Radiology Ch. 19, 6, 22

paralleling

Also know as extension cone paralleling technique, right-angle technique, and long-cone technique

perpendicular

The central ray of the x-ray beam is directed _____ to the film and the long axis of the tooth

object-receptor distance

Must be increased to keep the receptor parallel with the long axis of the tooth

target-receptor distance

Must be increased to ensure that only the most parallel rays will be directed at the tooth

beam alignment device

A device used to position the receptor in the mouth and retain the receptor in position during exposure

size 1 receptor

Used in the anterior region

Long portion in a vertical direction

size 2 receptor

Used in posterior region

Long portion in the horizontal direction

maxillary right to left and mandibular left to right

Exposure sequence for paralleling anterior teeth

shallow palate, bony growths, and mandibular premolar region

3 modifications in paralleling technique

shallow palate

Tilting of the bite-block results in a lack of parallelism between the receptor and the long axis of the tooth

Two cotton rolls can be used, one placed on each side of the bite-block

maxillary tori

The receptor must be placed on the far side of the torus and then exposed

mandibular tori

The receptor must be placed between the tori and the tongue and then exposed

5-15

In order to modify a radiograph for a shallow palate, the vertical angulation can be increased by how much degrees?

accuracy, simplicity, and duplication

What are the 3 advantages of paralleling

receptor placement and discomfort

2 disadvantages of paralleling

sharpness

the capability of the x-ray receptor to reproduce the distinct outlines of an object

penumbra

lack of image sharpness is present in a radiograph

focal spot, film composition, and movement

What are the 3 factors influencing sharpness

sharper image

Smaller focal spot=

magnification

Results from the divergent paths of the x-ray beam as they radiate from the focal spot

less

A longer PID and target-receptor distance results in ____ image magnification

increase

An increase in object-receptor distance results in an _____ in image magnification

distortion

A variation in the true size and shape of object being radiographed

distortion

Results from unequal magnification of different parts of the same object

object-film alignment

The object and film must be parallel to each other or there will be distortion

x-ray beam angulation

The x-ray beam must be directed perpendicular to the tooth and film or there will be distortion

unexposed receptor

The image is completely clear

Failure to turn on the x-ray machine or malfunction of x-ray machine

film exposed to light

The image is completely black

Turn off all lights in the darkroom except the safelight

overexposed film

Image appears dark

Excessive exposure time, kilovoltage, or milliamperage

overexposed film

underexposed receptor

The image appears light

Check the exposure time, kilovoltage, and milliamperage

absence of apical structures

The receptor was not positioned in the patient’s mouth to cover the apical regions of the teeth

absence of apices

underexposed receptor

dropped receptor corner

The occlusal plane appears tipped or tilted

The edge of the receptor was not placed parallel to the incisal- occlusal surfaces

dropped corner

angulation

Overlapped contacts

The central ray was not directed through interproximal spaces

overlapped contacts

foreshortening

Short teeth with blunted roots

Excessive vertical angulation

foreshortening

elongation

Long, distorted teeth

The vertical angulation was insufficient.

elongation

cone cut

A clear/white area appears on the image

The PID was not directed to the center of the receptor

cone cut

receptor too posterior

Distal surfaces of the canines are not visible on the pre-molar bitewing image

receptor too anterior

Third molar regions are not visible on molar bitweing image

film bending

Images appear stretched and distorted

Check film placement before exposure

film creasing

A thin radiolucent line appears on the image

film bending

film creasing

phalangioma

The patient’s finger was positioned in front of the receptor

phalangioma

failure to remove partial

Any removable appliance must be removed from the patient’s mouth prior to exposure of radiographs

failure to remove partial

thyroid collar

double exposure

The receptor was exposed twice in the patient’s mouth

double exposure

reversed film

Light images with a herringbone pattern appear on the radiograph

reversed film