Radiology

RADIOLOGY

Digital Rad

Which tlTe of digital image receptor is most common at tlris time?

. CID (Charge Injection

Device)

. CMOS/APS (Complementarv Metal Oxide Seniconductor/Atiive Pixel Sensor)

. CCD

(Charge-Coupled Device)

1

Copyright t) 20ll-2011 - Denhl Decks

A number ofcomponenls are required lbr direct digital image producrion. These components include an x-ray source, an elecffonic s€nsor, a digitil interface card, a computer with an analog-to-digilal con\efter lADC). a screen monitor, sofhvarc, and a printer Tlpically, systcms are PC based *ith a 486 or higher proccssor, 640 KB intemal memory cquipped .|.t'ith an SVCA graphics card, and a high-resolution monitor /1024 X 768 pi* e/j.). Direci digital senso$ are eilher a charge-cotlplcd device /Ca'D) or complemenlary metal oxide semiconductor active pixel sensot (CMOS-APS). The CCD is thc most common device used today.The CCD is a solid-state detcctor composed ofan anay of x-ray or light sensitive pixels on a pure silicon chip. A pixel or picture element consisN of a small electron well into which thc x-ray or light energy is deposited upon exposure. The individual CCD pixel size is approxirnately 40I wilh thc latest versious in the 20F range. Thc rows ofpixels are rrranged in a matrix of 5I2 x 512 pixels. Charge coupling is a process whereby the numbcr ofclcctrons deposited in cach pixel are transferred from one well 1{) thc next in a sequential manner to r rcad-out amplifier filr imagc display on the monitor. There are tuo typcs ofdigital sensor array designs: area and lin€ar. Ar€r arrays are used tbr intraorll radiography, while linear arrays are used in extraor|l imsging. Area arrays are available iD sizes comparablc to size 0, size l, and size 2 film. but the sensors are rigid and thickcr than radiographic film and have a smaller sensitive area for image capture. The sensor communicates with the computcr through all electrical cable. The complementary metal oxide s€miconductor active pix€l sensor fa'ryo.t-.4PS/ is the latest development in direct digiral sensor technology. Externally. CMOS sertsors appcar idcntical to CCD dctectors but lhey use an aclive pixel technology and are l€ss expensive to manufacturc. Thc APS technology rsduces by a factor of 100 the system power required to process the image conpared with the CCD. In addition. rhe APS system eliminates the nccd for charge transf'er and may improvc the reliabilify and lifespan ofthe sensor. In summary, CMOS sensors have scvcral advantages including design integration, low power requrremenls. mimu_ facturabiliry, and low cost. Horvever, CMOS scnsors have more fired pattern noise and a smaller rctive

area for image acquisition. The charge injection device or CID is another sensor technology used in dental digital radiograph). A CID is a silicon-bascd solid-state imaging rcceptor much like the CCD. Structurally, howevcr, the CID differs from the CCD. No computer is required to process lhe images. This system features a CID x-ray sensor. cord, and plug that are insc(cd into the light source on a camera platform; digital images are seen on the system monitor within seconds.

.

Superior gray-scale resolution

. Reduced patient exposure to x-radiation . Increased speed of image viewing

. Lower equipment .

and

film costs

Sensor size

. Increased efficiency

. Effective patient education tool . Enhancement ofdiagnostic image Cop).dght O 201 I -20 l2 - Dental Decls

. Indirect digital imaging . Direct digital imaging

.

Storage phosphor imaging

Cop)right O 201 I -20

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- Dmtal Decks

has bccn availablc lbr morc lhan a dccadc. lt is cslinatcd that l0-207o ofdcntal practitioncrs usc digital imaging tcchnology in thcir dcntal practicc. It is anticipatcd thcsc numbers will steadily increasc ovcr thc ncxt fivc to tcn ycars as dcntistry continucs to movc from film bascd to digital inraging. Film-based imaging consists ofx-ray inieraction with clcctrons in thc lilm cmulsion. production ofa lalcnl inragc, and chcnrical proccssing that transfoffns thc latcnt imagc into a visible onc.

Digital or electronic imaging

As such, radiographic fi1m providcs a mcdium for rccording. displayiDg, and sloring diaeirrosiic infbrmation. Filmbascd inragcs arc dcscribcd as analog images. Analog imagcs arc charactcrizcd by continuous shadcs ofgray liom onc arca to the next betwccn thc cxtrcmcs ofblack and \lhitc. Each shadc ofgray has an optical dcltrsity klarknet, rclatcd to lhe amount oflight that can pass through thc imagc ai a spccific silc. Film displays higher resolution than digilal rcccpfors wilh a rcsolving powcr ofabout l6lplmm (lnrcs puirs/nil/td"/"r'l. However, tilm is a rclativcly ineflicicnt radiation deiector ard, thus, rcquircs rclatively high radiation cxposurc.Thc usc oircctangular collimation and thc highest speed lilm arc mcthods thal rcducc rudiation cxposurc. Chcmicals ar(} nccded to process the image and arc olicn drc sourcc of crrors and rctakcs. Thc finalresult is a fixcd nnagc that is dillicult lo manipulalc oncc capis thc rcsult of x-ray intcrrction *ith clectrons in clectronic sensor pirels fpi./ru e ?l?nents), cotrvcrsion ofanalog data to digital data, computcr proccssing, and display ofihc visiblc imagc on a computcr scrccn. Data acquircd by thc scnsor is communicatcd to the conputcr in analog tbmr. Computcrs opcraic on thc binary number systcm in which hvo digits /0 dr./ // arc uscd to rcprcscnt data. Thcsc two charactcrs arc callcd bits (bi ar) digit), and thcy form words eight or morc bits in lcngth c^llcd bytes. Thc total nunrbcr ofpossible bylcs for 8-bit languagc is 28 = 256. Thc analog-tc.digital converter translbrms analog data into numcrical dala bascd on thc binary numbcr systcm. Thc vohagc of thc output signal is nrcasurcd and assigncd a numbcr trom 0 fbld.t/ to 255 (\'hit?) according to thc intcnsity ofthc voltagc. Thcsc numcrical assignmcnts translatc into 256 shades of gra!. Thc human eyc is ablc to detect approximatcly 32 gray lcvcls.

Digital imaging

Dircct digital imaging has dislinct advantagcs ovcr lilnt in Icrms ofcxposurc rcduclion, climlnation ofprocessing chcmicals, inslanr or rcal timc imagc production and display. imagc cnhanccmcnt, paticnt educatjon utility, and con\ cnicnt sloragc. Thc actual amount ofcxposurc rcduction is dcpcndent on a numbcr offactors including film spccd. s.nsor arca. collimation. and relakcs. Thc primary disadvantages includc drc rigidily and thickncss ofthc sensor, dccr.as.d rcsolution. highcr inilial systcm cost, unknown scnsor lifcspan. and pcrfccl scm iconduc tor chargc Iransfir. \ote: Infection controlprcscnts anolhcr chal lcngc forclinicians using dircct digitalimaging. CCD scnsors cannol bc :t.ri1i/cd. Carc nccds to bc tak.n to propcrly prcparc, covcr, and cnsurc thc barrier is nol damagcd during paticnt imaging proccdurcs. Dircct saliva contact with thc rcccptor and clcctrical cablc must bc avoidcd to p.cvcnt crossconta-

Three methods of obtaining a digital image currently exist: direct digital imaging, indirect digital imaging, and storage phosphor imaging. . To produce a direct digital x-ray image, three components are necessary: an x-ray machine, sensor, and a computer monitor The images are captured using a solid-state detector or sensor such as a charge-coupled device {CCDJ, a complementary metal oxide semiconductor/active pixel sensor (CMOS / AP.S/. or a charge injection device /C/Dl. The sensor then transmits the image to a computer monitor Within seconds of exposing the sensor to an

intraonl

x-rays. an image appears on the computer screen. Software is then used to enhance and store the image.

. The essential components ofan indirect digital imaging system include a CCD camera and computer. In this method, an existing x-my film is "digitized" using a CCD camera. The CCD camera scans the image, digitizcs or converts the image, and then displays it on the computer momtor

. A third method ofobtaining a digital image is storage phosphor imaging, a wireless digital radiography system. In this system, a reusable imaging plate coated with phosphors is used instead of a sensor with a fiber optic cable. The plates are described as "wireless" because they are not connected via cable or wire to the computer. The plates are similar in every way to conventional intraorul film, including size, thickness, rigidity and placement. These plates store the energy from incoming x-rays, and are then placed in a scanning device. The scanner stimulates the stored x-ray infonnation by subjecting the plate to a laser light. When the light strikes the phosphor material, energy is released as a light signal in an electronic waveform and is converted to a digital image by the computer. The image can not instantaneously be viewed on the monitor, but takes from 30 seconds to 5.5 ninutes depending upon the system and certain variables.

RADIOLOGY

Dig Rad

You have a patient who is extr€m€ly concerned about the radiation erposure he will receive when he gets intraoral pictures taken. You let him know that if he wants the least exposure then you will use:

. Digital radiography

.

E-speed films

.

F-speed films

. Panoramic instead ofa full mouth series

Copyflglu

a Tipof

1.

