PEDIATRIC DENTISTRY/Copyright © 1981 byThe American Academy of Pedodontics/Vol. 3, No. 1

A quality assurance program indental radiology

Richard W. Valachovic, DMDAllan B. Reiskin, DDS, DPhilSusan T. Kirchhof, RT

AbstractA quality assurance program in radiology provides the

basis for systematic measurement of various parameterswhich affect the quality and production of a radiographicimage. We have outlined a program which can beimplemented in dental offices by dentists or auxiliarypersonnel without sophisticated instruments. Tests designedto establish the adequacy of specific functions are describedtogether with reasons for poor image quality.Implementation of a quality assurance program results inreduction in expenditures, increased radiation thrift andimproved diagnosis.

IntroductionThe production of radiographs involves several

complex processes. Small variations in exposure geom-etry, beam quality or processing technique can havedramatic results on the final image. If one wishes togenerate consistent and diagnostic radiographs, care-ful regulation of the imaging process must be rigor-ously maintained. Simple steps can be taken to assurethat uniform image production is achieved throughthe utilization of a systematic quality assuranceprogram.1 In addition to its contribution to the pro-duction of high quality images, such a quality assur-ance program also plays a major role in keeping pa-tient exposure to a practical minimum.2

This paper will describe a quality assurance pro-gram that can easily be implemented in the privatedental office to efficiently monitor the various param-eters that affect the characteristics of the radio-graphic image. Through the regular application of thisprogram, problems in any aspect of image productioncan be readily identified and corrected.

Accepted: October 3, 1980

RADIOLOGY QUALITY ASSURANCE PROGRAMValachovic, Reiskin, and Kirchhof

Parameters Which Affect Image QualityThere are four basic parameters which affect image

quality that may be measured: (1) image processing;(2) the basic characteristics of the x-ray generator; (3)image receptors; and (4) darkroom inte~,qdty (Table All of these parameters may be measured to a limiteddegree of sensitivity without sophisticated equipment.

The most frequently encountered reason for varia-bility in producing an image is in the processing of theexposed film; this is the one parameter over which thedentist has the most control. X-ray generator per-formance is generally quite stable and maintenance isusually delegated to a qualified serv~ceperson. Thequality of most commercial film products is not highlyvariable and is easily maintained through proper stor-

Table 1. Quality assurance tests and frequency of performance.

Tests of Image Processing: Every DayA. Solution temperaturesB. An index of speedC. An index of contrast

Tests of X-Ray Generator Performance: Every 3 MonthsA. Reproducibility of x-ray outputB. Linearity of mAs stationsC. Field size and densityD. Mechanical stability of suspension

Tests of Image Receptor Quality: Every MonthA. Base plus fogB. Film artifact identification

Tests of Darkroom (or Daylight Loader) Integrity: EveryMonth (or with every change of safelighting)

A. Light leaksB. Safelight conditions

Tabl

e 2.

Tro

uble

shoo

ting

the

poor

qu

ality

im

age

Poss

ible

Cau

ses

(Lis

ted

in d

esce

ndin

g or

der

Tes

ting

Proc

edur

es

Obs

erva

tion

of p

roba

bilit

y)

(if a

pplic

able

: see

text

)

1. S

ight

dev

elop

men

t 2.

Pro

cess

ing

erro

rs

Tes

ts o

f im

age

proc

essi

ng

A.

Exh

aust

ed s

olut

ions

B

. D

evel

opm

ent t

ime

too

shor

t C

. D

evel

oper

tem

pera

ture

too

low

D

. Im

prop

er m

ixin

g of

che

mic

als

Con

sist

ently

lig

ht

film

s 3.

Inc

orre

ct e

xpos

ure

fact

ors

4. E

xpir

ed fi

lm

5. V

aria

ble

gene

rato

r per

form

ance

Che

ck te

chni

que

char

t T

ests

of i

mag

e re

cept

or q

ualit

y T

ests

of g

ener

ator

per

form

ance

Cor

rect

ive

Act

ion

Sigh

t dev

elop

men

t sho

uld

not b

e us

ed

Rep

leni

sh/r

epla

ce a

t pro

per

inte

rval

s Fo

llow

man

ufac

ture

r’s r

ecom

men

datio

ns

Follo

w m

anuf

actu

rer’

s rec

omm

enda

tions

Fo

llow

man

ufac

ture

r’s r

ecom

men

datio

ns

Adj

ust e

xpos

ure

fact

ors a

s ne

cess

ary

Dis

card

exp

ired

film

C

all s

ervi

cepe

rson

1. P

roce

ssin

g err

ors

Tes

ts o

f im

age

proc

essi

ng

A.

