3.  X-ray films and accessories

Q. 2. Packaging of intraoral periapical films.

Ans.

An intraoral film is a film that is placed inside the mouth during X-ray exposure and is used to examine the teeth and supporting structures.

Intraoral film packaging

Each intraoral film is packaged to protect it from light and moisture.

The film and its surrounding packaging are referred to as a film packet.

Intraoral X-ray film packets have four basic components:

i. The X-ray film

ii. Paper film wrapper

iii. Lead foil sheet

iv. Outer film wrapping.

i. X-ray film

The intraoral X-ray film is a double-emulsion film. Double-emulsion film is used instead of single-emulsion film because it requires less radiation exposure to produce an image.

A film packet may contain one film (one-film packet) or two films (two-film packet).

A two-film packet produces two identical radiographs with the same amount of exposure necessary to produce a single radiograph. This is used when a duplicate record of a radiograph is needed either for insurance claims or patient referrals.

A small, raised dot known as the identification dot is located in one corner of the intraoral X-ray film. This raised dot is used to distinguish between the left and right sides of the patient after the film is processed; hence, it is significant in film orientation, mounting and interpretation.

ii. Paper film wrapper

The paper film wrapper within the film packet is a protective sheet of black paper that covers the film.

It also shields the film from light leak.

iii. Lead foil sheet

The lead foil sheet is a single thin piece of lead foil within the film packet that is located behind the film wrapped in black protective paper.

The thin lead foil sheet is positioned behind the film; it absorbs most of the X-rays that passes through the film and prevents them from reaching the tongue and other oral tissues. It also shields the film from back scattered or secondary radiation, which results in film fog.

It also gives sufficient strength to the whole film packet.

If the film packet is inadvertently positioned reverse in the mouth, then the shadow of the foil is seen on radiograph as ‘tyre track’ marks or ‘Herring bone’ appearance, which is the embossed pattern placed on the lead foil by the manufacturer.

iv. Outer Package Wrapping

The outer package wrapping is a soft-vinyl or a paper wrapper that hermetically seals the film packet, protective black paper and lead foil sheet.

This outer wrapper serves to protect the film from exposure to light and saliva.

The outer wrapper of the film packet has two sides:

a. Tube side

b. Label side.

a. Tube side:

The tube side is solid white and has a raised bump in one corner that corresponds to the identification dot on the X-ray film.

When placed in the mouth, the white colour side of the film packet must face the teeth and the tube head.

b. Label side:

The label side of the film packet has a flap used to open the film packet.

This side is colour-coded to identify films outside of the plastic packaging container. Colour codes are used to distinguish between one-film and two-film packets and between film speeds.

When placed in the mouth, the colour-coded side (label side) of the packet must face the tongue.

The following information is printed on the label side of the film packet:

A circle or dot that corresponds with the raised identification dot on the film

The statement “opposite side toward tube”

The manufacturer’s name

The film speed

The number of films enclosed

In dentistry, the terms ‘film packet’ and ‘film’ are often used interchangeably. Intraoral film packets are typically available in quantities of 25, 100 or 150 films per container.

Film packets are packaged in convenient plastic trays or cardboard boxes that can be recycled.

Boxes of intraoral film are labelled with the type of film, film speed, film size, number of films per individual packet, total number of films enclosed, and the film expiry date.

Short essays

Q. 1. Radiographic film composition (or) Dental X-ray film.

Ans.

The dental X-ray film serves as a recording medium or image receptor. A latent image is recorded in the X-ray film when it is exposed to information carrying X-ray photons.

Composition of the radiographic film

The X-ray film used in dentistry has four basic components:

i. Film base

ii. Adhesive layer

iii. Film emulsion

iv. Protective layer.

i. Film base

The film base is a flexible piece of polyester plastic (polyethylene terephthalate) 0.2 mm in thickness. It is transparent and exhibits a slight blue tint that is used to emphasise contrast and enhance image quality. Its primary purpose is to provide a stable support for the delicate emulsion.

ii. Adhesive layer

The adhesive layer is a subcoating consisting of a thin layer of adhesive material, which serves to attach the emulsion to the base.

iii. Film emulsion

The film emulsion is a coating on both sides of the film base to give the film greater sensitivity to X-ray radiation.

The emulsion is a homogenous mixture having two principal components: the silver halide crystals and gelatin matrix.

iv. Protective layer

The protective layer is a thin, nonabrasive, transparent super coat placed over the emulsion. It protects the emulsion surface from manipulation as well as mechanical damage.


Q. 2. Intensifying screens.

Ans.

An intensifying screen is a device that transfers X-ray energy into visible light, which in turn exposes the screen film.

As they intensify, the effect of X-rays on the film and the use of intensifying screens reduce the radiation required to expose a screen film, thereby reducing the patient’s exposure to radiation.

In extraoral radiography, a screen film is sandwiched between two intensifying screens of matching size and is secured in a cassette.

An intensifying screen is a smooth plastic sheet coated with minute fluorescent crystals known as phosphors. When exposed to X-rays, the phosphors fluoresce and emit visible light in the blue or green spectrum; the emitted light then exposes the film.

Conventional calcium tungstate screens have phosphors that emit blue light. The newer rare earth screens have phosphors that are not commonly found in the earth and emit green light.

Rare earth intensifying screens are more efficient than calcium tungstate intensifying screens at converting X-rays into light. As a result, rare earth screens require less X-ray exposure than calcium tungstate screens and are considered to be faster.

The use of rare earth screens means less exposure to X-ray radiation for the patient. Rare earth intensifying screens (Kodak Lanex Regular and Medium screens) are designed for use with green-sensitive films (Kodak Ortho and T-Mat films); whereas, conventional screens (Kodak X-somatic Regular screens) are used with blue-sensitive films (Kodak X-Omat and Ektamat films).


Q. 3. Grid functions and grids in radiography.

Ans.

Grid is a radiographic accessory, which helps in reducing the scattered radiation when placed between the patient and the film, as close as possible to the latter.

It helps to reduce the film fog and improves the contrast.

The grid is made up of alternate layers of radiolucent, i.e. plastics and radiopaque, such as lead, which are aligned in the direction of the primary beam either parallel to each other or at an angle/focused. In general, grid has 80 line pairs per inch.

Grid ratio – the ratio of the thickness of the grid to the distance between the spacer is termed as the grid ratio.

The moving grid is normally used to get rid of the radiopaque fine lines that may appear on the radiograph. It is also termed as the Potter–Bucky diaphragm.

Most of the extraoral radiographic projections of the skull-like PNS views, Caldwell view, submentovertex view are best visualised using grids with screen films.

Various types of grids are classified as follows:

A. Stationary grids

B. Moving grids.

They may also be classified as:

A. Focused grids

B. Nonfocused grids.

a. Stationary grids

i. Linear grid

In the linear grid, the strips of lead are placed parallel to each other.

While using the linear grid, cut-off of the beam can occur as some of the primary beam may get absorbed by the lead in the peripheral region. If the grid is not perpendicular to the central axis of the beam, this can also take place in the centre of the film.

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Apr 11, 2016 | Posted by in Orthodontics | Comments Off on 3.  X-ray films and accessories
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