document resume - eric · efficacy, dental radiology education curricula, professional...
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RD 200 762
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DOCUMENT RESUME
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Manny, Edward F. And OthersAn Overview of Dental Radiology. NCHCT MonographSeries.Food and Drug Administration (DREW), Rockville, 4d.Bureau of Radiological Health.; National :enter forHealth Care Technology, Rockville, Md.7 Nov 8053p.
MFO1 /PCO3 Plus Postage.*Allied Health Occupations: Allied Health )ccupj ionsEducation: *Biomedical Equipment: compete:toe;Continuing Education: Cost Effectiveness; Zosts;Demography: *Dental Evaluation; *Dental Technicians:Dentistry: Educational Needs; Guidelines; LaborNeeds; *Occupational Information; ProfessionalAssociations; Quality Control; *Radiology; Standards;State Programs: Vocational Education
ABSTRACTThis overview of dental radiology contains sections
on demographics, equipment, dental radiology quality assurance,efficacy, dental radiology education curricula, professionalorganizations' guidelines for training and use, and state activities.In section 1 dental personnel, population of dental personnel,employment add earning prospects, dentist-to-population ratio, dentalvisits, dental radiographs, dental care and x-ray costs, and selectedhealth characteristics are described. In section 2 conventionaldiagnostic x-ray equipment, performance standards, new technology,ancillary equipment, and an alternative modality are described. TheDental Surpak program, nationwide evaluation of x-ray trends, theNashville Dental Project, the Dental Exposure NormalizationTechnique, and the present status of quality assurance in dentalradiology are discussed in section 3. Section 4, which coversefficacy, contains information on examination frequency, trends, andcosts: radiation exposures, doses, and risks; routine x-rays,referral criteria, and post-treatment radiographs. Dentists, dentalauxilliaries, and continuing education are examined in section 5,which deals with dental radiology education curricula. Section 6outlines professional organizations' guidelines for training and use.It presents comments on curriculum development and the findings andrecommendations of professional organizations. State activities aredescribed in section 7. A total of 134 references and 29bibliographic citations are included. (MN,
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AN OVERVIEW OFDENTAL RADIOLOGY
Edward F. MannyKaren C. Carlson
Philip M. McCleanJay A. RachlinPhyllis SegalPolly C. Story
Food and Drug Administration Bureau of Radiological Health
U S DEPARTMENT OF HEALTH.EDUCATION / WELFARENATIONAL INSTITUTE OF
EDUCATION
THIS DOCUMENT HAS BEEN REPRO.(DIKED EXACTLY AS RECEIVED FROMTHE DERSON OR ORGANIZATION ORIGIN.ACING IT POINTS OF VIEW OR OPINIONSSTATED OD NOT NECESSARILY REPRE.SENT O FFICIAL NATIONAL INSTITUTE OFEDUCATION POSITION OR POLICY
NCHCTNational CenterFor Health CareTechnology
bure,u of ratfiolontcal health
Editorial Staff for the National Center for Health Care TechnologyPeter S. Alterman, Ph.D.Barbara Gastel, M.D., M.P.H.Michael Eliastam, M.D.
FOREWORD
Medical technologies pose many complex and interrelated issues for the health care professions, forpatients, and for society. To help address these considerations, Congress established the NationalCenter for Health Care Technology to conduct and sponsor assessments of health care technologies.Publ' Law 95-623 (the Health Services Research, Health Statistics, and Health Care Technology Act of1978), which created the Center, defines health care technology broadly to include any means to prevent,diagnose, or treat disease or promote health. Furthermore, it calls for evaluation not only for safety andefficacy, but also for the social, ethical, and economic implications of technologies.
To provide medical and scientific background on certain selected technologies generally considered tobe of particular significance, the Center has commissioned a series of overview papers, one of whichfollows. These were written by one or more authorities and are designed to review that state-of-the-artand identify, but not resolve, the key issues surrounding the subject. They are not intended to be corn-prehensive surveys of the literature. Each paper has been subjected to review by appropriate medicalspecialty societies, government agencies, and individual experts, and has been revised accordingy.
These overviews are likely to be of most immediate interest to clinicians and biomedical scientists; theyalso may provide valuable background for assessments undertaken by the Center and for exploring thebroad sjcietal implications of health care technologies.
This paper was prepared for the Center by experts at the Bureau of Radiological Health of the Food andDrug Administration. We are grateful for the time and effort they expended in the production of this corn-prehensive overview, and we look forward to other fruitful collaborations.
It is our hope that you will find this paper interesting and useful.
Seymour Perry, M.D.Director, National Center for Health Care TechnologyOffice of Health Research, Statistics, ar.d TechnologyPublic Health ServiceU.S. Department of Health and Human Services
November 7, 1980
=ill
PREFACE
This overview report has been prepared at the request of the National Center for Health Care Technology(NCHCT). It is one of several projects entered into jointly by the Bureau of Radiological Health (BRH) andNCHCT relating to the use of radiation for health care.
Dental radiation protection has been a long-time interest of BRH. Both our past and on-going efforts to
minimize population radiation exposure from electronic products have included specific action pro-grams directed at minimizing unnecessary radiation exposure to the population from dental radiology.
Our current efforts in quality assurance and referral criteria are two aspects of our own assessment of
this technology which are described within the larger picture presented in this overview.
The issues considered in this document go beyond the radiation exposure aspects of dental x-ray pro-cedures. To be responsive to the informational needs of NCHCT, the assessment includes various otherfactors that influence the practice of dental radiology. We hope this analysis will serve as the basis for
planning and conducting future programs to improve the practice of dental radiology.
I would like to express my appreciation to NCHCT for inviting and supporting our participation In
development of this publication.
John C. VillforthDirectorBureau of Radiological HealthFood and Drug Administration
TABLE OF CONTENTS
Page
FOREWORD iii
PREFACE v
INTRODUCTION
DEMOGRAPHICS 2
Description of Dental Personnel 2
Population of Dental Personnel 3
Employment and Earning Prospects = 4
Deotists.to-Population Ratio 5
Dental Visits 5
Dental Radiographs 6
Cost of X-Ray Examinations 6
Cost of Dental Care 7
Selected Health Characteristics 7
EQUIPMENT . . ..... . ........ . . . ... . . . . _ . . . . . 11
Introduction . . . . . . . . . - .. - . - - .. .... 11
Conventional Diagnostic X-Ray Equipment 11
Performance Standards 11
New Technology 12
Ancillary Equipment 15
An Alternative Modality 16
DENTAL RADIOLOGY QUALITY ASSURANCE 17
Introduction 17
Dental Surpak Program 17
Nationwide Evaluation of X-Ray Trends . ... . . . 18
Nashville Dental Project . . ... . . . . . . ....... . . . 18
Dental Exposure :-,lormalization Technique (DENT) 19
Present Status of Quality Assurance In Dental Radiology 19
EFFICACY 21
Introduction 21
Examination Frequency and Trends 21
Examination Costs and Trends 23
Radiation Exposures, Doses, and Risks 23
Routine X Rays 24
Referral Criteria ... . . . .. . ...... . . ...... . . . . 25
Post-Treatment Radiographs 26
Recommendations 26
DENTAL RADIOLOGY EDUCAT -)INI CURRICULA 27
Introduction ... . . ..... . . ...... . . . . . . . . . . . . ... 27
Dentists . . . . . . .. . . . .... . . . . . . .. . ... . . ... - 27
Dental Auxiliaries . . .. . .. .. . . . .. . ... . . 28
Continuing Education 29
vii
Page
PROFESSIONAL ORGANIZATIONS' GUIDELINES FOR TRAINING AND USE 30
Introduction 30Curricula Development 30Findings and Recommendations of Professional Organizations 33
STATE ACTIVITIES35
SUMMARY AND CONCLUSIONS
REFERENCES
BIBLIOGRAPHY
viii
38
39
45
AN OVERVIEW OF DENTAL RADIOLOGY
INTRODUCTION
Intraoral and extraoral radiographs are an ex-tremely valuable diagnostic tool in dentistry.Common chronic diseases such as caries andperiodontal problems may present few physicalsymptoms during their early stages. Similarly,developmental abnormalities may remain hid-den to direct clinical observation until well ad-vanced. The consequences of failing to detectdental diseases range from relatively slight bio-logic disability to fatality in the case of malig-nant tumors or oral-source blood-borne infec-tions_ Radiographs can permit early detection,diagnosis, and treatment of many conditions.
Nonetheless, public concern about radiation ex-posure and health care costs is increasing. Re-cently, both the news media and Congressionalhearings have focused substantial attention onthe potential hazards of exposure to ionizingradiation. Accordingly, the present state of den-tal radiographic practice should be appraised_The scope of this report is a broad examinationof the safety, efficacy, cost effectiveness, andeconomic, social, and ethical impacts of dentalradiology.
Dental radiology is used extensively in deliver-ing dental care. Approximately 145,000 dentalx-ray machines are in operation in the UnitedStates, and according to 1976 information335,702,000 dental visits were made by102,620,000 individuals. In 1978, 82 percent ofdental patients received radiographic services.Total 1978 expenditures for dental careamounted to $10 billion, $730 million of whichwas for dental radiographic services.
Another cost perceived to be associated withthe use of ionizing radiation in diagnosis is thepotential for detrimental effect on biologicaltissues. Although dental x-ray procedures con-tribute only about three percent of the averagetotal adult active bone marrow dose for a year,sources of unnecessary exposure to dentalradiation should be eliminated.
Several specific measures can minimize unpro-ductive exposure to dental x rays; each has asits goal the enhancement of x rays as a safe,cost-effective method of diagnosis in dentistry,First, unnecessary examinations should beeliminated, since they increase both risk andconsumer costs. Second, the diagnostic quality
of dental radiographs should be improved, be-cause poor quality can lead to misdiagnosis, re-peat exposure, and added cost. Third, develop-ment and use of techniques to reduce dose with-out compromising diagnostic quality should befostered.
Various factors influence radiation exposureand cost in dental radiology, and thus criticallyaffect attainment of the above objectives. One isthe practices of personnel who actually exposeand process dental radiographs, which arelargely shaped by the training they receive. Theadequacy of equipment is another factor, but amore fundamental influence is the collective at-titude of the dental profession regarding selec-tion of patients for x-ray examinations.
In an attempt to understand these factors sothat recommendations for improvement can bemade, this review addresses a wide range ofareas. The first section consists largely of dataon dentists and allied professions, and on ex-penditures for dental care. A summary of con-ventional equipment and new technologies isthen followed by a discussion of quality assur-ance in dental radiology, with special considera-tion given to the manner in which x rays are usedin dentistry. This is followed by a section on theefficacy of dental radiographic practices. Cur-ricula and training requirements are analyzed fortheir impact on performance. The remaining twosections outline existing guidance from profes-sional organizations and State agencies for thepractice of dental radiology, either voluntary ormandatory. Where feasible, recommendationshave been included in relevant sections of thereport.
Because the report refers to various Bureau ofRadiological Health programs at severalpoints, it is advantageous to define them at theoutset. The X-Ray Exposure Study (XES) of 1970is an important source of data regarding thevolume and rates of x-ray examinations. NEXT(Nationwide Evaluation of X-Ray Trends), a jointFDA/State surveillance program, currently pro-vides data on patient exposures for a set of spe-cific projections in different facilities within theStates. DENT (Dental Exposure NormalizationTechnique) is a quality assurance program de-signed to identify and correct exposure prob-lems in individual dental offices.
DEMOGRAPHICS
DESCRIPTION O DENTALPERSONNEL
Dentists
The key member of the dental health care teamis, of course, the dentist. Most dentists aregeneral practitioners who provide many types ofdental care; only about 10 percent are special-ists. The largest specialty group are the ortho-dontists, who correct dental malocclusions. Thenext largest group, oral surgeons, operate on themouth and jaws. The remaining specialties arepedodontics (dentistry for children); periodontics(treatment of diseases of the gums); prostho-dontics (the making of dentures); endodontics
(root canal therapy); public health dentistry; andoral pathology (diseases of the mouth). (1) SeeTable 1.
About 4 percent of all dentists teach in dentalschools, engage in research, or administer den-tal health programs on a full-time basis. Addi-tionally, many dentists in private practice par-ticipate in these activ 'Lies on a part-timebasis. (1)
Table 1. Number of Dental Specialists: Selected Years1955 through 1973 (2)
' Endodontics was not recognized as a dental specialty in
Dental Hygienists
In general, dental hygienists scale, clean andpolish teeth, and instruct patients in proper oralhygiene. They are the only dental auxiliary per-sonnel required by each State to be licensed,although specific responsibilities vary depend-ing on the law of the Stata where the hygienist isemployed. Among the tasks usually performedby hygienists are removing deposits and stainsfrom teeth, counseling and instructing patients
ws,
955 or 1960, and data are unavailable for 1965.
in care of teeth and in nutrition, applying fluo-ride for prevention of tooth decay, and perform-ing radiographic services. In addition, dentalhygienists often take medical and dental his-tories and make model impressions of teeth. (1)
Most hygienists work in private dental officesand many are employed part-time. Others workin school systems, public health agencies, gov-ernment, industrial plants, hospitals or clinics,or are involved in teaching or research. (1)
9 '
Dental Assistants
The dental assistant helps the dentist treat thepatient by performing such tasks as handing thedentist instruments, keeping the patient com-fortable and the operating field clean, and pre-paring materials for the restoration of teeth orthe making of impressions of teeth. Many dentalassistants also expose and process dentalradiographs. Dental assistants frequently per-
POPULATION OF DENTAL PERSONNEL
As might be expected, the number of dental per-sonnel in the U.S. is increasing (see Table 2).Hygienists, for example, more than doubledtheir ranks over the past decade. Concomitantly,there has been an influx of practitioners into
form non-chairside duties such as receiving pa-tients, arranging and confirming appointments,keeping records, sending bills, and orderingsupplies. (1)
Most dental assistants work in private officesler dentists in either individual or group prac-tices. Others work in dental schools, hospitaldental departments, or public health depart-ments_ Unlike dental hygienists, only about oneout of 10 works part-time. (1)
specialty areas (see Table 1). Immigration is alsoa source of additional dentists. According todata prepared by the U.S. Immigration andNaturalization Service, 421 dentists entered theU.S. in fiscal year 1973, in contrast to 182 infiscal year 1965_ (2)
Table 2. The Population of Dental Personnelby Selected Years
-1970 MALE FEMALE
Dentists 87,691 (97%) 3,11©( 3%)Hygienists 942 ( 6%) 14,863 (94%)
Dental assistants 1,866 ( 2%) 86,309 (98%)
As Table 3 shows, most dentists and hygienistsare practicing in private offices. Although perti-nent data are lacking, the concentration of den-tal assistants follows the same pattern. Amongauxiliaries, assistants far outnumber hygienists(see Table 4), a significant fact for the radio-
logical process, because although both hygien-ists and assistants commonly perform radio ,graphic examinations, educational and testingrequirements to monitor and promote compe-tence have received far less emphasis for dentalassistants than for hygienists.
