THE DENTAL X-RAY MACHINE: COMPONENTS AND FUNCTIONS Chapter 3.

THE DENTAL X-RAY MACHINE: COMPONENTS AND FUNCTIONS

Chapter 3

Copyright ©2012 by Pearson Education, Inc.All rights reserved.

Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth EditionEvelyn M. Thomson • Orlen N. Johnson

Objectives

Define the key words. Identify the three major components of a

dental x-ray machine. Identify and explain the function of the

five controls on the control panel. State the three conditions necessary for

the production of x-rays. Draw and label a dental x-ray tube.



Objectives

Identify the parts of the cathode and explain its function in the production of x-rays.

Identify the parts of an anode and explain its function in the production of x-rays.



Objectives

Trace the production of x-rays from the time the exposure button is activated until x-rays are released from the tube.

Demonstrate, in sequence, the steps in operating the dental x-ray machine.



Introduction

The role of exposing dental radiographs is an important one for the dental assistant and dental hygienist, making it essential that these professionals possess an understanding of how the x-ray machine works to produce ionizing radiation.



Introduction

To operate dental x-ray equipment safely and competently, the radiographer needs to develop a base knowledge of the components of the dental x-ray machine and possess an understanding of how these components work together to produce ionizing radiation.



Evolution of the DentalX-ray Machine 1913: Coolidge hot cathode vacuum

tube, invented by Dr. W. D. Coolidge Mid-1950s: Variable kilovoltage

machines were introduced 1966: Recessed PID was introduced



Evolution of the DentalX-ray Machine 1974: Federal government began

regulating the manufacture and installation of all dental x-ray machines

Today: Dental x-ray machines are safe,compact, easy to position, and simple to operate



Figure 3-1 Comparison of conventional and recessed tube position within the tube head. (A) Conventional position with tube in front of tube head. Note how quickly the x-ray beam pattern flares out. (B) With a recessed tube a relatively more parallel x-ray beam is produced. This will produce a sharper radiographic image.



Figure 3-2 Typical wall-mounted dental x-ray machine.(Image courtesy of Progeny, A Midmark Company)



Dental X-ray Machine Components Typical dental x-ray machine parts:

Control panel with regulating devices Extension arm or bracket enabling tube

head to be positioned Tube head containing x-ray tube from

which x-rays are generated

Dental X-ray Machine Components




Control panel: may be integrated with the extension arm and tube head for ease of access during exposures or it may be remote from the unit.

Increasingly, dental x-ray machines, come with pre-set controls by the manufacturer.



Figure 3-3 Control panel integrated with tube head support. (Image courtesy of Gendex Dental Corporation)



Figure 3-4 Control panel mounted in protected area.



Figure 3-5 Control panel of a dental x-ray machine that allows for manual adjustment of exposure variables. (1) Exposure button holder, (2) main ON/OFF switch, (3) mA control, (4) x-ray tube selector (this master control accommodates three remote tube heads), (5) power ON light, (6) x-ray emission indicator light, (7) timer control, (8) kVp meter, (9) kVp control. This control panel allows the operator to choose settings of 50 kVp to 90 kVp at 15 mA, and 50 kVp to 100 kVp at 10 mA.




Five major controls: Line switch Milliampere (mA) selector Kilovolt peak (kVp) selector Timer Exposure button

Dental x-ray machines are required to be equipped with a “dead-man” exposure switch.



Figure 3-6 Operator setting the exposure time. The display indicates 16 impulses. Note the preset milliamperage and kilovoltage values.



Figure 3-7 Exposure button on the handle of the timer cord. Operator is exposing a panoramic radiograph from behind a lead-lined glass window.



Electricity

Direct current (DC) flows continuously in one direction

Alternating current (AC) changes its direction of flow 60 times per second

Electrical circuit is the path that electricity flows.



Electricity

Transformer is an electromagnetic device for changing the current coming into the dental x-ray machine (step up and step down)

Autotransformer: a voltage compensator that corrects minor fluctuations in the current flowing through the wires.

Amperage measures number of electrons that move through a conductor



Electricity

Voltage or volt (V) electrical pressure between two electrical charges

Kilovolt (kV) 1,000 V Polychromatic beam x-rays of many

different energies Kilovolt peak (kVp) highest voltage to

which the current in the tube rises during an exposure



The X-ray Tube

Three conditions must exist for x-rays to be produced: A source of free electrons High voltage to impart speed to the

electrons A target that is capable of stopping the

electrons



The X-ray Tube

Anode Cathode Thermionic emission Incandescence



Figure 3-9 Sine wave of 60-cycle alternating current operating at 90,000 V (90 kVp). Ordinary household electric current is called 60-cycle alternating current because the current changes its direction of flow 60 times a second. During the time that the x-ray tube is producing x-rays, the cathode and the anode each change from negative to positive 60 times per second. The crest of the wave represents the maximum voltage when the current is moving in one direction, while the trough of the wave represents the maximum voltage when the current is moving in the other direction. The total cycle takes place in 1/60 sec. This alternation in current direction occurs every 1/120 sec (twice during each full cycle) on x-ray machines of conventional design. It produces the x-rays in a series of bursts, or impulses, rather than in a continuous flow.



