self study paralleling

8/13/2019 Self Study Paralleling

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The following slides describe the

Paralleling Technique for taking

periapical films.

X-ray Technique


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Patient Preparation

Prior to starting to take films, the patient must

be positioned properly. Seat the patientand ask

them to removetheir glasses and any removable

appliances. Adjust the headrestto support the

head while taking films. Raise or lower the chair

to a comfortable height for the operator. Place

the lead apron and thyroid collaron the patient.

You are now ready to begin taking films.

It is a good idea to inform the patientabout the

number of films you will be taking so they know

what to expect.


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Paralleling

Technique


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Film/tooth/ring all parallel

X-ray beam perpendicular to tooth/film

In the paralleling technique, the film is placed in the

mouth so that the long axis of the film is parallel with

the long axis of the teeth being radiographed. A

paralleling instrument with an aiming ring is normallyused to orient the film, teeth and ring in a parallel

relationship. When the x-ray beam is aligned with the

ring, the x-ray beam will be perpendicular (right

angle) to the teeth and the film.


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Paralleling Technique (Advantages)

There are two techniques for taking periapical films, the

paralleling and the bisecting angle techniques. Whencomparing the two techniques, the advantages of the

paralleling technique are:

1. Better dimensional accuracy: the paralleling

technique results in less distortion of the image of

the teeth. (The shape of the teeth and the

relationship of the teeth to surrounding structures

is more accurate).

2. When using the paralleling instrument with the

aiming ring, the alignment of the x-ray beam is

simplified.

(continued next slide)


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Paralleling Technique (Advantages)

3. It is easier to standardize films. Because you areusing the positioning instrument, it is easier to

position the film in approximately the same

position at different appointments. This can be

helpful if you are trying to compare theappearance of a periapical lesion from one visit

to the next.

4. Head position is not as critical. Because of the

paralleling instrument, with its aiming ring, it iseasy to properly align the x-ray beam no matter

how the head is positioned.


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When the long axis of the film is parallel with the

long axis of the tooth, the image of the tooth on

the film looks the same as the tooth itself (nodistortion). The image will be slightly larger than

the actual tooth (magnification), but the shape is

the same.


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Paralleling Technique (Disadvantages)

When comparing the paralleling and bisecting

angle techniques, the paralleling technique is:

1. Less comfortable. Because the film is

usually more upright when using the

paralleling technique, it impinges more onthe palate or floor of the mouth, thus making

it more uncomfortable.

2. More limitedby the anatomy of the patients

mouth. A shallow palate or floor of the mouthmakes it harder to position the film using the

paralleling technique.


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correct incorrect

Paralleling Film Placement

As mentioned previously, the film is placed in the

mouth so that the long axis of the film is parallel withthe long axis of the teeth. Since all teeth are inclined

toward the middle of the head (not straight up and

down), the film will be slightly angled in the mouth

(see below left). If the film is maintained in an uprightposition (below right), the patient will not be able to

close on the biteblock and the film will not be parallel.


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To facilitate film placement, the film may be tipped up

to 20 degrees beyond parallel.



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As a result, the film must be

positioned away from the

teeth (farther back in the

mouth) to achieve parallelism.

Because the palate and

floor of the mouth are

shallower as you approach

the lingual of the teeth, the

film often cannot be

positioned properly close tothe teeth.



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Because the film is farther from the teeth, there will

be increased magnification (larger size) and

decreased sharpness (less detail). To compensate

for this, the target-film distance should beincreased (the target is where the x-rays are

produced).

Target

16 Target

8

size of image at 8 target-film distance

size of image at 16 target-film distance


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Long PID Short PID

Recessed target

Medium PID

Recessed target

The target-film distance is increased by using a longer

PID, using a machine with a recessed target (opposite

side of the tubehead from the PID) or a combination.

The medium PID with a recessed target is a good

compromise. The disadvantage to increasing the PID

length is that the exposure time must be increased. If

you change from an 8 target-film distance to a 16

target-film distance (double the distance) theexposure time will be four times as much (see Inverse

Square Law).