Table 3. Employment Distribution (1970 4)
Den
63,4301,246
102,049
15711
1,172
88,075
Dentist officesPhyslolan.officesChiroOractic officesHospitala_ _
Convalescent instffutionsOffice of practitioners (other)Health service
Total
Hygienists
12,863154
24624
1,479
14,771
DentalAssistants *
*Breakdown of dental assistants not available; how-ever, almost all are in dental offices (see above).
Table 4. Percent of Independent Dentists Who Employ Auxiliaries:Selected Years 1955.1975 (5)
'Includes dental laboratory technicians and secretary-receptionists, as well as dental hygienists anddental assistants. These employees may be either full-time or part-time.
EMPLOYMENT AND EARNINGPROSPECTS
Dentists
After graduation, many dentists open their ownoffices, purchase established practices, or gointo group practice. Others enter the ArmedForces or the Public Health Service. Some go onfor advanced specialty or academic training.Employment opportunities for general practi-tioners look very good through the mid-1980s.Dental school enrollment has grown in recentyears, but without further expansion the numberof dentists is expected to fall short of the de-
mand for services. Population growth, increasedpublic awareness of the role of regular dentalcare in preventing and controlling dentaldiseases, and the expansion of prepayment ar-rangements are expected to increase the de-mand for dental services. (1)
Based on the limited data available, the averageincome of dentists in 1976 was about $39,500.Urban areas have greater demands for dentalservices, and therefore afford larger incomes fordentists than do smaller communities. Mostdentists work 5 days a week, averaging 40 to 45hours per week. Some offer evening hours. Manydentists practice part-time well beyond theaverage retirement age. (1)
A I
Dental Hygienists
Employment opportunities for dental hygienistsare expected to be good through the mid-1980s.Although the number of graduates is increasing,demand is expected to exceed supply. Oppor-tunities should abound for those seeking part-time employment or location in rural areas. (1)
Earnings of dental hygienists are affected by
type of employer, education, experience, andgeographic location. According to the limiteddata available, a full time dental hygienist work-ing in a private office earned an average salaryof about $12,900 in 1977. Dental hygienists em-
DENTIST-TO-POPULATION RATIO
Public demand for dental care has been increas-ing as the population, standard of living, andlevel of education have risen, and as private andFederal mechanisms for providing payment fordental services have become more widely avail-able and accepted. (2)
Between 1940 and 1975, the number of dentistsincreased from 76,000 to more than 100,000.However, this increase failed to keep pace with
DENTAL VISITS
In 1976, an estimated 335,702,007 visits to den-tists were made by 102,620,000 pe:sons. (4) De-
spite overall increases in utilization of dental
ployed by the government earned somewhatless. Usually, dental hygienists employed inprivate offices work from 35 to 40 hours perweek. (1)
Dental Assistants
The employment outlook for dental assistantsalso is excellent through the mid-1980 s. Salaryis largely dependent on education, experience,duties and responsibilities, and geographiclocation. In 1977, the average salary for a dentalassistant ranged from $7,400 to $8,300. The pre-vailing work week is 40 hours. (1)
population growth, so that the dentist-to-popu-lation ratio actually decreased from 57 per100,000 to 52 per 100,000. (6)
By 1990, the ratio of dentists per 100,000 popu-lation is projected to rise 24 percent. Approxi-mately 850 geographic areas, with a total popu-lation of about 13 million, have been identifiedas having critical shortages of dentists (general-ly indicating fewer than one dentist per 5,000persons); about nine-tenths of these areas arerural. (5)
services, ne number of visits per year has re-mained relatively constant for the various agegroups (see Table 5). The greatest percentage ofvisits occurred within six months of a prior visitsee Table 6).
Table 5. Number of Dental Visits Per Person Per Year
Table 6. Interval Since Last Dental Visit
1,mos. 1 yr. 2-4 yrs. Never Unknown Total Ref.
4.1%
5.0%
'14.5%
122%
13.1% 12.9% 13.9% 9.3% 1.1% 100% (7)13.2% 1123/4 .14.1% 9.7% 1.0% 100% (8)
STATISTIC ,NOT AVAlLABLE FOR 1975102° 44 % 132% 103% 1.5% 100% (9)11.0° a =14.0% 132% 11.2% 1.0% 100% (10)11.7% :14.8% 13.9% 11.8% 1.1% 100% (11)11.7% 32% 13.4% 12.3% 1.6% 100% (12)11.6% 118°/1-1377%-127% 1.4%- f00°A- 113)112% 14.2% 112% 13.3% 2.5% 100% (14)
DENTAL RADIOGRAPHS
In 1978 over 417 million packets of dental filmwere sold, (15) among which intraoral films werethe most frequently used. Nearly all dentistsnow use high-speed film. (16) The use of pano-
COST OF X-RAY EXAMINATIONS
In 1969, Americans spent an estimated $268.4million for dental radiographs. (18) A samplingof a population with dental insurance showedthat radiographic services accounted for 7.3 per-
ramie radiographs is increasing, but statisticsare not available. Statistics from the Bureau ofRadiological Health, however, do indicate anaverage of 4.1 exposures per x-ray experienceper patient. (17)
cent of total dental charges in 1978. (19)Extrapolation from this figure leads to anestimate of $730 million for the annual nationalexpenditure for dental radiography. Table 7presents the costs for various dental x-ray ex-aminations as a function of dental specialty.
Table 7. Cost of X-ray Examinations (1975) by Dental Specialty (20)
Copyrig t icy the American Dental Association. Reprinted by permissi
COST OF DENTAL CARE
During 1975 the average family spent $134 fordental bills, and as family income rises, so doesout-of-pocket expense. However, out-of-pockethealth spending takes a larger share of family in-come in lower income groups than in higher in-come groups. (21) The average per capita ex-pense for dental service in 1975 was $41. (22)
Dental Service Corporations, known as the DeltaDental plans, were the first providers of dentalcare coverage. By the end of 1974, an estimated23 million people were covered by some form ofdental insurance by -more than -140 carriers offer-ing dental prepayment. (23, 24) During the years1969 to 1977, the number of Americans with den-tal insurance increased from 7 million to 48
million. Between 1970 and 1977, the moneyspent annually for dental care more than doub-led from $4.4 billion to $10 billion. (19) By 1982,70 million Americans are expected to be coveredby dental insurance. (19) The Health Care Finan-cing Administration's Medicare program pro-vides some dental care, as do cooperative Stateprograms. Additionally, thirty-three of the totalfifty-three States/jurisdictions provide somedental coverage through Medicaid.
For each major category of dental service, Table8 indicates the proportion of patients in aselected, insured population who receive theservice, and also the contribution of that serviceto total charges during a 1-year period. Radiog-raphy accounts for 7.3 percent of all charges,and is the service most frequently provided.
Table 8. The Percentage of Patients Receiving a Service and thePercentage of Total Charges for the Service in an Insured Population (19)
`Approximately 17% of total charges are for services not included in this table.
SELECTED HEALTHCHARACTERISTICS
Utilization of dental care services depends upona number of variables, the most significant ofwhich are income and education. As family in-come increases, so does the use of dental ser-vices. Educational level has a similar effect.Fewer years of schooling are associated withlower utilization of services, even when financialbarriers are disregarded. (19)
Proportion of Persons Making an AnnualDental Visit
Based on 1979 data, an estimated 50 percent ofthe population sees a dentist during a given12-month period. This proportion decreases withadvancing age, with slightly over one-half of the
people 17-44 years old seeing a dentist, com-pared to about one-third of the population over65. The percentage of the population makingdental visits increases as family income rises.Among the 6-16 year age group, the percentagerises from 52 at a family income under $7,000, to79 at a family income of $25,000 and over. Racialdifferences are also noted; the proportion ofcaucasians making dental visits was 52 percentcompared to 36 percent for non-caucasians.This difference in utilization of dental servicesby race is striking (see Figure 1).
Between 1964 and 1979 the proportion of thepopulation making at least one annual dentalvisit rose from 42 to 50 percent, with femalesmaking a higher percentage of visits than malesduring both years. The proportion of caucasianswho made dental visits was twice as high as forall other persons In 1964, but the difference haddecreased somewhat by 1979,
Perc
ent o
f Pe
rson
s w
ith V
isits
00
0
1 =
IcII
I
0 0
White
All Other
1
5-64 65 Years?ars and Over
visits?5)
Visits by Residence and Age
Children 6-16 years of age and young people liv-ing in standard metropolitan statistical areas(SMSA) visited dentists more frequently than did
3
2
0
July 1957-June 1958
Urban
EA Nonfarm
FarmRural
children and young people living outsideSMSAs. Among children 6-16 living outsideSMSAs, those living in both nonfarm and farmareas visited the dentist at the same rate (seeFigure 2).
1979
SMSA
Nonfarm OutsideFarm ) SMSA
0
0-4 5 -14 15.24 25 and Over 0.1Age In Years
*Figure does not meet standards of reliability or precision.
6-16 17.24 2 andOver
Figure 2. Number of dental visits per person per year, by place ofand age: July 1957-June 1958 and 1979. (25, 26)
Visits by Place of Residence andGeographic Region
In 1979, the average number of dental visits perperson per year was 1.7 for the total population,1.9 for those in a Standard Metropolitan Static-
Visits by Income and Age
-amily income substantially affected the rate ofental visits. Among children 6-16 years of age,
those living in families with incomes of $7,000or more visited dentists about 40 percent more
9
esidence
tical Area (SMSA), and 1.3 for those living out-side an SMSA. The Northeast had the highestper capita number of dental visits (2.1), followedby the West (1.8), North Central region (1.6) andSouth (1.4). (27)
frequently during 1979 than those living infamilies with lower incomes. Similar differenceswere also found on the basis of family incomeas shown in Figure 3 for July 1957-June 1958 and
for 1979.
16
July 1967. June 1958 1979
Less Than $4,000
$4,000or More
OA
0.2
0.8
2A
2.7
1.0
2.1
Less Than $7,000
pm $7,000or More 2.3
0.5 0.5
1.61.5
1.7
1.2
0-4 5.14 1524 25 and Over 0.5 8-16 17-24 25 and Over
Age In Years
Figure 3. Number of dental visits per person per year, byfamily income and age: July 1957-June 1958 and 1979. (25, 26)
10
EQUIPMENT
INTRODUCTION
In assessing the efficacy, safety, and costaspects of dental radiographic practice, the in-fluence of x-ray equipment must be considered.This chapter will therefore attempt to discusscurrent applications of dental x-ray equipment.In addition, newer technologies that promise toreduce x-ray exposure and/or improve the qual-ity of radiographic images will be reviewed.
CONVENTIONAL DIAGNOSTIC X-RAYEQUIPMENT
Conventional dental x-ray machines are typic-ally self-rectified, with both x-ray tube and trans-former contained within the tube housing.Modern conventional dental units employ anopen-ended position-indicating device (cone)used primarily for aiming the tube head prior tomaking an x-ray exposure. Many newer position-indicating devices also help reduce scatter radi-ation by incorporating a metal cylindrical col-limator within the open-ended plastic cone.Some older dental units are still equipped withplastic pointed cones. Since they may lead todecreased image quality aid increased scatterradiation, their use is strongly discouraged.Position-indicating devices, commonly 4 to 16inches in length, are designed to insure that aminimum source-to-patient skin distance ismaintained during the exposure. Conventionaldental units typically operate between 45 and100 peak kilovolts (kVp), but most examinationsare performed at 60 to 75 kVp. Although machinetube currents typically range from about 5 to 15
milliamperes (rnA), most modern radiographictechniques specify 10 or 15 mA. Conventionaldental units are generally wall- or ceiling-mounted, but may be used as mobile units aswell
Radiographic films are of two basic types:screen and direct exposure. Direct exposurefilms are exposed directly to the x rays. Screenfilms are exposed primarily by the fluorescentlight given off by intensifying screens followingabsorption of x rays. Radiographic films canalso be classified as intraoral and extraoral,according to their placement during use. Intra-oral projections usually employ direct exposurefilm whereas extraoral projections generally usescreen film.
Intraoral dental film is a direct exposure filmconsisting of an emulsion spread on both sidesof a relatively rigid but flexible film base. It issupplied in individual light-tight packets readyfor use. These film packets may be placed infilm holders and held in place by the patient dur-ing the radiographic exposure. Intraoral filmsare manufactured as single or double packets,the latter being used when duplicate radio-graphs are desired.
Extraoral films are exposed while positionedoutside of the oral cavity. They are screen or(rarely) direct exposure film and are usually 5" x7" or larger.