2. The opaque

nose

line -+ Hard palate/floor ofnasal fossa

3. The lucent area

-+

Orbit

4. The opaque line

Hard palate/floor ofnasal fossa

5. The opaque line

Floor of n.raxillary sinus

6. The opaque

structure

-+

-+ Air between the soft palate and the dorsum

7. The radiolucent space

8. The opaque

-+

Shadow of opposite mandible (re.ferred to as ghost image)

oval -+ Mental foramen

The diffuse opacity

-+

Shadow ofcervical spine

12. The broad lucency

-+

Submandibular gland fossa

11.

13. The

of tongue

line -+ Dorsum oftongue

9. The opaque line (dots) 10. The lucent

Soft palate

opacity -+ Articular tubercle

oflilm processing is trlofoldi . To conven thc latent (invisible) imagc on the film into a visible imagc proccss -der'eloping . To presene the visiblc image so that it is pemanent and docs not disappear tiom the dental x-ray

The purpose

fi\ing

process

\\-hen a bcam ofphotons exposes an x-ray film, it chemically changes thc photosensitivc siher halide crystals in the film emulsion lldtent image). Important: Exposed arcas will becomc radiolucent, s hereas nonexposed areas will become radiopaque.

\-rat.' developing solution contains the following:

.,\

developing agent, such as hydroquinone, which is a chemical compound that is capablc ofchanging the exposed silvcr halide crystals to black mctallic silvcr. At the same time, it produces no appreciablc cffcct on thc unexposed silver halidc crystals in the emulsion. Gives detail to the x-ray image. Note: Elon, also kno\r'n as metal, acts quickly to produce a visible radiographic inage. It scncraics the many shadcs of gray. . An lntioxidant preserrativ€, for example. sodium sulfite, prevents the developer solution from ox-

idizing in the presencc ofair. . An

accelerator

an alkalt (sodium

carbonate)

activates thc dcveloping agents and maintains the

alkalinity ofthe developer at the correct value. It softens geiatin ofcmulsion. . A restrainer, such as potassium bromide, is added to dcvclopcrs to conffol the action ofthe developing agent so that it does not develop the uncxposcd silvcr halide crystals to prodrtce fog. Noter Thc optimal iemperature for thc dcvcloper solution is 68oF.

Importanti The function ofdeveloping solution is to remove the ha)idc portion ofthc enposed, energized silver halide crystals to black rnctallic silver, this is refened to as reduction. The developer solution softcns the film emulsion during this proccss. The function offixing solution is lo stop developmcnt and remove remaining unenergized, unexposed silvcr halide crystals ftom the film emulsion. The fixer hardens thc film emulsion during thc proccss. Film processing involves the following 5 steps:( I ) immerse film in developer (2) rinse film in water bath (rinsing dilutes lhe de*loper slott,ing the development process br removing lhe alkali accelerllor, Prevnting neutralizution ofthe acidfxer) (3) immerse film in fixcr (4) q'ash film in watcr bath and (5) dry the

film.

''.' L-'

Which ingredient of lixer solution fuDctions to remove ill unerposed and underdweloped silver halide crystals from the trlm emulsion?

. Fixing agent . Acidifier

. Hardening agent . Preservative

30 Coplright O

.

Decrease the temperature

.

Increase the temperature

20ll-2012

Dental Deck5

ofthe developing solution ofthe developing solution

. Replenish the developing solution

. Increase the mA setting .

Increase the

kvp setting

31

Coplrighr O 20ll-2012 - Denral Dects

X-.ay fixing solrtion conlains thc following: . Thc fixing agent f. /e.7rirg ager, is madc upofsodium thiosulfate orammonium thiosulfate and is commonly called hwo. The purposc ofthc fixing agcnt is to remove or clear all unerposed and underd€veloped silver halide crystrls liom thc film emulsion. Thc chcmical "clcars" thc film so that thc black silver rmagc produccd by the dcvclopcr bccomcs distinctly pcrccptiblc. whcn the film is impropcrly cicarcd, the rcmaining unexposed silvcr halide crystals darkcn upon exposure to light and obscure ahe imagc. . An antioxidant preservative, thc samc prcservativc uscd in thc dcvclopcr solution. sodium sulfite, is also uscd in the fixer solution. lt prevcnts thc chcmical dctcrioration ofthc fixing aSent. An acidifier such as acetic acid or sulfuric acid is uscd to ncufalizc thc alkaline dcvclopcr Any unncutralizcd alkali may cause the uncxposcd crltals to continue to dcvclop in thc fixcr It also produccs thc neccssary acidic cnvironmcnt required by lhc fixing agcnt. . Thc hardener agcnt used is potassium alum, lt shrinks and hardcns thc gclatin in lhc film cmulsio affcr it has been softcned by the accclcmtor in thc developing lolution. It shoflcns drying timc and protccts the cmulsion fionr

l'ollowing lixation, a walcr bath is used to wash the tilm.This stcp is ncccssary to thoroughly rcmovc all cxccss chcmicAls (i.e., thnsufaE ions atd sil\,er thiosurli?re.rnpldi€r, from thc cmulsio . Thc final step in rhc film proccssing is the drying ofthc films. Iiilms nay be air-dricd at room Ienpcraturc in a dus! lrec area or placcd in a hcated drying cabinct.

Ntanual processing is a simplc mcthod uscd to dcvclop, rinsc, fix, and wash dcntal x_ray films lhc csscntial piecc ofcquipmcnt rcquircd for manual proccssing is a proccssing lank, which is containcr dividcd into compartmcnts for thc dcvclopcr solution, walcr bath. and fixcr solution. Notel Thc optimum tcmpcraturc lbr ihc devclopc. is bct$ccn 68'F and ?0'F, tnical timc in developer is 5 minutcs. nnsc lor 30 seconds, placc in fixcr solution for l0 minutcs and wash for at lcast l0 minulcs and

dry

to proccss dental x-ray fillll. Thc essential piccc ofcquipmcnt required for automatic processing is thc automatic processor, which automalcs all film proccssing steps

Automatic processing is anothcr simplc way

.- . 1. Fixing timc is always at lcast twice as long as thc dcvcloping limc. j\ote* 2. wirh both automalic and manual processing,8 oz. offrcsh dcvclopcr and fixcr should bc added per gallon of solution per dr]. ''&r! L tf u ariea radiograph werc proccsscd a sccond rime, thcrc would bc no cbangc in contmst or dcnsity. Safelighting providcs illumination in thc darkroom lo carry out proccssing activities safely without cxposing or damaging the film. Thc GBX-2 safelight filter by Kodak with a l5-watl bulb at lcast 4 fcct from thc workinq surfacc is rccommendcd. ,1.

As thc dcvcloping solution g€ts weaker, the films will get lighter. Both the devcloping and fixing solutions should be replenished on a daily basis Remember: with both automatic and manual processing 8 oz' of fresh dcvclopcr and fixcr should be tdded per gallon of solution per da].These solutions also need to be changed on a regular basis, and the tanks need to be scrubbcd and cleancd as well. The following factors affcct the life ofa developing solutionl the clcanliness ofthe tanks, the sizc ofthe films processed, the number of films processcd, and the tempcrarure ofthe solution

l. Yellowish-brown film will result from insufficient tlxing or rinsing

(See

Jigute #l).

film storage or outdated films. 3. Low solutio levels will appear as: developcr cut-off fJll?lg, I vhile boftler SeeJigure #?or {ixer cut-offfs/rdight hlack border, Seetigure #3). 4. Light spots on film may result from contact with thc fixer beforc processing (Seefgrre 2. Fogged

film may

also result from improper

#1). 5. Developer spots appear dark or black (See

Fig

AI

Jigure #5).

#!

prctures .eprinFd from Hanng. Joen Iannucci and Laura Jdsen Lrnd: Rad iogrnphic Inrerprerltion for lhe

$itb pemission iom Elsevier

Dotal Hygienisl. O

1993.

.

Aft€r processing a film, you notice that is rppears too dark What is the most likely caused of this problem?

. Inadequate development time

. Developer solution too cool . Depleted developer solution . Excessive developing time

Copright O 201l-2012 DenlalDecks

A straight white border appears on the x-ray film. What is the most likely cause of this?