Dev

elop

er te

mpe

ratu

re t

oo h

igh

B.

Dev

elop

men

t tim

e to

o lo

ng

Follo

w m

anuf

actu

rer’

s rec

omm

enda

tions

Fo

llow

man

ufac

ture

r’s

reco

mm

enda

tions

C

onsi

sten

tly

C.

Dev

elop

er to

o co

ncen

trat

ed

Follo

w m

anuf

actu

rer’

s re

com

men

datio

ns

dark

D

. So

lutio

n co

ntam

inat

ion

Avo

id c

ross

con

tam

inat

ion

films

2. I

ncor

rect

exp

osur

e fa

ctor

s C

heck

tech

niqu

e ch

art

Adj

ust e

xpos

ure

fact

ors a

s ne

cess

ary

3. F

ogge

dfilm

s A

. E

nvir

onm

enta

l exp

osur

e B

. L

ight

leak

s T

ests

of i

mag

e rec

epto

r qu

ality

T

ests

of d

arkr

oom

inte

grity

S

tore

film

pro

perl

y (s

ee te

xt)

Secu

re p

roce

ssin

g ar

ea fr

om li

ght l

eaks

4.

Var

iabl

e ge

nera

tor p

erfo

rman

ce

Tes

ts o

f gen

erat

or p

erfo

rman

ce

Cal

l ser

vice

pers

on

1. P

roce

ssin

g er

rors

T

ests

of i

mag

e pr

oces

sing

Fo

llow

man

ufac

ture

r’s r

ecom

men

datio

ns

2. V

aria

ble

gene

rato

r per

form

ance

T

ests

of g

ener

ator

per

form

ance

C

all s

ervi

cepe

rson

V

aria

ble

A.

Tim

er m

alfu

nctio

n A

. lin

eari

ty a

nd re

prod

ucib

ility

dens

ity

C.

Vol

tage

inst

abili

ty

C.

repr

oduc

ibili

ty

film

B.

mA

inst

abili

ty

B.

linea

rity

3. X

-ray

tube

det

erio

ratio

n T

est o

f fie

ld s

ize a

nd d

ensi

ty

Cal

l ser

vice

pers

on

1. F

ogge

dfilm

s A

. E

nvir

onm

enta

l exp

osur

e T

ests

of i

mag

e rec

epto

r qua

lity

Sto

re fi

lm p

rope

rly

(see

text

) V

aria

ble

B.

Lig

htle

aks

Tes

ts of

dar

kroo

m in

tegr

ity

Secu

re p

roce

ssin

g ar

ea fr

om li

ght l

eaks

fil

m

C.

Impr

oper

han

dlin

g T

est o

f film

art

ifac

t H

andl

e fil

m w

ith c

are

duri

ng p

roce

ssin

g co

ntra

st

2. U

nsta

ble

deve

lope

r tem

pera

ture

T

ests

of im

age

proc

essi

ng

Follo

w m

anuf

actu

rer’

s rec

omm

enda

tions

3.

Var

iabl

e ge

nera

tor p

erfo

rman

ce

Tes

ts of

gen

erat

or p

erfo

rman

ce

Cal

l ser

vice

pers

on

Blu

rred

1.

Pat

ient

mov

emen

t W

atch

pat

ient

dur

ing

expo

sure

im

age

2. I

nsta

bilit

y of

sus

pens

ion

Tes

t of m

echa

nica

l sta

bilit

y A

djus

t sus

pens

ion as n

eces

sary

m

1. C

one

cutt

ing

8 Pa

rtia

l A

. T

echn

ical

mal

posi

tion

Alig

n fie

ld w

ith

imag

e re

cept

or

imag

e B

. P.

I.D.

mal

alig

nmen

t T

est o

f fie

ld si

ze a

nd d

ensi

ty

Tes

ts o

f im

age p

roce

ssin

g A

djus

t as n

eces

sary

or c

all s

ervi

cepe

rson

R

eple

nish

/rep

lace

at p

rope

r int

erva

ls

2. I

nade

quat

e im

mer

sion

of f

ilm

into

solu

tions

1. P

roce

ssin

g er

rors

T

ests

of im

age

proc

essi

ng

Avo

id c

ross

cont

amin

atio

n Fo

llow

man

ufac

ture

r’s r

ecom

men

datio

ns

A.

