80 years of dental radiography Richard A. Glenner, DDS, Chicago
During the 80 years since Roentgen's dis covery in November 1895, many uses for the X ray have been found in medicine. Its value for dental diagnosis was realized immediately. Ra diography was first used in dentistry in the re moval of impacted and fractured teeth; it pro vided more information for these operations and, despite the early technical limitations of radiography, teeth were easily seen. The primi tive radiograph was made with a glass plate and a 20-minute exposure time. On April 24,18% , at a special meeting of the New York Odontological Society (reported in "Dental Cosmos," 1896, p 478), William James Morton briefly described the radiographic ap paratus and displayed radiographs, several of which showed restorations and crowns. Speak ing to the dentists on the application of radiog raphy, he concluded that "the X ray more than rivals your exploring mirror, your probe, your most delicate sense of touch, and your keenest powers of hypothetical diagnosis." Three months later on July 29, C. Edmund Kells gave the first dinic in this country on the use of the X ray for dental purposes at the an nual meeting of the Southern Dental Associa tion at Asheville, NC ("Dental Cosmos," 1896, p
1 0 1 2 ).
Because efficient diagnostic methods were not available in endodontics, materials and techniques were the concern of early workers.
Radiographs disclosed, for the first time, infec tion at the apexes of endodontically treated teeth and helped precipitate the "focal-infection hysteria." Dr. Kells was the first dentist to make use of radiography in root canal therapy. He recount ed the incident in t h e j o u r n a l of June 1926: "May 10, 1899 (according to my records) I was attempting to fill the root canal of an upper cen tral incisor for a little boy. . . . It occurred to me to place a lead wire in this root canal and then take a radiogram to see whether it extended to the end of the root or not. I carried out this in spiration, for an inspiration it surely was, and the result was all that was anticipated. The lead wire was shown very plainly in the root canal.. . ." Weston A. Price, in the February 1900 issue of "Dental Cosmos," called attention to incom plete root canal fillings as evidenced in radio graphs. He suggested that radiographs be used to check the adequacy of root canal fillings in the June 1901 issue of "Items of Interest." Radiographs were mentioned early as an aid in orthodontics. In his October 1899 article "Roentgen rays" in "Dental Cosmos," Dr. Kells said that the radiograph is "indispensable" in orthodontics. Dr. Price pointed out in his 1900 article that the effect of tooth movement could be seen in radiographs. In the March 1900 issue of Dental Cosmos in "The X-ray for diagnosing orthodontia," J. N. McDowell described, with JADA, Vol. 90, March 1975 ■ 549
ROENTGEN
W ilhelm Conrad Roentgen used this Hittorf-Crookes tube (above
his hand between the tube and the fluorescent screen, and to
right) to make the first radiograph. H e did his work in W iirzberg,
confirm his observation, he asked his wife Bertha to repeat the
Bavaria (Germany). The prominent experimental physicist was
experiment using a photographic plate. She placed her hand on
investigating cathode ray effects on Nov 8, 1895, when he ob
a holder loaded with a photographic plate; for 15 minutes,
served that a platinobarium screen, some distance away, emitted
Roentgen directed the rays from the tube onto the plate. O n the
light when the tube that he had previously covered with black
developed plate, the bones of her hand appeared light within
cardboard was supplied
In subsequent tests
the darker image of the flesh. Two rings on her finger almost
Roentgen determined that the energy penetrated paper, a play
completely stopped the rays. For his w ork, Roentgen received
with
current.
ing card, a book, w ood, and thin sheets of metal with the excep
numerous awards, among them the Nobel Prize in 1901. (Photo
tion of lead, and that it affected a photographic plate as well as
graph of tube courtesy of A. Haupt & Cie, W iirzberg, Germany.)
the fluorescent screen. During these tests, Roentgen placed
the use of reports of cases, how radiographs aided him in determining proper diagnosis and a correct treatment plan. In his article in the February 1900 issue of "Dental Cosmos," Dr. Price included a radio graph of a periodontal pocket. However, the use of radiography in periodontics is not seen in the literature until the late 1920s and early 1930s because no attempt was made at routine radiographic examination. During the first 15 years after Roentgen's dis covery of X rays dentists recognized the value of radiographs, but many thought the procedure was too difficult for persons who were not spe cially trained and that radiography's usefulness was limited to rare cases. In the next decade, the value of radiographs as a preliminary step in all operative procedures was recognized. Dissemination of information on dental ra diography then became important. In 1913, Howard Riley Raper, who in 1924 invented the
550 ■ JADA, Vol. 90, March 1975
bite-wing film, wrote the first book on dental radiography. Also in 1913, standard terminol ogy was adopted by the American Roentgen Ray Society. LeRoy M . Ennis, in the Henry Kline Fixott, Sr., memorial lecture in 1961 (published in Oral Surg in 1962), said that papers published on radiography between 1915 and 1920 primar ily praised the value of the radiograph, and that some good articles on interpretation were writ ten. During the 1920s, more than 550 articles on radiography were written, he reported. An ear ly pioneer in the field, Dr. Ennis published one of the fine early dental radiography books in 1931; his book is currently in its sixth edition. Dr. Ennis also recalled "a most important ad vancement in the field" when in about 1910 dental radiography was introduced into the curriculum of the Indiana dental school by Dr. Raper. Another early pioneer at introducing the teaching of dental radiography in the schools was F. L. Saterlee of the New York Col
Within 14 days of the announcem ent of Roentgen's experiment that showed that X rays would penetrate solid substances impervious to light, Dr. O tto Walkhoff (at that time of Braunschweig, Germany, later professor
O ne of the earliest dental radiographs was made by
in M unich) made the first dental radiograph. He used
W . König of Frankfort, Germany, in February 1896.
