self-study-x-rayfilm-screens

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The following slides describe the composition and uses of intraoral and extraoral films and intensifying screens.

Films and Screens

Intraoral Film

Intraoral film is used for (1) bitewing films (named for the tab that sticks out from the side of the film which resembles a wing and on which the patient bites); this film shows the crowns of both maxillary and mandibular teeth on one film; (2) periapical films, which show the entire length of the teeth in either the maxillary or mandibular arch and (3) occlusal films, which are usually exposed at approximately right angles (perpendicular) to the occlusal plane and show broad areas of the teeth and bone.

Bitewing Film

The bitewing film is used to identify interproximal caries (where the teeth contact each other; black arrows) and the appearance of the alveolar bone (red arrows). The white areas on the film are amalgam restorations.

Periapical Film

Periapical means “around the apex”. This film is intended to show the area around the root of the tooth. Normally, the entire tooth is seen, allowing the identification of root problems, interproximal caries, and the condition of the bone surrounding the teeth. This film is also used in endodontic treatment of a tooth.

periapical pathology

internalresorption

caries

Occlusal Film

The occlusal film is used to identify the extent of larger pathological conditions, to locate an object in the buccolingual direction, to show the developing dentition in children and to image patients with trismus (inability to open the mouth).

Anterior dentition - Child

Impacted maxillary canine

Extraoral Film

Extraoral films used in Dentistry include the Panoramic, Lateral oblique jaw film, Skull film, Cepahalometric and TMJ (temporomandibular joint). These will be discussed briefly in the following slides.

The panoramic film is the most common extraoral film used in dentistry. It does not provide the detail that intraoral films do but it gives an overall view of the entire dentition, both maxillary and mandibular. It is very helpful for third molar extractions

The lateral oblique jaw film can be used to image the third molar region in adults and to show the developing posterior dentition in children. It is only used if a panoramic x-ray machine is not available. The panoramic film is preferred.

Skull films, such as this PA (postero-anterior) view, are used to evaluate trauma and developmental problems. This patient had external fixation appliances placed to help expand the bone.

Cephalometric films, such as the lateral cephs above, are used to identify both the bone and the soft tissue outline on the same film. This film is used routinely by orthodontists in developing treatment plans for their patients. It is also used by oral surgeons for evaluating trauma and conditions requiring surgical correction.

Surgery patient- mandibular implantOrtho-surg. patient – jaw realignment

Temporomandibular joint (TMJ) films provide information on the components of this joint, including the head of the condyle, the glenoid fossa and the articular eminence.

Transcranial film Tomogram

Film Composition

An x-ray film is composed of a plastic (polyester) base covered on both sides with an emulsion; this is called a double-emulsion film. The emulsion contains silver halide crystals which are surrounded by gelatin. The silver halide crystals are affected by the x-rays and eventually form the image during film processing. The gelatin, similar to that used in desserts, is porous, allowing processing chemicals to reach the silver halide crystals, and is also clear, allowing light to readily pass through when viewing films.

(continued on next slide)

The emulsion (gray lines below) is attached to the base with a very thin layer of adhesive (green lines below). The base has a slight bluish tint which makes viewing the films easier on the eye. The emulsion is covered with a thin layer of gelatin, a “supercoat,” which helps to protect the film (yellow lines below).

Film Composition (continued)

blue-tinted base

supercoat emulsion with silver halide crystals and gelatin

Double emulsion(emusion on both sides)

adhesive

tabular globular

top view

side view

There are two types of silver halide crystals. Tabular (flat) crystals are used in F-speed (Insight) film and in T-Mat and Ektavision film. The crystals are placed in the emulsion so that the flat surface (top view below) is parallel with the surface of the film. Globular (rounded) crystals are used in D-speed (Ultraspeed) film; these crystals are like small pebbles.