The x-ray machine market has undergonesteady growth, both in the number of x-ray unitsassembled and in the number of manufacturers.A Bureau of Radiological Health (BRH) study in1967 reported 9 manufacturers of dental x-rayequipment, (28) whereas BRH recorded 31 man-ufacturers in July, 1979. (29) In addition, Bureaudata collected for the years 1975 through 1977indicated slow growth in the number of yearlyassemblies of conventional radiographicequipment. (29)
PERFORMANCE STANDARDS
History
Numerous reports of studies conducted fromthe late 1950s through the early 705 indicate thatmany dental x-ray units were operated withoutadequate provision for patient (or operator)safety. (30.34) For example, Miller reported thatprior to 1960 approximately 75 percent of thedental units in the U.S. would not meet recom-mended standards. (30) In a sample of almost34,000 medical and dental x-ray facility surveys,Fess, et al. found that in 1962, 36 percent of den-tal machines were inadequately collimated and46 percent were inadequately filtered. (21) OUPing the mid-sixties, a large percentage of dentalx-ray machines did not meet the recommenda-tions of the National Committee on RadiationProtection and Measurements (35) or of theAmerican Academy of Oral Roentgenology. (36)Responding to the need for a national dentalradiological health program, the Bureau ofRadiological Health initiated a dental qualityassurance program that was successful ineliminating much of the unnecessary x-ray ex-posure from dental x-ray units (see p. 18 ).
8
Equipment Performance Standards
In March, 1970, the National Council on Radia-tion Protection and Measurement (NCRP) pub-lished Report No. 35, which provided radiationprotection guidance in the use of ionizing radia-tion in dentistry. (27) Specifically, it offered userrecommendations for the dentist and safety rec-ommendations for persons conducting radiationprotection surveys. The report also providedmanufacturers' standards for the design ofequipment, including standards for collimation,filtration, leakage radiation, and source-to-patient distance.
The diagnostic x-ray equipment performancestandard was issued by the Bureau of Radio-logical Health, FDA, and became effective onAugust 1, 1974. (38) The x-ray standard requiresthat all new dental x-ray equipment meet certainminimal performance requirements before beinginstalled for use by the dentist. The standardspecifies minimum filtration requirements andlimits the maximum x-ray beam to no more than7 centimeters in diameter (2.75 inches) at asource-to-skin distance of 18 cm (7.1 inches) ormore. It is important to note that this standardonly applies to the exposure of intraoral films,except for occlusal-size films. Minimum source-to-skin distances are also specified to reduceabsorption of lower energy x rays in facialtissue. Other provisions of the standard call for"beam-on" indicators and methods to insure ter-mination of exposures at preset time intervals.In addition, standards for exposure accuracyand reproducibility are specified.
In 1974 the American Dental Association, incooperation with the American National Stan-dards Institute, issued ADA Specification No.26. These specifications closely paralleled therequirements of the diagnostic x-ray equipmentperformance standard and were issued asguidance to all dentists for implementation, ef-fective August 1, 1975. (39)
NEW TECHNOLOGY
Panoramic Dental X-Ray Units
Panoramic radiography is relatively new to thedental radiologist's armamentarium. Panoramicunits first became commercially available in1959, and their use has grown over the last twodecades. Panoramic units include both extraoraltomographic units (40, 41) and intraoral sourceunits. (42) For purposes of this overview,however, the term-panoramic unit" refers to anextraoral tomographic unit. A discussion of in-
12
traoral source machines is presented in the nextsection.
During a panoramic x-ray examination, both thex-ray tube and the radiographic film move aboutthe patient's head on two or more commoncenters of rotation. The resultant radiograph is atomographic view of a curved plane through thedental arches. The anatomic structures showninclude a broad view of the dental arches, themandible, the maxilla, the nasal fosse, and eachzygomatic arch. The panoramic radiograph pro-vides a limited trough of focus in the area of thedental arches. (43,44) Objects lying outside thistrough are blurred by the tomographic processand may not be visualized. In addition, tomo-graphic motion and the use of screen film limitsavailable detail. Thus, these radiographs may bea useful adjunct to conventional dental films ora technique for examination of a wider area ofteeth and jaws. The ADA's Council on DentalMaterials and Devices (now the Council on Den-tal Materials, Instruments, and Equipment), hasprepared a brief summary discussing the ad-vantages and disadvantages of dental tomo-graphic radiography. (45)
Since their introduction 20 years ago, panoramicx-ray units have steadily increased in popularity.White estimates that there are about 25,000panoramic machines in the United States. (46)Most are located in the offices of general prac-titioners and many are found in those of oralsurgeons and pedodontists. Generally, pano-ramic radiographs are used at a patient's firstvisit and periodically thereafter.
Several investigators have studied the amountof radiation exposure to patients during pano-ramic and conventional intraoral dental radio-graphs, (47) White and Rose have determinedthat the bone marrow dose from a panoramicunit is approximately 20 percent or less thanthat received from full mouth intraoral periapicalradiography. (47) Other studies performed dur-ing the last several years indicate that thethyroid gland may receive a significant dose dur-ing panoramic procedures. Antoku suggestedthat panoramic procedures deliver a greaterthyroid dose than intraoral radiography sincethe thyroid is irradiated during the entire pro-cedure. (49) Block, Goepp, and Mason reportedthat large potential thyroid exposure hazards areassociated with panoramic examinations. (50)Knowledge is still incomplete regarding thyroidhazards during panoramic procedures, howeverradiation exposure could be reduced significant-ly by use of smaller film sizes and by careful pa-tient positioning.
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Intraoral Source X-Ray Units
Much of the development and growth of intra-oral source dental x-ray machines has occurredwithin the last decade. The intraoral source ma-chine employs a miniature rod-anode x-ray tubepositioned inside the mouth to expose a filmmounted extraorally. X rays are emitted from aregion near the end of the cylinder and radiateoutward from the anode tip. The anode target isshielded except for a filtered window permittingtransmission of the primary beam.
The first rod-anode unit, Westinghouse Corpora-tion's "Panoramix," was marketed in the UnitedStates in the early 1980's and was designed totake panoramic ful!-mouth radiographs of theupper and lower arches with a single expo-sure. (52) The rod-anode source was positionedintraorally in the mid-sagittal plane (mid-lineplane) and radiographs of the entire maxillary(upper) and entire mandibular (lower) arch wereradiographed onto films bent in a curved planearound the patient's face.
The Panoramix failed to become a commercialsuccess in the United States. The major factorscontributing to the failure included:
lack of patient and practitioner acceptance;a large and expensive generator;nonuniform magnification of image struc-tures because of very short source-subjectdistances; .radiological risks, since the unit could beoperated without the shielding orcollimator;large rod-anode diameter, interfering withintraoral positioning;inconvenience in maintaining an asepticenvironment;use of nonscreen films, since the output ofthe unit could not be sufficiently reduced.Radiai!on dose was, thus, believed to begreater than necessary;strong competition from extraoral pano-ramic equipment;high doses of radiation to those tissuesclosest to the anode.
Recent innovations in imaging technology, how-ever, have helped to overcome these early prob-lems. For example, x-ray generators have beenmade smaller, less costly, and more flexible;better collimators and shielding have signifi-cantly improved radiation safety; recently devel-oped high-speed film/screen combinations havebeen coupled with microfocus x-ray sources tosubstantially lower patient doses; and hygieniccontrol has been improved to prevent intraoral-source contamination.
Practical Considerations of IntraoralSources
Ina paper entitled "Practical Considerations forthe Application of Rod-Anocl a Sources in DentalRadiography," Schoenfeld compares intraoralsource radiography with conventional periapicalbitewing radiography and with curved surfacetomography (extraoral panoramic units. (53) Thethree modalities were compared using fivecriteria: image quality, radiation dose, clinicalconvenience, economics, and compliance withFederal performance standards. Schoenfeldconcluded that "the intraoral use of rod-anodesources appears to provide image quality advan-tages for many diagnostic tasks along with awell-documented reduction in patient radiationdose. Also, intraoral source radiography com-pares favorably with conventional extraoralsource techniques with regard to clinical conve-nience and economics. Compliance with(Federal) regulations does not appear to createan inordinate barrier to the initiation of clinicalstudies of the concept of intraoral source. ".
In August_ 1978, Lieberman and Webber pub-lished the results of a clinical evaluation of aprototype intraoral source x-ray system consist-ing of a modified intraoral source machine and aPolaroid film/screen combination. (E4) The re-searchers found that although incipient enamellesions were identified less often than by con-ventional nonscreen techniques, larger lesionswere reliably detected. The intraoral sourcetechnique was predicted to reduce total patientdose by as much as 98 percent and producedpositive dry prints in 15 seconds, precluding theneed for darkroom processing. The clinical testsconfirmed that the intraoral source device of-fered potential advantages over existingtechnology for certain specific applicationssuch as presurgical examinations and endodon-tic procedures. The authors concluded thatmost of the clinical objections encounteredwere largely technical and could be corrected bymodifications to the prototype design.
Xeroradiography
Among the most promising new dental x-rayimaging technologies is intraoral xeroradiog-raphy. Xeroradiography is the recording of x-rayimages by using xerographic copying principles.The process involves exposing a positivelycharged selenium plate to x rays. X rays trans-mitted through the patient are absorbed by theselenium plate, causing selective discharge.The amount of discharge is proportional to theamount of radiation striking the plate, therefore
13 2 0
information in the transmitted x-ray beam isrecorded as a residual charge pattern on theplate, known as the latent image. Developmentof the image is accomplished by the depositionof a fine, blue, negatively-charged powder,called toner, on the latent electrostatic image.The final image is prepared for viewing by trans-ferring the toner from the selenium plate topaper by a heat fusion process.
Dental Applications
The principles and early applications of xero-radiography have been described in detail byWolfe, (55, 56) McMaster, (57) and Rawls andOwen. (58) More recently, Lopez (59) and Hymanand Bakker (60) have described the potentialuses of xeroradiography in dentistry. Bothstudies stated that the xeroradiographic imagesobtained were in some respects more detailedand of higher quality than those obtained withconventional radiographic techniques. Hymanand Bakker reported that the xeroradiographwas slightly superior to the conventional radio-graph in its ability to depict carious lesions andbony radiolucencies. This advantage was moreclearly demonstrated in certain applicationsthan in others; for example, root canals andperiodontal ligaments appeared particularlywell-defined. Other advantages of xeroradi-ography include elimination of darkroom re-quirements, decreased development time, andability to make cephalometric tracings directlyon the xeroradiograph. In their early studies,Gratt and associates at the University of Califor-nia, San Francisco, demonstrated that extraoralxeroradiographic techniques could producehigh-quality images of soft tissue, bone, andteeth at radiation exposures 7 times less thanfor conventional intraoral-film radiography. (61)Despite these merits, the need to developsemiconducting plates small enough to beplaced inside the patient's mouth remained.
In an effort to overcome this problem, research-ers at Xerox Corporation developed a new xero-radiographic system designed specifically forintraoral use. (62) This system included imagereceptors small enough for intraoral positioningand a self-contained, portable, daylight operat-ing processor that differed in several respectsfrom the Xerox 125 System used for medicalxeroradiograpy. (63) Gratt, White, Sickles, andJeromin evaluated the imaging properties of theprototype unit and demonstrated its substantial-ly superior image quality, which resulted mainlyfrom the wide latitude and edge enhancementproperties of the xeroradiographic process. (64)Radiation doses of one-third those received
14
from conventional intraoral films weremeasured.
Most recently, White and Gratt conducted thefirst clinical trials of the newly-designed xero-radiographic processor at UCLA and UCSF, re-spectively. (65) During three months, twelve hun-dred clinical xeroradiographs were compared tothe conventional radiographs of the same pa-tients for their ability to depict both hard andsoft tissues. White and Gratt reported that thedental xeroradiographic images allowed visual-ization of oral tissues with greater clarity andmore detail. They found that small structuresdiffering in density from surrounding structures,e.g., the periodontal ligament, pulp canals nearthe root apex, and thin plates of trabecular bonetended to be more easily seen on the xeroradio-graphs because of the edge enhancement prop-erties of the xeroradiographic process. Cariouslesions could be seen equally well on the xero-radiographs as on conventional images, and inpatients being treated for periodontal disease,the alveolar bone could be seen better on xero-radiographs. The University of California re-searchers also found that, with the xeroradio-graphic process, exposure times could be re-duced by one-half to one-third compared to con-ventional "13" speed film. Lastly, they found thattheir image receptors could be comfortably andconveniently used intraorally.
Thus, many of the technical problems associ-ated with dental xeroradiography appear to havebeen minimized or eliminated. A remaining prob-lem is that of a higher incidence of artifacts thanwith conventional radiography. Although Whiteand Gratt call for additional controlled evalua-tion, particularly comparisons of the incidenceof disease detection by xeroradiography andconventional radiography, they are optimisticthat xeroradiography will play an important rolein the future of dental radiology.
Field- Emission Units
Field emission x-ray tubes most differ from con-ventional x-ray tubes in their mode of electronproduction. In conventional units, electrons areproduced by heating a cathode (thermionicemission); in field emission tubes the-- electronsare drawn off the cathode by high-potential elec-tric fields. Field emission x-ray units can pro-duce very short pulses of x-ray energy, therebyessentially stopping all patient motion. In addi-tion, slight movement of film and/or tube/headcan be tolerated without loss of radiographicquality.
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Manson-Hing evaluated the Fexitron 845 port-able field emission unit and found its shortpulse, small size, and battery-operated capa-bility offered distinct advantages over conven-tional machines for portable use. (66) However,he determined that the x-ray source size waslarge and the pulse rate slow relative to conven-tional dental x-ray machines, thus precludingsharp images at short exposure times. Current-day image recording devices are considerablymore sensitive, however, and may offer a solu-tion to the problem of poor image quality.
The Low intensity X-Ray Imaging Scope(Lixiscope)
The lixiscope is a fully portable, compact x-rayimaging system. It consists of three basic com-ponents: a photon-emitting radiation source; aphotocathode or scintillator screen which con-verts the photon image into a visible light image;and a microchannel plate, image intensifiertube. This hand-held device produces real-timefluoroscopic images that can be viewed directly,photographed, or coupled to other imagingdevices.