. Fixer cut-off . Developer cut-off . Overlapped films

. Static electricity

Coprigh

O 201 I -20 12

'

Dental Decks

- Inadequate delelopmmt time - Developer solution too cool - lnaccurate trmer or thermometer - Depleted developer solution

- Check development nme - Check developcr tcmperxrure

- Replace

t_aul9"

timcr or lhermometer vith fiesh

- Replenish developcr

- Excessive developing time Chcck dcvclopment tjme - Check developer temperaturc - Developer solution too hot - lnaccurate tim€r or lhermometer - Replace faulty timcr or thcnnometer - concenEated developer solution ' Replcnish dcveloper with fresh Sudden t€mperature change Check tempcrature of processing between developer and water bath solutions and *dter brthi a!'oid

- Exrmine film p.rckets for defects - Never unwrap films in the trcsence lvhite lighr Gray: lack ofdetail

- Improper safe lighting

'Light

leaks in dark'room

- outdated

fitms

- Improper

film storage

" Contaminated solutions

- Developer solulion too hot

Lxample Developer

cut-off

- Check the filter and bulb wattage of th€ safe light - Check rhc darkroorn fbr light leaks - Check rhe erpiration date offilln packages ' Srorc films in a cod. dry. proiected arc! - Aroid contaminated solurions by cover-

ing tanks alier each usc - Check temperature ofdeveloper

Solutions

Problems

Appearance Stmight u'hite border

Underdeveloped portion film due to low level of

of

Fixet

Straighi black border

Unfixed portion

offilm

due to

low level offixer

Overlapped

whitc or dark

films

appear on film where overlapped

areas

Airbubbles whitc spots

Check developer levcl bcforc processing: add solulion if needed

developer

cu!-off

of

Chcck fixer Ievel befbrc processingl add solution ifneeded

Two films contacing each other during processing

Separate films so thal no contact

Air trapped on ihe film

cenlly agitale film racks aftcr

surface after being placed in the processing solutions

placing in processrng solutions

iakes placc during processing

Film emulsion damaged by cenlly handle films by the edScs the opemtoa's fingemail during onlY rough handling

Fingemail

Black crescent

al.ifact

shaped lnarks

Fingerprint artifact

Black fingcr?rint

Fi:m louched by ingers that are contaminated with fluoride or developer

Wash and dry hands thoroughly before processing

Static

Thin. black, branching

- occurs when film packet is opened quickly - Occurs when film pack is opened before the radiographer touches a conduciive object

- Open film packel slowiy

electricjty

Soft emulsion removed from the film by a shalp objecr

Scratchcd

film RqJr.rerl

li.r

- Touch a conductive object before unwrapping films Use care when handling films and film racks

Hrnng..loen tannu.ci and Lluri Jahen: Denlal RadDgrlphy: Pnnciples and Te.hnlques Thrd Ediri.n

I)enni$ron from !l\e\rer

!'

1000.

*nh

. REM

.RAD . Roentgen

.Qy

34

Coplrighe20ll-2012

- Dentd Dect3

. Mature bone cells . Muscle cells . Nerve cells

. Epithelial cells

Coplright C 2011-2012 - Denral Decfts

The rad (radiotion absorbed dose) is a unit used to measure a quantity called absorbed dose. This relates to the amount ofenergy actually absorbed in some material, and is used for any type ofradiation and any material. One rad is defined as the absorption of 100 ergs per gram of material. The unit rad can be used for any type of radiation, but it does not describe the biological effects ofthe different radiations.

The rem (roentgen equivalent man) is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage ofthe radiation. Not all radiation has the same biological effect, even for the same amount ofabsorbed dose. Equivalent dose is often expressed in terms ofthousandths ofa rem, or mrem. To detenrine equivalent dose (rent),yon multiply absorbed dose (rad) by a quality factor (QF) that is unique to the type ofincident radiation. The QF is a t'actor used lor radiation protection purposes that accounts for the exposure effects of different types of radiation. For x-rays QF : 1. The roentgen is a unit used to measure a quantity called exposure. This can only be used to describe an amount of gamma and x-rays, and only in air

Exposure is a measure ofradiation quantity, the capacity ofthe radiation to ionize air.

Equivalent dose is used to compare the biologic efl'ects ofdifferent types ofradiation to a tissue or organ.

Effectiye dose is used to estimate the risk in humans.

Gra\ /Gr,

:

js a unit lor measuring absorbed dose; the Sl unit equivalent to the rad:

I gray

100 rad.

and produccs chemical changes th.rt rcsults in biologic damsge in liviDg tissuc. spccific mcchanisms olradiation injury are possiblc: ionization and frec radical formation /1, is is l|rc pritnd^'

All ioniting radiation is h:rrmful

T\o

l

hcorics ofradialim injury:

. Thc direct theort: suggcsts lhal ccll damagc rcsuhs whcn ionizirg radialion directll hits crilical arcas. or tar!.rs. q Jlhin $c ccll. Dircct altcration ofbiologic molccrlcs (i.c., (u bohrlrat$, 14il!, prct?int, DN 1/ occuts. Ap pro\rrnalcl) one-third ofdrc biologic cffccls ofx-ray cxposurc rcsult from dircct cllccts. . Th. indircct theort suggcsts that x-ray photons arc absorbed wilhin thc ccll and causc lhc lbnnation oi loxins. \ hich in tum d.rnagc rhc ccll For cxamplc. \'hcn x-ray pholons arc absorbcd by watcr within a ccll. free radicalforDaiion rcsul1s. Thc iicc radicals combinc to form loxins /s.g, l/r(r. which causc ccllular dysfunction and rro'lrg1. danl3sc. Aboul two{hirds of radiation-induced biological damagc rcsults fiom indircct ctlccls.

lmponant: I)amag. lo thc DNA molecul€ is lhc primafv ncchanism fbr radiation induccd

\

cel1 dcirth.

nutation, and

dos€ response curve is uscd to dcmonslratc thc rcsponsc i/drndgel of(issucs to thc dosc arr?ornr.) ofradiation rc-

Biological cfTects ofradiation can bc classificd as: . Stochastic cftcctsi occur as a direct function of dosri lhc probabilirr" ofoccurrcncc incrcascs \\'iih incrcasing ibnrrbcd dose: howeve., lhc sclcrity ofcliccls does not dcpcnd on thc magnitudc ofthc ahsorbcd dose. Examrlc\ ofsrochastic cficcls includc cancer r.€.. trrro,-./ induction and genetic m|Itations (i.?., DNA tld"ng.') . \ on sroc h a stic cffects /.le ter ti i\ ti( L'[e. ts)t arc somatic cficcts tha! havc a th reshold and i n creasc in scvcrily $ith increasing absorbcd dosc.Eranrplcs of nonslochaslic eilccts includc erylhcma. oral changes. loss of hair, cararact ibnnation, and dccrcascd fcriility. Importanl When comparcd fi-cts require Iarger radiaiion doscs to seriously impair hcalth.

silh slochastic eflects. nonstochastic cl-

\ot

.rll cclls rcspond 1r) r:rdidlion in thc samc manncr In general, thc gre.tcr thc rate or potential for mitosis and thr morc immsture rhc cclls and tissues are, thc greatcr the sensitiritl or susccplibility to radiation. Cclls that arc radiosensitire includc blood cclls. immaturc rcproductivc cclls, epithelial cclls, and iroung bonc cclls. Thc ccll that rs most scositive to radiation is ths small lymphocyrc. Radioresistant cclls includc cclls ofbonc. musclc and ncrvc. Rsdiosensitive organs composcd ofradioscnsitive cells includc lymphoid tissucs. bone marro$,, tcstcs. and inlcstincs. Examplcs of rad iorcsista n t tissues includc thc salivary glands. kidncy and liver

. Latent period . Period ofcell injury . Recovery period

. Cumulative effects

36 Cop)ri8hr O

201

1,2012 - Dental Decks

. Osteoradionecrosis . Bisphosphinate related Osteonecrosis ofthe jaw

. Rampant periodontal

disease

. None ofthe above

37 Coplriglrt €i 201l-2012, Denial Decks

Chemical reactions /e.g., ioni:dtkr1. .lree rudi(al fornalion) lhal lollo."\, the absorption of radiation occur rapidly at thc molecular level. I lonever. varying amounts of time are required fbr these changcs to alter cells and cellular functions. As a result, the obsenable effects ofradiation are not visible immediately aftq cxposurc. Instead, following exposurc, a lat€nt period occurs. The latent period is the pcriod of time between radiation exposure and the ons€t ofsymptoms. It may be short or lonc, depending on the tohl dose olradiation received and the amount of time it look to receive the dosc. Thc period ofcell injury fbllo$ s the latent period. Cellular injury may result in cell death. changes in ccll tunction or abnormal mitosis ofcellsThe r€covery p€riod is the last event in the sequcnce ofradialion injury Some cells rccover fioni the radiation ir1jury, especially ifthe radiation is "low level." Note: The eflects ofradiation exposure are additive and rhc damagc that rcmains unrepaired accumulatcs in the tissues. The cumulative effects ofrepealed radialion exposure can lead to various serious health problems le.g., carcinogenesis, r|hi.h leuds to r\trious caxilonar, genetit nutatiotis whi.h cdure hirth defets. diflerent kinds of lculienia and utdrads).

Radiation effects can be classified

as

cithcr:

. Shorl-term effects: ellecls ofradiation

that appear within minutcs. days, or \r'eeksl associated with largc short period oltime. These effects are not applicable !o dentistry. . Long-1€rm effects: effects of radiation that appear aftcr years, decades, or generations; associated with small amounts ofradiation absorbed repeatedly over a long period oftimc- Repeated low levcls ofradiarion erposure are linked to thc induction ofcancer, birth abnormalities, and genctic defects. amounts ofradialion absorbed

ir1 a

Radiation elTects on rells: . The cell nucleus is morc sensitive to radiation than the cytoplasm. Damage !o the nucleus allccts thc chro' mosomes con{aining D\A and resuhs in disnlplion ofcell division, \l'hich in tum may lead !o disruprion ot cell lirnction or cell death. . lllitotic delay occurs afier irrldiation ofa population ofdividing cells. . Radialion causcs cell death by damaging chromosomcs! preventing successful mitosis and also by apposit.s /proNromnted cell de.tth). . Cell recovery involvljs enzymatic repair of sirgle-strardcd brcaks of DNA.

