THE EDITOR'S CORNER
The contribution that orthodontic diagnostic x-rays may make to the overall hazards of radiation and the precautions to be taken to protect patients and personnel are usually included in a general discussion of hazards and precautions. The orthodontist has been on the defensive about the number of diagnostic x-rays he may wish to take, and he is generally cautioned to err on the side of safety which makes good sense. Nevertheless, it would be well to try to understand what the scope of the radiation problem is and what part the orthodontic x-rays play in it.
To shed some light on the question of the dentists' contribution to the problem of radiation and on guidelines to radiation protection in the dental office, the following quotations are taken from Reports 35 and 39 of the National Council on Radiation Protection and Measurements.
"With conventional radiographic projections, the direct exposure of the gonads to the useful beam does not occur and the use of a lead apron is not indicated. In proper dental radiography, gonadal exposure of the patient is due almost always to the scattered radiation alone. Although the gonadal exposure of the dental patient is extremely small when the recommendations of this report are followed, a further reduction in gonadal exposure is possible with the use of gonadal shielding. In terms of its practical significance, this reduction is relatively unimportant. However, when unconventional projections are used and the gonads may be in line with the useful beam, gonadal shielding is mandatory."
"The gonadal exposure from a complete mouth examination performed under proper conditions is of the same order of magnitude as one day's exposure to natural background radiation . "
(The one time in an orthodontic diagnostic examination when the gonads may be in line with the useful beam is in taking an occlusal film of the upper teeth with the patient in a conventional upright position. It seems clear that the method of taking this view should be changed. The patient may still be seated in an upright position, but the head should be thrown back as far as possible. This would throw the useful beam far away from a direct line with the patient's gonads. ED.)
"Uncertainty remains as to the nature and degree of presumed radiation effects at and below the recommended exposure levels.... However, it should be noted that the difficulties of obtaining information at low doses are due mainly to the extremely low frequency with which effects might occur."
"Natural radiation varies, from 30 millirems a year in Dallas to 130 millirems per year in Denver. However, this degree of difference is not currently regarded as of sufficient magnitude to suggest that a person move, for example, or change his occupation."
"The average annual genetically significant dose (GSD) from diagnostic procedures in the United States has recently been the subject of intensive and continuing studies. From initial results it would appear that the U.S. average annual GSD in 1964 was about 55 millirems per year from diagnostic procedures. About 0.15 millirems can be added for dental examinations, and a rather uncertain 10 millirems for therapy contributions. In total, medical irradiation (as genetically significant dose) is probably between 50 and 70 millirems per person per year."
"The radiation response differs with age. The high sensitivity of certain embryonic stages is well known, and has led to special precautions in the exposure of pregnant women. Also, there may be critical periods of organ development between birth and maturity, where the effect of radiation exposure may be relatively more significant."
"It is clear, that if the absorbed radiation energy is sufficiently spread in space and time, much damage can be repaired."
"It is necessary, at the present time, to accept a large degree of uncertainty in the estimation of the genetic consequences of radiation exposure in man. In view of this uncertainty, conservative exposure guides are indicated for individuals capable of reproduction."
Table 1 is reprinted from NCRP Report No. 35. It is presented to give some further perspective to this problem, keeping in mind that one rem equals 1000 millirems and that dental diagnostic x-rays contribute 0.15 millirems per person per year to the total radiation received; and with the caution that the figures are conditioned by the qualifications and comments provided in the report. It is recommended that all orthodontists purchase and study Reports 35 and 39. Together they cost $3.50 and are available from NCRP Publications, P.O. Box 4867, Washington, D.C. 20008.
When one considers that the average orthodontic office may conduct less than 100 initial diagnostic examinations per year and less than 100 final studies per year; that additional films taken might not total 500 a year; that all of this may be 3000 x-ray exposures per year with a maximum exposure of ½ second at 10 milliamps, making a total of 60 exposures a week or a generous maximum of 300 milliamp seconds per week; we are not talking about very much radiation for the individual patient, for the office personnel, or for the environment.
Nevertheless it makes good sense to have a healthy respect for a radiation source and to observe protection precautions that will produce the lowest practicable dose commensurate with a realistic evaluation or measurement of the hazard. For the orthodontic office, in my opinion, mandatory precautions should include:
1. Minimal size of the useful beam.
2. Adequate filtration, determined by measurement.
3. Minimal leakage of tube housing.
4. Timer to permit exposures as short as 1/60th of a second.
5. Adequate timer switch and circuit breaker.
6. Adequate wall protection for personnel and neighbors, and safe position for operator, based on measurement.
7. Exposure for useful films only; not for training purposes.
8. No holding of films or tube housing by operator.
9. Number of films kept to minimum consistent with clinical objectives.
10. Speed of film kept to maximum consistent with clinical requirements.
11. Using techniques for taking and processing the films which will minimize the need for retakes.
12. Avoiding the pointing of the useful beam directly at the gonads.
Secondary or optional precautions in the orthodontic office could include:
1. Lead apron for gonadal shielding.
2. Film badge monitoring for personnel.
3. Long cone technique for intraoral x-rays.
Report No. 39 concludes its section on lowest practicable dose with this statement: "Ultimately, realistic interpretation in various applications derives from public understanding of, and eventual approbation of, practices developed from recommendations of responsible technical bodies. In particular, it is believed that while exposures of workers and the general population should be kept to the lowest practicable level at all times, the presently permitted exposures represent a level of risk so small compared with other hazards of life, and so well offset by perceptible benefits, that such approbation will be achieved when the informed public review process is completed.
