Foundations of Radiography, Radiographic Equipment, and Radiologic Safety Chapter 38 Copyright © 2009, 2006 by Saunders, an imprint of Elsevier Inc. All

Foundations of Radiography, Foundations of Radiography, Radiographic Equipment, Radiographic Equipment,

and Radiologic Safetyand Radiologic Safety

Chapter 38Chapter 38

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


Lesson 38.1Lesson 38.1


Learning Objectives Learning Objectives

Pronounce, define, and spell the Key Terms.Pronounce, define, and spell the Key Terms. Describe the uses of dental radiographs.Describe the uses of dental radiographs. Describe the discovery of x-radiation.Describe the discovery of x-radiation. Name the highlights in the history of dental Name the highlights in the history of dental

radiography.radiography. Explain what happens during ionization.Explain what happens during ionization.


Introduction Introduction

The dental assistant must have a thorough The dental assistant must have a thorough knowledge and understanding of the knowledge and understanding of the importance and uses of dental radiographs. importance and uses of dental radiographs.

The dental assistant must understand the The dental assistant must understand the fundamental concepts of atomic and fundamental concepts of atomic and molecular structure and have a working molecular structure and have a working knowledge of ionizing radiation and the knowledge of ionizing radiation and the properties of x-rays. properties of x-rays.

(Cont’d)(Cont’d)


IntroductionIntroduction


Radiation used to produce dental radiographs Radiation used to produce dental radiographs has the capacity to cause damage to all types of has the capacity to cause damage to all types of living tissues. living tissues.

Any exposure to radiation, no matter how small, Any exposure to radiation, no matter how small, has the potential to cause biologic changes to has the potential to cause biologic changes to the operator and the patient. the operator and the patient.

The dental assistant must have a thorough The dental assistant must have a thorough understanding of the characteristics of radiation understanding of the characteristics of radiation to minimize radiation exposure to both the dental to minimize radiation exposure to both the dental patient and the operator. patient and the operator.


Discovery of RadiationDiscovery of Radiation

Wilhelm Conrad Roentgen (pronounced rent-Wilhelm Conrad Roentgen (pronounced rent-ken), a Bavarian physicist, discovered the x-ray ken), a Bavarian physicist, discovered the x-ray on November 8, 1895.on November 8, 1895.

For many years x-rays were referred to as For many years x-rays were referred to as roentgen rays, radiology was referred to as roentgen rays, radiology was referred to as roentgenology, and radiographs were known roentgenology, and radiographs were known as roentgenographs.as roentgenographs.

During his lifetime, Roentgen was awarded During his lifetime, Roentgen was awarded many honors and distinctions, including the first many honors and distinctions, including the first Nobel Prize ever awarded in physics, in 1901. Nobel Prize ever awarded in physics, in 1901.


Fig. 38-1 A, Wilhelm Conrad Roentgen (1845–1923), discoverer Fig. 38-1 A, Wilhelm Conrad Roentgen (1845–1923), discoverer of x-rays.of x-rays.

(From Frommer HH, Stabulas-Savage J: (From Frommer HH, Stabulas-Savage J: Radiology for the dental professionalRadiology for the dental professional, ed 8, St Louis, 2005, Mosby.), ed 8, St Louis, 2005, Mosby.)


Fig. 38-1 B, Crookes tube, which Roentgen worked with Fig. 38-1 B, Crookes tube, which Roentgen worked with at the time of the discovery of x-rays in 1895.at the time of the discovery of x-rays in 1895.

(From Frommer HH, Stabulas-Savage J: (From Frommer HH, Stabulas-Savage J: Radiology for the dental professionalRadiology for the dental professional, ed 8, St Louis, 2005, Mosby.), ed 8, St Louis, 2005, Mosby.)


Pioneers in Dental Radiography Pioneers in Dental Radiography

Otto Walkoff made the first dental radiograph.Otto Walkoff made the first dental radiograph. Dr. C. Edmund Kells, a New Orleans dentist, Dr. C. Edmund Kells, a New Orleans dentist,

is credited with the first practical use of is credited with the first practical use of radiographs in dentistry, in 1896.radiographs in dentistry, in 1896.

Dental radiography has progressed from Dental radiography has progressed from these early discoveries to the science it is these early discoveries to the science it is today.today.

New technology continues to improve our New technology continues to improve our diagnostic abilities.diagnostic abilities.


Radiation PhysicsRadiation Physics

All things in this world are composed of All things in this world are composed of energy and matter.energy and matter.

Energy is defined as the capacity to do work.Energy is defined as the capacity to do work. Matter is anything that occupies space and Matter is anything that occupies space and

has form or shape.has form or shape.


Energy Energy

Although energy can neither be created nor Although energy can neither be created nor destroyed, it can change form. destroyed, it can change form.

Atoms contain energy.Atoms contain energy. The energy that holds the nucleus together is The energy that holds the nucleus together is

called nuclear-binding energy.called nuclear-binding energy. The energy holding electrons, negatively The energy holding electrons, negatively

charged particles, in their shells is known as charged particles, in their shells is known as electron-binding energy. electron-binding energy.


MatterMatter

Matter has many forms, including solids, Matter has many forms, including solids, liquids, and gases. liquids, and gases.

Matter is composed of atoms grouped Matter is composed of atoms grouped together in specific arrangements called together in specific arrangements called molecules.molecules.