an ordinary glass photographic plate, wrapped in
The exposure tim e was nine minutes. W e will probably
black paper and covered with rubber dam; the
never know for sure who made the first dental radiograph
exposure tim e was 25 minutes. This dangerous experiment is typical of the lack of caution of pioneers in the field.
in the Western Hemisphere, but probably it was either W . ). Morton (M D ), W illiam Herbert Rollins, or C. Edmund
This first dental radiograph is crude by today's standards
Kells.
and of little diagnostic value; yet it was a start.
lege of Dentistry. In a report to the Institute of Dental Pedagogics, Dr. Raper said that 15 col leges in 1913 were offering a course in radiog raphy and that others incorporated the subject in other courses. However, dentists most often took private courses, and many of those who did not have X-ray machines sent their patients to laboratories to have radiographs made. As late as 1929, Eastman Kodak offered an intensive course in the technique for dentists and assis tants. As the years went on, the training den tists received in radiography was taken over completely by the dental schools. During the 1950s a fear campaign about radi ation exposure erupted when the National Academy of Sciences released its report, "The biological effects of atomic radiation." The re port warned about the danger that some radia tion might reach the reproductive organs. In response, numerous articles appeared in the dental literature on the biologic effects of radi
ation exposure, on surveys of radiation safety in dental offices, and on techniques to de crease or control radiation exposure such as collimation and filtration of the beam, accur ate automatic timers, and high-speed radiographic film. More recently, reports of the Na tional Council on Radiation Protection and the ADA Council on Dental Materials and Devices (the latest recommendations in radiographic practices were published in the January issue of t h e j o u r n a l ) and the new federal standard for diagnostic X-ray systems emphasize safe radia tion hygiene practice, with protection of the patient and office staff, use of modern equip ment, high-speed film, and correct darkroom procedures.
Dr. Glenner's address is 3414 W Peterson Ave, Chicago, 60659.
Glenner: DENTAL X-RAY UNITS ■ 551
By July 1896, less than seven months after the American announcem ent of Roentgen's discovery (first reported in the "N e w York H erald ," Jan 7, 1896), W illiam H . Rollins had invented an intraoral cassette and intraoral fluoroscope (left). In the same year, he also invented an X-ray tube arm and bracket for use in the dental office (above). This equipm ent was described in the literature at the tim e but never commercially manufactured. This undoubtedly was the first dental X-ray apparatus.
Dr. Rollins realized that X rays were harmful and took steps to nullify the danger. The danger became evident to him w hen, in the course of his experim ents, the skin of his hands showed bum s. In 1901, he suggested (as reviewed in the first num ber of Dent Radiogr Photogr 1960) that persons using X-ray devices should wear glasses of the "most non-radiable m aterial," that the tube should be enclosed in a radiation-proof box, and that the patient should be covered with radiation-proof material. According to the June 1914 issue of the "American journal of Roentgenology," Roentgen used a lead shield interposed between himself and the tube in all his experiments.
552 ■ JADA, Vol. 90, March 1975
C. Edmund Kells, one of the early X-ray martyrs, used a technique called “ setting the tube" to adjust for variations in the quality of the X rays. O ne hand held the fluoroscope (hand variety) and the other hand was placed between the tube and the fluoroscope. The rheostat of the X-ray machine was adjusted according to how sharp the bones in the hand showed up on the fluoro scope. The hand was exposed to a few seconds of radiation every time the tube was set. No harmful effects were noticed for at least five to
This is the X-ray laboratory of Dr. Kells in 1896. The X-ray gas tubes were energized by a Tesla coil. Notice the numerous tubes on the top shelf. These were required because of the poor reliability of the tubes as a result of the variability of their vacuums. Under
ten years of this continued exposure. Then the
continued use, the vacuum changed and, hence, the number
hands of the early pioneers started to show evi
of electrons available to produce X rays varied.
dences of malignant growths. Before his death, Kells had had three fingers amputated, then his hand, and finally his arm.
For his experiments, Roentgen used a Hittorf-Crookes tube agitated with a rather large Ruhmkorff induction coil, equipped with a Deprez interrupter that produced 40 to 70 kv. Almost immediately after his announcem ent, others made use of static electric machines to produce direct current. These machines were unpredictable as a source of electricity because variation in atmospheric conditions, particularly humidity, had a tremendous effect on their efficiency. Dentists bought calcium chloride by the barrel to cope with the humidity inside the machine's case. Even then, the machine might not work properly. At this tim e, no devices were available for measuring milliamperage or kilovoltage; also, flexible film had not been introduced and only the ordinary photographic plate was available; furtherm ore, exposure times were long. Indeed, the ingenuity and patience of the operator were taxed to the limit. Glenner: DENTAL X-RAY UNITS ■ 553
i
4
This is a 1905 European commercially manufactured dental X-ray outfit. Called the "Record" and manufactured by Reiniger-Gebbert and Schall of Germany (predecessors of Siemens C orp.), it was probably the first so manufactured in Europe and possibly in the w orld. The gas-filled X-ray tube was partially lead-shielded for protection against direct radiation, but notice the exposed high-voltage wires. The device included a collimator for intraoral radiographs.
The induction coil was used by Roentgen in his experiments to generate current for the X-ray tube. The coil could be operated by a storage battery if commercial current was not available. This is an induction (Ruhmkorff) coil machine. O ther types of machines were the high-frequency (Tesla) coil machine and the "interrupterless" transformer machine. All of these machines were used with X-ray tubes and with commercially manufactured or improvised tube stands.