Thc clinical complications that occur in bone following inadiation relate to lhe marked reduction in vascularity and the consequcnt d.crcased capacity oflhc bonc to resist infection. Therc is a strong possibilily that inf'eclion and nccrosis ofbone will resuh in a nonhealing \lound if the orrl mucous rtembrancs aQlredd] tomprotniscd b) r|rddidli.r,l breaks do\,'n. This may occur spontaneously or fbllowing a loolh extraclion or denture sore and is kno\\ n as osteorrdionecrosis, Osteoradionecrosis is morc common in the mandible than in thc maxilla. becausc oflhe richer vascular supplv to the nra\illa and lhc fact that lhe nandible is morc frequently inadialcd. Thc mosl conlmon faclors precipitating osleoradionecrosis arc pre- and pos!ilradialion extractions lnd periodonta] disease. Note: Damage to lhe blood lessels /d-f.)ppor_erl /o nen,es, ius(le, eL., predisposes a patient 1o thc developmen! of osteoradionecrosis Histopathologically, ihe I Hs ofORN arc hypocellu)ar bone. hypovascular tis\ue, and h),poxic tissue and bone To prerent osleoradionccrosis: extract all hopelcss tceth three weeks prior to bcadineck radiation trcattncnl, If cxrracting afler radiolherupy, lhc use ofsystemic antibiolics is recommended. Sonc sludies suggesl hypeftaric oxygcn rrealmcnls bcfore and afler lrcaimcnt to reduce the risk ofosleoradionecrosis flrr:r r soncrhd (ontn'

Eflccls ofl'hole t ody irradiation: . When the whole body is exposed to low or moderate doses of radialion. thcre are ch.rracleristic changes kolled the aute rddiation slndtomc) th develop, which are quitc different irom thal secn when a relatively small volume oftissue is exposed. . Embryos and fetuses are considerably more radiosensitive than adults bccause mosl embryonic cclls are relatively undifferenliatcd and rapidly mitotic. Prenatal irradiation may lead to dcadr or lo spccific devclop menlal abnonnalilies depcnding on the stage of developmcnl at the tine of irradialion. \otc: No effccts on en'lbryos or fetuses have been shown from low doses used in denlal rldiography.

Late somatic effects: . Somatic eflects are those seen in the irradiated individual. The most important are radialion-induccd cancers. . Carcinogenesis: - Radiation-induccd cancers are not distinguishable from cancers produccd by odrer causcs. - Thc incidence ofleLlkcrnia bther thdn CLL) rises following cxposure ofthe bonc marrow lo radialion - Radiation induced solid canccrs, including in lhe thyroid. brain, and salivary glands. generally appeer 10 or more yean aftcr exposure and elevdled risk remai.s for lifetime. - Pcnons younger than 20 ycars ofage are more al risk for solid tumors and leukcmias than adults

. The first statement is true; the second statement is false

. The first statement is false; the

second statement is true

. Both statements are true

. Both statements are false

38

Coplrighi o 201l'2012 Dental Decks

. kvp

.mA . Tirne (sec) .

All of the above

39 Coplrighr O 20ll-2012 - Dental tr€cks

The oral cavity is irradiated during the course oftreating radioscnsilivc oral malignant tumors. usually squamous cell carcinoma. Radiation therapy for malignant lesions in the oral cavity is usually indicated when the lesion is radiosensitiv€, Ndvanced, or deeply invasiv€ and cannot be approached surgically. Fractionation ofthe totalx-ray dose into multiple smalldoses provides greater tumor destruction than would be possible with a largc single dosc. Fractionation also allows incr€ased cellular r€pair of Dolmal tissues, \\+ich are believed ro havc an iiheritantly grcatcr capacity for recov€ry than tumor cells. Another vahrc offractionation is that i1 increases the mean orygen tension in an inadiated rumor, rendering the turnor cells morc radiosensitive.

Radiation effect on oral tissu€s: . Oral mucous membranes: by the end of the sccond weck ofthempy the mucous mcmbrancs bcgin to show areas ofrcdness and inflammation (zac.rrr'ti9. As therapy continues. lhe mucous membmne begins to break down, u,ith the fomation ofa white to yellow pseudomembralne ldesquamated epithelial larcr). At the cnd oftherapy the mucositis is usually most severe, secondary infection by Candida albicans is a common complication. After inadiation the mucosa bcgins to heal rapidli, and is usually complete by about 2 months. . Taste buds: arc sensitive to radiation. Therapeutic doses cause extensive degeneration ofnormal histologic architccture oftaste buds. Patients often notice a loss oftastc acuity during the second o. third week ofradiotherapy. . Salivary glands: during the first lew weeks ofthenpy thcre is usually marked and progtessive loss ofsali\'ary secretion. fi€ extent ofreduced flow is dose-dependent. The mouth becomes dry freloslomldl and tender, and swallo$'ing is difliculr and painful. xcrostomia that has persisted belond a year is lcss Iikely to show significant retum of function. Importrnt: Salivary changcs hav€ a profound influence on thc oral microflora and secondarily on the dentition, often leading to radiation caries. . Teeth: inadiation ofteeth with therapeutic doses during their development severely tetards their growth. \ote: Aduh reeih are vcry resistant to the direct effects ofradiation exposure. . Radiation cariesi is a rampant lonn ofdentaldecay that may occur in patients who have received a course ofradiotherapy. The carious lesions result lronl changes in the salivary glands and saliva, including reduced tlo(. decreased pH. reduced buffering capacity, and increased viscosiLv. . Bone: lhc primary damagc to maturc bone rcsults from radiation-induced damagc to lhe fine vasculature, \\ hrch is normally already sparse in a dense bone such as the mandible. Subsequent to irmdialion lhere may be a replacement ofnormal marrow with f'atty narrow offibrous connective tissue. ln addition, the endosreum become atrophic, sho*,ing a lack ofosteoblastic and osteoclastic acti\.ity, an indication ofn€crosis.

The speed with which electrons travel from the filament ofthe cathode to the target ofthe

anode depends upon the potential difference between the two electrodes (kilovoltage). This, in turn, has a very important effect on the x-rays produced at the focal spot. The kilovoltage has nothing to do with the number of electrons that compose the stream flowing from cathode to anode. The numb€r of electrons (vhich determines the quantity o-fx-rals producedl is controlled by the temperature of the tungsten filament (milliumperage setting). The hotter the filament, the more electrodes are enitted and available to form the electron stream (the x-ra1,tube cut-rent).Inthe x-ray tube the number ofelectrons flowing per second is measured in milliamperes. The intensity of x-rays produced at a particular kilovoltage depends on that number. Note: Setting the x-ray machine for a specific milliamperage actually means adjusting the filament temperature to yield the current flow indicated. The milliamperage range for dental radiography is 7-15 mA.

r

Note*,'

l. In dental radiography, the quality ofthe x-ray beam is controlled by kVp. 2. The kilovoltage range for most dental x-ray rnachines is 65-100 kV. 3. Digital units use a range from 8-40 kvp. 4. A higher kilovoltage produces x-rays with greater energy Ievels, shorter wavelengths and more penetrating ability. 5.To increase film density, you should increase mA, kVp and time. Also, you should decrease the source-object distance.

. One-fourth

as intense

. One-eighth

as intense

. Four times

as intense

. Eight times

as intense

40 Coplright O 201l-2012 - Dental Dects

.

Decreased density

. More latitude . A shorter scale of contrast

. A longer scale ofcontrast

41

Cop)aiglit O

20ll

2012, Denial Decks

The Inverse Square Law is stated as follows: The intensity ofan x-ray beam at a given point is inversely proportional to the square ofthe distance from the source ofradiation. Important: Changing the distance between the x-ray tube and the patient thus has a marked effect on beam intensity.

The intensity of an x-ray beam at a given point is dependent on the distance ofthe measuring device from the focal spot. The reason for this decrease in intensity frtr,l, il rs ,nversely proportional) is that the x-ray beam spreads out as it moves from the source. The "spread out" beam is less intense.

For example, when the PID length is changed from 8 to l6 inches, the sourcelo-film distance is doubled. According to the Inve6e Square Law, the resultant beam is one-fourth as intense. When the PID length is changed from l6 to 8 inches, the source-to-film distance is reduced by one-half. According to the Inverse Square Law, the resultant beam is four times as intense. The following mathematical formula is used to calculate the Inverse Square Law:

original intensity new

= new distance2 intensity original distance':

Remember: The intensity ofthe radiation is inversely proportional to the square ofthe distance.