Silver Halide Crystals

tabular

There are two types of film used in Dentistry. The first of these, Direct Exposure Film, is used intraorally. It is exposed when x-rays come in contact with it. The film is sealed in a light-tight packet because visible light, a type of electromagnetic radiation along with x-rays, will also expose the film. There are two types of direct exposure film: D-speed, also called Ultraspeed, and F-speed, which is called Insight.

Film Types

The other type of film is Screen Film. Screen films are used for extraoral radiographs. Screen film is made to be especially sensitive to the effects of light from an intensifying screen. When these screens, on either side of the film in a cassette, are exposed to x-rays, they emit light which in turn exposes the film. (The x-rays contribute a very small percentage of the actual exposure of the film). Using the screen-film combination allows a very large reduction in the amount of radiation needed to expose the film (30-60 times less radiation than that required by direct exposure film).

Film Types (continued)

Intensifying Screen Function

One of the properties of x-rays is that they cause certain materials to fluoresce (emit light); the phosphor crystals found in intensifying screens are one of these materials. The light emission is usually green or blue, depending on the type of phosphor crystal used. The composition of the films used with these screens is adjusted by the manufacturer to be sensitive to either blue light or green light. It is important to make sure that the correct film is used with whichever type screen is selected. (Blue-sensitive film with blue light-emitting screen, etc.)

Intensifying Screen Composition

The base of the screen (yellow line above) is made of plastic and provides support. A reflecting layer (silver line) reflects light emitted by the phosphor back toward the film. The phosphor layer (green line) contains the phosphor crystals that emit the light. The surface of the phosphor layer is covered with a protecting coat (white line) , which is a thin layer of plastic that protects the phosphor layer from damage when the screens are handled.

(this side toward film)

= phosphor crystal

The most common type of phosphors being used are the rare earth phosphors, which emit blue or green light depending on the type of rare earth material being used. (Click to show interaction of x-rays with phosphor crystals)

film

Rare Earth Phosphor

Intensifying Screen Speed

The speed of the screen depends on crystal size and the thickness of the phosphor layer (larger crystals and thicker layer increase speed). Image quality decreases as the screen speed increases. The three speeds are:

• Fast (Rapid): requires the least exposure but the images are less sharp

• Medium (Par): medium speed, medium sharpness

• Detail (Slow): produces the sharpest images but requires the most exposure

Rigid metal cassette

Flexible vinyl cassette

CassetteA cassette holds two intensifying screens (one on each side) in tight contact with the film. The cassette is either rigid (metal) or soft (vinyl), depending on the type of panoramic machine. The rigid cassette has a layer of foam padding under each screen to assure tight contact with the film. (See next slide)

foam (rigid cassettes)

cassette front

screen supportphosphor/coating

filmphosphor/coating

screen support

foam (rigid cassettes)

cassette back

x-rays

Cassette/Screens/Film

The surface of the screens must be kept very clean. Any debris in the cassette (between the screen and film) will result in a white spot on the film (red arrow). The other white spots (green arrows) represent tonsillar calcifications.

The two types of screen film used with rare earth screens are T-Mat and Ektavision. These films are available in three styles: G, which is used to provide the best contrast; L, which has the widest latitude (long-scale contrast) and is good for soft tissue visualization and H, which is used to provide an extra film for referral purposes (two films are placed in the cassette at the same time).

The advantage of Ektavision film over T-Mat film is that it has anti-crossover layers incorporated into the film. This prevents light from one screen affecting both emulsion layers; this produces a sharper image on the film. (See following slides).

Screen Film (continued)

T-Mat (crossover)

film

Light produced by the phosphor crystal spreads out as it goes toward the film and with T-Mat film it affects the emulsion on both sides. Since it has spread out more when it reaches the emulsion on the opposite side of the film (crossover), the sharpness (edge detail) of the image is decreased.

Ektavision (anti-crossover)

film

Ektavision film has a crossover control layer on each side of the film base. These layers allow the light from a phosphor crystal to reach the emulsion on the same side as the crystal but prevent the light from reaching the emulsion on the opposite side of the film. X-rays easily pass through this anticrossover layer.

