radiology

RADIOLOGY LEGEND

..•.,....

Major Topic Abbreviation

Image Characteristics , - 1m CharMiscellaneous Misc.Normal Anatomy N AnatProcessing ProcRadiation Biology R BioRadiation Characteristics R CharRadiation Physics R PhysRadiation Protection R ProtTechiques TechX-rays X-rays

Copyright © 2001 - DENTAL DECKS

RADIOLOGY

Which x-ray is designed for diagnosis of basilar skull fractures?

• Water's• Submental-vertical• Towne's• Panorex


X-rays

• Submental-vertical (also called submentovertex)

It also gives some diagnostic information about the zygoma, zygomatic arches andmandible. This film is taken with the source below the mandible and the film abovethe head.

X-raysRADIOLOGY

Which of the following is the standard radiograph of choice for showing an anterior viewof the paranasal sinuses and of the mid-face and orbits?

• Panorex• Towne's view• Water's view• Cephalog ram


• Water's view

This is a posterior-anterior projection with the patient's face lying against the film andthe x-ray source behind the patent's head. It is one of the best films for radiographicdiagnosis of mid-facial fractures. It is also used for diagnosing sinus infections .

X-raysRADIOLOGY

Which of the following is the best film for visualizing the condyles and neck of themandible from an A-P projection?

• Water's view• Caldwell's view• Towne's view• Panorex


• Towne's view

The patient lies on his back with the film under his head. The x-ray source is from the front, butrotated 30% from the Frankfort plane and is directed right at the condyles .

The Towne view is often of value in assessing thestatus of the condyles, condylar neck and rami ~

because superimposition of the mastoid and zygomaover the condylar neck region in the straight posteroanterior projection often makes interpretation difficull. The Towne view eliminates this superimposition, thus giving 990d visualization of the condy·lar area and rami. -

Note: The "Reverse Towne's View" is used to identify fractures of the condylar neck and ramusarea.

The following can be demonstrated on conventional _~~~~§~~~~~~~~~TMJ radiographs: t::tl:i:.• Position of the condyles in the glenoid fossa• The range of antero-posterior movement of the condyles• Areas of bone destruction on condylar heads

RADIOLOGY

Explain what is meant by the term "cervical burnout" on an x-ray.


X-rays

• This term refers to diffuse radiolucent areas with ill-defined borders that may beapparent radiographically on the mesial or distal aspects of teeth in the cervicalregions between the cervical edge of the enamel cap and the crest of the alveolarridge.

It is caused by the normal configuration of the affected teeth (the cementoenamel junction), which results in decreased x-ray absorption in those areas.

Important: These radiolucencies should be anticipated when viewing x-rays of almostany tooth and should not be mistaken for a carious lesion.

RADIOLOGY

All of the following are advantages of a panoramic radiograph excep t:

• It shows areas that may not be visible on a full mouth series• It shows both arches on the same film• It gives better detail and definition than periapical radiographs• It is more comfortable for the patient (eliminates gagging)• It requires less time than a full mouth series


X-rays

• It gives better detail and definition than periapical radiographs

"'This is false; a panorex gives less detail and definition than periapical radiographs due tointensifying screens, movement of the x-ray tube and film and increased object-film distance.

Indications for a panorex:• Diagnosis of oral pathology that may not be visible on periapical radiographs• Treatment planning (especially orthodontic cases)• Evaluation of anomalies• As one part of the follow-up evaluation in surgical and trauma cases• Edentulous patients (prior to constructing full dentures)• Patients that are unable to tolerate intra-oral x-rays

*"The drawback of a panorex is that there is a loss of image detail (it is hard to diagnose earlycarious lesions). Bite-wing x-rays are required for the diagnosis of carious lesions .

Other disadvantages of a panorex:• Distortion of image due to increased object-f ilm distance• Inadequate for interproximal caries detection or for detecting periodontal breakdown (bone

loss)• Proximal overlapping (especially in premolar and molar areas)• Added exposure to a large area of body tissue, in addition to the oral tissues

RADIOLOGY

The screening x-ray for pathology of the jaws is:

• A panorex• A cephalogram• A periapical x-ray• An occlusal x-ray


X-rays

• A panorex

The panorex is excellent for third molar pathology as well as to observe the TMJ,the sinuses and in sialography (which is a technique used in radiology in which a salivary gland is filmed after an opaque substance is injected into its duct). A sialolithwhich is located in Wharton's duct, however, can best be viewed by using a cross sectional occlusal x-ray.

One inadequacy of the panorex is in the definition of interproximal caries. However,by supplementing the panoramic film with posterior or anterior bite-wing films if indicated, a more complete radiographic survey of the patient can be obtained.

X-raysRADIOLOGY

Which of the following types of intra-oral radiographs are most useful in detecting interproximal caries?

• Periapical radiographs• Bitewing radiographs• Occlusal radiographs


• Bitewing radiographs"'Show crowns of both Max. and Mand. teeth; not root apices.

The primary reason for taking bitewing radiographs is to detect interproximal caries. They arealso useful in detecting periodontal disease. Bitewing films generally show the crowns of theteeth, the alveolar crest, and the interproximal areas. In order for the film to be of use diagnostically, the quality of the following must be excellent: dimensional accuracy, image density, andcontrast and clarity of the image.

When taking bitewing radiographs, the film must be placed either horizontally or vertically.Vertical bitewings will provide more periodontal information, such as boney defects and furcationinvolvement. Remember: A loss of crestal bone is often associated with early periodontitis.Theperiapical film is used (pedo or adult) with either cardboard tabs, sticky tabs, or a bitewing holder. Two bitewings are usually taken on a child and four (molar and premolar views) are usuallytaken on an adult (or two long films-size 3).