A molecule is the smallest particle of A molecule is the smallest particle of substance that retains the property of the substance that retains the property of the original substance. original substance.

The fundamental unit of matter for discussion The fundamental unit of matter for discussion in this chapter is the atom. in this chapter is the atom.


Atomic StructureAtomic Structure

The atom consists of two parts:The atom consists of two parts: Central nucleusCentral nucleus Orbiting electronsOrbiting electrons

An atom is identified by the composition of its An atom is identified by the composition of its nucleus and the arrangement of its orbiting nucleus and the arrangement of its orbiting electrons; at present, 105 different atoms are electrons; at present, 105 different atoms are known to exist.known to exist.



Atomic Structure Atomic Structure


The arrangement within the atom is similar to The arrangement within the atom is similar to that of the solar system. that of the solar system.

The atom has a nucleus as its center or sun, The atom has a nucleus as its center or sun, and the electrons revolve (orbit) around it like and the electrons revolve (orbit) around it like planets. planets.

The electrons remain stable in their orbit The electrons remain stable in their orbit unless disturbed or moved. Orbiting electrons unless disturbed or moved. Orbiting electrons can be disturbed by x-rays. can be disturbed by x-rays.


Fig. 38-3 Diagrammatic representation of an oxygen atom.Fig. 38-3 Diagrammatic representation of an oxygen atom.


NucleusNucleus

The nucleus, or dense core, of the atom is The nucleus, or dense core, of the atom is composed of particles known as protons and composed of particles known as protons and neutrons.neutrons.

Protons carry positive electrical charges; neutrons Protons carry positive electrical charges; neutrons carry no electrical charge.carry no electrical charge.

Dental x-rays do not affect the tightly bound Dental x-rays do not affect the tightly bound nucleus of the atom and are only changed in nucleus of the atom and are only changed in direction or scattered. direction or scattered.

Dental x-rays cannot make atoms radioactive; Dental x-rays cannot make atoms radioactive; therefore patients do not give off x-rays after the x-therefore patients do not give off x-rays after the x-ray machine stops producing x-rays.ray machine stops producing x-rays.


ElectronsElectrons

Electrons are tiny negatively charged Electrons are tiny negatively charged particles with very little mass. particles with very little mass.

Electrons orbit around the nucleus of an Electrons orbit around the nucleus of an atom. atom.

The orbit path of an electron is called an The orbit path of an electron is called an electron shell. Each shell can contain only a electron shell. Each shell can contain only a specific number of electrons. specific number of electrons.

The electrons are maintained in orbit by The electrons are maintained in orbit by electron-binding energy, a force similar to the electron-binding energy, a force similar to the force of gravity on earth.force of gravity on earth.


IonizationIonization

The electrons remain stable in their orbits The electrons remain stable in their orbits around the nucleus until x-ray photons collide around the nucleus until x-ray photons collide with them. (A photon is a minute bundle of with them. (A photon is a minute bundle of pure energy that has no weight or mass.) pure energy that has no weight or mass.)

X-rays have enough energy to push an X-rays have enough energy to push an electron out of its orbit, producing an ion (an electron out of its orbit, producing an ion (an atoms that gains or lose an electron and atoms that gains or lose an electron and becomes electrically unbalanced) in a becomes electrically unbalanced) in a process called ionization.process called ionization.



IonizationIonization


Ionization is the process by which electrons are Ionization is the process by which electrons are removed from the orbital shells of electrically removed from the orbital shells of electrically stable atoms through collisions with x-ray stable atoms through collisions with x-ray photons. photons.

When an electron is removed from the atom, an When an electron is removed from the atom, an ion pair results. ion pair results.

The harmful ionizing effect of x-rays in The harmful ionizing effect of x-rays in human beings can result in a disruption of human beings can result in a disruption of cellular metabolism and can cause permanent cellular metabolism and can cause permanent damage to living cells and tissues. damage to living cells and tissues.


Fig. 38-4 A molecule of water (HFig. 38-4 A molecule of water (H22O) consists of two atoms O) consists of two atoms

of hydrogen connected to one atom of oxygen. of hydrogen connected to one atom of oxygen. (From Haring JI, Jansen L: (From Haring JI, Jansen L: Dental radiography: principles and techniquesDental radiography: principles and techniques, ed 2, Philadelphia, 2000, Saunders.), ed 2, Philadelphia, 2000, Saunders.)





Learning Objectives Learning Objectives

Describe the properties of x-radiation.Describe the properties of x-radiation. Label the parts of the dental x-ray tubehead Label the parts of the dental x-ray tubehead

and tube.and tube. Explain how radiographs are produced.Explain how radiographs are produced. Identify the range of kilovoltage and Identify the range of kilovoltage and

milliamperage required for dental milliamperage required for dental radiography.radiography.



Learning ObjectivesLearning Objectives


Describe the effect of the kilovoltage on the Describe the effect of the kilovoltage on the quality of the x-ray beam. quality of the x-ray beam.

Describe how the milliamperage affects the Describe how the milliamperage affects the quality of the x-ray beam.quality of the x-ray beam.


Properties of X-RaysProperties of X-Rays

The dental assistant must be familiar with the The dental assistant must be familiar with the unique characteristics of x-rays. unique characteristics of x-rays.

