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DENTAL RADIOGRAPHY

KAMARUL AMIN BIN ABDULLAH @ ABU BAKAR

Components of the Dental X-Ray Machine

• Dental x-ray machines may vary somewhat in size and appearance, but all machines will have three primary components:

– The tubehead

– An extension arm

– The control panel

Copyright © 2009, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Fig. 38-8 Dental x-ray machine and arm. A, Tubehead. B, Position-indicator device (PID).

C, Extension arm.


The Tubehead

• The x-ray tubehead is tightly sealed; heavy metal housing contains the x-ray tube that produces dental x-rays.


Fig. 38-9 Diagram of the dental x-ray tubehead. (From Haring J, Jansen L: Dental radiography: principles and techniques, ed 2, Philadelphia, 2000, Saunders.)


Fig. 38-10 X-ray tube. (Courtesy of Xintek Inc.)


Components of the Tubehead

• The metal body of the tubehead that houses the x-ray tube is called the metal housing. It is filled with insulating oil.

• Insulating oil surrounds the x-ray tube and prevents overheating by absorbing the heat created in the production of x-rays.

• Tubehead seal is made of leaded glass or aluminum. It seals the oil in the tubehead.

• The x-ray tube is the heart of the x-ray–generating unit.

(Cont’d)


Components of the Tubehead

(Cont’d)

• The transformer alters the voltage of incoming electric current.

• The aluminum filter is aluminum sheets 0.5 mm thick.

• The lead collimator is a metal disc with a small opening in the center to control the size and shape of the x-ray beam as it leaves the tubehead.

• The PID is the open-ended, lead-lined cylinder that extends from the opening of the metal housing of the tubehead. It is

used to aim the x-ray beam.


The X-Ray Tube

• The vacuum environment allows the electrons to flow with minimum resistance between the electrodes:

– Cathode

– Anode


The Cathode

• The cathode consists of a tungsten filament in a focusing cup made of molybdenum.

• The purpose of the cathode is to supply the electrons necessary to generate x-rays.

• Electrons are generated in the x-ray tube at the cathode.

• The hotter the filament becomes, the more electrons are produced.


The Anode

• The anode is the target for the electrons.

• It is composed of a tungsten target (a small block of tungsten) that is embedded in the larger copper stem.

• The copper around the target conducts heat away from the target, reducing wear and tear on the target.

• The purpose of the tungsten target is to serve as a focal spot and convert the bombarding electrons into x-ray photons.

• The x-rays at the center of this beam are known as the central

ray.


Fig. 38-16 The production of dental x-rays occurs in the x-ray tube.

(From Haring J, Jansen L: Dental radiography: principles and techniques, ed 2, Philadelphia, 2000, Saunders.)


The PID

• The open end of the lead-lined PID is placed against the patient’s face during film exposure.

• The PID may be cylindrical or rectangular. The rectangular PID limits the size of the beam to that of a dental film.

• PIDs used in dentistry are usually 8, 12, or 16 inches long.

• The choice of length is determined by the radiographic technique being used.

• The long (12- to 16-inch) PID is more effective in reducing exposure to the patient than a short (8-inch) PID because

there is less divergence (separation) of the beam.


The Extension Arm

• The extension arm encloses the wire between the tubehead and the control panel.

• It also has an important function in positioning the tubehead.

• The extension arm folds up and can be swiveled from side to side.

• If the extension arm is left in an extended position when the machine is not in use, the weight of the tubehead can cause it to become loose, and the tubehead will drift (slip out of position) after it is positioned for an exposure.


The Control Panel

• The control panel of an x-ray unit contains:– The master switch

– Indicator light

– Exposure button

– Indicator light

– Control devices (time, milliamperage [mA] selector, and kilovoltage [kVp] selector)

• A single centrally located control panel may be used to operate several tubeheads located in separate treatment rooms.


End of Chapter

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