Notes :1. The vertical angulation for bitewing radiographs should be between +8 and +10 degrees.2. Adjust horizontal angulation to direct the central ray toward the center of the film.3. Alveolar bone resorption is best demonstrated on bitewing x-rays,4. Vertical bitewing x-rays will show more alveolar bone than traditional horizontal bitewings.

RADIOLOGY

Which of the following are uses for cephalometries in orthodontics?

• Diagnosis• Analysis of treatment results• Longitudinal study of growth• All of the above


X-rays

• All of the above

The lateral head radiograph (cephalometric x-ray) must be compared with "normal"lateral radiographs from an accepted norm. Linear and angular measurements areobtained utilizing known anatomical landmarks in the lateral head radiography of thepatient. These measurements are then compared with those considered within normallimits and in that way enable the orthodontist to assess aberrations in the dentition andjaw structures which result in malocclusion.

Analysis of cephalometric radiographs is not limited to the hard structures such asbone and teeth, but also includes measurements of soft tissue structures such as thenose, lips, and soft tissue chin.

Superimposition in longitudinal cephalometric studies is generally on a referenceplane and a registration point. This will best demonstrate the growth of structures farthest from the plane and the point. The most stable area from which to evaluatecraniofacial growth is the anterior cranial base because of its early cessation ofgrowth.

Cephalometries are useful in assessing tooth-to-tooth , bone-to-bone, and tooth- tobone relationships. Serial cephalometric films can show the amount and direction ofgrowth.

RADIOLOGY

Foreshortening and elongation are produced by:

• Incorrect horizontal angulation• Incorrect vertical angulat ion• Either of the above


Tech

• Incorrect vertical angulation

Important: Foreshortening refers to a shortened image and elongation refers to anelongated image. Both are produced by an incorrect vertical angulation. Excessivevertical angulation causes foreshortened images. while insufficient vertical angulationcauses elongated images.

Vertical angulation is directing x-rays so that they pass vert ically through the partbeing examined. This is accomplished by positioning the tubehead and direction of thecentral ray in an up-and-down (vertical) plane.

Horizontal angulation is maintain ing the central ray at 0 degrees as the tube is movedaround the head. This is accomplished by positioning the tubehead and direction of thecentral ray in a side-to-side (horizontal) plane. Note: The general rule for horizontalangulation is that the central ray should be perpendicular to the mean anteroposterior plane of the teeth being x-rayed.

The central ray is said to be at 0 degrees when the x-ray tube is adjusted so that thecentral ray is parallel to the floor. If the tubehead is directed at the floor, it is called plusangulation; if it is directed toward the ceiling, it is called minus angulation.

Important: Incorrect horizontal tube angulation causes overlapping (teeth images aresuperimposed on each other).

TechRADIOLOGY

Which of the following errors in radiographic technique is the most likely reason that animage on a radiograph would appear elongated?

• Too much vertical angulation• Too little vertical angulation• Incorrect horizontal angulat ion• Beam not aimed at center of film


• Too little vertical angulation

Some errors often made when taking dental radiographs:• Elongation (most common error): teeth appear too long - may be caused by too

little vertical angulation, the occlusal plane not being parallel to the floor, or poor filmplacement

• Foreshortening: teeth appear too short - may be caused by too much verticalangulation or poor chair position

• Cone cutting: portion of film will appear clear with a curved line - the beam wasnot aimed at the center of the film

• Herringbone effect: zigzagged pattern appears on the film - the film was placedbackwards in the mouth

• Poor film placement: the film was not placed far enough back or not forwardenough in the mouth

• Overlapping: interproximal areas are overlapped, reduces diagnostic qualityof film - due to incorrect horizontal angulation (the central x-ray was not perpendicular to the center of the film)

TechRADIOLOGY

The herringbone markings that appear on the film below were caused by what technical error?


• The film was exposed with the film packet in reverse position

Other artifacts:

See picture # 30 in booklet See picture #31 in booklet

TechRADIOLOGY

One of the films in a full mouth series of dental radiographs has crescent-shapedmarks on it. What is the most likely cause of these marks?

• Overbent films• Patient had glasses on• Exposure to secondary radiation• Cone cutting• X-ray arm drifted


• Overbent films (cracked emulsion)

Some other common errors made when taking dental radiographs/cause:• Light films (underexposed, image NOT dense enough) / Incorrect milliamperage

(too low) or time (too short); incorrect focal film distance; cone too far from patient'sface

• Dark films (overexposed, image too dense) / Incorrect milliamperage (too high) ortime (too long)

• Double exposure / film was used twice• Fogged films / exposed to radiation other than primary beam• Artifacts / patient didn't remove eyeglasses, earrings , or removable prosthetic appli-

ances• Poor contrast / incorrect kVp (too high)• Blurred image / patient movement or drifting of x-ray arm• Clear films / were not exposed to radiation

TechRADIOLOGY

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 ofthe 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 II FILM '2

Copyright @) 2001 - DENTAL DECKS

• The object lies lingual to the first molar

The buccal object rule (also called the tube shift technique) is used to determine anobject's spacial position within the jaws. This technique utilizes two radiographs of anobject exposed with slightly different tube angulations. It then compares the object'sposition on the radiograph with respect to a reference point (e.g., the root of a tooth).