Important: The thickness of alumrrr,tm (approxinateb'2 mm) placed n

the path ofthe x-ray For example, if an termed the half-value layer. the intensity by one-halfis beam that reduces would be mm of aluminum half-value of4 mm, a thickness of4 x-ral beam is said to have a layer determines the Measuring the half-value necessary to decrease its intensity by one-half. penetrating quality of the beam. The higher the half-value layel the more penetrating the beam.

ofa change in kilovoltage is a changc in the penetrating power ofthe x-rays. Incrcasing kilovoltage reduces subject cont ast (and the longer lhe scdle ofcontt?saJ; decreasing kilovoltagc incrcascs subject contrast fard rhe shorter lhe scale of conlrasl. A second effect ofan increase in kilovoltage is that not only are neu', morc pcnctrating x-rays produced, but morc ofthe less pcnctrating rays which were also produced at the lower kilovoltage are omitted. Remember: Kilovoltagc controls the speed ofelecOne effect

trons. Conclusion: kilovoltage influences the x-ray be.m and radiograph by: . Altering contrast quality ([or patienls v,ilh thick jaws, iro"ase I ilovoltage) . Detcrmining the quality ofthe x-rays produced . Detcnninillg the velocity ofthe electrons to the anodc Sharpness refers to thc capability ofthe x-ray film to reproduce the distinct outlines ofan objcct, or, in othcr s ords. to how well the smallcst dctails ofan object are reproduced on a dental x-ray. A ccrtain lack oi imagc sharpness is prescnt in every dental x-ray. The fuzzy. unclcar area that sunounds a radiographic image is termcd the penumbra. Thc sha.pness ofa film is influenced by three factors: . Focal spot siz€: the tungsten target ofthc anode senes as a focal spot; this small area convcrts bombarding electrons into x-ray photons. The focal spot concentrates the electrons and crcatcs an cnor_ mous amount ofheat. The size ofthe focal spot ranges from 0.6 mm: to 1.0 mm:and is determined bt rhe manufacturer ofthe equipment. lmporlant: The smaller the focal spot area, the sharper the inlage appears: the larger the focal spot arca, the greater the loss of imagc sharpness . Fitm composition: sharpness is relative to the size ofthe crystals found in the emulsion. The emulsion offastcr film contains larger crystals that produce less image sharpness, whcreas slowcr film contains smaller crystals that produce more image sharpness. . \Iovement: a loss of image sharpness occurs ifeither the film or the paticnt moves during x-ray cxposute.

Note: Image sharpness can also be improved by increasing the distance between the focal spot and thc object by using a long, open-cndcd cylinder and also by decreasing thc distance betwceil the object and the film.

'kVp .mA . Exposure time . Whether the film is

a one-film packet or a

two-film packel

t2 Coptr'glt

@

2011,2012, Denial Decks

. Positive anode

. Negative anode

. Positive cathode . Negative cathode

43

Coplriglt O20ll-2012

- Dental Decks

Density rcfcrs lo thc ovcralldarkncss r/b/d(izer, ofa radiograph: . Dcnsit_v will increase as mA. kvp, or cxposurc limc is incressed . Dcnsity will decrease as mA, kVp. or cxposurc timc is decreased . Reducing lhc distancc bctwccn thc focal spot and thc film also increases thc dcnsit) Note: Thc thicker thc objcct or thc grcatcr its dcnsity, thc morc thc x-ra] bcam is attcnuatcd and lhc lighter thc rcsultant image will bc. Thc blackening oflhe fi1rn Nflcr x-ray cxposurc is cxprcsscd in tcnns ofits optical densit!: D = log l0 (lo.l1)

whcrc

l0 is thc rnlcnsity

ofincidcnt light /e,.a.,/.),r a vi4 rar./ and Ir is thc intcnsity of

thc lighl transmittcd through thc lilm.

In roulinc radiogr.phy thc uscful rangc ollilnr dcnsilics is approximatcly 0,j ften light) to 2 l|e^ dort.t. Bcyond thcsc cxtrcmcs thc imagc is usually too light or 1oo dark to bc diagnoslically uscful. Not€: ln a \\,cll-cxposcd and proccsscd radiograph. thc opticaldcnsit_v ofcnamcl is about 0.,1, dcntin is about L0, and soli lissuc 1s about 2.0.

Rcmcmber: Thc operator ofan x-my unil is in conirol ofthrcc factors:

L Kilo\oltage: thc quality or penetrating power ofthc x-ray bcam 2.}{illiamperrge: the quantity or numbcr of x-rays produccd

*** lncrcasing nrillianrpcragc rcsults in an increase

in thc numbcrofx-rays produced and an increase in lhc tcmocralurc of thc filamcnt. 3. Exposure time: thc lcngth of time x-rays are produccd and patient is cxposcd to lbcm. ljxposurc tnnc is mcasurcd in impulses bccausc x-rays arc crcalcd in a scrics ofbursts or pulscs rathcr than a continuous skcam. Onc inrpul\c occurs clcry 1160 ofa second; thcretbrc, 60 impulscs occur in I second.

L Radiographic

Notc.

speed is thc amounl ofradialion rcquircd 1o prodlcc a radiographic film cuncntly availablc is F-spccd.

tilm ofslandard

dcnsir,v. Thc fastcst dcntal

2.Thc film characlcristic thal js ihc rcvcrsc ofcontrast is film latitude. Thc highcr thc contrast. thc smallcr thc laiitudc and the lowcr thc contrast, thc grcalcr Ihc latiludc. La{itudc is. thercforc, thc rangc ofradlation intensitics that a film is capablc ofrccording. l. Radiographic not(le /o/-nrrre) is thc appcarancc ofuncvcn dcns;ty ofan cxposcd radiographic film. .l Rrdiographic artifact$ arc dcfccts causcd by cnors in film handling or crrors in film proccssing. or marks or scratchcs fiom rough handling. 5. Sharpness is thc ability ofan x-ray lo dcfinc an cdgc prcciscly. 6. Rcsolulion. or rcsolving powcr, is thc ability ofan x-ray to rccord scparalc structurcs that a.c closc logcthcr.

Thc r-ral tubehead is a tighlly scalcd. hcavy mctal housing that conlains thc x-ray tubc thal produccs dcnlal x-ray!. Thc componen! pans ofthc tubchcad includc the following:

. Ntetal housing: is thc mctal body oflhc tubchcad lhat sunounds ihc x'ray tubc and transfonncrs and is iillcd \lith oil: it prolccts thc x ray tube and grounds thc hiSh-voltagc componcnts .Insulating oil: ;s thc oil tha! srmounds thc x-ray tubc and transformcrs insidc thc lubchcadi it prcvents ovcrhcating by absorbing thc heat crcalcd by thc produclion ofx-rays

'Tubeherd seal: or thc aluminum or lcadcd glass covcring thc tubchcad that pcrmits lhc cxil ofx-rays lionl thc tubchcadt it scals lhc oil rn lhc tubchcad and acts as a flltcr to Ihc x'ray bcam . X-ray tube: is thc hcart ofthc x-ray gcncrating systcm . Transformer: is thc dclicc that altcrs thc voltagc ofincoming clcctricilv . Aluminum di$ksl shccts of0.5-mn thick alurninum placcd in thc path ofthc x-ray bcaml they filtcr out non' pcnctrating, longcr wavclcngth x-mys . Lead collimator: is a lcad platc wilb a central holc that fits dirccily ovcr thc opcning ofdrc mcial housing whcrc thc x-rays cxit; ii rcstricts lhc sizc ofthe x-ray beam . Position-indic:rting device (PID)r is an opcn'cndcd. lcad-lincd cylindcr that cxtends from thc opcning ofthc mctal housing ofthc tubchcad; it aims and shapcs thc x-ray beam Thc x-rar" tube is thc hcarl ofthc x-ray gcncrating systcm. It consists ofa lead-glass housing, a negative cathode, and a positive rnode. Electrons arc produccd in thc cathode and acceleratcd toward thc anodc; thc anode con\cr(s lhc electrons into x-ravs.

. l,eaded-glass housing: is a leaded-glass vacumm tubc that prevents x-rays liom cscaping in all dircclions. Onc ccnlral arca ofthe ieadcd-glass tubc has a "window" that pcrmils lhc x-ray bcam lo cxit the lubc aDd directs lhe x-ray bcan toward thc aluminum disks, collimator and PID. . Cathodc /r/ r€gdrtrt, r1e. rftr.L,/: consists ofa tungsten wire lilament in a cup-shapcd holdct nradc of molybdenum. The purposc oflhc calhodc is to supply the electrons nccsssary to gcncralc x-rays. Thc clcclrons pro duced in rhc nega(i!e cathodc arc accclcratcd loward thc posjlivc anodc. Thc cathode includcs thc ibllorling: . Tungsten filament: is a coilcd wirc madc oftungstcn. which produccs clcctrons \vhcn heatcd .llollbdenum cup: tbcuscs thc clcctrons into a narro$,bcam and dirccts thc bcam across thc tube lo*,ard drc tungstcn targcl ofthe anode . (ot poriti\,t ?l?(rod4r consisls ofa waftr-thin tungstcn platc cmbcddc'd in a solid coppcr cord. Thc pw' ^node pose oithe anode is to convert elcct.ons into x-ray photons. The anodc in€ludcs thc following . Tungsten target: scrv€s as a focal spol and convcrts bombarding clectrons into x-ray photons . Copper stem: funclions to dissipatc thc hcat away from thc tungstcn largct

. Copper stem . Filament . Vacuum

. Molybdenum cup

44 Coplrighr O

. A neutral atom without

a

201 I

-2012 - D€ntal Drcks

nucleus

. An atom with equal numbers ofprotons and electrons . A neutral atom that loses an electron and becomes a positive ion . None ofthe above

45 Coplrighr

@ 201 I

-2012 - D€ntal D€cks

ReFinrcd ti.m Haring. Joen Ia.nuc.i and l-lura Ja.rn: Dental RxdioErdy Princlties rnd Tec|'

.\ue\: lhinl Ldilron O

1000.