Solu

tion

cont

amin

atio

n B.

Inc

ompl

ete

agita

tion

“f

9;

Z

G

-4

Fi

lm

C.

Impr

oper

han

dlin

g H

andl

e fil

m w

ith c

are

duri

ng p

roce

ssin

g A

rtif

act

D.

Soile

d pr

oces

sor

rolle

rs

Cle

an p

roce

ssor

at r

egul

ar in

terv

als

2. F

ogge

dfilm

s A

. E

nvir

onm

enta

l exp

osur

e B

. L

ight

leak

s T

ests

of im

age r

ecep

tor q

ualit

y T

ests

of d

arkr

oom

inte

grity

S

tore

film

pro

perl

y (s

ee te

xt)

Secu

re p

roce

ssin

g ar

ea fr

om li

ght l

eaks

N

3.

Def

ectiv

e fil

m q

ualit

y T

ests

of im

age r

ecep

tor q

ualit

y D

isca

rd d

efec

tive film

-I

age; however, all film packages should be routinelytested before use. Finally, the integrity of the dark-room (or daylight loader of an automatic processor) iseasily evaluated and corrected as necessary (Table 2).

Quality Assurance Testing ProceduresA test object or step wedge which will be used

throughout these quality assurance procedures, andwhich is sized for use with No. 2 dental x-ray film maybe purchased commercially" or constructed using dis-carded sheets of lead foil saved from used No. 2 dentalx-ray film packets. Figure 1 illustrates the method of

aSpectroline X-Ray Analyzer Model 8958, Spectronics Corp.,29 New York Ave., Westbury, Long Island, NY 11590.

Figure 1: Construction and utilization of an office-constructed test

object for use with No. 2 dental film.

IA: Cut a paper template to the size of a No. 2 dental film. Draw

lines horizontally at '/•" intervals.

1 B: Tape pieces of lead foil saved from used No. 2 dental film

packets at each marked interval. Cut off excess lead foil to size of

paper template.

1C: Insert template to which the pieces of lead foil have been

taped into an empty No. 2 dental film packet.

1 D: When using test object, place it on top of film to be exposed

on a flat surface. Place tip of P.I.D. over test object and film in con-

tact with flat surface.

28RADIOLOGY QUALITY ASSURANCE PROGRAM

Valachovic, Reickin, and Kirchhof

construction. A thermometer for measuring solutiontemperatures is the only other instrument that isneeded.1. Image Processing. Film processing is the singlemost variable step in the production of an x-rayimage. Therefore, the following tests should be per-formed on a daily basis. Reproducible results can onlybe obtained if a time/ temperature method of develop-ment is adhered to.3 "Sight developing" should neverbe used during these quality assurance tests or routineprocessing.

A thermometer should be allowed to come to equi-librium in the developing solution before any testingof image processing begins. If at all possible, the opti-mal time and temperature recommended by the man-ufacturer should be used; with most products, this willbe 68 °F and five minutes.

A standard test film which will be the basis of fu-ture comparisons of image processing should be pre-pared using a machine which is known to be properlycalibrated and its performance verified. Expose a No.2 dental film through the test object using normalmandibular molar technique. This radiograph shouldbe processed in freshly prepared solutions according tothe manufacturer's recommendations. After the filmhas been properly washed and dried, it should bemounted and kept in a safe place for future daily com-parisons. When similar exposures are made on a dailybasis, changes in film speed can be determined by therecognition of overall decrease or increase in density(Figure 2A). A similar test for automatic processorscan be performed by deriving a standard using thesame procedures described above. Alterations in filmcontrast can be recognized by non-uniform changingof density on the steps exposed through the test object(Figure 2B). The step with the least amount of leadshould be completely black, representing near maxi-mum density. Each individual step should have a uni-form density; variation within a step being an indica-tion of artifact.

2. Tests of the Basic Characteristics of the X-rayGenerator. The basic characteristics of the x-ray gen-

A B

Figure 2: A: Left side: standard test film (see text). Right side:

test film showing change in film speed as evidenced by overall

changes in density.