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Best OKOK

Paralleling Technique

Head Position

As mentioned previously, head position is not as

important when using the paralleling technique.

However, in general it is best to position the head

in an upright position so that the maxillary arch is

parallel to the floor.


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#2#1

anterior posterior


Film Selection for Adults

The # 1 size film is used for anterior periapical films

using the paralleling technique. The long axis of the

film is vertical. For posterior films, # 2 size film is

used with the long axis horizontal.


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#0 #0

anterior posterior


Film Selection for Children

For children with small mouths, the # 0 size film is

used for both anterior and posterior periapical

films. However, if the childs mouth is large

enough to reasonably accommodate the larger

size films (# 1 anterior, # 2 posterior), and the child

is cooperative, they should be used.


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Rinn Paralleling Instruments

ANTERIOR

POSTERIOR

The Rinn paralleling instruments are used at the Ohio

State University College of Dentistry. They are color-coded, with yellow being the posterior instrument and

blue being the anterior instrument. The metal bar

connects to the side of the biteblock and the ring slides

on the bar.


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front back

oppositeside

toward tube

The film is placed in the biteblock so that the all-white

side of the film packet faces the teeth and, by

extension, the ring. (The colored portion of the film isagainst the back support of the biteblock). When you

look down through the ring, you should see the all-

white side of the film packet centered in the opening.


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Anterior Periapical

long axis vertical

F E Speed1-Film

INSIGHT

Dental Film

Kodak

dot

slot

For the anterior periapical, the # 1 size film is placed

vertically in the biteblock. The film is rotated so theidentifying black dot is down; this end of the film goes into

the slot of the biteblock (dot-in-the-slot). Push the film

back against the biteblock support and slide it down into

the slot.

colored side of film

white side of film

white side facing teeth/ring


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Posterior Periapical

long axis horizontalOPPOSITE

SIDE

TOWARD TUBE

KODAK

INSIGHT

1- FILM F E

slot

dot

For the posterior periapical, the # 2 size film is placed

horizontally in the biteblock. The film is rotated so theidentifying dot (faint embossed circle) is down; this side of

the film goes into the slot of the biteblock (dot-in-the-slot).

Push the film back against the biteblock support and slide

it down into the slot.

colored side of film

white sideof film

white side facing teeth/ring


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For all periapical films, the teeth being radiographed

must be in contact with the biteblock to avoid not havingthe apices of the teeth on the film (see errors section of

slide show). Make sure patient doesnt just close lips

tight around biteblock; have them part their lips so you

can confirm the contact.

correct incorrect

General Technique Guidelines


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As shown above, cotton rolls may be used in any area

of the mouth to help support the biteblock, especially

if an edentulous region or uneven teeth oppose theteeth being radiographed. Using a cotton roll also

makes it more comfortable for the patient to bite in

some situations. The cotton roll should be placed

against the arch opposite the one being radiographed.



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If a patient has a partial denture or a complete

denture in one of the arches, the appliance canbe used to help support the biteblock when the

patient closes. This is normally preferable to

using cotton rolls. Make sure that the denture is

only used in the arch opposite to the one beingradiographed. Partial dentures can not be left in

the arch being radiographed because the metal

framework will be superimposed over the images

of the teeth (see Errors).


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After the patient is biting on the biteblock, and before

aligning the PID, the ring needs to be moved closer tothe patients face. While supporting the bar with the

fingers of one hand, slide the ring down close to the

face with the other hand.



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Always make sure

the head is

supported by theheadrest before

aligning the PID

and exposing the

films.



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The PID should be aligned with the ring so that the end

of the PID is equidistant from the ring and within of

the ring. The PID doesnt have to touch the ring and the

placement doesnt have to be perfect. Dont spend

excessive time making adjustments when aligning the

PID. (Remember: the paralleling technique is not very

comfortable and the patient wont appreciate any delaysin exposing the film).