The lixiscope has generated much interest sinceits development was first reported by Dr. Lo I.Yin of the Goddard Space Flight Center in No-vember, 1977. Because of its small size and port-ability, many potential medical, dental, and in-dustrial applications have been suggested. (67)
To date, however, because of various designcharacteristics, only a prototype device hasbeen built. Several researchers have tested thelixiscope on a limited scale, but no formal, large-scale clinical evaluations have yet been
performed- (68)
Dental Applications
Dental investigations of the lixiscope aredirected by Dr. Webber of the National Instituteof Dental Research, NIH. There, researchershave replaced the x-ray generating source with a50 millicurie source of iodine-125. In thisconfiguration, the complete lixiscope fluoro-scopic system is lightweight, rugged, and fully
-:-portable. The 1251 source is housed in a leadcapsule 3-mm thick, which in turn is containedin a stainless steel housing lined with a leadwall 3-mm thick. Photons are directed towardthe detector by means of a spring-loaded pushbutton "trigger." Depressing the "trigger"rotates the source capsule until it is aligned witha hole in the housing, producing a collimatedx-ray beam that Illuminates the detector screen.
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The lixiscope permits the dentist to irradiatesmall volumes of tissue. Unnecessary radiationoutside of the image receptor is eliminated.necessary radiation outside of the image re-ceptor is eliminated.
Although a number of potential dental applica-tions employing the lixiscope have been identi-fied, several remaining limitations severelyreduce the device's usefulness:
The 28 keV average energy gamma emis-sion of the iodine-125 source has insuffi-cient energy to penetrate thicker dentalstructures (other higher energy radio-nuclide sources are unsuitable because ofunacceptable half-lives or secondary emis-sion problems);Geometric conditions such as smallsource-object distances relative to object-receptor distances cause image unsharp-ness and magnification problems whichseriously degrade lixiscope images;
o The user must obtain a Nuclear RegulatoryCommission (NRC) or agreement Statelicense to possess radioactive material. Hemust also comply with all safety proce-dures for leakage testing and radioactivesource disposal:
* Replacement of the 1251 radioactive sourceevery 3 to 4 months is costly.
Because of these limitations, use of a portablefluoroscopic device does not appear to be aviable alternative for use in general dentistry.However, technical modifications such as intra-oral source imaging and improvements in imagereceptor storage capabilities are being investi-gated. (69) Such devices offer special promisefor applications in dental research, and possiblyfor endodontic root-canal procedures.
Another promising technology is digital imageprocessing. Image enhancement techniquesmay eventually result in significant gains inresolution. (69).
ANCILLARY EQUIPMENT
Modern film-screen combinations and collima-tors designed to attenuate all but the useful por-tion of the x-ray beam can greatly reduce patientradiation exposure. The use of rectangular col-limation in lntraoral radiography significantlydecreases the exposed area and thus patientdose. Rectangular collimation has been avail-able for about 10 years in the form of a metalshield sold by Precision X-Ray Company. (70)More recently, rectangular position indicatingdevices have become available from the RinnCorporation. (71) In an April, 1979, study of ab-sorbed bone marrow dose in various dental
22
techniques, White and Rose demonstrated thatthe use of rectangular collimation reduced thebone marrow absorbed dose from an intraoralseries by 60 percent. (47) Much of this exposurereduction derived from dos_ wings in theanterior region of the mandible. Thus, the use ofrectangular collimation is a radiation dosereduction technique particularly well-suited forperiapical radiography.
The choice of appropriate film and screen speedcan reduce patient radiation exposure during ex-traoral radiography. The film or screen speedrefers to the relative amount of exposure neededto produce a given degree of density. Thus, a-fast" speed screen requires less exposure thana "medium" speed screen. In general, the use ofa "slow" speed screen results in somewhat im-proved image quality at the expense of patientradiation exposure.
White and Rose compared bone marrow dosesfrom three extraoral panoramic techniques tothose from intraoral techniques and found thatthe former gave a dose of approximately one-fifth or less than the latter during periapical radi-ography. (47) While the presence of intensifyingScreens in panoramic units permits the use of
16
lower doses, Reiskin et al. suggest that the useof rare earth intensifying screens could reducedoses still further. (72)
AN ALTERNATIVE MODALITY
The fiber optic transilluminator, a technology in-volving the use of a nonionizing radiationSource, is worthy of mention at this point. Thisdevice produces a pencil-thin beam of light thatshines through the teeth and highlights decay,fractures, calculus, and other tooth damagewithout exposing patients to ionizing radiation.
The advantage of transillumination is that someoral areas such as proximal tooth contacts canbe examined without x rays. However, transillu-mination does not provide a lasting record forstudy, although development of a recordingsystem, probably electronic, should be possible.
Marketed in 1976, the fiber optic transillumina-tor is used in about 5 percent of dental offices.The device could serve a useful adjunctive ser.vice by identifying areas to which x-ray examina-tion can be limited.
DENTAL RADIOLOGY QUALITY ASSURANCE
INTRODUCTION
The meaning of the term "quality assurance"has rapidly evolved as scientists and clinicianshave come to appreciate the importance of re-producible, reliable systems to generate radio-logical images. Quality assurance can improvethe overall radiographic process and thus re-duce both costs and patient radiation exposure.The Bureau of Radiological Health began devel-oping methods of quality assurance for medicalradiology facilities in 1974. In 1979, the Bureaupublished recommendations for qualityassurance programs in diagnostic radiology fa-cilities in the Federal Register. (73) Thesegeneral recommendations pertain to both dentaland medical diagnostic facilities_
The term "dental radiology quality assurance"as used here means any systematic action to en-sure that a dental office will produce consis-tently high quality images with minimal ex-posure to patients and personnel. A ca ripletequality assurance program includes not only ad-ministrative procedures, but also quality controltechniques to monitor the components of anx-ray system. That system includes, at a mini-mum, the high voltage generator, the x-ray con-trol, the tube-housing assembly, the beam-limiting device, and the necessary supportingstructures. Aecompanying components,such asimage receptors, image processors, view boxes,and darkrooms are also considered parts of thesystem.
The status of quality assurance in dental radi-ology can be summarized briefly by reviewingpast and present programs and by describingprospective efforts.
DENTAL SURPAK PROGRAM
The Dental Surpak Program was an early venture(1961-1965) in quality assurance initiated by theU.S. Public Health Service. The term Surpak isderived from the two words SURvey and PAcKet.The packet was a light-tight envelope containinga sheet of Kodak Industrial X-Ray Film backedwith a sheet of lead. A 2 mm Al filter and a 0.5mm Cu filter were centered on the front side ofthe film. The outside of the envelope listedgeneral instructions for the dentist. The follow-ing parameters could be estimated from a pro-perly exposed Surpak: beam size at cone tip, ex-posure, total filtration, beam symmetry, andleakage radiation in the direction of a patient's
face. The Surpak program was designed andcarried out by the Division of RadiologicalHealth, the forerunner of the Bureau ofRadiological Health. Surpaks were supplied toState health agencies, which were then respon-sible for their distribution and use. This programaided in screening large numbers of radio-graphic installations for gross defects such asimproper collimation and filtration. After identi-fying machines lacking sufficient filtration andcollimation, the State health department wouldsend the dentist corrective devices such asaluminum disks and lead washers to bring themachine into compliance with establishedstandards.
The following numbers indicate the success ofthis early program: In 1960, 45.2 percent of themachines surveyed had a beam diameter of 3.00inches or less. By 1963, the figure had increasedto 63.6 percent. At that time, the recommendedstandard of the Public Health Service stated thatthe beam diameter should be 2.75 Inches atcone tip (regardless of length) and should notexceed 3 inches. (30) Similar improvements wereseen for filtration. In 1960, 42.2 percent of themachines surveyed had total filtration of 1.5 mmAl equiv. or greater. In 1963, the proportion hadincreased to 60.2 percent. The recommendationat the time was 1.5 mm of Al equiv. for equip-ment capable of operating up to and including70 kVp, and 2.5 mm total for equipment operat-ing above 70 kVp. (30)
Most machines produced in the 1930s and 1940swithout proper collimation or filtration had beenidentified and corrected by the mid-1960s, andthe Dental Surpak Program was terminated.Beginning in the mid-1950s, new dental x-raymachines were sold with at least 1.5 mm Alequivalent filtration and a beam size not greaterthan 3.0 inches in diameter at cone tip.
The X-Ray Exposure Studies (XES) of 1964 and1970 documented the continuing improvementin collimation. (17) Table 9 below shows the per-centage distribution of dental films by beam di-ameter as estimated from these studies.
Table 9. Estimated Percent Distribution ofDental Films by Beam Diameter (17)
Today, the maximum beam diameter at cone tiprecommended by the National Council on Radia-tion Protection and Measurements (NCRP) is 3inches, (37) and that recommended by the Amer-ican Dental Association is 2.75 inches when thesource-to-skin distance is greater than 7
inches. (74)
In 1970, all dental machines surveyed that oper-ated below 50 kVp had at least 0.5 mm Al equiv.filtration, 87.8 percent of those that operated be-tween 50 and 70 kVp had at least 1.5 mm Alequiv. filtration, and 70.7 percent of those thatoperated above 70 kVp had at least 2.5 mm Alequiv. (75)
The 1960 and 1963 values for filtration and colli-mation were based on an analysis of dental x-rayequipment, whereas the values for 1964 and1970 were derived from population-basedstudies (XES). Nevertheless, the figures indicatea continuing upward trend in the proportion ofdental x-ray machines operating within recom-mended parameters.
A reduction in patient radiation exposureparalleled this improvement in collimation andfiltration. The mean exposure at skin entranceper film for the dental bitewing examination was1249 mR in 1964 and 910 mR in 1970. (8, 76) Itmust be remembered, however, that these wereaverage values. Later studies such as theNationwide Evaluation of X-Ray Trends (NEXT)showed wide latitude in the amount of radiationused.
NATIONWIDE EVALUATION OFX-RAY TRENDS
In the Nationwide Evaluation of X-Ray Trends(NEXT), a current program coordinated national-ly by the Bureau of Radiological Health, Stateradiation control agencies measure x-ray outputusing a standardized field survey technique.This allows determination of radiation exposureto the patient from standard dental examina-tions. NEXT first began collecting data in 1972.Some statistical parameters for NEXT data col-lected during 1978 for the posterior dental bite-wing film are shown in Table 10. (77)
The wide range shown in Table 10 indicates thatthe amount of radiation received by patients dur-ing this examination varied from facility to facili-ty. NEXT is an on-going program that continuesto collect data useful to professionals in thefield of radiological health; however, the survey
18
protocol was not designed to determine thecauses of overexposure.
Table 10. Statistical Parameters Based on1374 Posterior Dental Bitewing Surveys
Performed During January 1, 1978 toDecember 31, 1978 (77)
Exposure at Skin Entrance(mR)
NASHVILLE DENTAL PROJECT
The Nashville Dental Project was conducted bythe Bureau of Radiological Health during 1972and 1973 in Nashville, Tennessee. (78) Theobjectives of the Project that relate to qualityassurance were:
1. to provide additional data detailing causesof unnecessary exposure in the everydaypractice of dental radiology;
2. to determine what changes could andshould be made in the practice of dentalradiology to eliminate unnecessary ex-posure and maximize information derivedfrom radiographic procedures.
The project consisted of three phases. Duringthe first, a team visited each participating dentaloffice tolnake a radiographic survey and obtainrelated information. During the second, eachdental office was visited by a consulting team,which recommended changes to improve radio-graphic practice. The third phase was a replica-tion of the first.
The study showed that 28 percent of the facili-ties surveyed before the educational phasesight-developed their films. The average skin ex-posure at those facilities was calculated to be720 mR/film. The average exposure for films pro-cessed by the established time-temperaturebasis was 404 mR/film. Inadequate darkroomfacilities were frequently encountered.
When the facilities were surveyed one year later,after the educational phase, the percentage thatwere sight-developing had dropped to 18 per-cent and the average exposure for properly pro-cessed films had decreased to 325 mR/film.
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The initial survey also indicated that timers wereinaccurate in half of the x-ray machines andshowed poor reproducibility in one-fourth. Ac-curacy of timers changed little from 1972 to 1973because the consultants concentrated more onestablishing a correct timer setting for the ex-posure factors than on correcting timerinaccuracies.
It can be said that the sources of overexposurerelated to equipment now are more subtle thanfiltration and collimation. As indicated above,one equipment-related problem is the timer. Thefaster or more sensitive dental films requireshorter exposure times, usually of the order of afraction of a second, at which timer accuracy be-comes more critical. Likewise, timer unreliabil-ity can necessitate repeat radiographs, thuscausing needless exposure to the patient. TheNashville Dental Project found significant prob-lems with the accuracy of both mechanical andelectrical timers, and with reliability of theformer.
The Nashville project revealed other areas notdirectly related to x-ray equipment which canlead to unnecessary radiation exposure to thepatient. One such area is film processing proce-dure. Five minutes are required to fully develop afilm at the recommended temperature for mostconventional developer solutions (68 degrees F).Then, following development, films must befixed for 10 minutes and washed for 20 minutes.Some operators save darkroom lime by over-exposing and then underdeveloping the film.This procedure subjects the patient to un-necessary radiation. However, the use of rapidprocessing solutions or automatic processorsmay reduce the total processing timeconsiderably.
.A study by Pennsylvania Blue Shield pointed tosimilar problems in processing. In that study,1,000 preauthorization radiographs submitted tothe Pennsylvania Blue Shield were evaluated bya simplified quality rating system developedspecifically for the study. Twenty percent of thefilms were judged unsatisfactory because ofpoor density or improper processing. (79)
Automatic film processors, which are receivinggreater acceptance, present their own set ofproblems. A processor that is not properly clean-ed, or that does not contain the proper quantityof fresh chemicals, will produce poor qualityradiographs. (80, 81)
The Nashville Dental Project was designed totest the feasibility of using an educational ap-proach for voluntary improvement of dental
radiographic practices. Based upon the successof that project, the Bureau of RadiologicalHealth promoted adoption of a similarmethodology, known as the Dental ExposureNormalization Technique or DENT program, foruse by health agencies nationwide.