If 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 theobject lies lingual to that reference point. Conversely, if the tube is shifted mesially andthe object in question moves distally , it lies on the buccal aspect of the referenceobject.

Remember the acronym SLOB: ~ame-bingual, Qpposite-~uccal.

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

TechRADIOLOGY

Which of the following positioning errors is the most likely cause of a reverse occlusalplane curve on a panorex (panoramic radioradiograph)?

• Chin tilted too far upward• Chin tilted too far downward• Head turned slightly


• Chin tilted too far upward' **Mandibular structures look narrower and maxillary structures look wider (looks like a"frown")

Chin tilted too far downward:1. Occlusal plane shows an excessive upward curve (looks like a "big smile")2. Severe interproximal overlapping, anterior teeth appear very distorted

Note: Although this is an extra-oral radiograph, there is a bite piece which is heldbetween the patient's front teeth. This bite piece should either be sterilized after eachuse or covered with a disposable plastic slipcover.

RADIOLOGY

Image magnification may be minimized by:

• Using a short cone• Placing the film as far from the tooth as possible• Using a long cone• Shortening the exposure time


Tech

• Using a long cone

Five rules for accurate image formation when taking x-rays:1. Use the smallest focal spot that is practical.

Note: The size of the focal spot influences radiographic definition or sharpness.They are inversely proportional.

2. Use the longest focus-film distance that is practical in the particular situation.3. Place the film as close as possible to the structure being radiographed.4. Direct the central ray at as close to a right angle to the film as anatomical struc

tures will allow.5. As far as is practical, keep the film parallel to the structure being radiographed.

TechRADIOLOGY

Name some of the advantages and disadvantages of the paralleling technique.


• Advantages1. Little or no root superimposition on a maxillary molar view2. Accurate diagnosis of periodontal bone height (given minimal distortion)3. Image formed is dimensionally accurate

• Disadvantages1. Film placement may be difficult in some areas (i.e., low palatal vaults)2. Increased exposure time due to long cone3. XCP holders can be cumbersome to work with and may cause patient discomfort

TechRADIOLOGY

Which of the following is not a disadvantage of the bisecting technique?

• Image on x-ray film may be dimensionally distorted (amount may vary)• Increased exposure time• Due to the use of a short cone (which results in divergent rays), the image is not a

true reproduction of the object• May not be able to judge the correct alveolar bone height


• Increased exposure time'''The exposure time is actually decreased

The bisecting angle technique is based on the geometric principal known as the ruleof isometry. The rule states that two triangles are equal if they have two equal anglesand share a common side. The following best describes the bisecting technique:• The dental x-ray film is placed along the lingual surface of the tooth.• At the point where the film contacts the tooth, an angle is formed by the plane of the

film and the long axis of the tooth.• The person taking the x-ray needs to visualize a plane that bisects this angle. This

plane is called the imaginary bisector (this creates two equal angles and provides acommon side for the two imaginary equal triangles).

• The central ray is positioned perpendicular to the imaginary bisector.

Important: When this technique is followed strictly, the image of the tooth produced is accurate.

TechRADIOLOGY

Which of the following is a major disadvantage of the paralleling technique?

• The image formed on the film will not have dimensional accuracy• Due to the amount of distortion, periodontal bone height cannot be accurately diag

nosed• An increase in exposure time is necessary due to the use of a long cone• An increase in exposure time is necessary due to the use of a short cone


• An increase in exposure time is necessary due to the use of a long cone

The paralleling technique is based on the concept of parallelism. Other names for thistechnique include XCP (extension cone paralleling technique), right-angle technique,and long-cone technique.

Basic Principles:• Film is placed parallel to the long axis of the tooth being x-rayed .• Central x-ray is directed perpendicular to both the film and the long axis of the tooth.• A film holder (XGP) must be used to keep the film parallel to the long axis of the

tooth.• The ob ject-film distance ml lst be incl"4il i sed tg kQQjJ thQ film parallel This results_

in image magnification and loss of definition• The target-film distance must also be Increased ,10 compensate for the image

magnification and to make sure that only the most parallel rays will be aimed at thetooth and the film. Using a long cone (16 inch target-film distance) results in greaterdefinition and less image magnification .

TechRADIOLOGY

Name the two x-ray techniques that are utilized in dentistry for taking periapical films.


1. Bisecting technique (see Figure 1)2. Paralleling technique (see Figure 2)

PID

Long axisof tooth

Film~~~

Filmholder~

Figure 2Positions of the film. teeth, and central ray ofthe x-ray beam in the paralleling technique.Film and long axis of the tooth are parallel. Thecentral ray is perpendicular to the tooth andfilm. An increased target-film distance (16inches) is required.

Centralray

Imaginary

bisector "'\

Film ".

~~".~Figure 1

The image on the film is equal to the length ofthe tooth when the central ray is directed at 90degrees to the imaginary bisector. A tooth andthe radiographic image will be equal in lengthwhen two equal triangles are formed that sharea common side (imaginary bisector) .

Reproduced with permission from Haring, Joen Janucci and Laura Jansen Lind, Dental radiographyPrinciples and Techniques. WB. Saunders Company, Philadelphia, Pennsylvania, 1996.

TechRADIOLOGY

Name the two x-ray techniques that are utilized in dentistry for taking periapical films.


1. Bisecting technique (see Figure 1)2. Paralleling technique (see Figure 2)

Film holder

Long axisof tooth

Figure 2Positions of the film. teeth, and central ray of[he x-ray beam in the paralleling technique.Film and long axis of the tooth are parallel. Thecentral ray is perpendicular to the tooth andfilm. An increased target·f ilm distance (16inches) is required.