This X-ray tube stand was one of the first used by Dr. Kells for dental purposes. In the picture, published in 1919, the tube has not been placed in the proper position in order to show the patient's face and the bandage which binds the head to the headrest. The long exposure times necessitated immobility of the head. 554 ■ JADA, Vol. 90, March 1975
Dr. Frank van W o ert, a pioneer in oral radiography, gave a practical demonstration of radiography before the New York Odontological Society in 1897. He was among the first to use film in intraoral radiog raphy. The first dental X-ray packets consisted of glass plates or roll 81m cut into small pieces and wrapped, by the radiographer, in black
paper and rubber dam. The first commercial handwrapped dental X-ray film packet was made by Eastman Kodak and became available
in 1913. A very im portant advancement in dental radiography was made in 1941 when Eastman Kodak introduced high-speed dental X-ray film (Ultra-speed Periapical Dental Film). -
i
Before 1913, there was no such thing as an American dental X-ray machine on the market; medical machines w ere adapted for dental purposes. Dental X-ray tube stands or wall-bracket X-ray tube holders were used with medical machines. These tube stands and holders w ere advertised in a 1917 catalog.
Even in the pre-W orld W ar I days, there was much concern about radiation protection. By 1915, the dental profession, well aware of the danger, was doing something about it.
The first American commercially manufactured X-ray machine made especially for the dentist was manufactured in 1913 by the Am er ican X-ray Equipment Co. of M t. Vernon, NY. It was an induction coil machine, used with an X-ray tube stand for a "com plete outfit." Alternating o r direct current could be used. This 1917 model of the machine sold for $320. Notice the lead glass tube shield.
Glenner: DENTAL X-RAY UNITS ■ 555
This machine, used with an X-ray tube stand, had a high-frequency "therapeutic" attachment on top. In 1914, some believed in the therapeutic value of X rays in dentistry. They claimed that, after thorough instrumentation, "pyorrhea" improved when treated with a combination of high-frequency current and X rays. The technique never became popu lar. Another example is found in Sturridge's 1914 book on dental electro-therapeutics: "In cases of obstinate pericementitis in which the ordinary remedies do not yield relief, one or two exposures of 20 to 40 seconds according to the strength of the current and the severity of the case should by all means be tried."
Some induction coil X-ray machines were wall mounted. With a machine installed in this man ner, "overhead w iring" was usually necessary, and it was considered a great convenience.
Shortly after the first commercial dental X-ray machines w ere m arketed, the need for a m ore compact outfit was realized. The unit at left is considered the first American dental X-ray unit; it was made by the American Xray Equipment Co. The unit was no more than the induction coil X-ray machine with the tube holder m ounted on the cabinet. Units of the Tesla or high-frequency type (right) were placed on the market shortly afterward. These w ere small and inexpensive ($225) and could be used with alternating or direct current. The exposure time was 10 to 20 seconds.
m 556 ■ JADA, Vol. 90, March 1975
Probably the most widely used dental X-ray u n itat the time was the induction coil unit, with an exposure time of 1 to 8 seconds. This unit sold for $347 in 1917 and was manufactured by the American X-ray Equipment Co.
O ()fh o d e
A'-.-fJ&fn t? I f rtf n a !
Many types of tubes were devised for the purpose of p ro du dn gX rays. Whatever the type, all contained gases and w ere extremely tem peramental. The Snook hydrogen tube was used quite extensively for a time because the amount of the hydrogen within the tube could be regulated. (The vacuum could be raised or lowered by the removal or addition of hydrogen.) These tubes demanded the continuous alertness of the operator to maintain the proper vacuum, and a considerable amount of time was required in this effort. This is a later m odel, low-vacuum gas tube with a vacuum regulator attached, made by General Electric.
This 1922 dental unit manufactured by Reiniger-Gebbert and Schall (predecessors of Siemens Corp.), Germ any, was called the "Ergos." It was similar to a unit manufactured in the United States.
Glenner: DENTAL X-RAY UNITS ■ 557
Early X-ray machines had a dangerously exposed high-tension wire that caused several serious accidents and a few fatal ones. As one example, a dentist was about to expose a film when his pa tient excitedly pointed out the w indow to a run-away horse. At that instant, the dentist pressed the button, touched the high-tension w ire, and was thrown across the room into a solid wall; he sustained a fractured skull. In 1923, the exposed wire was eliminated in the first electrically safe X-ray machine, the Victor CDX.
In 1913, William 0 . Coolidge, a scientist with the General Electric Co., designed an X-ray tube in which the electrons were supplied by an incandescent cathode, thereby eliminating the necessity of gas to create the electrons. He had previously found a way to make brit tle tungsten workable and as strong as steel. He applied ductile tungsten to the targets of the tubes, increasing the target's heat con ductivity and permitting it to absorb more energy. The improved hot-cathode, highvacuum tube (top) had a stable reproducible output and independent control of radiation quality and quantity. Although a tube es Cork Bushing
pecially
Curve "Washer " A ”
designed
for
dental
application
(bottom) was developed a few years later, it did not become available until the early 1920s. Dr. Coolidge, who was director-emer-
--- \ Anode
U pper half o f leadglass shield
Low er half of lead-glass shield Thum b Screw
558 ■ JADA, Vol. 90, March 1975
—
itus of the research laboratories of GE, died Feb 3 at the age of 101.