DENTAL EXPOSURE NORMALIZATIONTECHNIQUE (DENT)
The Dental Exposure Normalization Technique(DENT) program was developed to identify den-tal x-ray facilities where patient exposure is out-side an accepted range. (82) The DENT programconsists of three phases. In the first phase, theState health agency mails dosimeter cards to alldental x-ray facilities within the State. Dentiststhen expose the cards and return them foranalysis. In the second phase, facilities showingexcessive exposures are visited to determinethe cause of the high exposure and to recom-mend correct procedures. Phase III is directed atidentifying and surveying any new dental x-raymachines, as well as resurveying those con-tacted in Phase. I.
Data from the first phase of the DENT programshowed that about 40 percent of the dental x-rayunits surveyed used exposures in excess of therecommended ranges. Much of this overex-posure was caused by poor darkroom practice,inadequate equipment or conditions, or de-pleted processing chemicals. In many cases thefilm was overexposed in order to compensatefor deficiencies in processing or darkroomdesign. After a subsequent visit by a trainedsurveyor (Phase II), the exposure was reduced byan average of 200 mRi:ilm. (83) The quality of thedental radiographs did not decrease and inmany cases improved.
PRESENT STATUS OF QUALITYASSURANCE IN DENTALRADIOLOGY
The state of quality assurance in dentalradiology presently appears to lag behind that ofmedical radiology. Most of the current dentalquality assurance programs are in dentalschools. The DENT program is the one widelyavailable quality assurance program, and hasbeen quite successful as a public health pro-gram conducted by health departments on aStatewide basis. At present, however, no off ice-based comprehensive quality assurance "pack-age" is available to dentists.
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In order to encourage the development of office-based quality assurance programs, the Bureauof Radiological Health issued a Request for Ap-plications (RFA) on March 16, 1979, (84) the 1-
ject of which was to fund grant research for medevelopment of a simple and effective system tobe used in a dental office by dentists and/or den-tal auxiliaries to identify exposure and process-ing problems. It was requested that the systembe as inexpensive as possible, with the cost notto exceed $200.
At present, the literature contains little informa-tion regarding dental radiology quality assur-ance programs. Dr. Manson-Ring recently haspublished a book, Fundamentals of DentalRadiography, that contains a chapter entitled"Quality Control in the Dental Office." (85) Thischapter presents simple and inexpensive teststhat can be performed in the dental office toidentify some problems in dental radiology.Information is given on how to check solutionstrength, darkroom integrity and safelight condi-tions, timer accuracy, machine output, collima-tion and beam alignment, and focal spot size.Moreover, several papers given at the AnnualSession of the American Dental Association,
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October 21-25, 1979, discussed radiographicquality assurance in dentistry. (86)
The Diagnostic Radiology Quality AssuranceCatalog published by the Bureau of RadiologicalHealth lists publications, such as that on theNashville Dental Project, that pertain to qualityassurance. (87) Most of the material in thecatalog relates to medical radiology, but someof the references address dental radiology.
The "Recommendations for Diagnostic Radi-ology Facilities Qulity Assurance Programs,"promulgated by the Bureau of RadiologicalHealth, appeared in the Federal Register on De-cember 11, 1979. This recommendation, whichapplies to both medical and dental radiologyfacilities, contains guidelines for specifyingresponsibility for the program, purchase specifi-cations, parameters to monitor, standards forimage quality, and aspects of program admInis-traiion. This recommendation, and increasedconcern about the effects of repeated exposureto low doses of ionizing radiation, will no doubtincrease the demand for quality assurance pro-grams in dental radiology.
EFFICACY
INTRODUCTION
Any attempt to describe the role of radiographyin dentistry must address efficacy. Efficacy canbe defined in several ways. One is simply "thepotential of a given type of examination to pro-vide information useful to the practitioner in thecare of the patient." A more specific definitionwould require the inclusion of such concepts asbenefit and risk. A consideration of patterns ofx-ray utilization makes possible the construc-tion of a general profile of dental radiographicpractice. The major question to be addressed inconnection with the patterns of utilization iswhether or not x-ray examinations are used in anoptimal fashion and only when necessary. A pre-cise definition of such use may be difficult toformulate but would have to include such fac-tors as diagnostic yield and patient manage-ment. Regardless of these conceptual problems,concern regarding possible overutilization ofdental x rays has been expressed. (16, 88)
Some of the reasons often cited for the per-formance of unnecessary examinations relatedirectly to efficacy. Testimony presented onbehalf of the American Dental Associationbefore the Subcommittee on Health and the En-vironment of the Committee on Interstate andForeign Commerce, pointed out that "some den-tal settings, schools, clinics, and practitionersstill routinely conduct x-ray examinations on allnew patients regardless of indicated need." (16)This practice persists despite the ADA's officialrecommendation that x-ray examinations beconducted only when there Is an indicated needfor each patient. (74) Another dentist at thesame hearings alleged that, "Overexposure andoverutilization occur because of inadequateeducation and the lack of meaningful guidelinesor controls." (88) Other potential causes ofoverutilization might include the monetary in-centive of self referral, third party payments,post-treatment radiographs, non-uniform criteriafor taking dental x rays, and excess reliance on
new technologies (e.g., panoramic units). For ex-ample, it was recently observed that from 1969to 1977, the number of Americans with dental in-surance as an employment benefit increasedfrom 7 million to 48 million. (19) The same reportstated that national expenditures for dental carewent from $4.4 billion to $10 billion from 1970 to1977. According to this source, x-ray examina-tions in the population sampled accounted for7.3 percent of total charges and were received atleast once in the course of a year by 82 percentof all patients presenting for services. Thus, itappears likely that third-party payment in-fluences the utilization of dental services.
To analyze the Impact of these elements on den-tal radiology, this chapter will attempt to deline-ate the extent to which dental x rays are used,look at trends in examination rates and conse-quences of dental radiation exposure, andsurvey the literature pertaining to the efficacy ofvarious procedures.
EXAMINATION FREQUENCY AND TRENDS
The 1970 X-Ray Exposure Study has providedthe basis for most of the estimates of examina-tion rates found in the literature. (17) It wasstated during the previously mentioned Con-gressional Hearings that 59.2 million personsreceived dental x rays in 1970. (88) Moreover, atthat time 67 percent of all dental visits includedx-ray exposure. In 1978, by contrast, 82 percentof all patients received on or moreradiographs. (19)
As part of an Environmental Assessment Reportsupporting the performance standard for diag-nostic x-ray systems and loeir major compo-nents, the Bureau of Radiological Health devel-oped the following data relating to the fre-quency of specific types of dental x-ray pro-cedures in 1970: (89)
Table 11, Estimated Relative Frequency of Various Dental Radiographic Examinations, 1970*
Examination ypeNumber of exams
(millions)Number of films
(millions)
1. bitewing2. bitewing and periapical3. full mouth series4. .-arlapical5. other (panoramic, cephalome ic, etc.)6. total
27.28.97.4
19.9
4.467.8
67.548.4
109.741.711.9
279.2
Unpublished data obtained from 1970 XES study. (17)
Because some individuals received multipleexaminations, the total number of exams (61.8million) exceeds the number of persons receiv-ing x-rays. The number of films exposed in-creased 23 percent, from 227 million to 279million, during the interval 1964 to 1970. (17)Meanwhile, the U.S. population increased by 8percent. This figure corresponds to 4.9 films perpatient, or approximately 1.3 films per memberof the total population. (90, 91) Like otherradiographic examination rates, the dental examrate exhibits an age correlation. (92) A peak isreached in the 15 to 24 year age group, and thena sharp decline commences.
A survey of 72 private dental offices establishedan average workload of 80 films per week per of-fice. (93) Those offices producing the most filmsappeared to yield the lowest radiationexposures.
Number of Films per Examination
Considerable variability exists in the number offilms employed per examination by differentdental practitioners. Consequently, the numberof exams alone does not adequately reflecteither radiation exposure or cost incurred for aspecific procedure. Some estimate of total filmsexposed is therefore necessary. Such informa-tion also provides insight into the range of atti-tudes within the dental profession regarding thediagnostic value and utility of x rays,
The American Dental Association, through itsCouncil on Dental Materials and Devices (nowknown as the Council on Dental Materials,Instruments and Equipment), recommends thata minimum number of exposures be made. (74)More professional judgment should be applied
22
in each case, so that exposure is confined to in-stances in which there is a reasonable expecta-tion of gaining information useful to diagnosisor treatment. The general injunction to limit ex-posure can be found throughout the literature onthis topic. However, at least one researcher hascautioned against "overzealousness while striv-ing to achieve maximum radiographic efficien-cy.- (43) This dentist contended that if all filmstaken produced positive findings, not enoughradiographs were being made.
Data on this aspect of dental radiography illus-trate the prevailing diversity of practice and in-struction. One survey of private offices showedan average number of films per full mouth seriesto be 15, with a range of 12 to 21. (93) Interprox-imal examinations were done with two films innearly 7:J. percent of these offices. UnpublishedXES data show little variation in the number offilms per full mouth examination on a regionalbasis. (17)
It is probably more instructive to look at what isbeing taught in dental schools, because this willaffect future use patterns, In a 1968 study elicit-ing responses from 42 dental schools queriedabout the number of films used in intraoralsurveys of average adult patients, (94) the figurevaried from 14 to 32 films (periapicals plusbitewings).
Guidance given to students in dental radiologytexts is frequently inconsistent with the pro-fessed position of the American Dental Associ-ation. For example, a text of recent vintagestates that no less than 14 films should be usedfor a complete periapical exam. (95) An oldertext asserts that, "No examination should beconsidered complete without a full series ofroentgenograyps." (96)
EXAMINATION COSTS AND TRENDS
The inflationary pressures operating elsewherein the economy have been experienced in thedelivery of dental care as well. The expansion ofdental insurance has also contributed to anescalation of costs. A 1979 publication provideddata leading to an estimate for annual expen-di-tures for dental radiography of $730 million. (19)Testimony given at the July, 1978, Congres-sional hearings assigned a cost of $22.11 for acomplete full mouth series. (88) This estimate,based on the ADA's latest review of dental fees,was tied to an opinion that the overall cost ofconducting an x-ray exam would be under$10.00, although this figure probably did nottake into account the dentists' professional feecomponent for radiographic interpretation.
RADIATION EXPOSURES, DOSES, ANDRISKS
Another cost associated with the use of x rays indentistry is the potentially detrimental effects ofradiation exposure. Growing public awarenessand concern can be seen in all matters involvingradiation. As a result, an inquisitive public isforcing the scientific, medical, and dental com-munities to carefully scrutinize the use of x raysin diagnosis, and to search for ways to optimizethat use. Moreover, efforts to define more ac-curately the risks and benefits of diagnostic xrays are continuing.
Although an extensive body of literature onradiation biology has accumulated, this discus-sion will be restricted to a consideration ofdoses and their implications in dental radiology.Numerous researchers have made exposure anddose measurements and various risk assess-ments have been derived from them. For themost part, the latter have their origin in the 1972Biological Effects of Ionizing Radiation Reportof the National Academy of Sciences. (97) Abrief summary of the status of this knowledgeas it relates to dental radiology follows; datatypifying radiation exposures and doses en-countered in dentistry will be presented, and theconcept of risk from dental x-rays will beexplored.
Although several factors combine to yield spe-cific exposure and dose levels unique to eachexamination, some illustrative values can be re-ported. A Japanese study reported ranges ofdoses from the full-mouth x-ray examination tobe 12-17 rads to the skin, 260-1800 mrads to thelens of the eye, and 340 to 2500 mrads to thethyroid. (49) A patient exposure study performed
2
at the Baltimore Public Health Service Hospital,however, determined that the maximum ex-posure at any location during a 14-film full-mouth survey was 827 mR. (90) Exit exposurewas found to be one to two percent of entranceexposure.
The Bureau of Radiological Health has cal-culated mean skin exposure and active bonemarrow doses per film for various types of ex-aminations. (92) For anterior teeth projections,the figures are 1110 mR and 2.9 mrads respec-tively; for posterior teeth they are 1170 mR and0.8 mrads. These low bone marrow doses meanthat despite the high rate of utilization, dentalexams contribute only about 3 percent of thetotal adult per capita mean active bone marrowdose. Moreover, both skin exposure and meanactive bone marrow dose in dental examsdecreased significantly from 1964 to 1970.Presumably, this decline can be attributed to in-creased use of faster speed films.
Educational efforts can also be effective in re-ducing exposures. In a study of 72 private of-fices, machine output for interproximal filmsdecreased from an average of 542 mR in 1972 to340 mR in 1973, following visits and consulta-t ion with radiological healthrepresentatives. (93) Furthermore, others havenoted that the mean exposure per film at skinsurface is a function of the year of the dentist'sgraduation from dental school. Mean exposurewas 1,230 mR for 1940-1949, 850 mR for1950.1959, 650 mR for 1960-1964, and 560 mR for1965-1970 graduates. (91) Overall, a 20 percentdecrease in mean exposure per film at skin sur-face from 1,140 mR to 910 mR, for all types ofexams took place between 1964 to 1970. (17)
One of the numerous variables affecting ex-posure, and ultimately dose, is the particulartechnique employed. The survey of private of-fices cited earlier showed that the mean ex-posure per film was 595 mR for the bisecting-angle technique as opposed to 359 mR for theright-angle technique. (93) This lower dose mayoccur in part because dentists using the paraal-leling technique are likely to be younger, and touse better processing methods and newerequipment. Similar differences were noted whenvarious types of panoramic units were com-pared. (51) For panoramic machines producedby three separate manufacturers, exposure tothe thyroid ranged from 5 to 13 mR, and ex-posure at the base of the tongue ranged from 50to 272 mR.
Although radiation exposure of several otherorgans (thyroid, salivary glands, eye, skin,
31-)
gonads) also are of concern during dental x-rayprocedures, the bone marrow is often regardedas the major critical organ. For this reason theprincipal risk from dental radiography is be-lieved to be the potential for induction ofleukemia. (91) One researcher has shown thatpanoramic techniques result in a bone marrowdose approximately a fifth or less of thatdelivers it by conventional periapical radi-ography:197) Lateral cephalometric projectionsgave bone marrow doses equivalent to thosearising from panoramic exams. In the samestudy, it was found that the bone marrow doseto the head and neck was greater from a set offull-mouth films than from extraoral radiography.
