Radiographs, radiation, safety. (Received for publication June 1999. Revised August 1999. Accepted August 1999) History Wilhelm Roentgen accidentally discovered X-rays in 1895 when he produced an unintentional radiograph of his own hand. He called the radiation ‘X’ because of its ‘unknown’ qualities.1 Just two weeks after Roentgen’s announcement about the new ‘Xrays’, Dr Otto Walkhoff produced the first dental radiograph – this was an extra-oral film of a

patient’s jaws and he used an exposure time of 25 minutes. A few months later, in early 1896, Dr C Edmund Kells, a New Orleans dentist, took the first intra-oral radiograph.1 *Endodontist, Senior Fellow, School of Dental Science, The University of Melbourne, Victoria. 208 Early reports of radiation damage Dr Kells was the first person to note problems associated with the use of X-radiation. He reported that long exposures caused a mild skin irritation which was similar to sunburn, although it vanished after a short time. The early X-ray machines needed to be set and adjusted for each use. To do this, the operator would place his hand between the actively radiating tube and the film plate to check the apparatus was working and was focused on the film. After 12 years of taking radiographs in this way, Kells noticed cancerous tumours on his fingers. He subsequently had 35 operations to his fingers, including several amputations, as a result of these tumours. He committed suicide in

1928, aged 721 In the intervening years, other effects of radiation have become evident, with a high occurrence of bone sarcomas in workers using radium luminous paints on watches, lung cancers in uranium miners, skin erythema and leukaemia in radiologists, and leukaemia and other malignancies among the survivors of Hiroshima and Nagasaki.1,2 How does X-radiation damage tissues? X-radiation is a form of energy. The X-rays can pass through matter and disperse this energy. The effect of energy dispersion will depend on the atomic structure of the object and the energy of the beam. Soft tissues are particularly susceptible to radiation damage since they are essentially weak aqueous solutions. Radiation damage to tissue can be classed as either direct or indirect damage.1-2 Direct damage occurs when there is a direct hit of a molecule by a photon or electron. Direct hits are likely to affect the DNA and RNA molecular bonds since their natural bond forces are only a few electron volts

compared to the many thousands of electron volts produced by X-ray photons. Molecules affected in this way are unable to pass on important genetic information which results in mutilation, cell death, carcinoma or genetic abnormalities.2 Heat is also generated which may cause cellular changes which are usually followed by normal physiological healing processes. Australian Dental Journal 2000;45:3. Table 1. Relative tissue ‘radiosensitivity’* Tissue Gonads Breast Bone marrow Lung Thyroid Bone surfaces Remainder Total Relative radiosensitivity† 0.25 0.15 0.12 0.12 0.03 0.03 0.30 1.00 *Adapted from Smith2 and the ICRP.8 †Proportion of risk when the whole body is irradiated uniformly. Indirect damage occurs when electrons hit other atoms in their pathway and cause further ionization and excitation – this creates highly reactive ionized molecules. Oxidation/reduction reactions occur which disrupt enzymes and nucleic acids with consequent damage to cell function and

reproduction.2 The biological effects of radiation can be classified as somatic or genetic.1-2 Somatic effects concern the individual person who has been irradiated and they can be either acute or long-term effects. On the other hand, genetic effects might undesirably influence the progeny of the person who has been irradiated. The actual effects that occur will depend on the tissue ‘radiosensitivity’ which is a function of the tissue’s mitotic activity and varies considerably throughout the body (Table 1). Typical acute effects of radiation are skin erythema, pigmentation and ulceration. Long-term effects include radiationinduced leukaemia, cancer and genetic damage1-2 Some authorities claim that any dose of radiation has the potential to induce malignant changes – even small doses can cause damage to tissues and there is no threshold dose below which radiation is predictably safe.2 Once a malignancy has been induced, the disease will follow its normal course until it is

