Dental X-Ray: An Improving Technology for Patients
Modern patients are so familiar with x-ray technologies that it is hard to believe that, as little as a hundred and twenty years ago, such technologies did not exist.
The man who became known as the Father of Diagnostic Radiation was Wilhelm Roentgen. Roentgen was not a doctor or dentist, nor was he involved in the work of medical technology. He was an academic physicist, and his 1895 discovery of the x-ray was accidental. The scientist was experimenting with the properties of gases using a cathode tube that he had intentionally covered so that it was opaque to the passage of light. During the experiment, he was surprised to observe luminescence, excited by the activity in the cathode tube, on a nearby chemically coated cardboard screen. In further observations, Roentgen realized that objects interposed between the plate and the cathode tube cast shadow images on the screen. These were images produced by an unknown emission which travelled where light could not, passing through materials, including human flesh and bone, with varying ease. By substituting a film plate for the original screen, Roentgen was able to produce the first picture x-ray. He developed a photograph of his wife’s left hand that showed the bone structure of that hand complete with wedding ring. Though Roentgen called his discovery the x-ray, it was also called the Roentgen Ray, and this name is still used for the x-ray in some of the world’s languages today.
Roentgen’s announcement of his discovery produced a huge sensation. Many people wanted to gain the eerie access that x-ray provided to the living skeleton. Theatrical shows featured live x-rays; photographers offered x-ray portraits; and, for a few cents, a patron to an exhibition could see through a door or count the number of coins in a closed purse. A host of privacy concerns were also raised at the same time. People became fearful of being viewed through their clothing, and some writers suggested that both research and researcher should be thrown out.
However, the medical community was quick to see the practical value of Roentgen’s academic work. Only one year after x-ray’s discovery, the Glasgow Royal Infirmary opened an x-ray department for its patients. X-ray technology was immediately used in obtaining information about bone fractures, about tumours and other physical abnormalities, and about foreign objects in the body. An obvious application was the location of bullets in the bodies of wounded soldiers, and the British military began using x-rays for this purpose in the second Boer War of 1899 – 1902.
Predictably, some of the earliest x-rays taken were taken by dentists. Two weeks after Roentgen’s publication of his findings, a German dentist, Otto Walkhoff, took intraoral x-rays of his own teeth while lying on his back with a glass receptor in his mouth. Other German and international dentists also experimented with dental applications. Dr. Frank D. Price, an instructor at the Canadian Royal College of Dental Surgeons, built the first dental x-ray machine in Canada in 1896, a year after Roentgen’s announcement of his x-ray discovery. By 1916, many dentists were using x-rays in practise though x-ray machines were not standardized or reliable.
X-rays, themselves, were painless, but the possibility that they might be damaging was known from the start. Roentgen had discovered that x-rays did not pass through lead and routinely shielded his own body when working with the rays. The Canadian dentist Frank D. Price produced aprons containing lead salts for protection of patients during x-ray procedures. As early as 1896, other experimenters noted the deleterious effects of x-rays in burned skin and hair loss. Even these destructive effects, however, could be seen to have a positive side. By the early 1900’s, x-ray use included treatment of skin diseases, including skin cancers.
Prior to the second half of the twentieth century, the dangers of x-ray were minimized in the public awareness. In 1920, in fact, an x-ray, shoe-fitting machine was introduced. It offered shoppers the chance to see the bones of their feet inside the shoes they proposed to purchase. The machine proved very popular in the 1930’s, 1940’s, and 1950’s in Britain, the United States, and Canada. As late as 1970, such machines persisted in parts of Canada and Britain with few questions arising, apparently, as to their safety.
The radiation released by the atomic bomb, however, did create a new public consciousness as to the effects of ionizing radiation on human health, and, especially after the Second World War, concerns have been increasingly expressed as to the need to curb such radiation in our lives. Since x-rays are a type of ionizing radiation, there has been increased consciousness of their use also.
More recently, dental x-rays have become a focus for safety concerns. Children are especially vulnerable to any kind of early physical damage, and many children have dental x-rays repeatedly throughout the childhood years. Additionally, most patients continue to have dental x-rays regularly during their adult lives. It is also true that, for many healthy people, dental x-rays represent their only exposure to medical radiography.
Several factors, however, suggest that general anxiety about dental x-rays is misplaced. First, with advancements in dental x-ray technologies, levels of ionizing radiation produced by x-rays have dropped precipitously over the years. A recent examination of the first anatomical x-ray machine, built in the Netherlands in 1896, revealed that the machine, in a period of about ninety minutes, subjected patients to 1500 times the radiation of a modern machine, and it did so for an exposure which now takes only a fraction of a second. Other estimates suggest that, in the development of standardized, reliable x-ray technology, radiation levels sometimes reached an incredible 10,000 times the present dosages used for x-rays. It is clear that patients in the past were at much greater risk from damaging radiation effects than are their modern counterparts.