Centralray

Imaginary

bisector .... ...

Film " .

''".".~Figure 1

The image on the liIm is equal to the length ofthe tooth when the central ray is directed at 90degrees to the imaginary bisector. A tooth andthe radiographic image will be equal in lengthwhen two equal triangles are formed that sharea common side (imaginary bisector) .

Reproduced with permission from Haring, Joen lanucci and Laura Jansen Lind, Dental radiographyPrinciples and Techniques. W.B. Saunders Company, Philadelphia, Pennsylvania, 1996.

R ProtRADIOLOGY

The most effective means in reducing the time of exposure , the amount of radiationreaching the patient and the amount of radiation scattered to the dentist is:

• A lead apron• Ultra-speed film• Lead diaphragms• Increasing target-film distance


• Ultra-speed film

All of the following reduce the amount of radiation to the patient:• A lead apron• Increased filtration using an aluminum disk• Ultra-speed film• Lead diaphragms placed within the cone of an x-ray tubehead• Collimating an x-ray beam• Increasing target-film distance• Intensifying screens (used for all extraoral radiography, i.e. panorex, cephs.)

Note: The committee on Radiation Protection of the National Bureau of Standards recommends that a person who works near radiation be exposed in one year to a maximum dose of 5 REM (0.1 REM per week). S con ary and scatter radi ation pose tfiegrea est hazard to the dental team.

Important: Carcinogenesis and genetic mutation are important and serious effectsof repeated exposure to low doses of x-radiation. The mechanisms involved may beframeshift mutations, synergism with chemical carcinogens and altered DNA repairenzyme functions.

RADIOLOGY

All of the following are true concerning collimation except

• It prevents overexposure to patients• It increases the area of patient exposure• It reduces secondary radiation to the film• It reduces secondary radiation to the patient


R Prot

• It increases the area of patient exposure

"'This is false; collimation reduces the area of patient exposure

Collimatio efers to the control 01 the size and shape of x-ray beam.

It is a basic rule of radiation hygiene that the radiation beam be as small as practical. For intraoral radiography, by state law, the diameter of a circular beam of radiation at the patient's skincan be no greater than 3 inches. One can use a diaphragm or metal cylinders, cones or tubesto collimate the beam.

These devices do not reduce the amount of radiation received by the exposed tissues, butreduce the radiation to surrounding tissues due to x-ray beam divergence.

Aluminum disc filtration:The x-ray beam consists of many different wavelengths. The short wavelength (high energy)rays have great penetrating power; long wavelength (low energy) rays have low penetratingpower and do not reach the film in reasonable quantities since they are attenuated by the softtissues. Low energy rays add only to the total amount of radiation the patient receives.Aluminum discs are used to filter out the useless long wave x-rays, Increasing the overallquality of the beam.

Important: Filtration reduces patient dose, decreases contrast and decreases the density ofthe film.

R ProtRADIOLOGY

Explain how filtration is an important element in the control of the emerging radiationfrom an x-ray beam.

Copyright @ 2001 - DENTAL DECKS

• Filtration absorbs the longer, less penetrating rays, which would otherwise beabsorbed by the patient's skin or scattered and absorbed by both patient and operator. It also i reases the penetrating qualities of the beam (bY' absorbing thelonger.. wave length x-rays).

There are two types of filtration:1. Inherent filtration - is caused by absorption of the beam by the glass window of the x-ray

tube, the oil surrounding the tube, the alll miRum filter iR the x ray head aAd IAe "Iasti c canfl....2. Added filtration - is obtained by placing thin sheets of aluminum in the cone to filter the use-

ful beam further.

"'lotal filtration is the sum of inherent and added filtration. Recommended tp tal: equivalentof 0.5 mm (below 50 kVp) and 2.5 mm (over 70 kVpJ of alumiiiU01.

Notes:1. Longer wavelength x-rays (those produced at lower kilovo/tages) are easily absorbed.2. Shorter wavelength x-rays (produced at higher kilovoltages) penetrate objects more read-

ily (they form image on the film).

Remember: The x-ray beam is composed 01 rays of different wavelengths and penetrating power(the term used for this is polychromatic) because the potential across the tube changes constantly as the voltage varies.

RADIOLOGY

What is meant by the term "half-value layer"?


; 4 i

A Phys

• When an x-ray beam encounters a mass of material, not all the x-rays areabsorbed. If a certain thickness of this material reduces a monochromatic beam by50%, the x-ray beam is said to have a half-value layer of the thickness used, measured in terms of the absorbing material - most often aluminum. The greater thehalf-value layer of aluminum, the more penetrating the radiation wavelengths.

In oral diagnostic radiography, the half-value layer of the beam of radiation is approximately 2 mm of aluminum. This means that half of the x-rays exiting the vacuum tubeare absorbed by 2 mm of aluminum. It should be noted that doubling the thickness ofaluminum will not absorb all of the x-rays, but only half of the remaining x-rays.

2x thit~ ",,\l ol..r~ -!t llf'~.

Important point to remember: The half-value layer is an indicator of th~fa~- .x-ray beam.

Note : X-rays and gamma rays are examples of non-particulate radiation energy.

RADIOLOGY

Explain the difference between primary and secondary radiation.


R Phys

• Primary radiation is referred to as the main beam of x-ray energy that is producedfrom within the x-ray tubehead .