clinically manifested, which may be many years later. For example, radiation-induced leukaemia takes an average of 12 years to manifest and solid tumours may take more than 20 years.2 Hence, it is difficult if not impossible to show a direct ‘cause and effect’ of a particular exposure to radiation to a particular cancer due to this latent period of onset of symptoms and the high possibility that numerous radiographs have been taken for medical and dental purposes throughout the patient’s life. There are also many other potential causes of malignancies to which people are exposed throughout normal life, such as chemicals, foods and food additives. Hence, not all malignancies are caused by exposure to radiation. Fortunately, the potential effects of radiation from dental X-ray machines are minimal. Whole body effects are unlikely as heat would burn out the X-ray machine before a sufficiently large enough dose Australian Dental Journal 2000;45:3. Table 2. Annual collective doses in

the United Kingdom in 1983* Source Effective % Natural Medical Fallout Occupational Nuclear waste Miscellaneous Total 77.80 20.90 0.41 0.45 0.11 0.34 100.00 *Adapted from Smith.2 could be generated. Partial body effects are possible but also very unlikely for the same reason.2 Sources of radiation There are many possible sources of radiation to which people are exposed every day. Man-made radiation accounts for about 25 per cent of the Annual Collective Dose (ACD) of radiation to which people are exposed, while natural background radiation provides the other 75 per cent of the annual dose.2 Typically, about 33 per cent of the natural background radiation comes from cosmic radiation (for example, the sun, stars, etc) and the other 67 per cent from terrestrial radiation (that is, natural radioactive substances on earth). The amount of natural background radiation is approximately 3µSv per year although the actual amount varies in different locations throughout the world; for

example, countries such as Brazil, India, China, France and Russia have 10-15 times more natural background radiation than Australia. Average figures for the ACD in the UK are shown in Table 2. The dose for the UK is equivalent to approximately 200µSv per year and the theoretically predicted number of malignancies arising from this level of exposure is less than three per year.2 Comparative doses of radiation In order to allow meaningful comparisons between various sources of radiation, the Background Equivalent Radiation Time (BERT) unit has been established. BERT is the number of hours, days, weeks, months or years of exposure to Table 3. Some examples of Background Equivalent Radiation Times (BERT)* Event One transatlantic flight One flight Europe to Australia Chest radiograph Dental panoramic film Intra-oral PA with D speed film and - round collimator - rectangular collimator BERT Effective dose (µSv) 5 days 15 days 4 days 28 hours 37.5 112.5 30.0 7.0 16 hours 8 hours 4.0

2.0 *Adapted from Macdonald3 and the NRPB.10 209 Table 4. Comparative radiation doses of some dental examinations compared with a chest radiograph and their Background Equivalent Radiation Times (BERT)* Investigations† Effective dose (µSv) Equivalent chest films BERT 4 16-20 40-60 7 30 0.13 0.6-08 1.3-20 0.2 1.0 16 hours 3.3 days 6.7-8 days 28 hrs 4 days 1 PA or BW† Endo (4-5 PAs)‡ FMS (10-15 films)‡ Panoramic film Chest *Adapted from the NRPB.10 †PA=periapical film; BW=bitewing film; endo=series of films for endodontic therapy on one tooth; FMS=full mouth survey. ‡Intra-oral films taken at 70kVp with D speed film and a round collimator. natural background radiation that would equate to an adult receiving the same ‘effective dose’ from generated ionising radiation sources such as a dental X-ray machine.3 Some examples of radiation doses expressed as BERT are listed in Table 3. X-ray examination of the chest has been a common procedure in medicine and one

the general public is usually familiar with. Hence, the dose of radiation from a single chest X-ray examination has become a ‘standard’ with which radiation doses from other radiological examinations are compared.4 Comparative radiation doses from a range of dental and medical procedures are shown in Tables 4-6. Risks of radiation There are various methods for calculating and expressing the risks of radiation. However, due to the latent period between the induction of a malignant lesion and its clinical manifestation, it is not possible to determine whether any one particular exposure has initiated some damage.2 Therefore, most of the published figures are estimates that should be considered with caution. Also, with the rapid advances in technology and image receptors, dose reduction is a continuous process; thus published figures are useful guides but they are often outdated before they can be published. Table 5. Comparative radiation doses of various medical examinations and