X-rays are a form of energy that can penetrate X-rays are a form of energy that can penetrate matter. Like visible light, radar, radio, and matter. Like visible light, radar, radio, and television waves, they belong to a group called television waves, they belong to a group called electromagnetic radiation.electromagnetic radiation.

Electromagnetic radiation is made up of Electromagnetic radiation is made up of photons that travel through space at the speed photons that travel through space at the speed of light in a straight line with a wavelike motion.of light in a straight line with a wavelike motion.



Fig. 38-6 Electromagnetic spectrum, showing the various Fig. 38-6 Electromagnetic spectrum, showing the various wavelengths of radiation typically used.wavelengths of radiation typically used.


Properties of X-RaysProperties of X-Rays


The shorter the wavelength, the greater its The shorter the wavelength, the greater its energy. energy.

The high energy of short wavelengths means The high energy of short wavelengths means that they can penetrate matter more easily that they can penetrate matter more easily than longer wavelengths can. than longer wavelengths can.

X-rays have unique properties that make X-rays have unique properties that make them especially useful in dentistry. them especially useful in dentistry.


A

B

Fig. 38-7 A, Wavelength is the distance between the crest (peak) of one wave and the crest of Fig. 38-7 A, Wavelength is the distance between the crest (peak) of one wave and the crest of the next. B, The shorter the wavelength, the greater the energy and penetration, the next. B, The shorter the wavelength, the greater the energy and penetration,

the longer the wavelength, the less energy and less penetration.the longer the wavelength, the less energy and less penetration. (From Haring J, Jansen L: (From Haring J, Jansen L: Dental radiography: principles and techniquesDental radiography: principles and techniques , ed 2, Philadelphia, 2000, Saunders.), ed 2, Philadelphia, 2000, Saunders.)


Components of the Components of the Dental X-Ray MachineDental X-Ray Machine

Dental x-ray machines may vary somewhat in Dental x-ray machines may vary somewhat in size and appearance, but all machines will size and appearance, but all machines will have three primary components:have three primary components: The tubeheadThe tubehead An extension arm An extension arm The control panelThe control panel


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

C, Extension arm.C, Extension arm.


The TubeheadThe Tubehead

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


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


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


Components of the TubeheadComponents of the Tubehead

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

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

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

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



Components of the Tubehead Components of the Tubehead


The transformer alters the voltage of incoming The transformer alters the voltage of incoming electric current. electric current.

The aluminum filter is aluminum sheets 0.5 mm thick. The aluminum filter is aluminum sheets 0.5 mm thick. The lead collimator is a metal disc with a small The lead collimator is a metal disc with a small

opening in the center to control the size and shape of opening in the center to control the size and shape of the x-ray beam as it leaves the tubehead. the x-ray beam as it leaves the tubehead.

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

tubehead. It is used to aim the x-ray beam.tubehead. It is used to aim the x-ray beam.


The X-Ray TubeThe X-Ray Tube

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


The CathodeThe Cathode

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

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

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

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


The AnodeThe Anode

The anode is the target for the electrons.The anode is the target for the electrons. It is composed of a tungsten target (a small block of It is composed of a tungsten target (a small block of

tungsten) that is embedded in the larger copper stem. tungsten) that is embedded in the larger copper stem. The copper around the target conducts heat away The copper around the target conducts heat away

from the target, reducing wear and tear on the target. from the target, reducing wear and tear on the target. The purpose of the tungsten target is to serve as a The purpose of the tungsten target is to serve as a

focal spot and convert the bombarding electrons into focal spot and convert the bombarding electrons into x-ray photons. x-ray photons.

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

the central ray.the central ray.


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

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


The PIDThe PID

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

The PID may be cylindrical or rectangular. The rectangular The PID may be cylindrical or rectangular. The rectangular PID limits the size of the beam to that of a dental film. 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.PIDs used in dentistry are usually 8, 12, or 16 inches long. The choice of length is determined by the radiographic The choice of length is determined by the radiographic

technique being used. technique being used. The long (12- to 16-inch) PID is more effective in reducing The long (12- to 16-inch) PID is more effective in reducing

exposure to the patient than a short (8-inch) PID because exposure to the patient than a short (8-inch) PID because

there is less divergence (separation) of the beam.there is less divergence (separation) of the beam.


The Extension ArmThe Extension Arm

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

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

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

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


The Control PanelThe Control Panel

The control panel of an x-ray unit contains:The control panel of an x-ray unit contains: The master switchThe master switch Indicator lightIndicator light Exposure button Exposure button Indicator lightIndicator light Control devices (time, milliamperage [mA] Control devices (time, milliamperage [mA]

selector, and kilovoltage [kVp] selector)selector, and kilovoltage [kVp] selector) A single centrally located control panel may A single centrally located control panel may

be used to operate several tubeheads located be used to operate several tubeheads located in separate treatment rooms. in separate treatment rooms.


How X-Rays Are ProducedHow X-Rays Are Produced

The x-ray machine is plugged into the wall outlet, and The x-ray machine is plugged into the wall outlet, and when the machine is turned on the electric current enters when the machine is turned on the electric current enters the control panel.the control panel.

The current travels from the control panel to the tubehead The current travels from the control panel to the tubehead through electrical wires in the extension arm.through electrical wires in the extension arm.

The current travels through the step-down transformer to The current travels through the step-down transformer to the filament of the cathode. the filament of the cathode.