Incorrect IncorrectCorrect

(not equidistant) (not close enough)



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Maxillary Central-lateral

The film is centered on the contact between the central and

lateral incisors. Make sure the mesial edge of the filmcrosses the midline slightly(into the opposite central

incisor), to insure getting all of the central incisor crown on

the film. The film should be placed well back in the mouth,

away from the teeth, where the palatal vault is the highest.


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This is a typical maxillary central-lateral periapical

film. Both the crowns and roots of the central andlateral incisors (#s 9 and 10 in this film) are

completely visible.


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Although we routinely use the # 1

size film in the anterior regionbecause it is easier to place in

the mouth due to its narrower

width, it is also possible to use

the # 2 size film (for all anteriorprojections). However, when the

# 2 size film is used for the

maxillary incisors, it is usually

centered on the midline, allowingyou to image all four incisors on

one film (the film at right is

slightly cropped, cutting off the

distal of the laterals).



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Maxillary Canine

The film is centered on the canine. The film should

be placed well back in the mouth, away from theteeth, where the palatal vault is the highest.

M ill C i


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Maxillary Canine

Make sure the long axis of the film stays in line

with the long axis of the tooth when the patientcloses. If the film tips, place a cotton roll between

the biteblock and the mandibular teeth to keep

the film aligned with the canine.


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This is a typical maxillary caninefilm (tooth # 11). Note the

overlap* (red arrow) between

canine and first premolar. This is

usually not avoidable in themaxillary canine region using the

paralleling technique.

Maxillary Canine

*overlap refers to the superimposition

of part of one tooth over a part of the

adjacent tooth. In this film, the mesial

of tooth # 12 is overlapping the

distal of # 11.


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The film should be equidistant from the teeth in an

anterior-posterior direction (the distance from the

front edge of the film to the lingual surface of the

teeth should be the same as the distance from the

back edge of the film to the lingual surface of the

teeth, indicated by red arrows below). The film

should be positioned in this manner for both thepremolar and molar radiographs. This helps to avoid

overlap (see errors).

correct premolar incorrect

(results in overlap)

All Posterior Films

correct molar


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The film is positioned so that the anterior edge

is at least in the middle of the canine, or moreanterior if possible. The film is approximately

centered on the 2ndpremolar. The top edge of

film is approximately in the center of the palate

(side-to-side).

Maxillary Premolar


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Maxillary Premolar

The premolar film below shows the first and

second premolars and the first molar completely;a portion of the second molar is also seen.


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The film is centered on the second molar. The top

edge of the film is in the center of the palate (side-to-side). The film should be centered on the second

molar even if the third molars are not present in

order to identify impactions, root tips or other

pathology that might be present in the third molarregion.

Maxillary Molar


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Maxillary Molar

The molar film below shows the first and second

molars and the third molar region (the thirdmolar has been extracted). The maxillary

tuberosity (red arrow) is easily identifiable.


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palatal torus

Some patients may have a maxillary torus, which is a

bony growth in the center of the palate. If a palatal

torus is present, place the film so that the top edge is

on the opposite side of the torus (away from the teeth

being radiographed). The film should not rest on the

torus. (See diagram below).

Some patients especially larger individuals will have longer


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Some patients, especially larger individuals, will have longer

than normal teeth. With the normal positioning of the film and

alignment of the beam, the apices of the teeth will be above

the edge of the film (not visible or cut off) as seen in the

film below. To compensate for this, increase the angle of thebeam and raise the PID slightly(illustration below right). You

are purposely foreshorteningthe image. You will not know

the teeth are longer from just looking at the patient, but if you

have taken previous films, or you get films from another

dentist, you can identify the need to alter your technique.

top edge of PID above ring

M dib l I i


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Mandibular Incisor

The film is centered on the contact between the central

incisors (midline). The film should be placed back in themouth, away from the teeth, as much as possible. The

bottom edge of the film is placed under the tongue and

as the film is uprighted into a parallel position, the

tongue is pushed back slightly.