their Background Equivalent Radiation Times (BERT)* Investigation Chest Skull Dorsal spine Lumbar spine CT exam – brain CT exam – chest Barium study – large bowel *Adapted from Perkins.4 210 Approximate equivalent number of chest films BERT 1 5 50 120 100 400 450 4 days 20 days 6 months 14 months 1 year 4 years 4.5 years Table 6. Relative exposures and radiation doses Highest Medical Lowest Radiotherapy treatment for carcinomas CT scans: chest > abdomen > pelvis > spine > brain Radiography: IV urogram > barium studies > spine > abdomen > pelvis > skull > chest > knee Dental Panoramic film Intra-oral periapical and bitewing films The risk of induction of fatal cancer or serious hereditary ill-health from radiation has been calculated to be 1 in 80 per Sv.2 This equates to an estimated risk from dental panoramic tomography of about one in a million (10-6) per film while the estimated risk from intra-oral radiography is about 1 in 10 million

(10-7) per exposure for intra-oral films such as periapical and bitewing radiographs.2 However, the risk-estimates depend on the shape and length of the collimator, or position-indicating device, as reported by Cederberg et al.5 They showed that long and short rectangular cones (23.3 and 35.3cm, respectively) have the lowest probability for stochastic effects (1 in 4.610-6), followed by long round cones (1 in 1610-6), short round cones (1 in 2310-6) and pointed cones (1 in 2610-6). All of these cones were open-ended except the short pointed cone which was closed.5 Danforth and Torabinejad6 estimated the risks of inducing various forms of carcinomas from endodontic radiography and compared them with other ‘everyday’ risks (Table 7). These figures can be compared with other ‘one in a million risks’7 (Table 8) and they can be used to reassure patients that the risk, although present, is extremely low and it is being consistently reduced by new technology. The estimates used by

Danforth and Torabinejad are based on an ‘endodontic survey’ which they defined as being eight periapical films.6 However, many practitioners would typically take less than this number of radiographs. An analysis of the author’s practice records over 16 years indicates an average of between four and five films per tooth are taken during the course of endodontic treatment. Danforth and Torabinejad’s report did not specify what type of cone was used but they did compare films taken with 70kVp and 90kVp machines. The results indicated that the use of 70kVp machines reduced the risks slightly.6 A further example from Danforth and Torabinejad’s study6 concerned radiation exposure to the eyes. The mean dose to the eye from one endodontic survey was calculated to be 182.75µSv The threshold dose to induce cataracts is 2 million µSv, so the number of ‘endodontic surveys’ of eight films per survey to equal this threshold is 10,900, Australian Dental Journal 2000;45:3. Table

7. Estimated radiation risks associated with taking eight periapical films during endodontic therapy with a 70kVp X-ray machine and D speed films* Tissue site X-ray dose (µSv) Risk of neoplasia† No of cigarettes‡ Km driven§ 56.3 122.6 938.0 1 in 909 million 1 in 833 000 1 in 1.43 million 0.8 8.7 5.1 3 34 20 Bone marrow Thyroid gland Salivary gland *Adapted from Danforth and Torabinejad.6 †The estimated risk of inducing neoplasia from the radiation dose received from the eight exposures. ‡The number of cigarettes that need to be smoked to have the same risk of dying from smoking-induced cancer. §The number of kilometres that need to be driven to have the same risk of dying in a car accident. which is 87,200 periapical films – an unlikely number of films to be taken on one patient! While the above figures indicate the risks are very low for each film exposed, it is important to consider that the effects of radiation may also be cumulative. Therefore, practitioners