• Secondary radiation occurs when the primary beam of radiation collides with matter. Secondary radiation that trayels out in all directions is referred to as "scatteredradiation."

Notes:1. lead is most effective in stopping x-rays (patients should always wear a lead

apron and thyroid collar)2. X-rays have more energy than light3. The following belong to a group of radiations known as electromagnetic radia-

tions: microwaves, x-radiation, visible light, and gamma radiation4. Approximately 1% of the energy released in the x-ray tube is released as x-rays5. MPD stands for maximum permissible dose of radiation exposuje6. The yearly MPD for a non-occupationally exposed person ' 0.5 RE compared

witl;Y5'"RE~for someone who works near radiation7. Th~1ypeOf cone (PIO) that best reduces the amount of scatter radiation that the

patient receives is a leaded, rectangular one since this greatly reduces the size ofthe beam (PID should always be open-ended)

RADIOLOGY

Identify the following parts of an x-ray tube.

R Phys

2 3 4

7 6 5


1. Glass envelope2. Anode3. Filament4. Cathode5. Focusing cup6. Tungsten target7. Window

X-rays are generated when a stream of electrons (which are produced by the filament)travels from the cathode to the anode and is suddenly stopped by its impact on thetungsten target. The filament located in the cathode is made of tungsten wire. The smallarea the target that the electrons strike is called the focal spot. It is the source of xrays.

Note : The size of the focal spot directly influences the x-ray definition (the larger thefocal spot, the greater the loss of definition and sharpness of image).

R CharRADIOLOGY

Suppose that in a periapical examination of the mandibular incisor region, an exposuretime of 1/4 second and focus-film distance of 8 inches were used. If you increase thefocus-film distance to 16 inches, what would be the new exposure time required to produce the same density in the radiograph?

• 1/2 second• 1 second• 2 seconds• 4 seconds


• 1 second

Explanation:The time required for a given exposure is directly proportional to the square of thefocus-film distance. The formula is:

Original Time = Original DistancesNew Time New Distances

Hence,1/4 = 82 = 1/4 X 162 = 1/4 x 256 = 64 = 1 = x (in seconds)x = 162 = 82 64 64

Important: The above formula holds true only if the rnA and kVp are constant.

Remember: The inverse square law formula is:

Original Intensity = Original DistanceeNew Intensity New Distances

Important: The intensity of radiation is inversely proportional to the square of the distance.

RADIOLOGY

Kllovoltage controls the speed of:

• Photons• Electrons• Anodes• Cathodes


R Char

• Electrons

The speed with which electrons travel from the filament of the 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 focalspot.

The kilovoltage has nothing to do with the number of electrons that compose thestream flowing from cathode to anode. The umber of electrons (which determinesthe quantity of x-rays produced) is controlled by the temperature of the cathode filament (milliamperage setting). The hotter the filament, the more electrodes are emittedand available to form the electron stream (the x-ray tube current). In the x-ray tube thenumber of electrons flowing per second is measured in millamperes. The intensity ofx-rays produced at a particular kilovoltage depends on that number.

Note: Setting the x-ray machine for a specific milliamperage actually means adjustingthe filament temperature to yield the current flow indicated.

To increase film density, you should increase mA, kVp and time. Also, you shoulddecrease the source-object distance.

RADIOLOGY

Increasing the kilovoltage (kVp) causes the resultant x-ray to have :

• Decreased density• More latitude• A shorter scale of contrast• A longer scale of contrast


R Char

• A longer scale of contrast

Remember: K ovoltage controls

One effect of a change in kilovoltage is a change in the penetrating power of the xrays. In,creasing kilovoltage reduces subject contrast (and the longer the scale of contrast); decreasing kilovoltage increases subject contrast (and the shorter the scale ofcontrast). A second effect of an increase in kilovoltage is that not only are new, morepenetrating x-rays produced, but more of the less penetrating rays which were also produced at the lower kilovoltage are emitted .

Conclusion:Kilovoltage influences the x-ray beam and radiograph by:• Altering contrast quality (for patients with thick jaws, increase kilovoltage)• Determining the quality of the x-rays produced• Determining the velocity of the electrons to the anode

RADIOLOGY

The number of x-rays produced is controlled by:

• Kilovoltage (kVp)• Milliamperage (rnA)• Exposure time


R Char

• Milliamperage (rnA)

The operator of an x-ray unit is in control of three factors:1. KiloYoltage - the quality or penetrating power of the x-ray beam2. Milliamperage - the quantity or number of x-rays produced3. Exposure time - the length of time x-rays are produced and patient is exposed to

them

Suitable ranges of dental x-rays are 50-100 kVp and 5-15 mA

Some x-ray machines are calibrated in "impulses" (there are 60 impulses in 1second)

Density refers to the overall darkness (blackness) of a radiograph• Density will increase as mA, kVp, or exposure time is increased• Density will decrease as mA, kVp, or exposure time is decreased

Contrast refers to the difference in degrees of blackness between areas on a radiograph• High - very dark and very light areas• Low - many shades of gray - preferred in dentistry• 0 I~ one exposure factor affects contra t=kiloYoltage (kVp) Note: filtration

plays a role here also.

R BioRADIOLOGY

Which of the following is a measure of the energy imparted by any type of ionizingradiation to a mass of any type of matter?

• Absorbed dose• Exposure• Equivalent dose• Effective dose


• Absorbed dose

mThe traditional unit of absorbed dose is the rad (radiation absorbed dose).

Exposure is a measure of radiation quantity, the capacity of the radiation to ionize air.The roentgen (R) is the traditional unit of radiation exposure measured in air. The roentgen applies only to x-rays and gamma rays.