B: Left side: standard test film (see text). Right side: test film show-

ing change in film contrast as evidenced by non-uniform changing

of density on the steps.

erator which may easily be measured by the dentist orauxiliary personnel without specialized equipmentare: reproducibility of x-ray output, linearity of mAsstations, field size and density, and mechanical stabil-ity of the tube head and arm suspension.

Reproducibility refers to the consistency of the x-ray output over time of an individual machine usingthe same technique factors.4 Linearity refers to the re-lationship between the change in x-ray output as afunction of time from an individual machine assumingall other technique factors remain constant.5 The sizeof the x-ray field as it exits the P.I.D. (position indi-cating device or "cone") must be no larger than a legallimit of the state in which the generator is located andits density should be uniform. The suspension of thetube head and arm must be stable in any given posi-tion to prevent motion distortion. It is our recommen-dation that the following tests be used to measurethese elements of x-ray generator performance per-formed at a minimum of three month intervals.

(a) Reproducibility of x-ray outputExpose a group of films through the test object one

at a time using normal mandibular molar technique atfive minute intervals for a total of six exposures. Whenall of the films are processed together in freshly pre-pared chemicals, the densities at each step shouldmatch precisely (Figure 3A). If the density at eachstep of the test object does not match on a set of filmswhich are processed together, one must presume thatthere is a fault in machine performance (Figure 3B).

B

Figure 3: A: Six test films with equal densities at each step show-

ing reproducibility of x-ray output.

B: Six test films with varying densities at each step showing lack of

reproducibility of x-ray output.

Several factors may contribute to this variability.Unstable line voltage is a common reason for the pro-duction of films of different densities and contrastlevels; however, in most parts of the country, electri-cal supplies are carefully regulated and informationabout the power supply can usually be obtained fromthe electric company or a building engineer. In addi-tion to fluctuations in line current, deteriorating per-formance of the x-ray timer or mA stabilizer can also

PEDIATRIC DENTISTRY

Volume 3, No. 1 29

produce differences in both density and contrast. Theend result of each of these problems is a loss of repro-ducibility which means that images on radiographs ex-posed using the same technique factors will not becomparable.

(b) Linearity of the mAs stationsOne film should be exposed through an office fabri-

cated test object using normal mandibular molar tech-nique. A second film should be exposed through thesame test object using one-half of the mAs of the firstexposure and a third film exposed using twice the mAsof the first exposure. When the three films are proc-essed together, step two on the first film (normalmolar technique) should be equivalent to step one onthe second film (one-half of the mAs of the first film)and step three of the third film (twice the mAs of thefirst film). Figure 4A illustrates this relationship.Should a comparable visible shift fail to occur, onemay presume that there is a lack of linearity in chang-ing from one mAs to another (Figure 4B). The end re-sult will be an inappropriate change in density as themAs is changed.

A B

Figure 4: A: Three test films with appropriate relationship (see

text) showing linearity of the mAs stations.

B: Three test films without appropriate relationship (see text) show-

ing lack of linearity of the mAs stations.

(c) Field size and densityThe field size at the end of the P.I.D. can be simply

measured by exposing an occlusal film which is in con-tact with the open end of the cylinder. The darkenedarea of the film should measure no more than 2.75inches or 7.0 centimeters.6 In addition, the densityacross the exposed part of the film should be uniform(Figure 5A). If the field size exceeds the legal limit orif the density is not uniform, the possibility of a badlyfitting or damaged P.I.D., or of a malpositioned x-raytube in the tube housing should be investigated (Fig-ure 5B). Machines which use a lead diaphragm for col-limation should be examined for improper positioningor alignment of the diaphragm if problems are evidentduring testing.

Malalignment of the x-ray field may result in cone-cutting or image distortion. Density aberrationsacross the field may result in non-uniformity of thedensity of the image. In general, defects found as a re-sult of these tests of machine performance cannot be

Figure 5: A: Occlusal test film showing acceptable field size and

uniform density.

B: Occlusal size test film showing unacceptable field size and non-

uniform density.

remedied by the dentist but require the efforts of aproperly trained serviceperson.

(d) Mechanical stability of the suspensionThe tube head of an x-ray generator is suspended

from its support by a retractable arm. If the suspen-sion is not stable, the tube head may drift or vibratewhile its arm is extended during use. The stabilitymay easily be measured by placing the tube head andarm at the maximum extension from the support.Watch for drift or vibration as the tube head is re-leased. If there is any movement of the tube head, theresult may be motion distortion. Such instability maybe corrected by adjusting the suspension as recom-mended by the manufacturer in the operator's manual.