should carefully consider the need and the potential benefits as well as the potential harm for every film proposed. The number of previous radiographs (both medical and dental) should not be ignored and patients’ concerns should be carefully considered and discussed with them. Radiation protection Dentists must be aware of, and use, safe practices for radiation procedures at all times. The International Commission on Radiological Protection (ICRP) has published guidelines8 for radiation protection since 1928. These guidelines have been updated from time to time and they concern protection for patients as well as protection for operators of radiation generating equipment. In Australia, in 1987, the National Health and Medical Research Council (NHMRC) published a booklet entitled Code of Practice for Radiation Protection in Dentistry.9 Although now somewhat out of date, this booklet provides guidelines for all aspects of dental radiography, including exposure levels, radiographic

techniques, processing techniques and interpretation of films. Without due care, due to their increased exposure to radiation at work, both dentists and their staff are at risk of developing radiation-induced diseases.This is in addition to any radiation they receive from Table 8. One in a million risks in everyday activities* Situation Cigarette (cancer) Living as a man (dying) Living in New York (pollution) Canoe accident Bike accident Car accident Commercial plane accident Plane travel (cosmic radiation) *Adapted from Pochin.7 Australian Dental Journal 2000;45:3. Quantity 1 20 minutes 2 days 6 minutes 16km 500km 1600km 9600km natural background and man-made sources during their leisure time. Any exposure at work has no therapeutic benefit and needs to be kept to an absolute minimum at all times.2 Reducing the risks of X-radiation All dentists have a professional responsibility to their patients, staff and themselves to minimize any risks which might be associated with radiation.

In order to reduce the risk of radiation damage to patients, practitioners should follow the ALARA (as low as reasonably achievable) principles.1-2,9 This applies to all aspects of radiography including when to take films, how many films should be taken, what dose to use, which techniques, etc. The ‘risk:benefit ratio’ should be considered and justified for each and every film taken.1 A lead apron with at least 0.25mm thickness of lead has been recommended2,9 although recently there has been some debate about the merits of such devices.3,10 Lead aprons help to reduce the amount of primary radiation reaching areas of the body that are in the direct pathway of the primary beam.10 However, it is now considered that they may instead potentiate the effect of scatter radiation that gets under the apron since the scatter beams become trapped between the apron and the body and are then reflected back toward the tissues they are supposed to protect.3,10 Since the risk of malignancy from the

primary beam during dental intra-oral radiography is one in 10 million and the extra risk from scatter radiation (without an apron) is much less, perhaps in the order of one in 100 million,2 and since only a small percentage of the primary beam is scattered with modern machines,3,10 the value of lead aprons is therefore questionable. However, lead aprons do provide some psychological security for patients who believe they are helping to protect their distant organs and they are recommended for pregnant women for a number of reasons (see below).9 Interestingly, a survey of Australian dentists in 1988 revealed that lead aprons were ‘always used’ by only 66 per cent of the respondents, while 22 per cent said they ‘occasionally used’ them and 22 per cent said they ‘never used’ a protective apron for their patients.11 211 Further protection can be achieved with good radiographic and processing techniques and with quality control to ensure films are taken and processed to

provide high quality and diagnostically useful information. However, unfortunately, the general standard in dental practices may not be ideal, as demonstrated by the results of the survey by Monsour et al.12 This study revealed that many radiographs need to be re-taken for reasons related to poor technique and radiation practices; 34.2 per cent were re-taken because of processing problems, 28.3 per cent due to incorrect techniques, 34 per cent due to exposure problems and 1.2 per cent of films had been lost from the patient’s record file. Some films were re-taken as an aid to diagnosis (7.2 per cent) and some showed insufficient information (2.7 per cent) for diagnosis A recent survey of radiographs sent to the author by dentists who had referred patients for endodontic treatment supports these findings, as 65 per cent of the films supplied were considered to be inadequate for diagnostic purposes and 89 per cent had not been processed adequately. The use of the parallel technique

