B
History

Discovery of x rays

On November 8, 1895, Wilhelm Konrad Röntgen (alternately spelled Wilhelm Conrad Roentgen), a professor of physics and the director of the Physical Institute of the Julius Maximilian University at Würzburg in Germany, while working in his laboratory discovered what we commonly call "x rays" (Fig. B1). On that day in his darkened laboratory, he noticed light emanating on a table located across the room, far from the experiment that he was conducting. Professor Röntgen was researching the effects of electrical discharge using a Crookes-Hittorf tube. The glowing object was a fluorescent screen used in another experiment. This perplexed him because electrons emanating from his electric discharge tube were known to only travel short distances in air. His fluorescing screen was too far away for these electrons to produce the fluorescence. In addition, his lab was completely darkened and the Crookes-Hittorf tube was completely covered with black cardboard to prevent light leakage. Light leakage otherwise could have caused the screen to fluoresce. It was obvious to Professor Röntgen that he was dealing with an unknown invisible phenomenon. Professor Röntgen called this new phenomenon "x rays." "X" because that is the universal symbol for the unknown and "ray" because it traveled in a straight line. He was a modest gentleman and did not wish to call these new rays "Röntgen rays" after himself which is standard protocol for new discoveries. Following his discovery of x rays, he was determined to learn what were the properties and characteristics of these mysterious invisible rays. He secretly tested this phenomenon for weeks and did not divulge any information about his new discovery to anyone. At first he experimented by placing objects in the path of the x rays between the tube and the fluorescent screen. Ultimately, he decided to place his own hand in front of the x-ray beam and he was amazed at what he saw on the fluorescent screen. He observed shadows of his skin and underlying bones. For the first recorded image, he asked his wife, Bertha, to place her hand on a photographic plate while he operated the experimental apparatus. Professor Röntgen was able to produce an x-ray image of her bones and soft tissue. This x-ray image, which includes the wedding ring on her finger, is recognized as the first x-ray image of the human body (Fig. B2).

Fig. B1 Wilhelm Konrad Röntgen: credited with being the first person to discover x rays.

Fig. B2 First x-ray image of the human body: Bertha Röntgen's hand.

On December 28, 1895, Professor Röntgen delivered his first of three manuscripts on x rays to the president of the Physical Medical Society of Würzburg. The first manuscript was entitled "On a New Kind of Rays, A Preliminary Communication." The unedited manuscript went to press immediately and was published in the Annals of the Society. Immediately afterwards, announcements were published in newspapers and in scientific journals around the world. In the United States, the announcement of Professor Röntgen's discovery was on January 7, 1896 in the New York Herald newspaper. The English translations of the original paper were printed in Nature, a London publication, on January 23, 1896 and in Science, a New York publication, on February 14, 1896. Professor Röntgen did not seek nor enjoy public acclaim and as a result he would make only a single presentation on the topic of x rays. This presentation was given to the Physical Medical Society of Würzburg on January 23, 1896.

The prevalence of Ruhmkorff coils and Crookes-Hittorf tubes in nearly every physics laboratory at the time permitted x-ray research to be conducted globally without much delay. These two ingredients were the primary components necessary for producing x rays. Consequently, prior to Professor Röntgen's discovery anyone who was studying high voltage electricity was unknowingly generating x rays. But no one prior to Professor Röntgen recognized this phenomenon, nor understood the value of it even if they did suspect something unusual. Sir William Crookes, whose collaboration produced the Crookes-Hittorf tubes, had outright complained to the manufacturer that unopened boxes of photographic plates were arriving at his lab already exposed. Sir Crookes surmised the problem was simply due to the manufacturer's poor quality control. It was not until after Professor Röntgen's discovery was announced that Sir Crookes and other scientists finally understood that x rays were the cause of some of their photographic plate problems.

Professor Röntgen was awarded the first Nobel Prize for Physics in 1901 for his discovery of x rays even though some tried to discredit his claim to the discovery. Sadly, Professor Röntgen became reclusive and very bitter in his later years as a result of this controversy concerning the discovery of x rays. He even stipulated in his will that all of his correspondences written regarding the discovery of x rays be destroyed at his death. He died on February 10, 1923. Unbeknownst to Professor Röntgen, his recognition of x rays is considered by many today to be the greatest scientific discovery of all time. X rays have truly revolutionized modern healthcare practices.

Who took the world's first "dental" radiograph?

Poor records make it difficult to say conclusively who took the first dental radiograph. However, Professor Walter König in Frankfurt, Germany, Dr. Otto Walkoff, a dentist in Brunschweig, Germany and Dr. Frank Harrison, a dentist in Sheffield, England have all been reported to have taken dental radiographs within a month of Röntgen 's reported discovery. Dr. Walkoff on January 14, 1896 used a glass photographic plate. The glass plate was wrapped in black paper to block out light and it was covered with rubber dam to keep out saliva. He inserted this glass plate into his own mouth and subjected himself to a 25 min exposure to radiation (Fig. B3). If not the first dental radiograph, it certainly was one of the earliest dental radiographs. Most people claim that Dr. C. Edmund Kells, Jr. took the first dental radiograph of a living person in the United States. It should be emphasized that this was on a living person because it had been reported earlier in a Dental Cosmos publication that Dr. Wm. J. Morton, a physician, presented his research work before the New York Odontological Society and it included four dental x-ray radiographs. But his dental radiographs were taken on dried laboratory skulls and not on a living person. According to Dr. Kells, "Just when I took my first dental radiograph, I cannot say, because I have no record of it, but in the transactions of the Southern Dental Association, there is reported my x-ray clinic given in Asheville in July 1896, and I remember full well that I had had the apparatus several months before giving this clinic and had developed a method of taking dental radiographs. Thus I must have begun work in April or May 1896." Regardless of who was first to expose a dental radiograph, the value of dental radiography was recognized almost immediately after Professor Röntgen's discovery of x rays.

Fig. B3 First dental radiograph (unconfirmed). In January 1896, Dr. Otto Walkoff, a German dentist, covered a small glass photographic plate and wrapped it in a rubber sheath. He then positioned it in his mouth and subsequently exposed himself to 25 min of radiation.

Dr. C. E. Kells, Jr., a New Orleans dentist and the early days of dental radiography

Shortly after the announcement of Professor Röntgen's discovery, Professor Brown Ayres of Tulane University in New Orleans gave a public demonstration of x rays using a crude apparatus set-up. Since the general public marveled at the thought of being able to stand next to a piece of equipment and shortly thereafter see a photograph of the inside of the body, he devoted a portion of his demonstration to expose a volunteer's hand. Although it required a lengthy 20 min exposure, the crowd was patient, including one curious soul, Dr. C. Edmund Kells, Jr. (Fig. B4). It immediately occurred to him that x rays would be an invaluable tool for observing inside the jaws and teeth. Dr. Kells met Professor Ayres and they discussed the idea of taking pictures of teeth. Professor Ayres became instrumental in assisting Kells to acquire the necessary equipment for building an x-ray laboratory to conduct his own research.

Fig. B4 Dr. C. Edmund Kells, Jr.: New Orleans dentist, inventor and author.

It was a crude and difficult procedure for taking x rays in the early days. For example, one of the original problems encountered was the variability in output of the x-ray tube. The few molecules of air that were inside the tube were vital for producing x rays. To do so, some of these air molecules would have to be bombarded into the walls of the tube, which would convert their energy into x rays. The air molecules received that energy when a very high voltage was supplied to the tube. In doing this, however, these molecules of air would gradually adhere to the inner walls of the tube and without any free air molecules...