The estimated average equivalent whole-bodyper-person exposure to the U.S. population fromdental radiography approximates 7 mR peryear. (91) It was projected that this exposurecould lead, at most, to an additional 8 to 11leukemia deaths per year in the U.S. population.Gregg concluded that the risk of developing anytype of cancer within 25 years of irradiation as aresult of a full-mouth exam of 21 films is 3 in 1million or 0.0003 percent per exam. (98)
ROUTINE X RAYS
The so-called routine use of x rays is attractingincreasing attention. In this context, routinemeans the automatic use of x rays without priorconsideration of the patient's history or clinicalsigns and symptoms. The degree to which prac-titioners routinely incorporate x rays into man-agement schemes for their patients raises thequestion of possible overutilization. It is impor-tant, therefore, to describe the extent of routinex-ray use and to consider the yields that areexpected.
The American Association of Dental Schools'position is quite clear:
"Patients should not be subjected to massradiographic screening examinations priorto initial clinical examination to determinethe need and desirability of specific radio-graphs to aid in evaluating their acceptabil-ity as clinic patients.
"Students should be taught to assess crit-ically the need for diagnostic radiographicinformation and to evaluate the risk to thepatient before ordering the radiographsneeded to diagnose the patient's oralhealth needs." (99)
Furthermore, the Radiation Protection Subcom-
24
mittee of the American Academy of Dental Radi-ology has stated that, "The patient shall not beexposed unnecessarily. There must be a goodand valid reason for each exposure." (36) Finally,recommendations entitled "Radiation Pro-tection Guidance to Federal Agencies for Diag-nostic X Rays- and given to Federal health carefacilities contain a clause that dental radio-graphs be taken only after a dentist has seen thepatient and established the need for x rays: afull-mouth or bitewing series is not justified aspart of periodic preventive dental care. (100)
Nevertheless, evidence exists that the prin-ciples embodied in this guidance are not uni-versally accepted. In her book X rays: MoreHarm Than Good?, Priscilla Laws relates the ex-perience of dental patients who encounteredproblems as a result of questioning the need forperiodic routine x rays. (101) Testimony given bythe ADA at the Congressional hearings acknowl-edged that, "Some dental settings, schools,clinics, and practitioners still routinely conductx-ray examinations on all new patients regard-less of indicated need." (7) It was also alleged atthose hearings that a "high number" of dentalschool clinics routinely give full-mouth x rays,albeit largely because many of the patients areof low income and have not had recent dentalexaminations.
A telephone survey conducted in the Bostonarea elicited some specific information on theroutine use of x rays in initial visits. (102) Ninety-five percent of the 40 offices sampled reportedthat x rays were routinely performed as part ofinitial exams of new patients. Forty-seven andone-half percent of the offices said that full-mouth series are routinely included in the initialexam. Only one office reported that the decisionto employ x rays was determined by the dentistfollowing his clinical exam. On the other hand,the Nashville Study indicated that only ten per-cent of the offices surveyed reported a policy ofdoing full-mouth series on all new patients. (78)
Another survey sought to learn what dentalschools recommended the intervals betweenx-ray examinations should be. (94) The research-ers found that the predominant time span rec-ommended between full-mouth examinationswas 1 year, although one school said that a5-year interval was recommended. Some, how-ever, answered that they taught no definiteroutine and determined the need for x-ray ex-amination according to the individual patient'sstatus and progress. The situation was anal-ogous for both bitewing and interproximalradiographs.
31
Older textbooks tend to perpetuate advice con-flicting with the ideals expressed by the ADA.One states simply that, "No examination shouldbe considered complete without a full series ofroentgenograms.- (96) A second adds that,"Routine intraoral periapical and bitewing roent-genograms should be available when the patientis examined." (103)
The professional literature contains other differ-ences of opinion. On the basis of reviewing a setof patients in seemingly good health in whomclinical exams revealed no abnormal conditionsbut x rays uncovered problems, one authorrecently argued that a complete x-ray examina-tion should be done during a patient's initialvisit. (104) It is true that "scouting" types of x-rayexaminations do yield unanticipated findings,however, more critical review of so-called sur-prise x-ray discoveries may reveal inattention tothe physical or historical aspects of a patient'sexamination. For example, the x-ray discovery ofan impacted third molar should not be a sur-prise, since physical examination should havedemonstrated the tooth's absence and the pa-tient's history should have indicated that thetooth had not been removed.
REFERRAL CRITERIA
A possible way to ensure more informed use ofradiographs is the development of criteria thatpractitioners can use in deciding the appropri-ateness of certain radiographs. Although rigidguidelines can not and should not substitute forprofessional judgment, referral criteria canrefine that judgment and foster a more effica-cious use of radiographs in dentistry.
Inspection of the available literature disclosesthat such referral criteria have not been broadlydeveloped. The foundation for such criteria maybe discerned in studies that focus on either theutility of a technique or the extent to which it isutilized by the dental profession. For example,the Bureau of Radiological Health is currentlyfunding a grant supporting the development ofreferral criteria for panoramic radiography.
When asked to indicate their preference in theuse of common radiographic projections, 66 outof 72 U.S. and Canadian dental schools respond-ed. (105) Ninety-five and one-half percent of therespondents identified the bitewing as one ofthe more frequently ordered exams, and 80.3percent said the same of the full-mouth exam.Seventy-seven and one-third percent of these in-stitutions reported using a combination of bite-wings and full-mouth periapicals. The full-mouth
25
series was viewed as not essential by 20 percentof these schools_
Several authors have compared the detection oflesions by intraoral and by panoramic radiog-raphy. One study observed that panoramic radi-ographs allowed the detection of lesions notseen in intraoral exams in 5.3 percent of thecases analyzed. (106) Only a very small fractionof these lesions required treatment, however_ Inthis instance, the utility of panoramic radiog-raphy appeared quite limited. Others have con-tended that the panoramic film either is ineffec-tive in early detection of lesions, or should beused only in special cases, as an adjunct tointraoral examinations. (107, 108)
Extraoral radiographic techniques have beendeemed an essential tool in generaldentistry. (109) Because the periapical filmdoes not always visualize an entire lesion,panoramic or other extraoral projections occa-sionally are needed. Recommendations havebeen made relative to the intervals at whichradiographs should be taken for the long termmanagement of cleft palate deformities. (110Radiographic procedures for such patients in-clude cephalometric, panoramic, andfluoroscopic exams. The recommended inter-vals between exams correlate with stages ofdentition.
Radiographs unquestionably contribute infor-mation beyond the clinical exam alone, butdisagreement persists as to how much addi-tional benefit accrues. A study of 10-/and11-year old children concluded that 66 percentof interproximal caries would have been mis-sed had radiographic bitewings been omittedfrom their exams. (111) On the other hand, whenradiologic and clinical findings in assessingcaries prevalence in children were compared inanother study, reasonable agreement wasnoted. (112) Moreover, even with standardizedexposure techniques, different tilting of theteeth in the maxilla and mandible and rotationscould produce error in the radiographic detec-t ion of caries. Such inconsistenciesdemonstrate the need for research that canresolve differences in expectation of yield andconsequent use of radiographs. In periodon-tics, radiographs have been deemed of littlevalue in assessing early destructivechanges. (113) Radiographic and clinicalmeasurements were found equally effective inevaluating the long term effects of periodontaltherapy. Finally, the suggestion has been madethat radiographic artifacts may cancel somediagnostic advantages. (114)
POST-TREATMENT RADIOGRAPHS
In the past, some third-party insurance carriershave required dentists to submit post-treatment radiographs so the carrier canmonitor or verify reimbursement claims fortreatment. This practice exposes the patient toclinically unnecessary radiation.
The Bureau of Radiological Health became in-volved with this issue when third- party carriersdeveloped policies requiring post-treatmentradiographs as a prerequisite for claim reim-bursement. The ADA and many State dentalsocieties have opposed the taking of x rays forthis purpose. In addition, in June of 1980, theBureau published a recommendation in theFederal Register discouraging thepractice. (115) Although past treatmentradiographs may not be a serious problem atthis time, their potential requirement on abroader scale must be recognized.
The number of Americans with dental in-surance went from 7 million in 1974 to 48million in 1979, and is expected to reach 70million by 1982. (19) In addition, over 200 in-surance or service carriers are now activelymarketing dental plans. (116) Thus, pressurewill grow to control costs. Moreover, some formof dental coverage is provided under Medicaidauspices, although the exact extent of thiscoverage varies among Medicaid jurisdictions.On the other hand, as insurance for dental ser-vices becomes more widely available, the useof pre-treatment radiographs is likely toundergo corresponding growth. This issue maymerit eventual investigation.
Although reliable data are not available on theextent to which post-treatment radiographs are
26
used nationally, the practice does not seem tobe common. The ADA, through its Council onDental Material and Devices and its Council onDental Care Programs, as well as State dentalsocieties, have strongly discouraged such useof radiographs. (34, 74, 117. 118, 119)
RECOMMENDATIONS
One recommendation of the ADA's Council onDental Materials and Devices to dentists is:"Use professional judgment to determine thefrequency and extent of each radiographic ex-amination. Determine the number of film ex-posures that will produce the desireddiagnostic information". (74) Programs thatcould be adopted to support that recommenda-tion include:
Convening a national conference to con-sider, among other matters, referral criteriafor dental radiographs. This conferencewould both generate interest in and focus at-tention on needs in this area;
Surveying current practices with respect toroutine exams and referral criteria, in orderto provide a necessary data base;
Conducting efficacy studies on various den-tal x-ray exams;
Establishing, in the absence of efficacystudies, consensus panels to develop widelyacceptable policies regarding such issuesas the number of films per exam and theutilization of various exams. The recommen-dations of these panels could be im-plemented through professional organiza-tions and educational programs.
DENTAL RADIOLOGY EDUCATION CURRICULA
INTRODUCTION
The competency of the individual who orders orperforms a dental x-ray examination is an ob-vious determinant of the general quality ofradiographic services. Training and curriculumrequirements, as they apply to the use of ioniz-ing radiation, vary according to category of per-sonnel. Applicable standards for both dentistsand auxiliaries must therefore be reviewed.
DENTISTS
The lack of uniformity in the radiological cur-ricula in American dental schools hinders anyanalysis of the educational methods currentlyused in teaching dental radiology. The problemof standardizing this aspect of the curriculumhas been recognized for over twenty years. In"An Analysis and Evaluation of the Methods Us-ed by Schools of Dentistry for Teaching OralRoentgenology," Budowsky, et at. concludedthat each dental school should evaluate its pro-gram in order to determine if radiology was be-ing taught in the most appropriate manner. (120)They suggested the following measures:
1. establish specific sections withindepartments of oral medicine orstomatology;
2. evaluate lecture material for properemphasis of the subject;
3. broaden the scope of subject matterto be included in radiology;
4. establish minimum clinical re-quirements to ensure sufficient prac-tical student experience;
5. establish postgraduate courses intheory, technique, and interpretation.
Nine years later (1967), Lincoln Manson-Hing,DMD, MS, again called attention to the problemin his "Study of the Teaching of Oral Roen-tgenology".94 The variability which Dr. Manson-Hing described still exists. Items such as re-quired courses, credentials of the facultyteaching radiology{, and the amount of practicalexperience offered to students vary widelyamong schools. Surveys of dental radiologyeducation suggest that other than requiringmany new patients to undergo x-ray examina-tion, dental schools lack policies concerning theuse of x-rays.
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Recognizing both the importance of ionizingradiation to dental practice and the need forcompetent handling of radiation in the dentalenvironment, the American Association of Den-tal Schools (AADS) recently issued a positionpaper on the teaching of dental radiology. It urg-ed dental schools to review their curricula toassure that "proper emphasis is given tobiological aspects of radiation". (99)
Although no mechanism exists for enforcingthis recommendation, the paper is an importantstep in elucidating the problem of uniform den-tal education in ionizing radiation.
Following is a description of those areas of thedental radiological curriculum in which a briefreview of dental college bulletins and conversa-tions with dentists indicate that variability ex-ists. A major obstacle to analysis is thatradiological techniques, as tools to assess con-ditions in the mouth, are refined throughout theeducational experience although they may notbe mentioned in course descriptions. The big-gest unknown is the basis individuals used todecide when radiographs were needed. Thisoften reflected a school's preference, or thatwhich an individual professor himself learned indental school, and presumably continuedthroughout his or her career. Such subjectivelearning experiences cannot be readily analyz-ed.
The American Dental Association and theAmerican Association of Dental Schools do notrequire that dental radiology be taught by aradiologist, although both recommend thatradiological techniques be taught by staff"knowledgable in radiographic procedures". (121) The AADS goes on to say that adental radiologist is preferable.
Manson-Hing found 17 dental schools offeringradiology in a separate department. Fourschools taught it as an independent sectionwithin a department. In eighteen schools (nearlyhalf of those reporting), radiology was taught aspart of oral diagnosis. (94) College cataloguesalso list radiological courses under oralpathology, stomatology, and forensic dentistry.
Programs: In addition to undergraduate coursesin dental radiology, several schools offerMaster's degree programs in oral radiography.Manson-Hing cited five schools offering ad-vanced degrees in this field, and four with one-year postgraduate programs. (94) The continu-
3d
ing education course listing of the Council onDental Education for July-December 1979 lists 9courses in dental radiology (interestingly, thesame listing contains 30 such courses for dentalauxiliaries). (122) Not all states require continu-ing education for licensure renewal. Those thatdo accept any of the accredited courses asfulfilling the licensure requirement. Thus, a den-tist need not take any further training inradiology after graduation from dental school.
Teaching time: A survey of the bulletins oftwenty-five dental schools showed that lecturetime devoted to dental radiology varies from 2 to30 credit hours (see bibliography). The fractionof this time allotted to various topics such asradiation physics, radiographic technique, inter-pretation, exposing, developing and mountingradiographs, and radiation hygiene also varies.In general. most of the instruction is devoted totechnique and interpretation.