with film holders will help to improve the diagnostic quality13 and the reproducibility of radiographs.14 This will consequently reduce the number of films required and the amount of radiation exposure to patients.1-2 However, despite the published recommendations of experts in dental radiography contained in textbooks and journals,13-14 the use of film holders is not common; in Australia, only 25 per cent of dentists ‘routinely used’ a device and 40 per cent ‘occasionally used’ one in the 1988 survey.11 Fortunately, the practice of the dentist holding a film in the patient’s mouth was not common; 60 per cent of Australian dentists never do this but 25 per cent will do so less than once every month and 1.5 per cent might do so more than 10 times a month.11 Good surgery design, with large rooms and appropriate wall thickness, and materials will help protect dental staff. Staff should be at least 2m away from the X-ray machine and the room should be designed so the X-ray beam

is never pointed toward the exit door where staff are sheltering.9 The workload should be monitored, although it is unlikely that dentists would reach the threshold level at which this becomes dangerous. Monsour et al11 reported that the average number of radiographs taken each week by Australian dentists is 22.1±145 intra-oral films and 6.2±78 extra-oral films, whereas the threshold level at which X-radiation may become harmful to an operator has been calculated as 360 dental exposures per week for 0.5 second each2 Well-maintained, modern equipment is essential for diagnostically acceptable radiographs and for radiation safety. Machines that are more than 10 212 years old may need maintenance, upgrading or even replacement. All aspects of every machine – including the filtration, beam size, timer, etc – should be checked regularly to ensure proper functioning.15 High-speed film should be preferred to lower speed films12 although it is recognized that the diagnostic quality of

the image might be compromised. Accurate processing techniques are also essential so that diagnostic-quality films are produced which can then be stored as a permanent part of the patient’s record.9 Another issue of patient and staff safety is crosscontamination. All films should be placed inside a plastic protective barrier while in a patient’s mouth. The barrier packet can then be opened and the film transferred to a dental assistant for processing without the assistant touching the contaminated packet. Intra-oral radiographic films can now be purchased with such barrier packets already applied or the packets can be purchased separately and applied individually to each film before use. X-radiation during pregnancy The most sensitive time for radiation effects to a foetus is between the 32nd and 37th day (approximately 4¹⁄₂-5¹⁄₂ weeks) of gestation, since this is the time for organogenesis.2 The general consensus of opinion is that more than 10µSv of radiation is

required for a significant risk to occur. Furthermore, the developing foetus must be in the direct pathway of this radiation.2 Both of these requirements are unlikely to occur during dental radiography and hence dental radiographs should not be contra-indicated if there is a potential benefit to be gained.2,9 However, practitioners should consider that if a congenital defect does occur, then people naturally try to blame someone or something and they may relate it to dental radiographs. It is also worth considering that very few women are aware they are pregnant within the first eight weeks of pregnancy. Therefore, it is important to take all possible precautions to minimize the risks, including the use of a lead apron2,9 (for radiation protection, for medico-legal protection and for psychological reasons). Section 6.24 of the NHMRC’s Code of Practice for Radiation Protection in Dentistry9 states ‘. dental radiography can be undertaken with negligible dose to the foetus at any

time during pregnancy if proper collimation is used and the equipment is properly shielded. There is no need on radiation grounds to defer dental radiography during pregnancy.’ Despite these very clear recommendations, Australian dentists still appear to be reluctant to take radiographs during pregnancy. Monsour et al found dentists’ attitudes vary in each state of Australia11 which may be a reflection of recommendations made Australian Dental Journal 2000;45:3. during dental school training. Overall, only 2 per cent of the dentists surveyed would routinely take radiographs during pregnancy. In an emergency situation, 52-64 per cent would take a radiograph but 36-46 per cent stated they would never take a radiograph of a pregnant woman.11 The future It is difficult to predict radiation practices but it is likely to involve the use of faster films to reduce exposure times and further development of electronically controlled timers to produce an optimum dose. Computers and

digital imaging technology are also being rapidly developed. Early forms of these devices for intra-oral radiography had limitations with respect to the sensor size and image clarity but many of these problems are gradually being overcome. The major advantage of digital imaging technology is the claimed reduction in exposure to radiation which may be as much as 80 per cent. However, the level of reduction in exposure is often overridden by the need to take more than one image to gain the same amount of diagnostic information as conventional films. The ability to enhance images (by altering the contrast, colour, etc) may also increase the diagnostic usefulness of the image generated. However, the cost and equipment needs are high and further development is still required. Manufacturers also need to develop software safeguards to ensure that images cannot be altered in such a way that the original information is lost or changed permanently16 since the ability to alter images could lead