The filament circuit uses 3 to 5 V to heat the tungsten The filament circuit uses 3 to 5 V to heat the tungsten filament in the cathode portion filament in the cathode portion of the x-ray tube. of the x-ray tube.

The heating of the filament results in thermionic emission. The heating of the filament results in thermionic emission. (Cont’d)(Cont’d)




When the exposure button is pushed, the high-When the exposure button is pushed, the high-voltage circuit is activated. voltage circuit is activated.

The electrons in the cloud are accelerated across the The electrons in the cloud are accelerated across the x-ray tube to the anode. x-ray tube to the anode.

The molybdenum cup in the cathode directs the The molybdenum cup in the cathode directs the electrons to the tungsten target in the anode. electrons to the tungsten target in the anode.

The electrons travel from the cathode to the anode.The electrons travel from the cathode to the anode. When the electrons strike the tungsten target, their When the electrons strike the tungsten target, their

energy of motion (kinetic energy) is converted to x-energy of motion (kinetic energy) is converted to x-ray energy and heat.ray energy and heat.





Less than 1% of the energy is converted to x-rays; the Less than 1% of the energy is converted to x-rays; the remaining 99% is lost as heat. remaining 99% is lost as heat.

The heat is carried away from the copper stem and The heat is carried away from the copper stem and absorbed by the insulating oil in the tubehead. absorbed by the insulating oil in the tubehead.

The x-rays travel through the unleaded glass window, The x-rays travel through the unleaded glass window, the tubehead seal, and the aluminum filter. the tubehead seal, and the aluminum filter.

The aluminum filter removes the longer-wavelength x-The aluminum filter removes the longer-wavelength x-rays. rays.

The x-ray beam travels through the collimator.The x-ray beam travels through the collimator. The x-ray beam then travels down the lead-lined PID The x-ray beam then travels down the lead-lined PID

and exits at the end of the PID. and exits at the end of the PID.


Types of RadiationTypes of Radiation

Primary radiation is the x-rays that come from Primary radiation is the x-rays that come from the target of the x-ray tube. the target of the x-ray tube.

Secondary radiation is x-radiation that is Secondary radiation is x-radiation that is created when the primary beam interacts with created when the primary beam interacts with matter.matter.

Scatter is a form of secondary radiation. It Scatter is a form of secondary radiation. It results when an x-ray beam has been results when an x-ray beam has been deflected from its path by interaction with deflected from its path by interaction with matter.matter.


Fig. 38-17 Types of radiation interaction with the patient. Fig. 38-17 Types of radiation interaction with the patient. 1, Primary. 2, Secondary. 3, Scatter.1, Primary. 2, Secondary. 3, Scatter.


Visual CharacteristicsVisual Characteristics

Three qualities are necessary for a good Three qualities are necessary for a good radiograph:radiograph: ContrastContrast DensityDensity Image detail Image detail

The dental assistant must understand how The dental assistant must understand how variations in the character of the x-ray beam variations in the character of the x-ray beam influence the quality of the resulting influence the quality of the resulting radiographs. radiographs.


Radiolucency and RadiopacityRadiolucency and Radiopacity

Radiolucent structures allow x-rays to pass through Radiolucent structures allow x-rays to pass through them. them.

Radiolucent structures appears dark or black on the Radiolucent structures appears dark or black on the radiograph. Air spaces, soft tissues of the body, and radiograph. Air spaces, soft tissues of the body, and the dental pulp appear as radiolucent images. the dental pulp appear as radiolucent images.

Radiopaque structures do not allow x-rays to pass Radiopaque structures do not allow x-rays to pass through them. through them.

Radiopaque structures appear white or light gray on Radiopaque structures appear white or light gray on the radiograph. Metal, enamel, and dense areas of the radiograph. Metal, enamel, and dense areas of bone appear as radiopaque images. bone appear as radiopaque images.


Fig. 38-18 Bite-wing radiograph showing a radiopaque (Fig. 38-18 Bite-wing radiograph showing a radiopaque (whitewhite, , aa) ) area of amalgam restoration and radiolucent (area of amalgam restoration and radiolucent (blackblack, , bb) area of ) area of

air and cheek tissue.air and cheek tissue.


ContrastContrast

The ideal contrast of a film clearly shows the The ideal contrast of a film clearly shows the radiopaque white of a metal restoration, the radiolucent radiopaque white of a metal restoration, the radiolucent black of air, and the many shades of gray between.black of air, and the many shades of gray between.

Higher kilovoltage produces more penetrating x-rays Higher kilovoltage produces more penetrating x-rays and lower radiographic contrast. and lower radiographic contrast.

A 90-kVp setting requires less exposure time and A 90-kVp setting requires less exposure time and produces a radiograph that has low contrast (more produces a radiograph that has low contrast (more shades of gray). shades of gray).

A 70-kVp setting requires a slightly longer exposure A 70-kVp setting requires a slightly longer exposure time and produces a radiograph with high contrast time and produces a radiograph with high contrast (fewer shades of gray). (fewer shades of gray).


Fig. 38-19 A, A radiograph produced with lower kilovoltage exhibits Fig. 38-19 A, A radiograph produced with lower kilovoltage exhibits high contrast. Many light and dark areas are seen. high contrast. Many light and dark areas are seen.