Film Sizes (Intraoral)

# 0: Used in children for both periapical (PA) and bitewing (BW) films; used for small mouths.

# 1: Used for adult anterior periapicals with the paralleling technique.

# 2: Used for adult posterior periapicals and bitewings and for children with larger mouths; also used in anterior region of adults for periapical films taken with bisecting-angle technique; may also be used for occlusal films in children.

# 3: Used for extra-long bitewing films; one film covers all teeth on one side of the mouth.

# 4: Used for occlusal films (primarily adults).(See next slide for comparative sizes)

#2 #3

#1

#0

#4

Adult PA, BW

Child occlusal

Adult ant. PA

Child PA, BW

Extra-long BW

Occlusal in adults

Film Sizes (Extraoral)

5” x 12” and 6” x 12”: Both of these films are used in panoramic radiography. Some machines use 5” x 12” and others use 6” x 12”.

8” x 10”: This size is used for cephalometric films, skull films and tomograms (TMJ).

5” x 7”: This size is not often used. It may be used for lateral oblique jaw films or for transcranial films (used for TMJ views).

Film Speed

The speed of a film represents the amount of radiation required to produce a radiograph of acceptable density. (Density is the degree of darkening of the film; the middle film below has acceptable density. The one on the left is too light and the one on the right is too dark). As the speed of the film increases, the amount of radiation needed to properly expose it decreases.

Intraoral Film Speed

D-speed (Ultraspeed): Once the most common intraoral film speed used, it is now gradually being replaced by F-speed film. Technically, this slower film produces sharper images, improving the diagnostic ability of the film. It has globular crystals.

F-speed (Insight): this film has larger silver halide crystals; they are flat tabular crystals. Because of the larger size, less radiation is needed to expose these crystals, resulting in a 60 % reduction in patient exposure when compared to D-speed film.

Extraoral Film Speed

The speed of extraoral film is increased with an increase in the size of the silver halide crystals. In general, the faster the film, the less sharp the radiographic image will be.

Extraoral film is always used with intensifying screens. Like films, screens have different speeds.

The overall speed of an extraoral film system (film plus screen) is determined by the combined speeds of the film and the screen.

front back

Clinasept Barrier PacketsClinasept barriers are sealed plastic covers that protect intraoral film packets from saliva contamination. After exposing the film, the barrier is opened at the notch (see below) and dropped into a bag without touching the film (see next slide).

notch

Removing the clinasept barrier from the film packet and dropping it into the film bag. The film packet must not be touched with the gloves that have been in the patient’s mouth. This helps to assure that the film packet is not contaminated when it is taken to the darkroom for processing.

D-speed(Ultraspeed)

F-speed(Insight)

#2

dot

plastic

paper

# of filmsin packet#2 #1

tab

The x-ray film packet is made of plastic or paper, depending on film size. The cover protects the film from light and moisture. The back side identifies the type of film (by color), the number of films in the packet (also by color), and the location of the identifying dot used for film mounting.

plastic

Film Packet

Black paper: surrounds film;protects emulsion.

Film: one or two films;raised dot in one corner used for film orientation.

Lead foil: protects film from backscatter (see next slide); reduces patient exposure; strengthens packet; pattern on foil identifies when film is placed backwards (back of film faces teeth).

Contents of Film Packet

Scatter (secondary) radiation is produced when the primary x-rays from the x-ray tube interact with the patient’s hard and soft tissues. Backscatter radiation refers to those scattered x-rays that go “back” toward the film.

Primary x-rays

Scatter (secondary) x-rays

Film Storage

• Films should be stored at 50–70 degrees F. Storage at high temperatures may result in film fogging.

• Opened boxes of screen (extraoral) film need to be kept in light-tight area (darkroom); need to be cool.

• Use film before expiration date to avoid film fogging.

• Do not store film in room where radiographs are taken

This concludes the section on Films and Screens. If you have any questions, you may e-mail me at [email protected].