Dental x-ray equipment (194?)

for thirty years the American Dental Association has co-opted with the National Bureau of Standards in research on dental materials in 1947 the program was enlarged to include the federal dental services the program includes studies of radiation protection this has contributed to the publication of handbooks containing the recommendations of the National Committee on radiation protection of special importance to dentists is handbook 59 permissible dose from external sources of ionizing radiation and book 59 deals with terminology radio biological considerations maximum permissible doses and recommendations for protection also recommended for every dental office is handbook 60 x-ray protection in this handbook there is a special section on dental x-ray installations these handbooks are available at small cost from the superintendent of documents Washington DC every dentist and dental assistant operating x-ray equipment should read these handbooks although the use of high-speed film provides the major reduction in radiation to the patient this picture deals principally with modifications of many dental x-ray machines to provide maximum safety there are about 80,000 of these dental x-ray machines in use in the United States every x-ray installation should be examined to determine whether the patient is receiving a minimum dose of x-rays in making good diagnostic films and whether adequate protection is provided for dental personnel let us consider first how the patient exposure may be reduced this beam of radiation exposes about 10 square inches of the skin at each exposure because this x-ray machine did not have a lead diaphragm that would restrict the beam one can easily be installed however now the radiation can escape only through the aperture which determines the size of the useful beam this beam of radiation is only two and three-quarter inches in diameter so less than 6 square inches of the skin are exposed the large red circle shows the area of skin exposure without the diaphragm the small green circle shows the area of skin exposure with the LED diaphragm this small change in diameter actually reduces the irradiated area 40% if you are unable to obtain a let diaphragm from the manufacture of your x-ray machine you can easily make one in this particular machine the outside diameter of the lead washer should be three inches for called lead sheet which is one sixteenth inch thick may be obtained at a plumber shop a three inch circle is inscribed on it with a compass the LED disc is easily cut out with a pair of shears the next step is to determine the diameter of the inner circle to do this a line two and three-quarter inches long is drawn this line represents the desired diameter of the useful x-ray beam as it strikes the skin find the center of the line mark this point s erect a line perpendicular at Point s the length of this line t s is the length of the target skin distance here line TS is seven inches long because a short cone is being used now measure from the tip of the cone to the point where the lead washer or diaphragm is to be installed in this instance the distance is 3 and 1/8 inches this diaphragm skin distance D s of 3 and 1/8 inches is laid out on line T s now lines are drawn from T to L Prime and from T to L the red area is a cross section of the useful beam from the target to the skin the area of radiation will be a circle two and three-quarter inches in diameter and point D where the lead diaphragm is to be located draw a line parallel to the base line now the distance ay B represents the diameter of the aperture in the lead diaphragm that will restrict the beam to a two and three-quarter inch circle as it strikes the skin in this instance line a B measures one and 9/16 inches now a circle one and 9/16 inches in diameter is inscribed in the center of the lead disc it can easily be cut out with a pocketknife the LED diaphragm is placed in the x-ray apparatus about 20% of the dentists use a long cone the target skin distance being from 12 to 20 inches this cone has a target skin distance of 15 inches again we note the lead diaphragm is missing but one can easily be installed the opening of the lead diaphragm for the long cone is smaller than for the short cone this is shown by comparing the two drawings and the two LED diaphragms another method of determining the diameter of the aperture is to place a cardboard circle of mounted pins in the path of a direct beam at the position where the lead diaphragm should be installed an exposure is made and the films are developed the number of pin images within a two and three-quarter inch circle are shown on the left the same number of pins on the cardboard at the right gives the diameter of the aperture one can expose across the films on which is laid some wires and thus determine the area of exposure the cross on the Left shows the radiated skin area without a diaphragm the right cross shows the reduced area with a diaphragm the dentist is responsible for safety in the use of his x-ray equipment every machine should be examined to see if there is adequate filtration this new machine does have the proper amount of filter however most of the older machines have no added filters and it is necessary to install them this aluminium disc absorbs much of the less penetrating radiation the so-called soft radiation represented by the red rays otherwise these rays are absorbed by the skin and cheek and do not reach the film the glass wall of the x-ray tube and any material through which the useful beam passes filters the radiation to some degree the amount of this inherent filter varies with the make and model of the x-ray machine this value can be obtained from the manufacture the manufacture will tell you the equivalent thickness in millimeters of aluminum by which the beam is filtered by one the wall of the glass tube to the housing and three the plastic cone this inherent filter may vary from one quarter to two millimeters of aluminum equivalent if the inherent filtration is less than two millimeters then additional filtration in the form of aluminum discs should be added if you are unable to obtain these aluminum filters from the manufacturer you can easily make them obtain an aluminum cookie sheet that is marked pure or commercially pure aluminum measure the thickness of the sheet with a micrometer caliper in this case the aluminum is one 1/2 millimeter think the inherent filtration of this machine is equivalent to 1 and 1/2 millimeters of aluminum there 4 and 1/2 millimeter to bring the total filter up to 2 millimeters the diameter of the port is measured a circle which has this diameter is inscribed on the aluminum sheet with the covers the disk is conveniently cut out with shears the thickness is one half millimeter the installation of the filter is a simple matter the machine now has a total filtration of the equivalent of 2 millimeters of aluminum if as much as 1 and 1/2 millimeters of aluminum have been added it will be necessary to increase your usual time of exposure by about 40% thus a one second exposure would be increased to 1 and 2/5 seconds with less added filter the exposure need not be increased as much however the dose to the patient will be decrease to about 1/2 because most of the less penetrating rays shown in red that would be absorbed by the tissues are absorbed by the added aluminum after installation of the lead diaphragm on the filters the tube head should be checked for leakage radiation through the tube housing by exposing a cross of dental films the clear areas outside the dark circle made by the useful beam show there is no dangerous leakage of radiation should it occur ask the machine manufacturer to correct this problem other sides of the tube head should also be tested for leakage the three-foot timer cord on this machine is too short the cord should be at least five feet long to permit the operator to stand out of the path of the useful beam and where the secondary radiation is within permissible limits if your x-ray machine has an exposed to bad and an exposed high tension cable such as these there is only one thing to do replace this obsolete and dangerous equipment mechanical timers cannot provide the short exposures required for the new high speed films inquire from the manufacturer if it is possible to install an accurate electronic or synchronous motor timer on your old machine that will permit the split-second exposures needed for operating with high speed films high speed film can be used with the slow mechanical timers by doubling the length of the cone I speed film can also be used with the slow mechanical timers by reducing the milliamp range exposure of the human body to x-radiation is biologically undesirable therefore the dentist should make certain that his x-ray machine is giving the minimum radiation to the patient consistent with a good diagnostic care how can this be done read the handbooks these Official handbooks will serve as your the x-ray protection for you your personnel and your patients limit the useful beam area as it strikes the face to do this use the proper LED diaphragm to control the x-ray beam area to two and three-quarter inches the useful beam must be filtered adequately the inherent and added filtration should be not less than the equivalent of two millimeters of aluminum these filters absorb the useless soft rays that are absorbed by the soft tissue and do not reach the film check tube head for leakage or example small intense escaping through gaps about the port and cone can be shown by exposing some films and the developed films should show no exposed section other than the area covered by the useful beam leakage through other parts of the tube can be similarly examined such as leakage through the end of the tube check length of timer cord the timer cord should be long enough to permit the operator to stand at least five feet behind the tube high speed film may be used with old-style mechanical timers if a long con or reduced milli ampere age are used remember it's you the dentist who is responsible for the safety of his x-ray equipment and for the protection of his personnel and patients from unnecessary exposure to x-radiation you