D r. Coolidge also discovered that if a very small Coolidge tube were immersed in oil along with the transformer, the oil would serve as electrical insulation for the tube and transformer and would also aid in cooling the tube. His patent application covering this principle bears the official dating of! Jan 24, 1919. The original CDX unit was the first to be "shock pro of," that is, to isolate all the high-voltage elements in a single electrically grounded housing (interior view, left). It was introduced in dental practice in 1923 by the Victor X-ray Corp. of Chicago, which in the next few years be came General Electric X-ray Corp. The new principle also permitted the use of much smaller high-tension transformers and the use of an autotransformer instead of a rheostat. These helped in making the X-ray unit more compact. Both wall-m ounted and mobile units w ere available (right).
The Coolidge tube was used in the new “ safe" units and also in open tube machines such as this Ritter unit of 1928. The unit had an exposed high-tension wire and, as a result, the dentist may have gotten an occasional shock. The open tube
Ten years after the original CDX unit was
machines with exposed high-tension wires were
introduced in 1923, General Electric
manufactured into the 1930s.
introduced its new and completely redesigned dental X-ray unit, the CDX m odel E. This model retained the original principle of oil immersion of the X-ray tube, but included new features and refinements.
559
This W eber no. 5 Raydex mobile dental X-ray unit is typical of those used in the late 1930s and the 1940s. In 1925, the dentist who took an X-ray was the exception. By 1930, however, 46% of dental school graduates purchased X-ray machines when first equipping their offices, according to an ADA survey of dental practice conducted in 1932. Many of the remaining 54% arranged to have access to machines of physicians or other dentists.
This North American Philips Oralix X-ray machine of the 1940s and 1950s had a small head and could be attached to the dental unit; wall-mounted or m obile models also w ere made.
The Ritter M od el E X-ray unit, introduced in 1956, provided kilovoltages of from 65 to 90 kvp. The Coolidge right-angle radiator tube was rated at a 3-inch spark gap (63 kvp). Thus, the voltage of the so-called 3-inch dental units influenced the design of units from 1917 to 1956 when the 90 kvp machines w ere developed. In the 1950s, other features such as electronic timers and beam collimation and filtration techniques had been developed with the idea of making X-ray units safer.
July 9, 1957
d .c .H u d s o n ¡t t a l 2,798,958 APPARATUS FOR PRODUCING RADIOGRAPHS OF SELECTED STRUCTURES WITHIN A SUBJECT S Sheets-Sheet 1
Filed Jan. 19, 1956
Prof. Yrjo V . Paatero of Helsinki, Finland, published in the Iate1940s reports of his experiments with panoramic radiography of the jaws. A prototype of this apparatus was made at the University of Washington in 1950 by Robert J. Nelsen and John W . Kumpula. Dr. Nelsen then joined the ADA group at the National Bureau of Standards, and Kumpula joined the NBS. In this early technique, three lead-backed films were separately placed and exposed in the patient's mouth. The radiation source was not rotated; the horizontal movement of this elem ent moved linearly for the exposure of the posterior teeth of either side and made changes in angulation. How ever, another procedure was developed in which the film was placed extraorally and the X-ray source and film holder w ere rotated. At the NBS, Kumpula continued his work in partnership with George Dickson and Donald Hudson. The unique machine they developed, at a cost of $85,0C9, produced a picture of the entire dental arch with the supporting bone
INVENTORS DONALD C. HUDSON JOHU W. KUMPULA
structure, on one film . It reduced the radiation exposure of the patient by as much as 90% over the traditional dental X-ray technique, according to G. G. Pettit in the January 1971 issue of "Dental Clinics of North America."
ATTORN
4 >■
A patent for the panoramic apparatus was taken out by Hudson and Kumpula, assignors to the United States
14' S0U 8C £~ SKIM DISTANCÍ
of America as represented by the Secretary of the Army. All manufacturers with an appropriate interest were thoroughly briefed on the discovery and told that the designs would be made available. The first commercial panoramic X-ray machine was the Panorex, made by S. S. W hite.
In July 1966, Prof. A. G. Richards published an article in "JADA" describing a new X-ray head design which is used today in some machines manufactured in the United States and Japan. The design permits the use of long cone techniques in offices that are only large enough for short cone size heads. It does this by placing the X-ray tube at the back of the head housing rather than in the conventional forward position.
An example of X-ray units designed in the 1960s is this Ritter M ark 75 (model H ), introduced in 1966. It provided a simplified technique with preset milliamperage and kilovoltage.
Glenner: DENTAL X-RAY UNITS ■ 561
1975 Models ê
w~
ü G S Q B [W SSSm i
1
1
D en tal X -R ay 065, B elm o nt E qu ipm ent Corp., S om erset, NJ
P a n e x Div., O ratro nics Inc., N ew York
:i i
■ l m
r ii m i p
ri,
r^ ä T i.i
M W —
I M e te o r II, R itter Co., R ochester, NY
S a fe -R a y , Litton D en tal Products, Toledo, Ohio
562 ■ JADA, Vol. 90, March 1975
O rtho pantom og raph , S ie m e n s Corp., Ise lin , NJ
P -O R IO I O rallx 50 D en tal X -R ay System , Philips M e d ic a l S ystem s, Inc.,
W e b e r D ental Mfg. Co., C anton, Ohio P an o re x , S. S. W h ite Co., P hiladelph ia
S helto n, C onn
! •Æ'-m* ' ""fl
II
JT*
P ane lip s e P a n o ra m ic X -ray S ystem , G e n e ra l E lectric Co., A m e ric a n a X -ray Co., E ng lew ood, NJ
M edical S ystem s Div., W a u k e s h a , Wis
Glenner: DENTAL X-RAY UNITS ■ 563
During the 80 years since Roentgen's dis covery in November 1895, many uses for the X ray have been found in medicine. Its value for dental diagnosis was realized immediately. Ra diography was first used in dentistry in the re moval of impacted and fractured teeth; it pro vided more information for these operations and, despite the early technical limitations of radiography, teeth were easily seen. The primi tive radiograph was made with a glass plate and a 20-minute exposure time. On April 24,18% , at a special meeting of the New York Odontological Society (reported in "Dental Cosmos," 1896, p 478), William James Morton briefly described the radiographic ap paratus and displayed radiographs, several of which showed restorations and crowns. Speak ing to the dentists on the application of radiog raphy, he concluded that "the X ray more than rivals your exploring mirror, your probe, your most delicate sense of touch, and your keenest powers of hypothetical diagnosis." Three months later on July 29, C. Edmund Kells gave the first dinic in this country on the use of the X ray for dental purposes at the an nual meeting of the Southern Dental Associa tion at Asheville, NC ("Dental Cosmos," 1896, p
1 0 1 2 ).
