Clinieal Communioation

Exposure to dental radiation — a perspectiveNeill J. Serman*

The aim of every operator should always be to expo.se the patient to as close to zeroradiation as possible. The atmntnts of radiation received from correctly taken dentalradiographs are contparable to the background radiation received by the population.The average increase in exposure to the patient lo radiation on an annual basis is notsignificant, and. without the infortnation obtained from the radiographs, a cotnpletedental assessment cannot be made. Provided thai the operator is takitig radiographsonly after a clinical assesstnent has been made that they are required at that stage atidprovided that minitnal doses and maxitncd radiation protection are ensured, ihe addi-tiotial amount of radiation to the patient is lo\i. Because of the probable advantages tothe patient under these circumstances, the operator should not hesitate to take the nec-essary radiographs. (Quintessence Int 1990:20:331-333.)

Introduction

The disturbing effect of unfavorable articles on patientexposure to radiation in the lay press is that the dentistand the hygienist are often placed on the defensivewhen recommending dental radiographs for their pa-tients. This renders the efforts of educating patientsto accept oral radiographie procedures all the moretrying.' Public concern often stems from insufficientknowledge or confusion.- Furthermore, because theharmful effects of low doses of radiation may not havebeen studied as a directly observable discrete changein specific individuals, the field is left open to conjec-ture.' The science of dental radiology suffers, becauseit attracts negative attention disproportionate to itspotential for causing radiation injury.'' The lay pressis replete with information about the harmful effectsof radiation. However, there may well be physiologicalbenefits from low levels of ionizing radiation.^ Minutedoses of ionising radiation benefit animal growth anddevelopment, fecundity, health, and longevity,̂ Lim-

• Professor and Head, Division of Diagnostic Sciences, School ofDental and Oral Surgery, 630 West 168th Street, Columbia Uni-versity New York, New York 10032,

ited data suggest that reproduction rates of protozoadecrease when they arc maintained in subambicnt ra-diation environments, which may be interpreted to bea radiation deficiency.̂

The aim of every operator should always be to ex-pose the patient to as close to zero radiation as pos-sible when radiographs are taken. For that reason, theprofessional must use careful judgment to determinethe type, frequency, and extent of each radiographieexamination. Radiation for diagnostic purposesshould be utilized only after a clinical examination andassessment of both the dental and general health needsofthat patient.^ Dentists in general have made a con-certed effort to reduce the amount of radiation towhich their patients are exposed.'*"

At the same time, radiographs arc often essentialfor the successful treatment of patients. It is thereforeimportant to examine all aspects objectively so thatthe practitioner is better informed when recommend-ing radiographs or when asked questions about ra-diation exposure or dangers by patients,

"From their prehistoric beginnings through geolog-ical periods of time, man as well as all living organismshave been exposed to natural background radia-tion , , . Radiation ofthe sun is deemed a prerequisitefor life to continue.'"'' Exposure to medical (and den-tal) radiation is only a minor source of ionizing ra-diation to humans. People are subject to radiationfrom both natural and manufactured sources. Naturalradiation anses from cosmic rays and naturally oc-

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Clinical Communication

Table I D-speed film'*

50 kV(p} 400-500 niR/per film65 kV(p) 300-400 mR/per film70kV(p) 215-365 mR/pcr film75 kV(p) 200-325 mR/per film90 kV(p) 100-200 mR/pcr film

curring radioactive elements on the earth,'" The hu-man body itself contains traces of radioactive carbon,which is deposited in bone.'"

In considering the effects of natural radiation onhumans, it is probably the dose to the gonads that ismost important. The average dose from all the abovesources has been estimated at roughly 0,1 rad per year,or about 3 rads per generation of 30 years,'" Takingall the manufactured sources of radiation together, thetotal gonadal dose is estimated to amount to 25% ofthe natural background radiation, or 1 rad in a gen-eration of about 30 years,'" Hill" estimates that med-ical and other industrial sources of radiation accountfor 16,5% of the radiation to which the population isexposed. Hall'- estimates that the doses of radiationfrom medical nses received by the human populationis 23,2 mrem per year (19,8%) whereas natural back-ground radiation accounts for 76.8% of the total ra-diation dose received by humans annually. On the oth-er hand, Goaz and White'' slate thai medical anddental sources of radiation are greater than only cos-mic sources of radiation. However, they state that thetotal natural background radiation accounts for56.1% of annual whole body dose rates in the UnitedStates 1970 (before the introduction of E-spccd dentalradiographie film, etc).

Grosch and Hopwood'' state that humans living ongranite at an altitude of 10,000 feet receive a totalnatural dose of 207 milhrad per year, while the dosefor people living at sea level drops to 142 millirad peryear. At sea level, for people living on sedimentaryrock, the total natural dcse would drop to 75 milliradper year. The estimated average for the whole worldper person per year receiving natural background,whole body radiation is 90 millirad. It is representativeof the level of radiation to which people are exposedin population centers on the eastern coast of theUnited States and much of Furope, However, thereare people living in different parts of the world who

receive doses more than ten titnes greater than Iheaverage without any obvious detrimental effects,'' Theearth's magnclic field influences the charged cosmicparticles so that they are deflected toward the poles,and the intensity is greater toward the higher lati-tudes,"

Goaz and White'-' report Ihut in the United Statesin 1964, 226.7 million denial radiographs were taken,and Ihis atnounl increased to more than 400 millionin 1982, On Ihe olher hand, an exposure study in 1964disclosed that the mean exposure per single denial filtnwas 1138 mrem. This decreased to an estimated ex-posure of 360 mrem in 1980, The average exposureusing D-speed film on an x-ray machine with a 50-kV(p) output varies from 425 to 575 mrem, and ex-posure decreases to 120 to 180 mrem at 90 kV(p) andD-speed film (Table 1¡, Using F-speed film and thesame kV(p)s, the dose to the patient is reduced lo 220to 320 mrem and 70 to 90 mrem, respectively. In the50 to 70 kV(p) range there is 1.5-mm Al filtration, andin the 90 kV(p) range the filtration is 2,5-mm Al equiv-alent,'^