A


Fig. 38-19 B, A radiograph produced with higher kilovoltage exhibits low Fig. 38-19 B, A radiograph produced with higher kilovoltage exhibits low contrast. Many shades of gray are seen instead of black and white.contrast. Many shades of gray are seen instead of black and white.


B


DensityDensity

Density is the overall blackness or darkness Density is the overall blackness or darkness of a film. of a film.

A radiograph with the correct density enables A radiograph with the correct density enables the dentist to view black areas (air spaces), the dentist to view black areas (air spaces), white areas (enamel, dentin, and bone), and white areas (enamel, dentin, and bone), and gray areas (soft tissues). gray areas (soft tissues).

The degree of density is determined by the The degree of density is determined by the milliampere seconds (mAs).milliampere seconds (mAs).


Other Factors Influencing DensityOther Factors Influencing Density

The distance from the x-ray tube to the patient: If the The distance from the x-ray tube to the patient: If the operator lengthens the source-film distance without operator lengthens the source-film distance without changing the exposure settings, the resulting changing the exposure settings, the resulting radiographs will be light or less dense.radiographs will be light or less dense.

The developing time and temperature can affect the The developing time and temperature can affect the overall density. If the processing time is too long, the overall density. If the processing time is too long, the radiograph will appear dark.radiograph will appear dark.

The body size of the patient: A patient who is very The body size of the patient: A patient who is very small or thin requires less radiation than a husky, small or thin requires less radiation than a husky, heavy-boned person.heavy-boned person.


Geometric CharacteristicsGeometric Characteristics

Three geometric characteristics affect the Three geometric characteristics affect the quality of the radiograph:quality of the radiograph: SharpnessSharpness MagnificationMagnification DistortionDistortion


SharpnessSharpness

Sharpness refers to how well the radiograph Sharpness refers to how well the radiograph reproduces the fine details or distinct outlines reproduces the fine details or distinct outlines of an object. of an object.

Sharpness is sometimes referred to as detail, Sharpness is sometimes referred to as detail, resolution, or definition. resolution, or definition.

The sharpness of an image is influenced by The sharpness of an image is influenced by three :three : Focal-spot sizeFocal-spot size Film compositionFilm composition MovementMovement





Learning ObjectivesLearning Objectives

Discuss the effects of radiation exposure on the Discuss the effects of radiation exposure on the human body.human body.

Identify the critical organs that are sensitive to Identify the critical organs that are sensitive to radiation.radiation.

Discuss the risks and benefits of dental Discuss the risks and benefits of dental radiographs.radiographs.

Describe the methods of protecting the patient from Describe the methods of protecting the patient from excess radiation.excess radiation.

Describe the measures used to protect the operator Describe the measures used to protect the operator from excess radiation.from excess radiation.

Discuss the ALARA concept.Discuss the ALARA concept.


Radiation SafetyRadiation Safety

All ionizing radiations are harmful and All ionizing radiations are harmful and produce biologic changes in living tissues. produce biologic changes in living tissues.

The amount of x-radiation used in dental The amount of x-radiation used in dental radiography is small, but biologic changes do radiography is small, but biologic changes do occur. occur.

The dental assistant must understand how The dental assistant must understand how the harmful effects of radiation occur and how the harmful effects of radiation occur and how to discuss the risks of radiation with patients. to discuss the risks of radiation with patients.


Ionization Ionization

Ionization is the harmful effect of x-rays in human Ionization is the harmful effect of x-rays in human beings that can result in a disruption of cellular beings that can result in a disruption of cellular metabolism and cause permanent damage to metabolism and cause permanent damage to living cells and tissues. living cells and tissues.

Ionization is the process by which electrons are Ionization is the process by which electrons are removed from electrically stable atoms through removed from electrically stable atoms through collisions with x-ray photons. collisions with x-ray photons.

The atoms that lose electrons become positive The atoms that lose electrons become positive ions; as such, they are unstable and capable of ions; as such, they are unstable and capable of interacting with (and damaging) other atoms, interacting with (and damaging) other atoms, tissues, or chemicals. tissues, or chemicals.


Biologic Effects of Radiation Biologic Effects of Radiation

Exposure to radiation can bring about Exposure to radiation can bring about changes in body chemicals, cells, tissues, changes in body chemicals, cells, tissues, and organs. and organs.

The effects of the radiation may not become The effects of the radiation may not become evident for many years after the x-rays were evident for many years after the x-rays were absorbed.absorbed.

This time lag is called the latent period. This time lag is called the latent period.


Cumulative Effects Cumulative Effects

Exposure to radiation has a cumulative effect over Exposure to radiation has a cumulative effect over a lifetime. a lifetime.

When tissues are exposed to x-rays, some When tissues are exposed to x-rays, some damage occurs. damage occurs.

Tissues have the capacity to repair some of the Tissues have the capacity to repair some of the damage; however, they do not return to their damage; however, they do not return to their original state. original state.

The cumulative effect of radiation exposure can be The cumulative effect of radiation exposure can be compared with cumulative effect from repeated compared with cumulative effect from repeated exposure over the years to the rays of the sun. exposure over the years to the rays of the sun.


Acute and Chronic Radiation Acute and Chronic Radiation Exposure Exposure

Acute radiation exposure occurs when a large Acute radiation exposure occurs when a large dose of radiation is absorbed in a short dose of radiation is absorbed in a short period, such as in a nuclear accident. period, such as in a nuclear accident.