Because efficient diagnostic methods were not available in endodontics, materials and techniques were the concern of early workers.
Radiographs disclosed, for the first time, infec tion at the apexes of endodontically treated teeth and helped precipitate the "focal-infection hysteria." Dr. Kells was the first dentist to make use of radiography in root canal therapy. He recount ed the incident in t h e j o u r n a l of June 1926: "May 10, 1899 (according to my records) I was attempting to fill the root canal of an upper cen tral incisor for a little boy. . . . It occurred to me to place a lead wire in this root canal and then take a radiogram to see whether it extended to the end of the root or not. I carried out this in spiration, for an inspiration it surely was, and the result was all that was anticipated. The lead wire was shown very plainly in the root canal.. . ." Weston A. Price, in the February 1900 issue of "Dental Cosmos," called attention to incom plete root canal fillings as evidenced in radio graphs. He suggested that radiographs be used to check the adequacy of root canal fillings in the June 1901 issue of "Items of Interest." Radiographs were mentioned early as an aid in orthodontics. In his October 1899 article "Roentgen rays" in "Dental Cosmos," Dr. Kells said that the radiograph is "indispensable" in orthodontics. Dr. Price pointed out in his 1900 article that the effect of tooth movement could be seen in radiographs. In the March 1900 issue of Dental Cosmos in "The X-ray for diagnosing orthodontia," J. N. McDowell described, with JADA, Vol. 90, March 1975 ■ 549
ROENTGEN
W ilhelm Conrad Roentgen used this Hittorf-Crookes tube (above
his hand between the tube and the fluorescent screen, and to
right) to make the first radiograph. H e did his work in W iirzberg,
confirm his observation, he asked his wife Bertha to repeat the
Bavaria (Germany). The prominent experimental physicist was
experiment using a photographic plate. She placed her hand on
investigating cathode ray effects on Nov 8, 1895, when he ob
a holder loaded with a photographic plate; for 15 minutes,
served that a platinobarium screen, some distance away, emitted
Roentgen directed the rays from the tube onto the plate. O n the
light when the tube that he had previously covered with black
developed plate, the bones of her hand appeared light within
cardboard was supplied
In subsequent tests
the darker image of the flesh. Two rings on her finger almost
Roentgen determined that the energy penetrated paper, a play
completely stopped the rays. For his w ork, Roentgen received
with
current.
ing card, a book, w ood, and thin sheets of metal with the excep
numerous awards, among them the Nobel Prize in 1901. (Photo
tion of lead, and that it affected a photographic plate as well as
graph of tube courtesy of A. Haupt & Cie, W iirzberg, Germany.)
the fluorescent screen. During these tests, Roentgen placed
the use of reports of cases, how radiographs aided him in determining proper diagnosis and a correct treatment plan. In his article in the February 1900 issue of "Dental Cosmos," Dr. Price included a radio graph of a periodontal pocket. However, the use of radiography in periodontics is not seen in the literature until the late 1920s and early 1930s because no attempt was made at routine radiographic examination. During the first 15 years after Roentgen's dis covery of X rays dentists recognized the value of radiographs, but many thought the procedure was too difficult for persons who were not spe cially trained and that radiography's usefulness was limited to rare cases. In the next decade, the value of radiographs as a preliminary step in all operative procedures was recognized. Dissemination of information on dental ra diography then became important. In 1913, Howard Riley Raper, who in 1924 invented the
550 ■ JADA, Vol. 90, March 1975
bite-wing film, wrote the first book on dental radiography. Also in 1913, standard terminol ogy was adopted by the American Roentgen Ray Society. LeRoy M . Ennis, in the Henry Kline Fixott, Sr., memorial lecture in 1961 (published in Oral Surg in 1962), said that papers published on radiography between 1915 and 1920 primar ily praised the value of the radiograph, and that some good articles on interpretation were writ ten. During the 1920s, more than 550 articles on radiography were written, he reported. An ear ly pioneer in the field, Dr. Ennis published one of the fine early dental radiography books in 1931; his book is currently in its sixth edition. Dr. Ennis also recalled "a most important ad vancement in the field" when in about 1910 dental radiography was introduced into the curriculum of the Indiana dental school by Dr. Raper. Another early pioneer at introducing the teaching of dental radiography in the schools was F. L. Saterlee of the New York Col
Within 14 days of the announcem ent of Roentgen's experiment that showed that X rays would penetrate solid substances impervious to light, Dr. O tto Walkhoff (at that time of Braunschweig, Germany, later professor
O ne of the earliest dental radiographs was made by
in M unich) made the first dental radiograph. He used
W . König of Frankfort, Germany, in February 1896.