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For all mandibular

films, do not force

the filmdown into

the floor of themouth trying to get

the biteblock to

contact the occlusal

surface of the

mandibular teeth.

Position the film in a

parallel relationship

and let the patient

guide the film intoplaceas they close

their mouth. Have

the patient bite

slowly and gently.

M dib l I i


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Mandibular Incisor

The incisor film below shows all four mandibular

incisors. The distal aspects of the lateral incisorsare often cut off but you can see these areas on

the canine films. All four roots are clearly visible.

M dib l C i


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Mandibular Canine

The film is centered on the canine. The film should be

placed back in the mouth, away from the teeth, as muchas possible. The bottom edge of the film is placed under

the tongue and as the film is uprighted into a parallel

position, the tongue is pushed back slightly.

M dib l C i


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Mandibular Canine

This canine film shows the mandibular canine (#

22) and most of the lateral incisor and firstpremolar.

Mandibular Premolar


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The anterior edge of the film is positioned at least in the

middle of the canine, or more anterior if possible. The film

is approximately centered on the 2ndpremolar. The filmshould be placed more toward the middle of the mouth,

away from the teeth. This will be more comfortable for the

patient. However, this is usually the most uncomfortable

film taken on a patient using the paralleling technique.

Mandibular Premolar


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Mandibular Molar


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Mandibular Molar

The film is centered on the 2ndmolar. The film can be

placed closer to the teeth than in the premolar region. This

film is more comfortable than the premolar film because

the floor of the mouth is deeper in this region.

Mandibular Molar


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Mandibular Molar

This mandibular molar film shows the first and

second molars and the third molar region (thethird molar was extracted).


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mandibular torus

Some patients may have bilateral mandibular tori,

which are bony growths on the lingual of the mandible

in the premolar region. If tori are present, place the

film so that it is between the torus and the tongue.Make sure the film doesnt rest on top of the torus.

(See diagram below).


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Patients with longer teethwill also require an alteration in

technique in the mandibular arch. Increase the angle of the

beam (increase the negative vertical angulation, e.g., change

from - 20 degrees to - 35 degrees)and lower the PID slightly(illustration below right). You are purposely foreshortening

the image.

Adult full mouth series Paralleling Technique


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Adult full-mouth series, Paralleling Technique

# 1# 2 # 2

R L

An adult full-mouth series of films consists of 15

periapical films; 7 anterior (from canine to canine,

4 maxillary and 3 mandibular) and 8 posterior

(premolar and molar films in each quadrant).

Anterior First


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Anterior First

When taking films on a patient, you should always

start with the anterior films. If you are doing a full

series, start with the maxillary canine film and

then finish all the anterior films, both maxillary

and mandibular. Then complete the posterior

films, starting with the premolar, then molar, in

each quadrant. When doing only a few films on a

patient, start with the most anterior film and work

your way back in the mouth. This sequence of

taking films allows the patient to get used to the

procedure with a minimum of discomfort and

helps to avoid stimulation of the gag reflex.


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Paralleling Technique Errors

The following slides identify some of the most

common errors seen when using the paralleling

technique.

Film Placement


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Poor film placementis the most common error seen

when using the paralleling technique. This usually

involves incorrect anterior-posterior positioning. Thepremolar film is often not far enough forward and the

molar film is frequently not far enough back. The

premolar film below is placed properly. The molar film,

however, is too far forward, failing to image the thirdmolar region.

Premolar - OK Molar - too anterior

Film Placement

Film Placement


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In the anterior region, failure to properly center the film

is a common error. In the film below, the mesial of thecentral incisor is not visible because the film was

positioned too far back. For the central-lateral film, the

film must cross the midline slightly in order to insure

that all of the central incisor will be seen.