3. X-Ray Receptors. The quality of most dental x-ray film is carefully controlled by the manufacturer incompliance with industry standards.7 A commoncause of spoiled film is fogging, often the result of im-proper storage. To measure the amount of base plus

30RADIOLOGY QUALITY ASSURANCE PROGRAM

Valachovic, Reiskin, and Kirchhof

fogb of dental x-ray film, process an unexposed film infreshly prepared solutions. Following adequate wash-ing and drying, most dental x-ray film should appeartransparent with a slight blue tinge. No artifactsshould be noted on the film. If fogging is noted on thetest film, one should examine the method of storageand rotation of the boxes of film. Dental film is bestkept refrigerated and away from any source of radia-tion, chemical vapor, heat or high humidity. Filmshould be purchased at intervals which insures useprior to its expiration date. Film which has passed theexpiration date should be discarded and never used fordiagnostic purposes0. This test should be per-formed monthly.4. Darkroom or Daylight Loader Integrity. It isimportant to insure that no light capable of sensitiz-ing the film be allowed into the darkroom (or daylightloader of an automatic processor). A simple test forthis problem is to remove a dental film from its packetin a safelighted darkroom and place it on a flat surfacein the area where film is normally handled (or on aflat surface inside of the daylight loader). On top ofthe film, place a coin or other opaque object which in-completely covers the film. Allow it to remain in placefor at least five minutes (this is presumed to representthe maximum time during which a film may be ex-posed to these conditions during normal processing).Following this interval, process the film using normaltechnique. If there are any light leaks from safelightdefects or breaches in darkroom integrity, the area offilm not under the coin will have been sensitized andappear to have an increased density after processing(Figure 6).

DiscussionThere are a number of reasons for developing qual-

ity assurance programs in dental radiography. Prior to1974, there were no requirements for machine perform-ance8 and the operating stability of many x-ray gener-ators in use today is uncertain. Studies have shownthat there are a variety of types of machine malfunc-tion which may occur as a result of use and aging.9.10

There is evidence to suggest that sight development isa common practice used to compensate for inadequatemachine performance, inadequate operator training,or defective processing chemistry.11 In a recent paper,we described how a quality assurance program may behelpful in minimizing patient exposure and radiationrisk.12 There is also an economic incentive for reducingthe number of retakes through a quality assurance

''Base plus fog: The amount of light attenuation which occurs whenlight passes through the celluloid backing plus any increased den-sity due to sensitization of the emulsion of the x-ray film.

cExpired unexposed film or other discarded film can be sold forsalvage because of their high silver content.

program which also minimizes the expenditure forlabor and materials13. In addition, serious liability canresult from mis-diagnosis caused by poor radiographs.

Governmental intervention in this area is becominga more likely possibility. Several states, such asIllinois,14 have established maximum allowable expos-ures for diagnostic x-ray procedures. The Commis-sioner of the Food and Drug Administration has re-cently proposed recommendations for the implemen-tation of quality assurance programs in all diagnosticradiology facilities including private dental offices.15

Several studies were cited by the F.D.A. as part of itsproposed recommendation. The first citation referredto information obtained from an examination of ra-diographs submitted to the National Institute of Oc-cupational Safety and Health under its pneumoco-niosis compensation program.16 Although facilitiesparticipating in this program were screened, Trout etal. found that 44% of the participating units had from10 to 40% of their radiographs rejected as being of in-adequate quality for the diagnosis of pneumoconiosis.

A second study by Beideman et al. examined pre-authorization dental radiographs submitted to thePennsylvania Blue Shield.17 A preliminary assessmentof these radiographs found that at least 50% of thefilms were not adequate as a basis for evaluating pro-posed treatment plans. The Food and Drug Admin-istration pointed out two consequences of poor qualityimages. In the first case, a suboptimal image deniesthe practitioner the full extent of diagnostic informa-tion that should be available. In the second case, thepatient may receive unproductive radiation exposuresas a result of radiographs which must be repeated.

The F.D.A. concluded that a considerable numberof inadequate films resulted from processing failures,and it estimated that a dose reduction to active bonemarrow could range from 209,000 to 330,000 rems an-nually by reducing the number of repeated radio-

Figure 6: Test film showing result of exposure by darkroom light

leak.