~quivalent dose is used to compare the biologic effects of different types of radiationto a tissue or organ.

Effective dose is used to estimate the risk in humans .

RADIOLOGY

All of the following are radioresistant cells except

• Muscle

• NeNe• Mature bone• Lymphocytes


R Sio

• Lymphocytes

Cells in the body have different sensitivities to radiation than others (see chartbelow).

Radiosensitive Cells Radioresistant Cells

Reproductive cells (sperm and ova) Muscle

Lymphocytes (immature blood cells) Nerve

Bone Marrow Mature Bone

Immature bone cells

In general, the greater the rate or potential for mitosis and the more immature thecells and tissues are, the greater the sensitivity or susceptibility to radiation.

R SioRADIOLOGY

It is recommended that the operator stand at least how many feet away from thepatient when taking radiographs?

• Two feet• Four feet• Six feet• Eight feet


• Six feet

Radiation exposure to the operator can be reduced by standin at least six feeway, behind a lead shield, or both when exposing radiographs. The operator should

never remain in the room holding the x-ray packet in place for the patient. If a film mustbe held in place by someone else (for a child), drape the parent and have him or herhold the film. All dental personnel should wear film badges that monitor exposuredosages.

Note: Regarding the taking and processing of dental radiographs, always remember to maintain proper infection control at all times!!!

R BioRADIOLOGY

The period between radiation exposure and the onset of symptoms is called the:

• Latent period• Period of cell injury• Recovery period


• Latent period

The-latent period is the period of time between radiation exposure and the onset ofsymptoms. It may be short or long, depending on the total dose of radiation receivedand the amount of time it took to receive the dose.

The period of cell injury follows the latent period. Cellular injury may result in celldeath, changes in cell function or abnormal mitosis of cells.

The r covery period is the last event in the sequence of radiation injury. Some cellsrecover from radiation injury, especially if the radiation is "low level".

Note: The effects of radiation exposure are additive and the damage that remainsunrepaired accumulates in the tissues. The cumulative effects of repeated radiationexposure can lead to various serious health problems (e.g. carcinogenesis, whichleads to various carcinomas, genetic mutations which cause birth defects, differentkinds of leukemia and cataracts).

ProcRADIOLOGY

Marilyn has taken three panoramic x-ray films today. During the day as she developedeach film, she noticed the films getting lighter and lighter. What needs to be done sothat this problem can be corrected?

• Decrease the temperature of the developing solution• Increase the temperature of the developing solution• Replenish the developing solution• Increase the mA setting• Increase the kVp setting


• Replenish the developing solution

As the developing solution gets weaker, the films will get lighter. Both the developing and fixing solutions should be replenished on a daily basis. These solutions alsoneed to be changed on a regular basis, and the tanks need to be scrubbed and cleanedas well.

The following factors affect the life of a developing solution : the cleanliness of thetanks, the size of the films processed , the number of films processed, and the temperature of the solution.

Notes:1. Yellowish-brown film will result from insufficient fixing or rinsing.2. Fogged film may also result from the improper film storage or outdated films.3. Low solution levels will appear as: developer cut-off (straight clear border) or fixer

cut-off (straight black border) .

RADIOLOGY

X-ray fixer contains all of the following except :

• A clearing agent• An antioxidant preservative• An accelerator• An acidifier• A hardener


Proc

• An accelerator

X-ray fixing solution contains the following:• clearIng agent, such as sodlum or. ammoni thiosulfate, commonly called hypo, dis-

solves and removes the underdeveloped silver salts from the emulsion (Note: This is one ofthe main functions of fixing solutions.) The chemical "clears" the film so that the blacksilver image produced by the developer becomes distinctly perceptible. When the film isimproperly cleared, the remaining unexposed crystals darken upon exposure to light andobscure the image.

• An anti ox idant preservative, for example sodium sulfite prevents the decomposition of thefixer chemical.

• An acidifi er such as aceti c acid that is necessary for the correct action of the otherchemicals and also neutralizes any alkaline developer that may be carried over by the film orhanger.

• A hardenel"such as pot assium alum that shrinks and hardens the gelatin in the emulsion. Itshortens drying time and protects the emulsion from abrasion.

Notes:1. If a dried radiograph were processed a second time, there would be no change in contrast

or density.2. Fixing time i always at least twice as long as the developing time.

RADIOLOGY

X-ray developer contains all of the following except:

• A developing agent• An antioxidant preservative• A clearing agent• An accelerator• A restrainer


Proc

• A clearing agent

X- ay dev loping solution contains the following:• A developing agent, uch as hydroquinone, which is a chemical compound that is

capable of changing the exposed grains of silver salts to metallic silver. At the sametime, it produces no appreciable effect on the unexposed grains of the emulsion.Gives detail to the x-ray image.

• An antioxidant preservative, for example , sodium sulfite, prevents the developersolution from oxidizing in the presence of air.

• An accelerator - an alkali (sodium carbonate) - activates the developing agentsand maintains the alkalinity of the developer at the correct value.

• A restrainer, such as potassium bromide, is added to developers to control theaction of the developing agent so that it does not develop the unexposed silver saltsto produce fog.

Remember: Developer is a chemical solution that converts the invisible image on afilm into a visible one composed of minute masses of black metallic silver.

Important: The function of developing solution is to reduce silver. halides to crystalsof pure silver, while the function of fixing solution is to stop aevelopment and dissolve remaining pure silver cry tals.