Early models of x-ray machines suffered from many, very practical problems with controlling or adapting x-ray generation to produce a usable picture. The invention of the tungsten filament tube by William D. Coolidge in 1913 made a more penetrating x-ray image possible, and the technology is still in use today. However, other problems more particular to dental x-rays were difficult to solve. In order to produce the desired image, a dental x-ray had to be taken at very short range, and dental machines were always at risk of producing serious shocks for patients. Though there were improvements, it wasn’t until the 1950’s that one very famous dental manufacturer ceased to produce its famous “Shock Proof X-ray Series,” a fact that suggests the persistence of this difficulty for a half-century or so. It is possible that early and immediate problems with dental devices simply overshadowed questions of harmful, longterm exposure levels for patients, as long as those exposure levels didn’t actually produce symptoms such as burnt skin or hair loss.
Some of the continued improvement in dental x-ray safety has come from film manufacturers. Immediately after the introduction of x-rays, film companies began supplying films for x-ray use, with the first dental x-ray film being produced by Kodak in 1913. The same company produced a further refinement, in 1919, to respond directly to x-rays. Notably, this 1919 film used sixty times the radiation needed for the same film today. The road to a better and faster x-ray film has obviously facilitated a great reduction in harmful radiation for modern patients.
Other improvements have come from direction and restriction of the x-ray beam. A series of grids and collimating devices has eliminated much of the scattered radiation which can be a threat to patients. In the past fifteen years, alone, these lead-lined collimating devices have reduced radioactive exposure by a factor of three.
1987 saw the introduction of digitalized x-ray technology. Digital x-rays do not use film and are far faster than film technologies. They also offer environmental benefits in that they eliminate the use of developing chemicals. They are easily stored and accessed through the computer programs which control their generation, making patient reference and record-transfer far more efficient. More importantly, however, they have opened the way for a further 60 – 80 % reduction in the ionizing radiation delivered during x-ray procedures.
Now, there is the possibility of future tooth-imaging without any radiation at all. However, it should be noted that radiation risks, today, for dental patients, have already been radically reduced, not only over the years, but especially through some very recent developments in x-ray technology.
A second factor which has led to a somewhat exaggerated distrust of the dental x-ray is that it is easy to identify x-ray as a source of ionizing radiation. Even the precautions used by dentists to lessen radiation exposures suggest danger, and, ironically, patients are sometimes made aware they are at risk simply because of the use of lead-lined aprons and neck collars. In fact, however, in a world of background radiation levels, dental x-rays deliver far lower levels than many other sources. Estimates suggest that dental x-rays are responsible for less than 2.5% of the ionizing radiation an average person receives in a lifetime. A full-mouth, dental x-ray typically exposes a person to the equivalent of one or two days of background environmental radiation, or the same amount of ionizing radiation regularly received on a cross-country plane flight. And, though dental x-rays are given more frequently than other forms of medical x-ray, the dosage is far smaller. A plain chest x-ray gives ten times the ionizing radiation of an average dental x-ray; a CT scan gives the equivalent of four or five years of background environmental radiation. Though a highly visible source of ionizing radiation, dental x-rays are far from the worst.
Finally, it should not be forgotten that x-rays have a positive impact on the patient’s general well-being. Bite-wing x-rays allow dentists to see interproximal caries, especially in posterior teeth, and to detect decay beginning under existing fillings. Early detection of such cavities helps avoid the need for more expensive treatments or extractions later. Periapical x-rays allow dentists to perform root canals, and to see root damage, bone loss, abscesses, abnormal growths, impacted teeth, and other tooth problems. Such information can save a patient’s life. Panoramic x-rays become important in evaluating sinuses, visualizing tooth structures for implants and braces, or in examinations of problems in the larger maxillo-facial structure. All of these applications offer essential assistance to the dentist in his or her work to preserve a patient’s oral and overall health.
It is also generally true that procedures involving higher dental radiation dosages are not performed as often. Panoramic extraoral x-rays will seldom be taken more often than once every five to seven years, and most adolescent and adult dental clients do not generally require full-mouth x-rays more often than once every two or three years. In the case of children whose tooth surfaces cannot be viewed without x-ray, such x-rays may be recommended once every one or two years. Of course, people who are more susceptible to dental caries may be advised to have more frequent x-ray screenings, and x-rays may be recommended as often as every six months. Moreover, any dental repair may call for localized periapical or bitewing x-rays so that the dentist can perform the best repair possible. However, more frequent exposure to ionizing radiation is closely linked to those with greater oral risks, and may be seen as justified in that context.
Dentists would be the first to agree that, because radiation damage is cumulative, it should be minimized wherever possible. However, it is also clear that dentistry today is responsible for a tiny and diminishing portion of modern exposure to destructive ionizing radiation. The recent rise of thyroid and salivary cancers might well have more to do with the nuclear testing of the post-war period and nuclear accidents in electrical generating plants than with dentistry. Certainly modern dentistry appears to be a very conservative partner in any public danger from overall exposure to ionizing radiation. Moreover, an overwhelming proportion of dental patients would agree that the advantages far outweigh the risks in dental treatments facilitated by this small level of exposure.