$nh t.nnss.n ftonr Flsc\icr

Refrinted no'n Haring..roen lrn nuccr trnd Laura J.nsen Denhl Rt

drgrdphl: tnncrples ard Techniqoes: Ihid ldiron '! 1000. wirh pennr$io. from FheYler.

X'.a\s arc gencratcd whcn a srrcam ot clcctrons (\'hkh are prod ed hr rre /i/drrertl tra\cls from thc calhodc to lhc anodc ond is suddcnlr- stoppcd by its impact on thc tungslcn larscl. Thc filancnt locrlcd in rhe carhodc is nradc is lhc source of \oilungrrcn Nirc Thc smallarca on thc targcl that thc clcclrons strikc is callcd drc focal spot

-il

\oles

L Thc sizc of thc fbcal spol directly influences thc x-nty dcfinition: thc larger the focal spot. thc greai€r rhe loss nfdcfin:(ion and r\c greater lhe lo\r oI rhc .hartnc.. ol lhc imalc

:

Copper rs uscd Io hous!' thc anodc bccausc it is a good thcrmal conduclor. dissipating hcat tiom thc tungstcn krgct and rcducing thc risk ofrnclring lhc largct-

Matter is anything lhat occupics spacc and has mass; rlhcn mattcr is altcrcd, energy rcsulls. Thc indamcntal unil ofmaller is thc atom. Thc atom consists oal\vo parls: . A ccntral nucl€us: is composcd of protons and neutrons. Protons carry positiv€ clcctnc!l chargcs, !{hcrcas ncutrons cary no clcctrical chargc and arc slightly hcavicr than lhc proton . Orbitin8 electrons: arc t;ny negatively chargcd particlcs ihal havc vcry little mass; rn clcctron wcrghs approximatcly 1/1800 as much orbits or shells

as a prolon

orncutron. Elcctrons rravcl around thc nuclcus in $cl1-dcllncd paths known

as

An atom contaiis a maximum ofsevcn shclls, cach localcd at a spccific distanc€ lion1lhc nuclcus and rcprescrtrng diflcrcnt cncrgy lcvcls. Thc shclls arc dcsignatcd wift lhe lclters K, L. N{, N, O, P and Q; thc K shell is locatcd clos' est ro rhe nucleus and has $c highestenergy level. Elccrrons arc maintaincd in thcir orbits by thc electrostalic forceJ orallraction. bclwccn thc posilivc nuclcus and thc ncgativc clcctrons. This is known as ihc binding energy ofan clcctron. Atoms arc capablc ofconibining wilh cach olhcr 1o lbrm molcculcs. A neutrrf atom conlains an cqual numbcr of protons (posi!i,e Lharyes) ]nd electrons /neg.?/a'. .rr4i.'.!/. An atorn with an incomplclcly Ullcd outcr shcll is clcctrically unbalanccd and aiicmpls 1o capturc an clcclton from an adjaccni atom. An aton that gains or loscs an clcclron and bccomes electrically unbalarccd is known as an ion. Ionization js thc producrion ofions. or thc proccss ofconvcning an elom inlo ions. Ionizalion dcals \\'ith electrons only and rcquircs sufticicnt encrgy ro ovcrcomc thc electrostatic lbrcc that binds thc clcctron to the nuclcus. Ionizing rad;ation is capable ofproducing ions and can bc classificd inlo two groups: . Particulate radiationr arc iiny particlcs ofmattcr that posscss mdss and lra!cl in straight lincs and al high spccds. Thcrc arc lbur typcs: . llfectrons: can bc class classificd as beta particle. lldst nnring ?l.cttotlj eniuetl lon the tt (k'tts ol rddioactir. otonts) ot c thode rays (strcams ol hi!:h-spe.l ek'( trcDs thut origindte in an .\ tut nh.) . Alpha particles: arc cniltcd from thc nuclci ofheavy mctals and cxisl as t\\'o protons and nculrcns. $ithout clcclrons

. Protonsi arc accclcrated paniclcs. spccifically hydrogcn nuclci, with a nlass of I and . Neutrons: are accclcratcd pariiclcs with a mass of I and no clectrical chargc

a chargc

of+l

. Electromagnetic radiation: can bc dcfined as lhc propagation ofwarc-likc cncrg)" /r'rrorlr l,alltr./ through spacc or mattct Illcctromagnctic radiations arc manmade, or occur nah.rrally;cxamflcs includc coirnic rr] \ camma ruyJ, x-r!!-s, UV rays. visiblc light. infrarcd light, radar $avcs, nicro$avcs, and radio wavcs. Thc particle concept (Q d,1tun l2orr) .haructcrizcs clcctromagnctic mdiations as discrctc bundics ofcncrg-v called photons or quanta, Thc wave concept characterizes cleckomagnctic radialion as lvavcs and focuses on thc propenies ofvelocit]'. $avclcnglh. and frcqucncy.

. The first statement

is true; the second statement is false

. The first statement is falsej the second statement is true

. Both

statements are true

. Both statements are false

a6 Coptright

,O 20 I 1,20 | ?

, Denial Decks

Which of the following occurs only at 70kVp or higher and accounts for a very small part ofthe x-rays produced in the dental x-rry machin€?

. Compton scatter . Coherent scatter . General (Bremsstahlung) radiation

. Characteristic radiation

47 CopFighr O

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Dental Decks

llcctricity is thc encrgy that is uscd (o make x-rays. Electrical encrgv consists ofa flow ofclcctrons through a conductor; this flo$'is known as thc clcctric currcn(. The clcctric currcnr is tcnned direct currcnt frcl whcn thc clcctrons flo$,in one direction through lbc co duclor Thc lcnn alternating current /-,14) dcscnbes a currcnt ;n which thc elcctrons flow in tl4o opposite dircctions. Rectitication is thc convcrsion otaltcmatiig currcnt lo dircct currenti thc dcntal x-ray tubc acts as r self-rectificr ir that it changcs AC irto DC \r'hilc producing x'rays. This cnsrLrcs that lhc current is alwa]s flor}ing in thc samc dircclion, morc spccilically, liom cathode to anode. Amperagc is thc rncasurcncDl ofthc number ofelectrons nroving through a conductor Current is measu.cd in amperes or milliamperes /rr,.1/. l'oltage is the meas rcment ofelectrical force thal causcs clcctrors lo movc fron a ncgativc pole to a posili\'e oDc. Voltagc is measured in volts or kilovolts /krr. Note: ID thc produclion ofx-rays. bofi thc lmpcrage and volfagc can bc adjuslcd on thc contfil pancl (mA aditstDrctt dnd kI? adiusttrcrt s\\itthes).

A circuit is a palh of clcctrica I currcnt. Two electrical circuits arc uscd in lhc production ofx-rays:a lolrrvoltage or filamcnt circuil and a high-voltage circuit. Thc Iilament circuit uscs J to 5 volts. regulatcs thc llo\\, ofclcckical currcnt to thc filament ofthc x-ray tubc, and is controllcd by thc milliampere settings. Thc high-r'oltage circuit uscs 65.000-100.000 ! olts. providcs thc high voltagc rcquircd lo accclcratc clcctrons and to gencratc x-rays in thc xray tubc, and is conlrollcd by thc lilovoltage settings. A transformer is a dcvjcc that is uscd to cithcr incrcasc or dccrcasc lhc vollagc in an clcctrical circuil. Transfbrncrs altcr thc \oltagc ofthc incoming eleckical currcnt and then routc lhc cleckical cncfgy to thc x-ray tubc. In lhc production ofdcntal x-ra)'s, thrce transfbrmers arc used to adjusl lhc clcctrical circuils: . Step-down transformcr: is uscd to dccrcasc thc vollagc fiom thc inconring I l0 or 220 line voltage to the 3 to 5 \ ohs rcauircd . Step-up transformer: is used to inc.casc the voltag€ from the I l0 or 220 linc roltagc lo thc 65,000 to 100.000 \0lts rcquired . Auto-transformer: scn,cs as a voltagc compcnsator that corrccis for miror flu!tuations in the currcnl I Thc milliamperage f/r,.|.) or tube current swltch on thc control panel regulates thc tempcr.tura of \ot{* th€ filament and thus thc number ofelectrons emitted, 2.Tube current or mA controls thc numbcr ofphotons gclcratcd //,rlersitt ol the bru , but rot thc beam cncrgy. Thc quantity of radiation produccd by an x ray tubc is dircctly proponional 1o lhc tubc currcnt /rr.,1/ cxposurc timc. L Thc livp control sclccts voltage from diftcrenl levels on thc autotransformcr and applies it across Ihc primary winding ofthc slcp-up transtbrmcr ,+. In dcntal x rays, the qualit) ofthe r-ray beam is controllcd by kvp. 5. Thc cflcct ofchanging timc is sinply 1l) control thc "quanlily" ofthe ex?osutc (the nunbcr ol phoIotts sencratel).