ProcRADIOLOGY

After processing a film, you notice that it appears brown in color. What is the most likely cause of this?

• Solutions are too strong• Solutions are too weak• Fixing time was not long enough• Fixing time was too long• Film was under-developed


• Fixing time was not long enough***A film will appear brown when it is not completely fixed

Some common errors made in the darkroom/cause:• Mounted films are improperly labeled (wrong patient name) / racks not labeled properly• Fogged film (gray/lack ot.conu. sty / faulty safelight in darkroom;-,white light leaking into dar!<

room• Lost films / films not secured properly on rack• Stat ic marks (multiple black lines) / friction when opening film packets causes static elec

tricity• Overdeveloped film (dark) / incorrect time (too long) and temperature (too hot)• Underdeveloped film (light) / incorrect time (too short) and temperature (too cold); weak

solutions (too old or diluted)• Torn emulsion / films were allowed to touch or overlap while they were drying• Stained film (dark/white spots) / dirty work surfaces; person developing film was sloppy• Scratched films (white lines) / film emulsion removed by sharp object (fingernails/racks

touching)• Clear films (emulsion washed away) / films left in water (wash) for over 24 hours• Air bubbles (white spots) / air trapped on film surface while being placed in processing solu

tions

NAnatRADIOLOGY

Which of the following is the name of the bony projection that arises from the sphenoid bone and extends downward and slightly posteriorly?

• The lingula• The hamular process• Sella turcica• Pubic symphysis

Copyright @ 2001 - DENTAL DECKS

• The hamular process

On the x-ray tube its image is seen in proximity to the posterior surface of the tuberosity of the maxilla. It varies greatly in length. width and shape from patient to patient. Itusually exhibits a bulbous point, but sometimes the point is tapered.

See pictures # 18, 19 and 20 in booklet

N AnatRADIOLOGY

The image of the coronoid process of the mandible often appears in periapical x-raysof:

• The incisor region of the mandible• The molar region of the mandib le• The incisor region of the maxilla• The molar region of the maxilla


• The molar region of the maxilla

As the mouth is opened, the process moves forward, and therefore it comes into viewmost often when the mouth is opened to its fullest extent at the time the exposure ismade. It is evidenced by a tapered or triangular radiopacity, which may be seenbelow, or in some instances, superimposed on the molar teeth and maxilla.

See picture #16 in booklet

N AnatRADIOLOGY

Identify the normal anatomy of the maxillary molar region.

.-::lP' ';''....."..",=,"__fB :>-.

H

G

oE

Reproduced with permission from Kasle, Myron J . An Alias of Dental Radiographic Anatomy , Fourth Edition.Philadelphia, Pennsylvania, W.B. Saunders Company, 1994.


Radiographic anatomy of the maxillary molar region:A. Maxillary sinus depressionB. The zygomatic processC. The lateral pterygoid plateD. The maxillary tuberosityE. The hamulus (part of the medial pterygoid plate)F. The coronoid process of the mandibleG. Film identification dotH. The floor of the maxillary sinus

N AnalRADIOLOGY

What is the most likely interpretation of the radiolucency seen in the x-ray belowbetween the maxillary central incisors? Note : The teeth are vital.


• The incisive foramen (also called the anterior palatine foramen)

As seen on x-rays, it's image may vary in relation to the roots of the incisor teeth andranges from a position near the crest of the alveolar ridge to one that may be at thelevel of the apex of the roots. In some instances, its image may be superimposed onthe apex of the root of the central incisor when x-rays of the adjacent teeth are made.and it may then be mistaken for a periapical lesion.

Notes:1. It is almost always elliptical in shape and variable in size.2. A cyst of the incisive canal with which it may be confused has a well-defined bor

der and tends to be round.

N AnatRADIOLOGY

Identify the anatomic structures labeled 1-5 of the anterior and premolar regions of themaxilla.

2

{.


1. The nasal septum2. The nasal fossae3. The floor of the nasal fossa as it extends posteriorly4. The anterior wall of the maxillary sinus5. The nasal spine

N AnatRADIOLOGY

Identify the normal radiographic anatomy of the maxillary incisor region.

E c

Reproduced with permission from Kasle, Myron J . An Atlas of Dental Radiographic Anatomy. Fourth Edition.Philadelphia . Pennsylvania. W.B. Saunders Company, 1994.

Radiographic anatomy of the maxillary incisor region:A. The nasal conchae in the nasal fossaeB. Nasal fossaeC. The anterior nasal spineD. A shadow of the lip lineE. The nasal septum

N AnatRADIOLOGY

Identify the normal radiographic anatomy of the mandibular incisor region.ABC

G F [

D

Reproduced with permission from Kasle. Myron J . An Atlas of Dental Radiographic Anatomy. Fourth Edition .Philadelph ia. Pennsylvania. W.B. Saunders Company. 1994.


Radiographic anatomy of the mandibular incisor region:A. The permanent lateral incisorB. The permanent central incisorC. Overlapping contactsD. The permanent canineE. The genial tubercleF. The lingual foramenG. The inferior cortical plate of the border of the mandible

N AnatRADIOLOGY

Identify the normal radiographic anatomy of the mandibular molar region.

A B

F

E D

c

Reproduced with permission from Kasle, Myron J. An Atlas of Dental Radiographic Anatomy. Fourth Edition.Philadelphia , Pennsylvania, W.B. Saunders Company, 1994.