Film Placement

Film Placement


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If the patient is not completely closedand biting on the

biteblock (photo below), the top of the film will not be

positioned to show the ends of the roots (below right).Usually the patient will tighten their lips around the

biteblock when this occurs; ask the patient to part

his/her lips so that you can make sure they are biting

properly.roots cut off

Film Placement

Cone Cutting


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Cone Cutting

Cone cutting occurs when part of the film is not covered

by the x-ray beam. It results in a white (clear) area on the

film because no silver halide crystals were exposed andwere not converted to black metallic silver during

processing. Using the paralleling instrument, it is very

easy to align the beam with the film. However, if the

instrument is not assembled properly (ring upsidedown; see diagram below), cone-cutting will result.

correct

incorrect

Reversed Film


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Reversed Film

If the film is placed in the biteblock so that the colored

portion of the film packet faces the ring/teeth, the lead

foil in the packet will be between the teeth and the

film. The pattern imprinted on the lead foil will be

visible on the film (right side of film below) and the

film will be lighter because the lead keeps some of the

x-rays from reaching the film.

Double exposure


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Double exposure

When taking films, you should always place each film in a

container or paper bag immediately after it is exposed.

Exposed films should never be placed in the same area

where unexposed films are located. If you inadvertently

pick up an exposed film and use it for another exposure,

the result is a double exposure. Two different areas of the

mouth are superimposed, making the images worthless.This is the worst error because two films have to be

retaken.

The film at left shows

images of mandibular

incisors and mandibular

molars. The film was

vertical for the incisors and

horizontal for the molars.

Patient Movement


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Patient Movement

If the patient moves slightly during the exposure

of the radiograph, the image will be blurred as inthe film below. Always advise the patient to

remain still for the very short time it takes to

complete the exposure.

Overlap


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Overlap

As mentioned previously, the film must be kept

equidistant from the teeth when taking posteriorradiographs. If the film is not placed properly, as in the

diagram below left, overlapping will result due to the

improper horizontal angulation. Overlapis the

superimposition of part of one tooth with part of the

adjacent tooth (dotted circles below right). The red

arrow represents the direction of the x-ray beam.

Overlap


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Overlap

The radiograph below shows the overlap in the

region of the crowns of the teeth.

Incorrect Exposure Factors


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overexposureunderexposure

Incorrect Exposure Factors

correct exposure

The standard exposure settings on your x-ray machine

will be acceptable for the majority of your patients.

However, if you are taking radiographs on a child you

would need to decrease the settings. If your patient is

very large, you would need to increase the settings.

Underexposureresults when the exposure factors are

set too low for the patient size. Overexposureresultswhen the exposure factors are set too high.

Glasses


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Glasses

It is recommended that glasses be removed before

taking radiographs, even if they are not expected to be

a problem (mandibular films or bitewing radiographs).

If the glasses are left on, they may be in the path of the

x-ray beam when taking maxillary films and produce

an image on the film (see below).

glasses

Failure to Remove Appliances


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Failure to Remove Appliances

Removable partial dentures, as the name suggests,

should be removed prior to taking films. If the RPD is

left in place in the arch being radiographed, the image

of the RPD will obscure the necessary diagnostic

information. However, an RPD may be left in the mouth

in the arch opposite the one being radiographed in

order to support the biteblock. This is more effectivethan using cotton rolls in the edentulous regions.

Film Bending


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If you soften the film excessively by bending the

edges before placing the film in the biteblock, black

lines may be produced due to disruption of the

emulsion in the areas where the film was bent. These

black lines can also be caused by bending the film

when inserting it into the slot of the biteblock. If you

just push down on the film without pushing back onthe biteblock support, this bending may occur.

Film Bending

Digital Image


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Digit al Image

Make sure the patient is biting firmly on the

biteblock before aligning the tubehead. Do notallow the patient to hold the instrument in

position. If this happens, the patients finger may

appear on the film (red arrows on film below).


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This concludes the section on Paralleling

Technique. If you have any questions, you

may e-mail me [email protected].
mailto:[email protected]:[email protected]

self study paralleling

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