to abuse of this technology which has many possible legal and ethical consequences. Then, even with new technology, there is still an absolutely essential need for good, predictable, accurate and safe techniques. This will ensure patients and staff are not unnecessarily harmed and useful diagnostic information is obtained, since new technology will not compensate for poor techniques. Summary Exposure to any form of radiation can be dangerous to health and this includes exposure to X-radiation. It is important to remember that any dose of radiation has the potential to induce malignant changes. Even small doses might cause damage to tissues and the current thought is there is no threshold dose below which radiation is totally and predictably safe. Some of the effects from radiation are cumulative throughout life and therefore every possible effort should be made to reduce these risks. Fortunately the relative risks associated with dental radiography are quite low – the risk of

induction of fatal cancer or serious hereditary illhealth has been theoretically calculated as Australian Dental Journal 2000;45:3. approximately one in 10 million for each intra-oral periapical or bitewing film. Extra-oral panoramic films have a suggested risk of one in a million. However, dentists should not be complacent about these risks and they have a professional responsibility to use radiography appropriately in their practices and to maintain good, safe radiation procedures at all times. Acknowledgement The assistance of Dr Ross Macdonald of Adelaide in providing some of the information is gratefully acknowledged. References 1. Goaz PW, White SC Oral radiology – Principles and interpretation. St Louis: CV Mosby, 1982:3-78 2. Smith NJD Dental radiography 2nd edn Oxford: Blackwell Scientific Publications, 1988:1-53. 3. Macdonald R Have you met BERT? ADA(SA) Newsletter 1997;10(9):8-9. 4. Perkins AC Nuclear medicine: Science and safety Montrouge: John Libbey, 1995. 5. Cederberg

RA, Frederiksen NL, Benson BW, Sokolowski TW Effect of the geometry of the intraoral position-indicating device on effective dose. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;84:101-109. 6. Danforth RA, Torabinejad M Estimated radiation risks associated with endodontic radiography. Endod Dent Traumatol 1990;6:21-25. 7. Pochin EE Nuclear radiation: Risks and benefits Oxford: Oxford University Press, 1985. 8. International Commission on Radiological Protection Recommendations of the ICRP. Publication 26 Oxford: Pergamon Press, 1977. 9. National Health and Medical Research Council Code of practice for radiation protection in dentistry. Canberra: Australian Government Publishing Service, 1987. 10. National Radiological Protection Board Guidelines on radiology standards for primary dental care. London: National Radiological Protection Board, 1994;5:No. 3 11. Monsour PA, Kruger BJ, Barnes A, Sainsbury A Measures taken to reduce X-ray exposure of the patient, operator, and staff.

Aust Dent J 1988;33:181-192. 12. Monsour PA, Kruger BJ, Barnes A, Gordon Macleod A A survey of dental radiography. Aust Dent J 1988;33:9-13 13. Bhakdinaronk A, Manson-Hing LR Effect of radiographic technique upon prediction of tooth length in intraoral radiography. Oral Surg Oral Med Oral Pathol 1981;51:100-107 14. Andreasen JO, Paulsen HU,Yu Z, Ahlquist R A long-term study of 370 autotransplanted premolars: Part 1. Surgical procedures and standardized techniques for monitoring healing. Eur J Orthod 1990;12:3-13. 15. Monsour PA, Kruger BJ, Barnes A X-ray equipment used by general dental practitioners in Australia. Aust Dent J 1988;33:81-86. 16. Bruder GA, Casale J, Goren A, Friedman S Alteration of computer dental radiography images J Endod 1999;25:275-276 Address for correspondence/reprints: Dr Paul Abbott, 5 Westley Avenue, Ivanhoe, Victoria 3079. 213