an ordinary glass photographic plate, wrapped in
The exposure tim e was nine minutes. W e will probably
black paper and covered with rubber dam; the
never know for sure who made the first dental radiograph
exposure tim e was 25 minutes. This dangerous experiment is typical of the lack of caution of pioneers in the field.
in the Western Hemisphere, but probably it was either W . ). Morton (M D ), W illiam Herbert Rollins, or C. Edmund
This first dental radiograph is crude by today's standards
Kells.
and of little diagnostic value; yet it was a start.
lege of Dentistry. In a report to the Institute of Dental Pedagogics, Dr. Raper said that 15 col leges in 1913 were offering a course in radiog raphy and that others incorporated the subject in other courses. However, dentists most often took private courses, and many of those who did not have X-ray machines sent their patients to laboratories to have radiographs made. As late as 1929, Eastman Kodak offered an intensive course in the technique for dentists and assis tants. As the years went on, the training den tists received in radiography was taken over completely by the dental schools. During the 1950s a fear campaign about radi ation exposure erupted when the National Academy of Sciences released its report, "The biological effects of atomic radiation." The re port warned about the danger that some radia tion might reach the reproductive organs. In response, numerous articles appeared in the dental literature on the biologic effects of radi
ation exposure, on surveys of radiation safety in dental offices, and on techniques to de crease or control radiation exposure such as collimation and filtration of the beam, accur ate automatic timers, and high-speed radiographic film. More recently, reports of the Na tional Council on Radiation Protection and the ADA Council on Dental Materials and Devices (the latest recommendations in radiographic practices were published in the January issue of t h e j o u r n a l ) and the new federal standard for diagnostic X-ray systems emphasize safe radia tion hygiene practice, with protection of the patient and office staff, use of modern equip ment, high-speed film, and correct darkroom procedures.
Dr. Glenner's address is 3414 W Peterson Ave, Chicago, 60659.
Glenner: DENTAL X-RAY UNITS ■ 551
By July 1896, less than seven months after the American announcem ent of Roentgen's discovery (first reported in the "N e w York H erald ," Jan 7, 1896), W illiam H . Rollins had invented an intraoral cassette and intraoral fluoroscope (left). In the same year, he also invented an X-ray tube arm and bracket for use in the dental office (above). This equipm ent was described in the literature at the tim e but never commercially manufactured. This undoubtedly was the first dental X-ray apparatus.
Dr. Rollins realized that X rays were harmful and took steps to nullify the danger. The danger became evident to him w hen, in the course of his experim ents, the skin of his hands showed bum s. In 1901, he suggested (as reviewed in the first num ber of Dent Radiogr Photogr 1960) that persons using X-ray devices should wear glasses of the "most non-radiable m aterial," that the tube should be enclosed in a radiation-proof box, and that the patient should be covered with radiation-proof material. According to the June 1914 issue of the "American journal of Roentgenology," Roentgen used a lead shield interposed between himself and the tube in all his experiments.
552 ■ JADA, Vol. 90, March 1975
C. Edmund Kells, one of the early X-ray martyrs, used a technique called “ setting the tube" to adjust for variations in the quality of the X rays. O ne hand held the fluoroscope (hand variety) and the other hand was placed between the tube and the fluoroscope. The rheostat of the X-ray machine was adjusted according to how sharp the bones in the hand showed up on the fluoro scope. The hand was exposed to a few seconds of radiation every time the tube was set. No harmful effects were noticed for at least five to
This is the X-ray laboratory of Dr. Kells in 1896. The X-ray gas tubes were energized by a Tesla coil. Notice the numerous tubes on the top shelf. These were required because of the poor reliability of the tubes as a result of the variability of their vacuums. Under
ten years of this continued exposure. Then the
continued use, the vacuum changed and, hence, the number
hands of the early pioneers started to show evi
of electrons available to produce X rays varied.
dences of malignant growths. Before his death, Kells had had three fingers amputated, then his hand, and finally his arm.
For his experiments, Roentgen used a Hittorf-Crookes tube agitated with a rather large Ruhmkorff induction coil, equipped with a Deprez interrupter that produced 40 to 70 kv. Almost immediately after his announcem ent, others made use of static electric machines to produce direct current. These machines were unpredictable as a source of electricity because variation in atmospheric conditions, particularly humidity, had a tremendous effect on their efficiency. Dentists bought calcium chloride by the barrel to cope with the humidity inside the machine's case. Even then, the machine might not work properly. At this tim e, no devices were available for measuring milliamperage or kilovoltage; also, flexible film had not been introduced and only the ordinary photographic plate was available; furtherm ore, exposure times were long. Indeed, the ingenuity and patience of the operator were taxed to the limit. Glenner: DENTAL X-RAY UNITS ■ 553
i
4
This is a 1905 European commercially manufactured dental X-ray outfit. Called the "Record" and manufactured by Reiniger-Gebbert and Schall of Germany (predecessors of Siemens C orp.), it was probably the first so manufactured in Europe and possibly in the w orld. The gas-filled X-ray tube was partially lead-shielded for protection against direct radiation, but notice the exposed high-voltage wires. The device included a collimator for intraoral radiographs.
The induction coil was used by Roentgen in his experiments to generate current for the X-ray tube. The coil could be operated by a storage battery if commercial current was not available. This is an induction (Ruhmkorff) coil machine. O ther types of machines were the high-frequency (Tesla) coil machine and the "interrupterless" transformer machine. All of these machines were used with X-ray tubes and with commercially manufactured or improvised tube stands.