Demonstration time per student for techniqueranged from 2 to 18 hours and averaged approx-imately 15 hours. The total time reported asteaching radiology ranges from 4 to 75 hours,with some of the variation occurring becausethe topic is often taught under several depart-ments.
Another influential training factor is the numberof complete full-mouth series required to betaken by the student. Manson-Hing reportedthat the requirement ranged from 10 to 70 com-plete surveys. In addition, the number of othertypes of radiographic examinations requiredvaried depending on such factors as types of pa-tients seen in the teaching clinics, number ofstudents, facilities, and faculty.
Recently, the Bureau of Radiological Healthreceived a letter from a student who expressedconcern that the dental school he attended re-quired that both pre-/and post-treatmentradiographs accompany the treatment recordsin order for him to receive credit. The studentcalculated that this requirement resulted in 70 to100 excess radiographs per year per student. Heconcluded that "between 8,000 and 10,000needless x-rays will be given to the populationjof his state] merely to comply with these in-structions." In the student's opinion, the schoolwas encouraging the taking of needlessradiographs, a habit that would be carried intostudents' private practices.
DENTAL AUXILIARIES
The training of other employees or auxiliariesworking directly In the dental radiographic pro-
28
cess is also important if dental x rays are to beused more efficiently.
Radiographic equipment is used by threegeneral categories of dental auxiliaries: dentalassistants, certified dental assistants, and den-tal hygienists. Each category requires differenttraining and, in some cases, licensure. Theresponsibilities of each group also differ fromState to State. Although the educational re-quirements for dental hygienists varysomewhat, most variation occurs within thecategory of dental assistants.
Dental Assistants
An estimated 135,000 dental assistants werepracticing in the U.S. in 1976, an increase of ap-proximately 61,000 since 1960. (1)
In most States, many dental assistants have hadonly on-the-job training. For example, anestimated 90 percent of the dental radiographsin the State of Connecticut were taken by dentalassistants with no "formal radiologicaltraining". (88) Three States and the District ofColumbia currently prohibit the dental assistantfrom taking x rays. Twelve States require thatassistants receive training in x rays, three re-quire a combination of training and a StateBoard Examination, and three require only aState Board Examination. The amount and typeof training specified by the various States varyconsiderably. It is usually up to the dentist todecide whether or not the taking of radiographswill be included in the assistant's duties, andthe dentist can, in effect, train someone with ahigh school education to take dental x rays. Forinstance, although California requires that theauxiliaries be certified before takingradiographs, the Bureau of Radiological Healthhas learned of a case in that state in which a 16year old volunteer dental assistant was takingdental films after receiving only on-the-job train-ing.
To become certified by the ADA, assistantsmust have one or two years of academic training(depending on the institution) from one of the280 (as of 1973) accredited dental assistant pro-grams in the United States. (1) The total numberof graduates from formal training programs indental assisting increased from 695 to 5,297 be-tween 1963 and 1973. (123)
The curriculum In a dental assisting program in-cludes courses5ip, radiation physics, radiation
biology, radiation techniques, and, in a fewcases, radiation safety, The number of hoursthat an assistant spends in dental radiologyvaries from two as many as 64, dependingupon the school. The student assistant also isgiven clinical experience, which in some casesinvolves the use of x rays. Both phantoms andpeople are used to train the students in using xrays, with the students sometimes practicing oneach other.
Assistants who attend a school in dentalassisting are eligible, but not required, upongraduation to take the National Certification Ex-amination given by the Certifying Board of theAmerican Dental Assisting Association. Moststates do not require that assistants be cer-tified.
Dental Hygienists
An estimated 27,000 dental hygienists werepracticing in the U.S. in 1976; the total had in-creased by approximately 5,000 from 1973. (1)
Dental hygienists are required to have two yearsof formal training from one of the 182 schools indental hygiene accredited by the ADA. (1)Courses that a dental hygienist takes are morein-depth than those taken by the assistantenrolled in a one-/or two-year training programexcept in radiology, where the course descrip-tions are in many cases identical. Both thehygienist and the assistant spend approximate-ly the same number of class hours in radiologycourses.
Upon completing their training, dentalhygienists in most states are required to takethe Dental Hygiene National Board Examina-tion. The hygienist must also pass the StateBoard Examination for the State in which he orshe wishes to practice.
In summary, the dental hygienist must have for-mal training and is required to take the DentalHygiene National Board Examination (writtenand clinical) before practicing dental hygiene. Inmost cases, the dental assistant's training is on-the-job rather than formal. In most States theassistant is not required to take any certifyingexamination before taking dental x rays.However, some States prohibit assistants fromtaking x rays.
There appears to be a need for regulating on-the-job training of dental auxiliaries.
CONTINUING EDUCATION
Continuing education courses in radiology areavailable for both dentists and dental aux-iliaries. These courses range in length from oneday to two weeks, depending on the sponsoringschool. Of 596 continuing education courseslisted in 1979 by the DADA, 39 pertainedspecifically to radiology. Approximately 80 per-cent of these 39 were described as primarily ap-plicable to auxiliaries and 20 percent to dentists.
Two consortia in continuing education, the NewEngland Foundation for Continuing DentalEducation and the Consortium on ContinuingDental Education Programming, are involved inpreventing the duplication of efforts among den-tal schools, hospitals, and other institutions.They are also attempting to increase the numberof practicing dentists, hygienists, andassistants in continuing education programs.The consortia do not plan any of the courses,butlist possible speakers and publish a newsletterindicating what courses are being offeredwhere.
A total of 77,715 students were enrolled in allcontinuing education courses in 1974-1975 withan estimate of 30 per class. There were 2,676 in-structors considered "regular faculty" involvedin continuing education, with 64 percent of thesrhools using nondental instructors. Twenty-three of the 59 dental schools said that they hadseparate facilities for continuing educationclasses ,and 20 percent of the schools usedoperatories or x-ray laboratory facilities in aSeparate clinic or hospital. (124)
The most popular format in all courses was thelecture followed by a question/answer session.Almost all of the schools used some patientdemonstration as well. Ninety-eight percent ofthe schools used topics suggested by the facul-ty and 79 percent of the schools used surveys offormer students to choose courses. Seventy per-cent of the schools took suggestions from den-tal societies.
Forty percent of the schools said that there wasroom for more participants and 62 percent saidthat there was "an unfilled need for more conti-
u i ng education programs in theirlocality". (124) Although the above statistics arefor all continuing education courses in dentistry,they may provide some insight as to the condi-tion of continuing education in dental radiology.
29 36
PROFESSIONAL ORGANIZATIONS' GUIDELINESFOR TRAINING AND USE
INTRODUCTION
This chapter, on guidelines for dental radiologytraining, traces the development of curricula inundergraduate and graduate programs,discusses several surveys that have provided in-formation on past and present dental radiologycurricula, and provides recommendations fordiagnostic radiology training as advocated bythe American Association of Dental Schools.Several factors external and internal to the pro-fession changed dental radiology training over aperiod of years. The changes have resultedprimarily, however, from the efforts of dentaleducators placing a high priority on the develop-ment of the educated professional.
CURRICULA DEVELOPMENT
Several milestones can be noted in the develop-ment of curricula for dental radiology training indental undergraduate and graduate programs asadvocated by professional organizations. In1966, the executive council of the AmericanAcademy of Oral Roentgenology approvedrecommendations for minimal curricula stan-dards for teaching dental radiology in Americandental schools. (125) These recommendationswere:
(1) Eliminate the use of dental students asx-ray technicians. It was felt that com-petency could be obtained without sub-jecting students to repetitive chairsideand darkroom service procedures.
(2) Fix 130 hours as a minimum necessaryto develop competency. The training in-cluded 32 lecture hours, approximatelyone week of intraoral procedure train-ing, and approximately two weeks ofclinic time for supervised small groupfilm interpretation seminars. Thedesignation of dental radiology as anautonomous discipline rather than as asegment of some other teaching activi-ty would best accomplish these objec-tives.
Lecture course content generally to in-clude:
History of radiologyFundamental concepts of radiationRadiation productionRadiation protection and measurement
30
Radiation biologyProjection geometryFilm types and characteristicsIntraoral, extraoral, and specialtechniques
Film-processing theoryFilm-viewing proceduresNormal intraoral and extraoralradiographic anatomy
Radiographic appearance of commonoral disease entities
Radiographic signs of less commondisease conditions
Radiographic signs of systematicmalfunction
Research potential and recentadvances in dental radiology andfuture trends
(4) In order to provide proper sequence ofteaching, lectures on technique andassociated clinical experience could beprovided in the second or third year.Lectures and then seminars on inter-pretation should follow completion ofthe course in oral pathology.
In 1973, the Oral Radiology Section of the AADStook the position that appropriate training andcertification of radiation users wasmandatory. (126) It was recognized thatradiology had previously been relegated to ser-vice rather than teaching status in most dentalschools. In order to upgrade the teaching ofradiology, an outline for a suggestedundergraduate dental radiology curriculum wasdeveloped. The Oral Radiology Section positionpaper noted that policies, philosophy, andeconomics differ among dental schools and thatsubstitute conditions might be necessary, butnevertheless urged that fulfillment of the re-quirements be judged as objectively as possi-ble.
The didactic portion of the course was dividedinto seven main categories and was to be sup-ported by laboratory exercises or seminars.After receiving didactic and demonstrative in-struction, the student should produce completemouth intraoral radiographic surveys and alsodemonstrate competency in the more commonextraoral radiographic procedures, includingpanoramic methods.
Revised guidelines for an advanced educationalprogram in dental radiology were prepared by
7
the American Academy of Dental Radiology in1974. (127) That document was intended to serveas a guide for institutions in establishing new,advanced educational programs in dentalradiology, and to assist directors of existingtraining programs in improving and upgradingtheir programs. Consultants to the Council onDental Education of the American DentalAssociation could also use the guidelines as astandard to evaluate new and existing advancedtraining programs in dental radiology.
The primary objectives of the 1976 ADA/AADScomprehensive study of dental curricula ofAmerican dental schools include: (128)
Collection of baseline information tofacilitate future comparative studies:
(2) Documentation of current practices inpredoctoral dental education;
Interpretation of the data collected toidentify reasons for curriculum change,and determination of ways to improvedental curriculums.
The study identified radiology as one of 23 majorteaching areas and subdivided it into:
a.b.c.
d.e.f.
9-h.
Radiation PhysicsInteraction of X-Radiation and MatterFactors Affecting Radiographic ImageProductionBiological Effects of X-RadiationRadiation Safety and Protectionlntraoral Radiographic TechniquesExtraoral Radiographic TechniquesInterpretation of Radiographs
Fifty-nine schools reported a range of from 19 to278 hours of required instruction in radiology(median = 70). State-related schools and schoolswith less than 4,400 total hours of instructiontended to have the fewest required hours inradiology. One school had no didactic instruc-tion in radiology and depended exiusively onself-instructional programs. Although almosthalf of the schools reported that emphasis in allareas of radiology instruction had increasedover previous years, fewer than a third reportedan increase in clock hours; improved instruc-tional methods apparently permitted more con-tent to be presented in the same amount of time.Radiation safety and protection and the inter-pretation of radiographs received the greatestincrease in attention. The report states thatthere is no "right number" of clock hours for anysubject area, and clock hours do not necessarilyreveal the depth or quality of instruction. Yet
31
numbers of clock hours do suggest the scope ofinstruction and indicate where instruction hasbeen omitted or minimized.
Finally, it should be noted that the OralRadiology Section of the American Associationof Dental Schools (AADS) and the AmericanAcademy of Dental Radiology are currentlyworking on revised guidelines for teaching den-tal radiology to dental students.
In order to determine the extent to whichschools were attempting to keep abreast of"new" technologies, faculty from variousdepartments were asked to indicate the numberof clock hours of instruction provided in the-new" topics. Panoramic radiographs werelisted as one of the most frequently taught"new" topics in the clinical science, with 58schools reporting some instruction in this sub-ject.
Surveys of instructional programs in dentalradiology have been conducted in dentalschools. A 1969 survey conducted by Greer andWuehrmann with support of the Bureau ofRadiological Health presented data on thequalifications and training of those teachingdental radiology at that time. (129) Forty-five ofthe 49 dental schools queried responded to theirquestionnaire. Their findings follow below:
Educational experience ofthose teaching radiology:
Entirely self taught 33%Limited, intermittentformal courses 25%
58%
Postgraduate workfor 6 months or more 14%Formal course workfor M.S. or Ph.D. 28%
42%
The authors thought that adequate instructionrequired at least 1.5 full-time equivalent (FTE)dental radiology teachers per 50 students (i.e. anFTE per student ratio of 0.03). Only four schoolsin this survey had that ratio. Ten schools hadratios between 0.02 and 0.03, while most hadratios less than 0.02.
In 1975, Boozer and Rasmussen conducted acurriculum survey of American and CanadianDental Schools. (130) In comparision with theresults of surveys in the previous two decades,
they observed: (1) a slight increase in thenumber of curriculum hours devoted to teachingradiology methods, (2) that the parallelingtechnique is the preferred procedure over bisec-ting angle method; and (3) owing totechnological advances, equipment used inradiology clinics also changed considerably.
Boozer and Rasmussen also provided recom-mendations for strengthening existing radiologycurricula: (1) guidelines for national or regional
32
requirements should be established; (2)diagnostic radiology courses should be taughtprior to or concurrently with oral pathologycourses; and (3) graduate programs in radiologyshould be expanded to meet the need forqualified faculty_ Also, graduate students inother specialties should be given the opportuni-ty to study advanced radiological techniques.
'Only 10°'o of these had advanced degrees in radiology.
FINDINGS AND RECOMMENDATIONS OFPROFESSIONAL ORGANIZATIONS
A summary of the most recent information ondental education was reported by the Council onDental Education, American Dental Association,in cooperation with the American Association ofDental Schools. (131) Highlights are:
The United States currently has 59 fullyoperational dental schools.
Between 1975 and 1979 the number ofapplicants to dental schools declined by35 percent (As a result, several schoolsthat had automatically rejected ap-plicants with low grade point averagesand Dental Admission Test scores haveceased to do so.)