-

Radiographic anatomy of the mandibular molar region:A. The external oblique ridgeB. An enamel pearlC. Film identification dotD. Cortical bone of the inferior border of the mandibleE. A healing extraction siteF. The mandibular canal

N AnatRADIOLOGY

Identify the normal radiographic anatomy of the mandibular premolar region.

ABC

J H

E

G

F

Reproduc ed with permissio n from Kasle, Myron J . An Atlas of Denial Radiographic Anatomy, Fourth Edition.Philadelphia, Pennsylvania, W.B. Saunders Company, 1994.


Radiographic anatomy of the mandibular premolar region:A. Tom film emulsionB. The buccal cusp of the mandibular permanent first premolarC. The lingual cusp of the mandibular permanent first premolarD. A portion of the metal film holderE. Metal restorationsF. The submandibular fossaG. The internal oblique ridgeH. The mandibular canalI. The mental foramenJ. Sclerotic bone

RADIOLOGY

It is best to retain dental radiographs for how many years?

• 2 years• 4 years• 6 years• Indefinitely


Misc.

• Indefinitely

The dental record must include documentation of informed consent and the exposureof radiographs (e.g. the number and type of films, the rationale for exposure and theinterpretation). Legally, dental radiographs are the property of the dentist. Patientsdo, however, have a right to reasonable access to the dental radiographs, whichincludes having a copy of the radiographs forwarded to another dentist.

Note: Patients may refuse dental x-rays, however, the dentist must decide whetheran accurate diagnosis can be provided and whether treatment can provided.

Remember: No document can be signed by the patient that releases the dentist fromliability.

RADIOLOGY

Osteoradionecrosis is more common :

• In the mandib le• In the maxilla


Misc.

• In the mandible

Osteoradionecrosis is more common in the mandible than in the maxilla, probablybecause of the richer vascular supply to the maxilla and the fact that the mandible ismore frequently irradiated.

Remember: Osteoradionecrosis is the necrosis of bone, produced by ionizing radiation.

The most common factors precipitating osteoradionecrosis are pre- and post-irradiation extractions and periodontal disease.

Note: Damage to the blood vessels (as opposed to nerves, muscle, etc.) predisposes a patient to the development of osteoradionecrosis.

Misc.RADIOLOGY

Your dental hygienist has a patient that says she needs bite-wing x-rays because it hasbeen six months since the last films were taken . Your hygienist should respond inwhich manner listed below?

• Agree with the patient• Tell the patient that bite-wing x-rays should be taken once a year• Tell the patient that dental x-rays are taken only when needed as judged by each

patient's needs• None of the above


• Tell the patient that dental x-rays are taken only when needed as judged byeach patient's needs

Decisions about the number, type and frequency of dental x-rays are determined bythe dentist based on each patient's needs. Every patient has a different dental condition and thus the frequency of x-rays is different as well. There are guidelines publishedby the ADA that aid a dentist in prescribing the number, type and frequency of dentalx-rays. Note : Patients who have tooth decay, periodontal disease, tooth mobility, painin one or more teeth or possible impacted teeth need more frequent radiographicexaminations than patients without such problems. Remember: For a pediatric patientwho is caries free (and asymptomatic), the first bite-wing radiographs should not betaken until the spaces between the posterior teeth have closed.

Note: Occult diseases (for example, smsll carious lesions, cysts and tumors) arethose presenting no clinical signs or symptoms. Because occult disease in the perioral tissues is so rare (except for caries), a radiographic examination of the jawsshould not be undertaken solely to look for it in an individual with teeth when there areno clinical signs or symptoms. However, every x-ray taken should be evaluated forthese lesions.

Remember: Caries is an exception to the above rule because of its much higherprevalence as compared to occult cysts or tumors.

RADIOLOGY

Which type of structure inhibits the passage of x-rays?

• Radiopaque• Radiolucent


1m Char

• Radiopaque

Radiopaque structures/materials:• Less radiation penetrates the structure and reaches the film• Radiopaque structures appear white on the processed film• Dense materials such as metals, enamel, dentin, and bone

Radiolucent structures/materials:• Allow radiation to pass through, absorbing very little• More radiation penetrates the structure and reaches the film• Radiolucent structures appear gray to black on processed film• Less dense materials , including soft tissue and air space

Note: Radiographs show shading from black to white (most radiolucent to mostradiopaque). Example: Least to most radiopaque: periodontal ligament space,dentin, enamel, ZOE, amalgam.

RADIOLOGY

The area from which x-rays emanate is cal led the:

• Target• Focal spot• Intensifying screen• Cone


1m Char

• Focal spot

···The focal spot is the area of tungsten on the anode that receives the impact of the speedingelectrons.

The target (also called the tungsten target) is a wafer of tungsten embedded in the face of theanode at the point of electron bombardment. Note: The focal spot is actually a small area of thetarget.

Remember: Intensifying screens are devices used in extraoral radiography that convert x-rayenergy into visible light. The light, in turn, exposes the screen film. Therefore, the radiation thata patient receives is decreased. A cassette holder is a light-tight device used in extraoral radiography to hold film and intensifying screens.

Important: Target film distance (also called source-to-film distance) is the distance from thesource of x-rays (focal spot on the tungsten target) and the film. It is determined by the length ofthe position-indicating device (also called PIO). Two standard target-film distances are used inintraoral radiography:

1. 20 cm (8 inches) is called the short cone, exposes more tissue by producing a more divergentbeam.

2. 41 em (16 inches) is called the long cone , reduces the amount of exposed tissue by producing a less divergent beam. Also results in smaller focal spot and better sharpness of the x-ray.

radiology

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