This X-ray tube stand was one of the first used by Dr. Kells for dental purposes. In the picture, published in 1919, the tube has not been placed in the proper position in order to show the patient's face and the bandage which binds the head to the headrest. The long exposure times necessitated immobility of the head. 554 ■ JADA, Vol. 90, March 1975
Dr. Frank van W o ert, a pioneer in oral radiography, gave a practical demonstration of radiography before the New York Odontological Society in 1897. He was among the first to use film in intraoral radiog raphy. The first dental X-ray packets consisted of glass plates or roll 81m cut into small pieces and wrapped, by the radiographer, in black
paper and rubber dam. The first commercial handwrapped dental X-ray film packet was made by Eastman Kodak and became available
in 1913. A very im portant advancement in dental radiography was made in 1941 when Eastman Kodak introduced high-speed dental X-ray film (Ultra-speed Periapical Dental Film). -
i
Before 1913, there was no such thing as an American dental X-ray machine on the market; medical machines w ere adapted for dental purposes. Dental X-ray tube stands or wall-bracket X-ray tube holders were used with medical machines. These tube stands and holders w ere advertised in a 1917 catalog.
Even in the pre-W orld W ar I days, there was much concern about radiation protection. By 1915, the dental profession, well aware of the danger, was doing something about it.
The first American commercially manufactured X-ray machine made especially for the dentist was manufactured in 1913 by the Am er ican X-ray Equipment Co. of M t. Vernon, NY. It was an induction coil machine, used with an X-ray tube stand for a "com plete outfit." Alternating o r direct current could be used. This 1917 model of the machine sold for $320. Notice the lead glass tube shield.
Glenner: DENTAL X-RAY UNITS ■ 555
This machine, used with an X-ray tube stand, had a high-frequency "therapeutic" attachment on top. In 1914, some believed in the therapeutic value of X rays in dentistry. They claimed that, after thorough instrumentation, "pyorrhea" improved when treated with a combination of high-frequency current and X rays. The technique never became popu lar. Another example is found in Sturridge's 1914 book on dental electro-therapeutics: "In cases of obstinate pericementitis in which the ordinary remedies do not yield relief, one or two exposures of 20 to 40 seconds according to the strength of the current and the severity of the case should by all means be tried."
Some induction coil X-ray machines were wall mounted. With a machine installed in this man ner, "overhead w iring" was usually necessary, and it was considered a great convenience.
Shortly after the first commercial dental X-ray machines w ere m arketed, the need for a m ore compact outfit was realized. The unit at left is considered the first American dental X-ray unit; it was made by the American Xray Equipment Co. The unit was no more than the induction coil X-ray machine with the tube holder m ounted on the cabinet. Units of the Tesla or high-frequency type (right) were placed on the market shortly afterward. These w ere small and inexpensive ($225) and could be used with alternating or direct current. The exposure time was 10 to 20 seconds.
m 556 ■ JADA, Vol. 90, March 1975
Probably the most widely used dental X-ray u n itat the time was the induction coil unit, with an exposure time of 1 to 8 seconds. This unit sold for $347 in 1917 and was manufactured by the American X-ray Equipment Co.
O ()fh o d e
A'-.-fJ&fn t? I f rtf n a !
Many types of tubes were devised for the purpose of p ro du dn gX rays. Whatever the type, all contained gases and w ere extremely tem peramental. The Snook hydrogen tube was used quite extensively for a time because the amount of the hydrogen within the tube could be regulated. (The vacuum could be raised or lowered by the removal or addition of hydrogen.) These tubes demanded the continuous alertness of the operator to maintain the proper vacuum, and a considerable amount of time was required in this effort. This is a later m odel, low-vacuum gas tube with a vacuum regulator attached, made by General Electric.
This 1922 dental unit manufactured by Reiniger-Gebbert and Schall (predecessors of Siemens Corp.), Germ any, was called the "Ergos." It was similar to a unit manufactured in the United States.
Glenner: DENTAL X-RAY UNITS ■ 557
Early X-ray machines had a dangerously exposed high-tension wire that caused several serious accidents and a few fatal ones. As one example, a dentist was about to expose a film when his pa tient excitedly pointed out the w indow to a run-away horse. At that instant, the dentist pressed the button, touched the high-tension w ire, and was thrown across the room into a solid wall; he sustained a fractured skull. In 1923, the exposed wire was eliminated in the first electrically safe X-ray machine, the Victor CDX.
In 1913, William 0 . Coolidge, a scientist with the General Electric Co., designed an X-ray tube in which the electrons were supplied by an incandescent cathode, thereby eliminating the necessity of gas to create the electrons. He had previously found a way to make brit tle tungsten workable and as strong as steel. He applied ductile tungsten to the targets of the tubes, increasing the target's heat con ductivity and permitting it to absorb more energy. The improved hot-cathode, highvacuum tube (top) had a stable reproducible output and independent control of radiation quality and quantity. Although a tube es Cork Bushing
pecially
Curve "Washer " A ”
designed
for
dental
application
(bottom) was developed a few years later, it did not become available until the early 1920s. Dr. Coolidge, who was director-emer-
--- \ Anode
U pper half o f leadglass shield
Low er half of lead-glass shield Thum b Screw
558 ■ JADA, Vol. 90, March 1975
—
itus of the research laboratories of GE, died Feb 3 at the age of 101.