Chronic radiation exposure occurs when Chronic radiation exposure occurs when small amounts of radiation are absorbed small amounts of radiation are absorbed repeatedly over a long period. It may be repeatedly over a long period. It may be years after the original exposure before the years after the original exposure before the effects of chronic radiation exposure are effects of chronic radiation exposure are observed. observed.


Genetic and Somatic Effects Genetic and Somatic Effects

X-rays affect both genetic and somatic cells. X-rays affect both genetic and somatic cells. Genetic cells are the reproductive cells Genetic cells are the reproductive cells (sperm and ova). Damage to genetic cells is (sperm and ova). Damage to genetic cells is passed on to succeeding generations. These passed on to succeeding generations. These changes are referred to as genetic mutations. changes are referred to as genetic mutations.

All other cells in the body belong to the All other cells in the body belong to the classification of somatic tissue. (Somatic classification of somatic tissue. (Somatic means “referring to the body.”) X-rays can means “referring to the body.”) X-rays can damage somatic tissue, but the damage is damage somatic tissue, but the damage is not passed on to future generations.not passed on to future generations.


Fig. 38-21 Comparison of somatic and genetic effects Fig. 38-21 Comparison of somatic and genetic effects of radiation. of radiation.



Critical Organs Critical Organs

Certain organs are considered critical: Certain organs are considered critical: SkinSkin Thyroid glandThyroid gland Lens of the eyeLens of the eye Bone marrowBone marrow


Radiation MeasurementsRadiation Measurements

Radiation can be measured in a manner Radiation can be measured in a manner similar to that used to measure time, similar to that used to measure time, distance, and weight.distance, and weight.

Two sets of systems are used to define the Two sets of systems are used to define the way in which radiation is measured. way in which radiation is measured.

The older system is referred to as the The older system is referred to as the traditional or standard system. traditional or standard system.

The newer system is the metric equivalent, The newer system is the metric equivalent, known as the Système Internationale, or SI. known as the Système Internationale, or SI.


Traditional Units of Traditional Units of Radiation Measurement Radiation Measurement

The roentgen (R)The roentgen (R) The radiation absorbed dose (rad) The radiation absorbed dose (rad) The roentgen equivalent [in] man (rem) The roentgen equivalent [in] man (rem)

SI unitsSI units Coulombs per kilogram (C/kg) Coulombs per kilogram (C/kg) Gray (Gy) Gray (Gy) Sievert (Sv) Sievert (Sv)


Maximum Permissible Dose Maximum Permissible Dose

The maximum permissible dose (MPD) of whole-body The maximum permissible dose (MPD) of whole-body radiation for those who are occupationally exposed to radiation for those who are occupationally exposed to radiation is 5000 mrem (5.0 rem) per year, or 100 radiation is 5000 mrem (5.0 rem) per year, or 100 mrem per week. mrem per week.

This amount of radiation to the whole body carries This amount of radiation to the whole body carries very little chance of injury. very little chance of injury.

For nonoccupationally exposed persons, the current For nonoccupationally exposed persons, the current MPD is 500 mrem (5 mSv) per year. MPD is 500 mrem (5 mSv) per year.

Dental personnel should strive for an occupational Dental personnel should strive for an occupational dose of 0 by adhering to strict radiation-protection dose of 0 by adhering to strict radiation-protection practices. practices.


Radiation Risks and BenefitsRadiation Risks and Benefits

Background radiation comes from natural Background radiation comes from natural sources such as radioactive materials in the sources such as radioactive materials in the ground and cosmic radiation from space.ground and cosmic radiation from space.

Exposure from medical or dental sources is Exposure from medical or dental sources is an additional radiation risk.an additional radiation risk.

When dental radiographs are prescribed and When dental radiographs are prescribed and exposed, the benefit of disease detection far exposed, the benefit of disease detection far outweighs the risk of biologic damage from outweighs the risk of biologic damage from receiving small doses of radiation. receiving small doses of radiation.


Responsibilities of the DentistResponsibilities of the Dentist

To prescribe radiographs only for diagnostic purposes.To prescribe radiographs only for diagnostic purposes. To ensure that all radiographic equipment is properly To ensure that all radiographic equipment is properly

installed and maintained in a safe working condition.installed and maintained in a safe working condition. To provide appropriate shielding to protect staff and To provide appropriate shielding to protect staff and

patients from the effects of radiation. patients from the effects of radiation. To require that anyone exposing radiographs be To require that anyone exposing radiographs be

properly trained and appropriately supervised while properly trained and appropriately supervised while exposing radiographs.exposing radiographs.

To obey all state radiographic licensing requirements, To obey all state radiographic licensing requirements, rules, and regulations. rules, and regulations.

To participate in obtaining informed consent. To participate in obtaining informed consent.


Equipment for Radiation ProtectionEquipment for Radiation Protection

The dental tubehead must be equipped with The dental tubehead must be equipped with certain appropriate components:certain appropriate components: Aluminium filtersAluminium filters Lead collimators Lead collimators PIDsPIDs

Equipment should be checked on a regular Equipment should be checked on a regular basis by state or federal regulating agencies. basis by state or federal regulating agencies.

Faulty or malfunctioning equipment should be Faulty or malfunctioning equipment should be repaired immediately. repaired immediately.