Fifty to 60 percent of recent graduatingdentists enter private practice im-mediately after graduation. Only about20 percent enter advanced dental educa-tion programs after graduation.
The proportion of dental schoolgraduates enrolled in first-year specialtyprograms declined from 28.3 percent in1974 to 22.8 percent in 1978.
Dental school tuition costs are increas-ing substantially and Federal support isdecreasing. State and local govern-ments have compensated for most of thedecrease in Federal monies, however.
The number of qualified teachers of den-tal radiology is extremely small.
Dr. Allan Reiskin, School of Dental Medicine,University of Connecticut, Farmington, testify-ing before the Subcommittee on Health and theEnvironment of the Committee on Interstate andForeign Commerce, on July 11, 1978, stated that"although x-ray diagnosis is considered to be anessential component of dental practice,radiology has never been given the recognitionaccorded to other dental specialties and it rarelyhas a position of prominence in dentalcurricula". (88) Dr. Reiskin went on to say, "Inthe long term, improvement of practice stan-dards will require substantial upgrading of oureducational system. It is important to recognize,however, that a decision to expand the radiologycurriculum in dental schools could not be readi-ly implemented because of the extremely smallnumber of qualified teachers. Therefore, in the
short term, it may also be necessary to regulatethe use of diagnostic x-ray equipment."
In response to the data that Dr. Reiskinpresented and to public concerns about the useand abuse of ionizing radiation, the American
ociation of Dental Schools adopted an of-ncial position on "Ionizing Radiation" at their1979 annual meeting. The position paper urgesdental educators to review their schools' pro-cedures to control the use of ionizing radiationand to modify any practices that do not conformto acceptable standards. (99) The position paperincludes the following recommendations:
3310
1. Physical facilities:
a. All existing radiographic, equipment andfacilities should be upgraded to meet allregulations specified and/or recom-mended by The Radiation Control ForHealth and Safety Act of 1968, NGRPHandbook 35 on Dental X-Ray Protec-tion, and the ADA recommendations onacceptable radiographic practices.
b. Radiographic facilities should bedesigned or modified to maximizestudent/operator/patient protection fromunnecessary exposure to ionizing radia-tion.
c. Film processing, including time-temperature relationships, should bemonitored regularly (preferably daily) toassure film quality.
2. Instructional/teaching support for clinicalactivities:
a. Faculty and supporting technical staffshould be knowledgeable and skillful inall radiographic procedures andpreferably licensed in the field of dentalradiology.
b. Students should be clearly supervisedby faculty or staff during all cl:nicalradiographic procedures conducted onpatients.
c. Techniques to minimize patient ex-posure, e.g., long open-shielded beamindicating devices (BID's), rectangularcollimating devices to collimate beamsto the size of the film packet, lead
aprons, film-holding devices, and high-speed film should be emphasized.
Institutional obligations to the patient:
a. 7atients should not be subjected to alarge number of retakes to satisfy tech-nical perfection rather than clinicalacceptability. (A minimally acceptablecomplete mouth radiographic surveyshould demonstrate, at least one time,each root apex and each interproximalspace, without overlapping and withclarity and accuracy.)
b. Students should not serve as live techni-que mannequins unless some benefit isto be received by taking and interpretingthe radiographs.
c. Patients should not be subjected tomass radiographic screening examina-tions prior to initial clinical examinationto determine the need and desirability ofspecific radiographs to aid in evaluatingtheir acceptability as clinic patients.
d. Radiographs should be made availableto private practitioners or other ap-propriate professionals when so re-quested by patients who indicate theyno longer desire treatment or care at theInstitution.
e. Radiographs should be limited to theminimum number needed for a completediagnostic workup of the patient's den-tal needs.
4. Institutional obligations to the student:
a. Students should be taught to assesscritically the need for diagnosticradiographic information and to evaluatethe risk to the patient before ordering theradiographs needed to determine the pa-tient's oral health needs.
b. Students should be well-prepared toassume the challenges of clinical dentalradiography and should receive ap-propriate guidance from faculty andstaff.
c. Technical perfection in radiographic pro-cedures should be achieved on manne-quins; students should be taught torecognize clinical situations in which itmay be necessary to compromisetechnical perfection.
d. Students should be allowed to take nomore than three retakes on a completemouth radiographic survey without thedirect supervision of faculty or staff.More than three retakes indicate a lackof minimally acceptable skills and closesupervision is justified.
e. Students should be prepared toestablish private practices in which ade-quate concern is given to selectingequipment and following proceduresthat will minimize radiation to the pa-tient and assure high-quality films fordiagnostic interpretation.
In March, 1978, the Council on Dental Materialsand Devices, American Dental Association, pub-lished 11 recommendations on the use of diag-nostic radiology. (74) Recommendation No. 1, onthe frequency of dental radiographic examina-tions, urges that professional judgment be usedto determine the frequency and extent of eachradiographic examination and the minimumnumber of exposures needed to produce the de-sired diagnostic information. Other recommen-dations provide advice for protection of the pa-tient, office personnel, and dentist, and onmodernization of x-ray equipment, use of fast-speed film, and proper darkroom procedures.
NCRP Report No.35 also provides recommenda-tions on proper operating procedures. (37) Heretoo,it is stated that deliberate exposure of anindividual to the useful beam for training ordemonstration purposes shall not be permittedunless necessary for diagnosis and _ the ex-posure is prescribed by a dentist or physician.
In addition, both the American Academy of Den-tal Radiology and the American Association ofDental Schools have noted that State and Na-tional Board Examinations do not thoroughlytest the competency of dentists inradiology. (126, 132) This deficiency may resultin part from the lack of an independent specialtyof dental radiology.
41
STATE ACTIVITIES
The information in this chapter is based mainlyon a report published in 1978 to provide informa-tion on State and local radiological health pro-grams to reduce or control population exposureto ionizing and nonionizing radiation. (133)Selected data on dental x-ray programs are pro-vided. This chapter also includes a brief descrip-tion of a Bureau of Radiological Health programto identify dental x-ray facilities in which ex-posure reduction and improvement In qualityassurance can be achieved. This program isknown as the Dental Exposure NormalizationTechnique (DENT) and is more fully discussed inthe section on quality assurance. Information onStates' requirements for licensing dental aux-iliary personnel is provided in the section ondemographics. Many States conduct com-pliance inspections under contract to FDA,although the number of these inspections forconventional dental x-ray equipment is decreas-ing.
State agencies, several local agencies, andregional offices of the Food and Drug Adminis-tration provide combined reviews of their radio-logical health programs in a series of reports.These reports are submitted by these agenciesas directed in the FDA contract with the Confer-ence of Radiation Control Program Directors,Inc. (CRCPD), formed approximately 10 yearsago as a means of exchanging Information be-tween State and Federal agencies, as well asamong States themselves, in areas of mutualconcern or interest. The Conference is sup-
ported primarily by the Food and Drug Adminis-tration, the Environmental Protection Agency,and the Nuclear Regulatory Commission.
In Fiscal Year 1977, (133) 38 States reportedregulatory programs for dental/medical x-rayactivities, 5 States reported voluntary activities,and 8 States reported combinedregulatory/voluntary programs. Seven of the 8States reporting combined activities changedfrom regulatory in 1976 to combined in 1977 inorder to highlight the voluntary user activitiesbeing carried out in the State programs. (For thepurpose of the report, Puerto Rico and theDistrict of Columbia were counted as States.Nevada did not report.)
Compliance information is provided on a facilitybasis, because most State programs record datain this manner. X-ray facilities are Inspected forcompliance In areas other than equipment per-formance, such as film development require-ments, registration, and shielding and use, de-pending on State regulations. Therefore, equip-ment need not be considered noncompliantwhen facilities are shown to be not in compli-ance with regulations.
Table 12 provides comparative information onthe reported estimated numbers of dental x-raymachines and inspections for Fiscal Years 1975,1976, and 1977. (133) Whereas the number of ma-chines increased between 1975 and 1977, thenumber of inspections decreased slightly.
Table 12. Number of Reported Dental X-R ediblesand Number of Inspections for Fiscal Years 1975, 1976, and 1977
35
Of the estimated 145,000 dental x-ray machinesin the United States in Fiscal Year 1977, 92.6 per-cent were registered with State agencies. The24,833 inspections conducted represent 17.2percent of the total estimated number of ma-chines reported. Of the estimated 82,123 facili-ties, 5.0 percent (4,165) were not in compliancewith State regulations. As noted above, compli-ance figures reflect not only machine per-formance, but also other variables. For a com-plete breakdown by State on Dental X-Ray Pro-gram Activities, see reference 133.
Suggested State Regulations for Control ofRadiation (SSRCR) have been published and re-vised since 1962. Approximately 40 States hadadopted the 1970 or 1974 revisions, or were in-tending to adopt the 1978 revisions of Part F,Rays in the Healing Arts," according to a recentsurvey conducted by the Executive Director ofRegional Operations, FDA. Dental x-ray systemsare subject to Sections F.3, General Requirerents; F.4, General Requirements for all Diag-nostic X-Ray Systems; F.6, Extraoral DentalRadiographic System Requirements; and the Re-quirements of F.7, which apply to X-Ray Equip-ment and Associated Facilities Used for DentalRadiography. (134)
The Bureau of Radiological Health has workedwith the States to develop a program called Den-tal Exposure Normalization Technique (DENT),which provides a means of identifying dentalx-ray facilities where patient exposure exceeds
the normal range, and for correcting this situ-ation through consultation and education. (82) Apanel of dentists established a range of ex-posures that would produce acceptable radio-graphs at various kVp settings. Pilot studiesconducted in cooperation with State radiationcontrol agencies in Rhode Island (1973) and NewHampshire (1972) showed that of all the knowndental x-ray machines in these two States, 46percent exceeded the upper limits of these ex-posure ranges. State personnel visited thesedental offices to normalize the x-ray system,demonstrate exposure and processing condi-tions that would enable the dentist to operatewithin the acceptable exposure range. Theaverage exposure after these site visits was one-fifth the former value, with diagnostic quality offilms maintained or improved.
The DENT program can be adopted by radiationcontrol agencies that actively and routinely con-duct compliance surveys, or the demonstrationaspects of DENT can be added to compliancesurveys. A radiation control agency with aminimal or nonexistent dental radiologicalhealth program could use the DENT program toidentify and correct excessive exposure condi-tions. A suggested methodology for organizingand coordinating a DENT program Is provided Inreference 134. Additional information and/orassistance is available from the Bureau of Radi-ological Health. Figure 4 shows DENT programparticipants as of January 1, 1979.
DENT Program Participants
AL Itl !IAN di ANIii
CAI ASi A!
iv A.'S'
IN PROGRESS (13) including Guam
COMPLETED (23) including Virgin Islands
PILOT PROGRAM (6)
(1011180)
PIA ft) fric0
ViNGI iSLAIJOS
44Figure4.DENT Pro Rm.participants
SUMMARY AND CONCLUSIONS
X-rays play an indispensable role in dental di-agnoses. Impressive technological gains havebeen made in equipment, and proven new mo-dalities, such as tomography, greatly enhancediagnostic capabilities. Xeroradiography, anewer experimental technique in dentistry, alsopromises to become a useful imaging tool.
Most States now have active regulatory pro-grams for registration and Inspection of equip-ment. In conjunction with Federal performanceStandards, these programs have been instru-mental in correcting equipment-related radia-tion exposure problems. In the past, significantexposure reductions were achieved through at-tention to such factors as beam filtration, col-limation, and timer accuracy. One matter thatbears consideration, however, is the assess-ment of new technology. A mechanism is neededto investigate and assess advances such as in-traoral sources and xeroradiography.
Unnecessary exposure to x rays can probably befurther decreased through conscientious imple-mentation of well-defined quality assurance pro-grams, which also would optimize informationyield and cost. Twenty percent of the radio-graphs submitted to Pennsylvania Blue Shieldduring a 1975 study were judged unsatisfactorybecause of poor density or improper processing.Data from the NEXT and DENT programs indi-cate that exposures often are outside of estab-lished acceptable ranges for various dentalradiographic procedures. This problem likelystems from lack of sufficient training In theradiographic process. The existing DENT pro-gram and the Nashville study are two examplesof quality assurance efforts based on an educa-tional approach. Both have successfully elicitedvoluntary, positive responses from practitioners.Uniform methods of systematically applyingquality assurance principles in dental radiologyneed to be developed and promoted.
Although Improvements in equipment have de-creased radiation exposures per examination,
ne
unnecessary examinations have been alleged.Excessive utilization is at least partially at-tributable to lack of agreement regarding howand when x-rays should be used in particularcases. For instance, opinions vary on such mat-ters as the frequency with which full mouth x-rayexaminations should be performed and thenumber of projections required for various ex-ams. The efficacy of some procedures (e.g.,routine and pre- and post-treatment radiographsfor third-party carriers) has been questioned. Ex-plicit guidance, in the form of referral criteria,could help to solve these difficulties. Althoughthe radiation risks associated with dental x-raysare relatively minor, in combination with costconcerns they generate a strong incentive tofoster more efficacious use. This is particularlytrue in light of expanding dental services andbroader insurance coverages.
One basic reason for differences in x-ray utiliza-tion patterns is the educational process. Curric-ula and training standards for dentists and auxil-iaries vary widely. A discrepancy exists betweenthe number of lecture hours recommended bythe American Academy of Dental Radiology andthe amount of time actually devoted to theteaching of this subject in most dental schools.The number of qualified dental radiologyinstructors in dental schools is small. Recogni-tion of oral radiology as a separate and autono-mous specialty by the ADA has been identifiedas a possible solution to this problem. Lastly,State and National Board Examinations havebeen termed deficient in the area of radiologyand thus do not serve well in promotingcompetency.
With the advent of new technologies and conti-nuing concern over radiation risk and healthcare costs, it is imperative that unproductiveradiation exposure be minimized. Referralcriteria for dental x-ray examinations, qualityassurance programs, and upgraded educationalstandards all would appear to contribute to thisgoal.
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