D r. Coolidge also discovered that if a very small Coolidge tube were immersed in oil along with the transformer, the oil would serve as electrical insulation for the tube and transformer and would also aid in cooling the tube. His patent application covering this principle bears the official dating of! Jan 24, 1919. The original CDX unit was the first to be "shock pro of," that is, to isolate all the high-voltage elements in a single electrically grounded housing (interior view, left). It was introduced in dental practice in 1923 by the Victor X-ray Corp. of Chicago, which in the next few years be came General Electric X-ray Corp. The new principle also permitted the use of much smaller high-tension transformers and the use of an autotransformer instead of a rheostat. These helped in making the X-ray unit more compact. Both wall-m ounted and mobile units w ere available (right).
The Coolidge tube was used in the new “ safe" units and also in open tube machines such as this Ritter unit of 1928. The unit had an exposed high-tension wire and, as a result, the dentist may have gotten an occasional shock. The open tube
Ten years after the original CDX unit was
machines with exposed high-tension wires were
introduced in 1923, General Electric
manufactured into the 1930s.
introduced its new and completely redesigned dental X-ray unit, the CDX m odel E. This model retained the original principle of oil immersion of the X-ray tube, but included new features and refinements.
559
This W eber no. 5 Raydex mobile dental X-ray unit is typical of those used in the late 1930s and the 1940s. In 1925, the dentist who took an X-ray was the exception. By 1930, however, 46% of dental school graduates purchased X-ray machines when first equipping their offices, according to an ADA survey of dental practice conducted in 1932. Many of the remaining 54% arranged to have access to machines of physicians or other dentists.
This North American Philips Oralix X-ray machine of the 1940s and 1950s had a small head and could be attached to the dental unit; wall-mounted or m obile models also w ere made.
The Ritter M od el E X-ray unit, introduced in 1956, provided kilovoltages of from 65 to 90 kvp. The Coolidge right-angle radiator tube was rated at a 3-inch spark gap (63 kvp). Thus, the voltage of the so-called 3-inch dental units influenced the design of units from 1917 to 1956 when the 90 kvp machines w ere developed. In the 1950s, other features such as electronic timers and beam collimation and filtration techniques had been developed with the idea of making X-ray units safer.
July 9, 1957
d .c .H u d s o n ¡t t a l 2,798,958 APPARATUS FOR PRODUCING RADIOGRAPHS OF SELECTED STRUCTURES WITHIN A SUBJECT S Sheets-Sheet 1
Filed Jan. 19, 1956
Prof. Yrjo V . Paatero of Helsinki, Finland, published in the Iate1940s reports of his experiments with panoramic radiography of the jaws. A prototype of this apparatus was made at the University of Washington in 1950 by Robert J. Nelsen and John W . Kumpula. Dr. Nelsen then joined the ADA group at the National Bureau of Standards, and Kumpula joined the NBS. In this early technique, three lead-backed films were separately placed and exposed in the patient's mouth. The radiation source was not rotated; the horizontal movement of this elem ent moved linearly for the exposure of the posterior teeth of either side and made changes in angulation. How ever, another procedure was developed in which the film was placed extraorally and the X-ray source and film holder w ere rotated. At the NBS, Kumpula continued his work in partnership with George Dickson and Donald Hudson. The unique machine they developed, at a cost of $85,0C9, produced a picture of the entire dental arch with the supporting bone
INVENTORS DONALD C. HUDSON JOHU W. KUMPULA
structure, on one film . It reduced the radiation exposure of the patient by as much as 90% over the traditional dental X-ray technique, according to G. G. Pettit in the January 1971 issue of "Dental Clinics of North America."
ATTORN
4 >■
A patent for the panoramic apparatus was taken out by Hudson and Kumpula, assignors to the United States
14' S0U 8C £~ SKIM DISTANCÍ
of America as represented by the Secretary of the Army. All manufacturers with an appropriate interest were thoroughly briefed on the discovery and told that the designs would be made available. The first commercial panoramic X-ray machine was the Panorex, made by S. S. W hite.
In July 1966, Prof. A. G. Richards published an article in "JADA" describing a new X-ray head design which is used today in some machines manufactured in the United States and Japan. The design permits the use of long cone techniques in offices that are only large enough for short cone size heads. It does this by placing the X-ray tube at the back of the head housing rather than in the conventional forward position.
An example of X-ray units designed in the 1960s is this Ritter M ark 75 (model H ), introduced in 1966. It provided a simplified technique with preset milliamperage and kilovoltage.
Glenner: DENTAL X-RAY UNITS ■ 561
1975 Models ê
w~
ü G S Q B [W SSSm i
1
1
D en tal X -R ay 065, B elm o nt E qu ipm ent Corp., S om erset, NJ
P a n e x Div., O ratro nics Inc., N ew York
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■ l m
r ii m i p
ri,
r^ ä T i.i
M W —
I M e te o r II, R itter Co., R ochester, NY
S a fe -R a y , Litton D en tal Products, Toledo, Ohio
562 ■ JADA, Vol. 90, March 1975
O rtho pantom og raph , S ie m e n s Corp., Ise lin , NJ
P -O R IO I O rallx 50 D en tal X -R ay System , Philips M e d ic a l S ystem s, Inc.,
W e b e r D ental Mfg. Co., C anton, Ohio P an o re x , S. S. W h ite Co., P hiladelph ia
S helto n, C onn
! •Æ'-m* ' ""fl
II
JT*
P ane lip s e P a n o ra m ic X -ray S ystem , G e n e ra l E lectric Co., A m e ric a n a X -ray Co., E ng lew ood, NJ
M edical S ystem s Div., W a u k e s h a , Wis
Glenner: DENTAL X-RAY UNITS ■ 563