It is estimated that a person living in an averagelocation (excluding the two extremes of backgroundradiation exposures) in the United States and receivinga set of complete-month radiographs as well as a pan-oramic radiograph every 4 months, would incur onlythe same risk of exposure to radiation (in terms ofbone marrow exposure) as a person living in Denver,Colorado, who is not exposed to any dental radia-tion,"'

Natural background radiation remains, by far, thegreatest source of radiation to the population today,''Any radiation dose that is small in comparison withbackground doses may be of trivial biological impor-tance and be accepted as part of the normal hazardsof living.̂ Dental sources account for a small per-centage of the total combined medical radiation ex-posures. Furthermore, the total amount of radiationreceived by the patient from dental sources is relativelylow.

On the other hand, it is equally important to con-sider the consequences and risks to the patient of nottaking radiographs when they should have been taken.Everyday pathology such as caries and periodontalbone loss is often first detected radiographically. Thelack of radiographs may make it more difficult to planappropriate treatment or may compromise treatment,resulting in a greater risk of failure of planned pro-cedures. In addition, it could result in irreversibledamage to bone and or teeth and in treatment having

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Clinieal Communication

to be redone or eventually costing the patient muchmore than if the radiographs had initially been taken.A lack of radiographs ean have disastrous tnedicolegalconsequences.

Discussion

The amounts of radiation received by the patient frommedical (and dental) uses are relatively small. In ad-dition, the amount of radiation per exposure has beenreduced considerably, and the protcssiou is continuallyattempting to reduce the radiation exposure to thepatient even further.

In the face of impressive evidence as to the benefitsthat many patients derive from early diagnosis as aresnit of information obtained from radiographs, it isunreasonable to crusade against the use of radi-ographs on the grounds that they may be hazardous,especially because the doses involved from dental ra-diation are small compared to those from naturalbackground radiation." With the improved tech-niques, such as iong rectangular cones and thyroidshields, and F-speed film on the horizon, etc, theamounts of radiation to the patient are being reducedeven further.

Conclusions

Pro\ided that the practifioner has made a clinical as-sessment that the probable advantages to the patientof having radiographs taken outweigh the possible dis-advantages, and the operator has taken all reasonablepreeautions to reduce the amount and voiume of ra-diation to the patient, it is the duty of every practi-tioner to take necessary radiographs, particularly ifthe average increase on an annual basis of exposureto radiation to that patient is not significant. The lackof information from not taking radiographs will oftenresult in the inability to make a complete dental as-

sessment of the case, which may often seriously jeop-ardize the treatment.

References

t. O'Brien tîC: Dentat Radiüfiraphy: An ¡mrriduction for De!UalHysieiils-!s and A.i.mtaiits.ed 3. Phikidclphia, Wtä Saundei-s Co.1977, pp 9-n,

2. Radiation — diffusion or conlusion. editorial. Am .1 Onhod1982;82:2S7-259.

3. Liingiiind OA, Langiais RP. McDavid WD, et at: PanoramicRadioloKy, ed 2. Philadelphia. Lea & Rbiger. I9B9, pp t7t-179.

4. Taylor LS; Dental radiology. Trends, issues and problems. J AmColl Dem t982;49:t4^20.

5. Luckey ID: Physiological benefits from low levels of ionisingradiation. Health Physics 19S2:43:771-789.

6. American Dentai Association Council on Dentai Materiais, tn-struments and Equipment: Recommendations in radiographiepractices. J Am Den! A.t.^oe 1984; 109:764-765.

7. Baum AT, Morgan EM: Reduction of x-ray dose by variablerectangular collimation and retles opliciil direction of dentai x..ray beams and by the supine position of the patient. J Am Den!Assoc 1972:85:1091-1098.

8. Liidlow JB; Reducing the risk of dental \.riiy exposure../ MiiliDen! Assoe 1984:66:256-261.

9. Grosch DS, Hopwood LE: Bhioaieid Effects of Radiaüim.ed 2, New York, Academic Press, 1979, pp 8-9, 279-28t.

to. Walter J, Miller H, Bomford G: Á Shor! Te.\!bovk af Radio-!tmupy, ed 4. London. J and A Churchill Ltd. t977, pp 172-t74.

11. Hill DR: Principles of Diagno,s!ic X-Rtiy Apparatus. Bath, Eng-land, Piltman Press, t977, pp 50-51.

12. Hall EJ: Radiation and Life. Oxford, England, Pergamon Press,1980, pp 178-181.

13. Goaz PW. While SC: Oral Radiology. Principtes and Interpre-nuion. St Louis, CV Mosby Co, 1982, pp 63-68.

14. Average Patient Exposure Guides: 1988. Conference of Radia-lion Control Program Directors, Inc, Committee on Q'^'ilityAssurance in Diagnostic Radiology. CRCPD publication No.88.5, 1988, p 3 .

15 Langland OA, Langiais RP: A Comprehensive Clinical Coursein Dental Radiology, manual. San Amonio, Texas. Departmentof Dental Diagnostic Science. University of Texas DenialSchool. 1985. pp 14-16.

16. White SC. Rose TC: Absorbed bone marrow dose in certaindenial radiographie techniques. J Am Dent Assoc 1979;98:553-556,

17. Fireman SM: Background radiation. Oral Health 1982;72(7|: 19-20 D

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