Aluminum FilterAluminum Filter

The purpose of the aluminum filter is to The purpose of the aluminum filter is to remove the low-energy, long-wavelength, and remove the low-energy, long-wavelength, and least penetrating x-rays from the x-ray beam. least penetrating x-rays from the x-ray beam.

These x-rays are harmful to the patient and These x-rays are harmful to the patient and are not useful in producing a diagnostic-are not useful in producing a diagnostic-quality radiograph.quality radiograph.

X-ray machines operating at 70 kVp or higher X-ray machines operating at 70 kVp or higher must have aluminum filtration of 2.5 mm. This must have aluminum filtration of 2.5 mm. This is a federal requirement. is a federal requirement.


CollimatorCollimator

The collimator is used to restrict the size and The collimator is used to restrict the size and shape of the x-ray beam as a means of shape of the x-ray beam as a means of reducing patient exposure. reducing patient exposure.

A collimator may have either a round or A collimator may have either a round or rectangular opening.rectangular opening.

A rectangular collimator restricts the beam to A rectangular collimator restricts the beam to an area slightly larger than a size 2 intraoral an area slightly larger than a size 2 intraoral film and significantly reduces patient film and significantly reduces patient exposure. exposure.


The PIDThe PID

The PID appears as an extension of the x-ray The PID appears as an extension of the x-ray tubehead.tubehead.

It is used to direct the x-ray beam. Round and It is used to direct the x-ray beam. Round and rectangular PIDs are available in two lengths: rectangular PIDs are available in two lengths: Short (8-inch) Short (8-inch) Long (16-inch) Long (16-inch)


Patient ProtectionPatient Protection

Lead apron and thyroid collar: Lead apron and thyroid collar: A lead apron and thyroid collar must be used on all A lead apron and thyroid collar must be used on all

patients for all exposures.patients for all exposures. This rule applies to all patients, regardless This rule applies to all patients, regardless

of the patient’s age or sex or the number of films of the patient’s age or sex or the number of films being exposed. being exposed.

The lead apron should cover the patient from The lead apron should cover the patient from the neck to the lap to protect the reproductive the neck to the lap to protect the reproductive and blood-forming tissues from scatter and blood-forming tissues from scatter radiation. radiation.

Many states mandate the use of a lead apron.Many states mandate the use of a lead apron.


Fig. 38-23 The lead apron and thyroid collar must be large Fig. 38-23 The lead apron and thyroid collar must be large enough to cover the seated patient from the neck to above enough to cover the seated patient from the neck to above

the knees.the knees.


Fast-Speed FilmFast-Speed Film

The size of silver bromide crystals is the main The size of silver bromide crystals is the main factor in determining the film speed: the larger factor in determining the film speed: the larger the crystals, the faster the film. the crystals, the faster the film.

A fast film requires less exposure to produce A fast film requires less exposure to produce a quality radiograph.a quality radiograph.

Fast-speed film is the single most effective Fast-speed film is the single most effective method of reducing a patient’s exposure to method of reducing a patient’s exposure to x-radiation. x-radiation.

Fast-speed film is available for both intraoral Fast-speed film is available for both intraoral and extraoral radiography. and extraoral radiography.


Film-Holding Devices Film-Holding Devices

The use of a film-holding instrument keeps The use of a film-holding instrument keeps the patient’s hands and fingers from being the patient’s hands and fingers from being exposed exposed to x-radiation. to x-radiation.

The film holder also keeps the film in a stable The film holder also keeps the film in a stable position and helps the operator proper position and helps the operator proper position the film and the PID. position the film and the PID.


Fig. 38-24 The patient’s fingers are unnecessarily Fig. 38-24 The patient’s fingers are unnecessarily exposed to radiation when film holders are not used.exposed to radiation when film holders are not used.


Exposure FactorsExposure Factors

Using the proper exposure factors also limits the Using the proper exposure factors also limits the amount of x-radiation the patient is exposed to. amount of x-radiation the patient is exposed to.

Adjusting the kilovoltage peak, milliamperage, Adjusting the kilovoltage peak, milliamperage, and time settings controls the exposure factors.and time settings controls the exposure factors.

A setting of 70 to 90 kVp keeps patient exposure A setting of 70 to 90 kVp keeps patient exposure to a minimum. to a minimum.

On some dental units, the kilovoltage peak and On some dental units, the kilovoltage peak and milliamperage settings are preset by the milliamperage settings are preset by the manufacturer and cannot be adjusted. manufacturer and cannot be adjusted.


Proper TechniqueProper Technique

Proper technique is necessary to ensure the Proper technique is necessary to ensure the diagnostic quality of films and reduce the diagnostic quality of films and reduce the amount of radiation to which the patient is amount of radiation to which the patient is exposed.exposed.

Films that are nondiagnostic must be retaken; Films that are nondiagnostic must be retaken; this results in additional radiation exposure to this results in additional radiation exposure to the patient. the patient.

Retakes are a major cause of unnecessary Retakes are a major cause of unnecessary radiation exposure in patients and must be radiation exposure in patients and must be avoided.avoided.


X-Rays During Pregnancy X-Rays During Pregnancy

The Guidelines for Prescribing Dental Radiographs, The Guidelines for Prescribing Dental Radiographs, issued by the American Dental Association in issued by the American Dental Association in conjunction with the Food and Drug Administration, conjunction with the Food and Drug Administration, state that dental radiographic procedures “do not state that dental radiographic procedures “do not need to be altered because of pregnancy.” need to be altered because of pregnancy.”