Not all x-ra)s produccd in thc x-ray lubc arc thc same; x-rays rlilltr in energy and wavclength Th€ cnergy and lvrvclcnglh ofx-ravs varies bascd on how the clcctrons intcract wilh thc tu'rgstcn atonrs in lhe anodc. Thc kinctic cn crgy of rhc clcctrcns is converted to x-ray pholons via onc oft$o mcchanisns: . Gene.^l (Rrcnsstrfihnrg or braking radiation: a fomi ofradialion lhat occurs lrhcn speeding clcctrons are slosed bccausc ofihcir intcraclions with thc nuclei oftarget alofis. Thc tcmr braking radiation, rcLrs to thc sudden stoppnrg or slowing ofhigh-speed eleclrons hitling the tarSet in thc anodc. Most x-rays arc produccd in lhis

lpprorimately 707o ofthc x-ray cncrgy produced at thc anodc can be classificd as gcncral radiation . Charactcristic radiationr is produccd wien a high-spccd clcctron dislodgcs an inncr shell elcctron liom thc tungslcn alonl and causcs ionization ofthat atom. This tlpc ofradiation accounts for a vert-' small part oi x rays produced in thc dcntal x-ray nrachinc and occurs only at 70 kvp and abovc bccausc thc binding cncrgy oflhc K nlanner;

shcll .lcctron is approxirnatcly 70

kcv

Priman radiation refcrs to lhc pcnctrating x-ray bcam that is produccd at lhe llrrgcl oflhc hJld Tlij \,rr] beam is olicn rcfcrrcd to as thc primary bcam or useful beam.

anode and cxjls thc lubc

is crc.rtcd whcn thc primary bcam inlcracls u'ith mattcr li tl tal rd' ,li ].t,rp/l.krutoitklud(skesolitissu(softheheud,thehotrcsolth"skull,adtheteeth).NoteiSccondaryisless

Secondarr r!diation reicrs to x-radialion that f Jn.rratrng lhan

primary radialion.

Coherent scaner is onc ofrhc intcracrions ofx-radialion rvith mattcr in which thc path ofan x-ray pholon is altcrcd b\ cr $ ith ou t a c h,lngc in cncrly. Cohcrcnt scattcr accounts for 8 o/" of t hc inicractions of mattcr with thc dcnia I 'ran

ComDton scatter

is onc

ofthe intcractions olx-radiation with matter in which thc x-ray photon is dcllcctcd from its

parh and loses cnergy. (lomplom scaitcr accounts ibr 6270

ofihc scaitcr that occurs in diagnostic radiography

Photoelectric absorption is onc ofthe intcractions ofx-radjation \\'ith mattcr, 3n x-ray photon intcracb with an or' brtrl .1cctron, and all of the cnerg! of the photon is absorbed by thc displaccd clcclron in thc form of kinctic en-

crg] Thrs

accounts for 307o

oflhc inlcractions ofmattelwith lhc dcntal x-ray bcam.

Dclennining the qurntily ofrudiation exposufc or dosc is tcrmcd "dosimetr)." . Erposure: is a measurc ofradiation quantily, the capacily of thc radiation to ionizc uir Thc roentgcn /Rl is thc tradilional unil ofradiation exposurc mcasurcd in arr o f enerey impartcd by any typc of ionizing radiatbn 1o a nass of any typc of (Gy). thc tradilional unit is lhe /ad . Effective dosc: is uscd to cstimalc lhc risk in humars. Thc unil ofcfteclive dose is thc Str'r'l?,'/ (Sv) . Radioactiritr: is thc decav ratc ofradioactivc matcriai. The unit is thc 8c(quercl(Bq)

. A bsorbed dose: is a m casurc

tcr Thc SI unit is thc

gr"d-r,

matl

All ofthe following rre components of inherent liltration EXCEPT one. Which one is the EXCEPIIOM

. oit . Unleaded .A

glass window

leaded cone

. Tubehead seal

48 Copyright O

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l-20 | 2 - Dental Decks

Rad Protection

Man has always been exposed to natural radiation arising from the earth as well as from outside the €arth. The radiation we rec€ive from outer space is called terrestrial radiation or terrestrial rays. We afso receive exposure from man-made (artificial) radiation, such as x-rays, radiation used to diagnose diseases and for cancer therapy.

. The first statement

is true; the second statement is lalse

. The first statement is false; the second statement is true . Both statements are true . Both statements are false

49 Cop)rlghr C

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There are two types of filtration used in the dental x-ray tubehead:

. Inherent filtration:

takes place when the primary beam passes through the glass

window of the x-ray tube, the insulating oil, and the tubehead seal. The inherent filtration of the dental x-ray machine is equivalent to approximately 0.5 to 1.0 tnm of aluminum. . Added filtration: refers to the placement of aluminum disks in the path ofthe x-ray beam between the collimator and the tubehead seal in the dental x-ray machine. The purpose of the aluminum disks is to filter out the longer wavelength, low-energy xrays from the x-ray beam. The low-energy, longer wavelength x-rays are harmful to the patient and are not useful in diagnostic radiography.

filtration ofthe x-ray beam before it reaches the patient consists of the inherent filtration plus the added filtration. Important: Govemment regulations require total filtration to be equal to the equivalent of 1.5 mm of aluminum for up to 70 kVp and 2.5 mm of aluminum for higher voltages. The total

, . .. l. Longer wavefength

x-rays (those produced ut lower kilovollages) are easily atrsorbed. .:.r-olcq',' '.:.ta,;tt... 2. Shorter wavelength x-rays (those produced at higher kilovoltages) penetrate objects more rcadlly (the!-Jbt"m the image on theJilm). 3. Filtration of the x-ray beam results in a higher energy and a more penetrating useful beam. Filtration reduces patient dose, decreases contrast and incr€as€s the density of film. Remember: The x-ray beam is composed ofrays ofdifferent wavelengths and penetrating po*er (the tern used Jbr this is polychromatic) because the potential across the tube changes constantly as the voltage varies.

***

The radiation wc rcceive liom outer space is called cosmic radiation or cosmic rays.

Sources of radiation exposure:

. Naturaf r:rdiation /rackgrourul rarliation)t

is by f'ar the largest contributor (8J%) to the radiafion exposufe ofpeople living in thc U.S. today. Background radiation, resulting fiom extemal and intemal sources, vrelds an a\erage annual E ofabout 3 msv.

Erternal: exposure in this category is due to cosmic and terrestrial (/iom lie rolll rtdiation or that originaling in thc cnvironment. These sources contribute about l670 ofthe radiation exposure lo lhe population. - Internal: sources ofintemal radiation include inhaled mdon fi6z,, and ingested radionuclides 111%/. -

. ArtificiAl radiation lnan-made radiation)i Ihese may be categorized into tbree major groups -medical diagnosis and treatmcnr (11%, of rJhich dental x-ray examinations are rcspottsible for only 2,5% ofthk alerage ual t-ru! diagnosrt etporrle/, consumer and industnal products and sources d9'o/, and nuclear medicine f4?ir. Artificial radiation yields an average annual E ofaboul0.60 mSv or l77o ofthe annual radiation exposure !o the U.S. population.

a

Radiation protection standards dictate the maximum dose ofradiation that an individual can receive. Thc maximum permissibl€ dose /MPD./ is defined by the N^tional Council on Radiation Protection and Measurements fNCRP) as the maximum dose equivalent that a body is pelmifted to receive in a specific period oftime. The MPD is the dose ofradiation that the body can endure with little or no injury Important: The yearly MPD for a non-occupationally exposcd person is 0.1 rem/year (.0001 Sv/year). The yearly MPD for occupationally cxposcd pcrsons, or persons who work with radiation, is 5.0 rem/year (0.05 Sv,/year). The IUPD for an occupationallv e!posed pregnant woman is the same as that for a nonoccupationally exposed pcrson, or 0.1 rem/year (.0001 Svlyear). Exposure and dose in radiography: The goal ofradiatiorl protectjon procedures is to minimize the exposure of ofllce perconnel and patients during the radiographic examination. The philosophy ofradiation protection currently used in practice today is based on the principles

ofALAR{

(As Low As Reasonabb' Ac hierah

le ).

Note: The primary risk from dental radiogEphy is radiation-induced cancer. Although the risk involved with dental radiography is extremely small in comparison with other risks such as smoking or consumption of fatty foods, no brsis exists to assume that it is zero.

. The first statement

is true; the second statement is false

. The first statement

is false; the second statement is true

. Both statements are true . Both statements are false

50 Cop)right O 201l-2012 - D€ntal Decks

. Discrimination . Collimation . Filtration

. Barrier placement

5t CoplriSht O 201l-2012 ' Dmtal Decls

.\ll ofthe lbllowing reduce the amount ofradiation to thc patient: . Lead aprons and collars. Lcaded thyroid collars are recommendcd in individuals undcr

30 years ofage. lvlany statcs mandate lhe use ofa lead apron on all patients. . Increased flhmtion using an aluminum disk . Use E-speed film. F-spced fitm or digiral imaging for pcriapical and bite$ing radiographs . Lead diaphragms placcd within the cone ofan x-ray tubehcad . Collimating an x-ray beam: using a r€ctangular collimator siSnificandy reduces patlenl exposure . Using a long 116 ircl, PID is prclcrrcd because it produces less divcrgence oflhe x-ray beam. By doing Ihis )ou are increasing the source-film distance and rcducing patient exposurc as \r'cll as inlproving imagc

. The use of rrre earth intensifying screens for all panoramic and cephrlomctric radiography

. Frlrn-holding

devices are also eflective in reducing a patient's exposufe to x-radistion

. E\posure iactor seleciion also limits the amount ofx-radiation cxposure reccivcd by thc patient The deniilassisrant can control thc cxposure factorsby adjusdng thc kilovoltage peak, milliamperage. and dre time ic:tings on thc control panel ofthc dcnlal x-ray machine. Note: On some machines the kvp peak and orA :eirings are presct by the manufacturff and cannot be adjusted.