PEDIATRIC DENTISTRY

Volume 3, No. 1 31

graphs in hospitals alone. The F.D.A. also estimatedthat elimination of retakes in non-hospital facilitieswould significantly add to this total, as would theelimination of unnecessary radiation exposure due toinappropriate films produced in both hospitals andprivate offices and clinics.

There are a number of programs which have at-tempted to improve radiologic practices in dentistry.The Dental Exposure Normalization Technique{DENT) programd is a federal project, managed byparticipating states, which is based on consultationwith dentists to identify causes of excessive exposureand to suggest corrective actions which have beenshown to effectively reduce the exposures.18 TheNashville Dental Project proved the effectiveness ofan educational approach for voluntary improvementof radiographic practice. Survey data were collectedon 110 x-ray units (72 dental offices) in Nashville,Tennessee in 1972. Dental consultants visited theoffices two months later to present the findings and todemonstrate techniques which would improve radio-graphic practice. In 1973, a follow-up survey was con-ducted to determine the effectiveness of the consulta-tion visits. Average exposures were reduced from 472mR/film in 1972 to 311 mR/film in 1973.19

In another Nashville study, Johnson and co-work-ers surveyed a number of dental offices to determinethe reasons for high skin exposures. They found thatalthough the dental x-ray generators surveyed were ingeneral compliance with recommended standards, theoverexposure was the result of dentists failing to useproper processing techniques20.

Summary

We have described a quality assurance program forcommon intraoral d~ntal x-ray generators and tradi-tional modes of film processing. Practitioners who per-form extraoral radiographic examinations will need toidentify other test procedures to deal with the use ofintensifying screens, cassettes, and adjustable collima-tors21,22.

Dr. Valachovic was assistant professor, Dr. Reiskin is professor,and Ms. Kirchhof is st~ff radiologic technologist at the Universityof Connecticut School of Dental Medicine, Division of Oral Radiol-ogy, Farmington, Connecticut. Requests for reprints should be sentto Dr. Valachovic who is now Research Fellow in Dental Care Ad-ministration, Harvard School of Dental Medicine, 188 LongwoodAvenue, Boston, Massachusetts 02115.

References

1. Nelson, R. E., Barnes, G. T., and Whitten, D. M.: "Economicanalysis of a comprehensive quality assurance program," RadiolTechnol, 49:129-134, 1977.

dDentists wishing to utilize the services of the DENT programshould contact their own states’ Departments of Radiation Con-trol or other appropriate agencies.

RADIOLOGY QUALITY ASSURANCE PROGRAM32 Valachovic, Reiskin, and Kirchhof

2. Goldman, L. and Vucich, J. J.: "Automatic processing Q.A.:impact on a radiology department," Radio1, 125:591-595, 1977.

3. Bureau of Radiological Health: "Fast film exposure and proc-essing in dental radiography," DHEW Publ. No. (FDA) 78-8039, Supt of Documents, Govt Print Off, 1978.

4. Gray, J. E.: "Photographic quality assurance in diagnosticradiology, nuclear medicine and radiation therapy," DHEWPubl. No. (FDA) 76-8043, Supt of Documents, Govt Print Off,1976.

5. Starchman, D. E., Johnson, R. G. and Howland, W. J.:"Linearity of exposure with indicated time and current for

¯ diagnostic radiography units," RadioI, 122:489-492, 1977.6. National Council on Radiation Protection and Measurements:

"Dental x-ray protection. NCRP Report No. 35," Washington,National Council on Radiation Protection and Measurements,1970.

7. A.N.S.I.: "Reg. U.S. Pat. Off. PH6.2-1970 (Rev. of PH6.2-1961)," Approved March 3, 1970 by the American NationalStandards Institute, Inc.

8. Bureau of Radiological Health: "Regulations for the admin-istration and enforcement of the radiation control for Healthand Safety Act of 1968 -- diagnostic x-ray systems and theirmajor components," DHEW Publ. No. (FDA) 75-8003. Supt Documents, Govt Print Off, 1974.

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17. Beideman, R. W., Johnson, O. N., and Alcox, R. W.: "A studyto develop a rating system and evaluate dental radiographssubmitted to a third party carrier," JAm Dent Assoc, 93:1010-1013, 1976.

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