When a lead apron is used during dental radiographic When a lead apron is used during dental radiographic procedures, the amount of radiation received in the procedures, the amount of radiation received in the pelvic region is nearly zero. pelvic region is nearly zero.

There is no detectable exposure to the embryo or There is no detectable exposure to the embryo or fetus with the use of a lead apron. fetus with the use of a lead apron.


Operator ProtectionOperator Protection

A dental assistant who fails to follow the rules A dental assistant who fails to follow the rules of radiation protection may suffer the results of radiation protection may suffer the results of chronic radiation exposure. of chronic radiation exposure.

By following these rules, dental personnel can By following these rules, dental personnel can keep their radiation exposure to zero. keep their radiation exposure to zero.


Rules for Operator ProtectionRules for Operator Protection

Never stand in the direct line of the primary Never stand in the direct line of the primary beam. beam.

Always stand behind a lead barrier, if one is Always stand behind a lead barrier, if one is available, or the proper thickness of drywall. available, or the proper thickness of drywall.

If a lead barrier is not available, stand at right If a lead barrier is not available, stand at right angles to the beam. angles to the beam.

Never stand closer than 6 feet to the x-ray Never stand closer than 6 feet to the x-ray unit during an exposure unless you are unit during an exposure unless you are behind a barrier. behind a barrier.


Fig. 38-25 For the sake of safety, the dental assistant must Fig. 38-25 For the sake of safety, the dental assistant must stand out of the path of the primary beam.stand out of the path of the primary beam.


Personnel Monitoring Personnel Monitoring

Three types of monitoring devices are used to Three types of monitoring devices are used to determine the amount of radiation exposure determine the amount of radiation exposure to personnel: to personnel: Film badgeFilm badge Pocket dosimeter (pen style) Pocket dosimeter (pen style) Thermoluminescent, or TLD Thermoluminescent, or TLD


Fig. 38-26 A film badge is used to monitor the amount Fig. 38-26 A film badge is used to monitor the amount of radiation that reaches the dental radiographer.of radiation that reaches the dental radiographer.

(Courtesy of Global Dosimetry Solutions, Irvine, Calif.)(Courtesy of Global Dosimetry Solutions, Irvine, Calif.)


Equipment MonitoringEquipment Monitoring

Dental x-ray machines must be monitored for Dental x-ray machines must be monitored for radiation leakage. radiation leakage.

If a dental x-ray tubehead has a faulty If a dental x-ray tubehead has a faulty tubehead seal, leakage results. tubehead seal, leakage results.

Dental x-ray equipment can be monitored Dental x-ray equipment can be monitored through the use of a film device that can be through the use of a film device that can be obtained from the manufacturer or from the obtained from the manufacturer or from the state health department.state health department.


If the Patient Cannot Cooperate If the Patient Cannot Cooperate

If the patient is a child who is unable to If the patient is a child who is unable to cooperate, he or she is seated on the cooperate, he or she is seated on the parent’s lap in the dental chair. Both the parent’s lap in the dental chair. Both the parent and child are covered with the lead parent and child are covered with the lead apron, and the parent holds the film in place.apron, and the parent holds the film in place.


Fig. 38-27 Child sitting on parent’s lap for dental x-ray.Fig. 38-27 Child sitting on parent’s lap for dental x-ray.


ALARA ConceptALARA Concept

The ALARA concept states that all exposure The ALARA concept states that all exposure to radiation must be kept to a minimum, or “as to radiation must be kept to a minimum, or “as low as reasonably achievable.” low as reasonably achievable.”

Every possible method of reducing exposure Every possible method of reducing exposure to radiation should be used to minimize risk. to radiation should be used to minimize risk.

The radiation-protection measures detailed in The radiation-protection measures detailed in this chapter should be used to minimize this chapter should be used to minimize patient, operator, and staff exposure, keeping patient, operator, and staff exposure, keeping radiation exposure “as low as reasonably radiation exposure “as low as reasonably achievable.” achievable.”


Patient QuestionsPatient Questions

Patients often have questions and concerns Patients often have questions and concerns about radiation. about radiation.

As a dental assistant. you must be prepared As a dental assistant. you must be prepared to answer such questions and educate the to answer such questions and educate the dental patient about the importance of dental patient about the importance of radiographs.radiographs.



Patient QuestionsPatient Questions


Here are some examples of comments you can Here are some examples of comments you can make to patients during informal discussions: make to patients during informal discussions: ““The doctor orders x-rays on the basis of your individual The doctor orders x-rays on the basis of your individual

needs.” needs.” ““Our office takes every step possible to protect you from Our office takes every step possible to protect you from

unnecessary radiation.” unnecessary radiation.” ““We use a lead apron and thyroid collar to protect your body We use a lead apron and thyroid collar to protect your body

from stray radiation.”from stray radiation.” ““We use a high-speed film that requires only minimal amounts We use a high-speed film that requires only minimal amounts

of radiation.” of radiation.” ““Do you have any questions before we begin?”Do you have any questions before we begin?”


Documents

Foundations of Radiography, Radiographic Equipment, and Radiologic Safety Chapter 38 Copyright © 2009, 2006 by Saunders, an imprint of Elsevier Inc. All