- \ .cI'irg

of ?0 lo c0 k\ p lecn. nalicnls cxf'osure ro 3 mitrimum - Scr m'\ value to high€st possible value ifvariablc. Iligher mn sefiings produce a beam \\ ith morc crlergt and increasc the intensity ofthe x-ray beam. - \diust exposure time to achieve optimum density Important: nrA and exposure time are inversely relatcd. \lllen altering mA, the exposure time nust bc adiusred to maintain diagnoslic density ofa film. Operator protectioni Radiation exposure to the opcralor can be reduced by standing at least six feet a\\'ay, _::.r:c a l.ed shield, or bolh when exposiDg €diographs. The operator should never remain in lhe room hold_: :-:: \-.3\ packcl irl place tbr the palicnt. If a film must be held in place by someonc else (/br d clliki). :::ac :h.' f,rr.nI and havc him or her hold rhe film. AII dental personnel should lvcar film badgcs thal moniior :\.r.,r:. lloiages. \otei The opemtor must avoid the primary x-ray beam by positioning lhemselves at a 90 ro l-15 degree angle ro ihe beam. taking and processing of dentr I radiographs, al$ays remcmber!o maintain prop€r infection controf /appl.l tniverssl prccauliohs) at all tim€s!:!

\ote: R:sarding the

In the x-ray tubehead a collimator (leatl plate \4ith a hole in the middlel is uscd to restrict the size and shape ofthe x-ray bea . A collimator may have either a round or rectangular opcniDE. . A rectangular collimator resfficts the size ofthe x-ray beam to an area slightly iarger than a sizc 2 InrrdL,ral film anJ \rgnificantll rcduccs paticnl c\lo\urc . A circular collimator produces a cone-shaped beam that is ?.75 inchcs /7 czrl in diameler, considerabJy Iargcr than a size 2 intraoral film. Important: wtcn using a circular collimator. fcdcral regulations require that thc x-ray beam be collimated to a diameter of no more than 2.75 inches 17 cD, as it exits from the PID and rcaches thc skin ofthe patient. The positioning-indicating device /P1Dl, or cone. is uscd to dircct thc x-ray beam. Therc are three basic types ofPlDs:

. Conical: appears as a closed. pointed plastic cone. Wlen x-rays exit from the pointed cone, they penetmte the plastic and produce scatler radiation. To climinatc cone-produced scattct radiation. the conrcal PID r\ no longer used in dcnliqlrv. . Open ended and lead-lined rectangular or round PIDs: arc uscd that do not producc scatter tadiation. Both rectangular and round PIDS are commonly available in n\,o lcngths:

. Short /8-i,r.r, . Long (16-inch) *** Thc long PID is preferred because less divergence of the x-ray bcam occlrrs. Of the three r-vpes

of PlDs. the rectangular type is most effective in rcducing patient exposurc.

These devices do not reduce thc amount of radiation rcceivcd by thc exposed tissucs. but reduce thc radiation to surrounding tissues duc to x-ray bcam divcrgcncc.

Remember: The x-ray beam consists ofmany different $'avelengths. The short w.velength (high ener'gl, rays have great penetrating powcr; long wavelength flox,erergl, rays have low pcnctrating po\r'er and do not rench ihe fiJm in reasonable quantitics since thcy are atlenuated by the soft tissues. Low encrgy rays add only to thc total amount ofradiation the patient receives. Aluminum discs are used to filter out the useless long wave rays. increasing the overall quality ofthe beam.

. The film is bent . The film is placed backwards in the mouth . An improper vertical angulation is used

. An improper horizontal angulation is used

52

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. Source-film

- Dental

D€ck

distance

. Film-object distance . Focal spot size . Central ray direction . Film parallelism

Copright O 201l-2012 - D€nbl Deck

Figure #3. Thc bcnt tilm appcars distorted.

Figure #1. A rcversed film appcars light lvith a hcrringbonc cfiect.

t_igure #2. The film dcmonstrates a doublc cxposure.

\ . .rlr thol(ri refnnred fionr HlrlngIIf .ennjrion liom Elsevier

Figure #4. Movcmcnt rcsulls in

a blurred image.

Joc.lannuccr and Laura J.nsen: DerialRadiography: Iri.ciples.nd Te.hniques:Ihrd F.dilion O :000.

Five rules for accurate image formation when taking x-rays:

l. Use the smallest focal spot that

is practical.

Note: The size ofthe focal spot influences radiographic definition or sharpness. They are inversely proportional. The operator cannot control the size

ofthe focal spot.

2. Use the longest source-film distance that is practical in the panicular situation.

i.

Place the

film as close as possible to the structure being radiographed.

J. Direct the central ray at as close to a right angle to the film as anatomical structures

ll ill allorv. 5. As far as is practical. keep the

film parallel to the structure being radiographed.

RADIOLOGY

Tech

A periapical of the left maxillary canine shows an elongated tooth which does not capture the apex of the canine. \yhile taking the periapical of the left maxillary canine, the operator had an:

. lncorrect horizontal angulation . Incorrect vertical angulation . Either ofthe above

54 Copyrighr C

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RADIOLOGY

Tech

The two radiographs below were taken with the buccal object rule in mind, In film #2, the x-ray tube was directed from a mesial angulation. What is the spacial position of the circular object in these radiographs?

. The object lies lingual to the first molar . The object lies buccal to the first molar . The object lies between the second premolar and the first molar . The object lies directly apical to the first molar

Film

#l

55 Copyright C:01l -1012 - Dental Decks

Film #2

Vertical angulation is directing x-rays so that they pass vertically through the part being examined. This is accomplishcd by positioning thc tubchcad and direction ofthc ccntral ray in an up-anddown (vertical) planc. lmportant: Foreshortening (See fgurc #1) rcfcrs to a shortcncd imagc and elongation /Seefgzrc #2) refers to an elongated image. Both are produced by an incorrect vertical angulation. Excessive vertical angulation causes foreshortened images, while insullicient vcrtical angulation causcs clongatcd images.

If the vertical angulation is too stccp. thc images a.c foreshoracned. Figure #1.

Figure #2. Ifthe venical angulation is too flat. thc imagcs arc elongatcd.

Borh phoros rerrinred from

Hlnng, Joen Iannucci and Laun J$sn: DenraL Radioelaphy: Principles and Tcchniquesl

ftnd

Ednion.

I)emission frcm

O

1000, rvilh

Eh.vi.r

Horizontal angulation is maintaining the central ray at 0 degrees as the tube is n]oved around the head. This is accomplished by positioning the tubehead and direction ofthe central ray in a sideto-side (horizotlt.il) plane. r-ote: The general rule for horizontal angulation is that the central ray should be perpendicular to the mean antcropostcrior plane ofthe teeth being x-rayed. Important: lncorect horizontal tube angulation causes overlapping (teeth images are superimpo,;ed on eaclt otlrcr).

Tle central ray

is said to be at 0 degrees when the x-ray tube is adjusted so that the central ray is parallel to the floor Ifthe tubehead is directed at the floor, it is called positive angulation; ifit is dirccted toward the cciling. it is called negative angulation.

The buccaf obj€ct rule falso called the tube shili technique) is used to determine an object's spatial position within the jaws. This technique utilizes two radiographs of an ob-

ject exposed with slightly different tube angulations. It then compares the object's position on the radiograph with respect to a r€ferenc€ point (e.g., /re root of a tooth,/.

lf

the tube is shifted and directed from a more mesial direction, and the object in

question appears to have moved mesially with respect to the reference point, then the object Iies lingual to that reference point. Conversely, ifthe tube is shifted mesially and the object in question moves distally, it lies on the buccal aspect ofthe reference object. Remember the acronym SLIQB

*** Ilthe

-+ $ame-!ingual,

Qpposite-guccal.

object in question appears to move in the same direction as the x-ray tube, it is on the lingual aspect. lfit appears to move in the opposite direction as the x-ray tube, it is on the buccal aspect.

Tech

After developing her bitewings, a d€ntist realizes that she has too much overlap t etween the contacts of adjacent teeth. This is an error caused by:

. Too much vertical angulation . Too little vertical angulation

. lncorrect horizontal angulation . Beam not aimed at center of fihrl

55 CoDtighr

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RADIOLOGY

Tech

Which of the following positioning errors is the most likely ofthe reverse occlusal plane curve on the panorex below?

cause

. Chin tilted too far upward . Chin tilted too far downward . Head tumed slightly

coplri8ht