The X-ray Tube

Cathode (negative electrode) Tungsten wire/filament Focusing cup

Anode (positive electrode) Target Copper stem/radiator

Focal spot



Figure 3-10 Photograph of a dental x-ray tube.



Figure 3-11 Cross section of a filament wire. The filament wire in the cathode is heated to incandescence. The attached electrons are literally boiled out of the wire and become available as a source of free electrons, thus fulfilling the first requirement for x-ray production. The milliamperage setting determines the number of electrons available to be accelerated across to the target of the anode.



Electrical Circuits

Filament circuit provides low voltage (3–8 V) to the filament of the x-ray tube to provide the source of electrons needed for the production of x-rays

High-voltage circuit provides the high voltage (65–100 kilovolts) necessary to accelerate the electrons from the cathode filament to the anode target



Transformers

Step-down transformer Step-up transformer Autotransformer



Operation of the Dental X-ray Machine Assumptions

The radiographer is competent and can follow radiation safety protocol.

The radiographer performs all radiographic procedures in accordance with federal, state, and local regulations and recommendations.

Infection control is maintained throughout the procedure.



Operation of the Dental X-ray Machine Assumptions

The procedure has been explained and the patient has given consent.

The patient has received verbal instructions and is able to cooperate with the procedure.

Image receptor holding devices are utilized for all intra-oral radiographs.



Review: Chapter Summary

All x-ray machines operate similarly and have the same components.

The control panel may be integrated with the x-ray machine tube head support, or it may be remote from the unit, mounted on a shelf or wall

There are five major controls that may be operated or will be pre-set on most dental

x-ray machines.




Three conditions must exist to produce x-rays.

Electric current flows into the x-ray machine and proceeds either through the step-down transformer or the step-up transformer.




The beam of radiation that exits the port seal of the tube head is the primary or useful beam. The polychromatic beam must be filtered to allow only x-rays with sufficient energy to reach the oral structures.




The radiographer must be familiar with the operation of the machine and the patient must understand the procedure and provide consent.



Recall: Study Questions

General Chapter Review



Reflect: Case Study

• To help you understand the practical use of altering exposure variables on a dental x-ray machine, consider the following patients with these characteristics:

1.A 9-year-old female, height 4’ 8” and weight 85 pounds, who has been assessed for bitewing radiographs to determine the evidence of caries.



Reflect: Case Study

2. A 21-year-old male college football player, height 6’ 1”, 280 pounds, who has been assessed for periapical radiographs of suspected impacted third molars.

3. A 58-year-old female, diagnosed with Bell’s palsy with slight head and neck tremors, who has been assessed for a full mouth series for the evaluation of periodontal disease.



Reflect: Case Study

Would you select an increased or decreased amount of radiation to produce diagnostic quality radiographic images for each of these patients?

Which of these three exposure variables — milliamperage, kilovoltage, or time — control(s) the amount of radiation produced?



Reflect: Case Study

Which exposure variable would be the best choice to alter to increase or decrease the amount of radiation produced for each of these patients?

Would you select an increased or decreased penetrating ability of the x-ray beam to produce diagnostic quality radiographic images for each of these patients?



Reflect: Case Study

Which of the three exposure variables —milliamperage, kilovoltage, or time —control(s) the penetrating ability of the x-ray beam?

Which exposure variable would be the best choice to alter to increase or decrease the penetrating ability of the x-ray beam?



Reflect: Case Study

Suppose that you wanted to decrease the amount of time of the exposure, as may be needed when patient movement is anticipated, (as in the case of patient 3) but still wanted to produce enough radiation to achieve a diagnostic quality radiographic image.



Reflect: Case Study

Which variable — milliamperage or kilovoltage — would you adjust? Would you increase or decrease this variable



Reflect: Case Study

Think of other characteristics patients may present with that would require you to adjust these x-ray machine variables. Keep in mind that increasing one factor may necessitate decreasing an opposing factor. Discuss the rationale for your choices.



Relate: Laboratory Application

Proceed to Chapter 3, Laboratory Application, to complete this activity.

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THE DENTAL X-RAY MACHINE: COMPONENTS AND FUNCTIONS Chapter 3.

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