dental machine.ppt

Chapter 38
Radiation Health & Safety
Copyright 2003, Elsevier Science (USA).
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Produced in the United States of America
ISBN 0-7216-9770-4

Copyright 2003, Elsevier Science (USA). All rights reserved.
Introduction
The dental assistant must have a thorough
knowledge and understanding of the importance
and uses of dental radiographs.
The dental assistant must understand the
fundamental concepts of atomic and molecular
structure and have a working knowledge of ionizing
radiation and the properties of x-rays.

Introduction- cont’d
 Radiation used to produce dental radiographs has
the ability to cause damage to all types of living
tissues.
 Any exposure to radiation, no matter how small,
has the potential to cause biologic changes to the
operator and patient.
 The dental assistant must have a thorough
understanding of the characteristics of radiation to
minimize radiation exposure to both the dental
patient and the operator.

Discovery of Radiation
 Wilhelm Conrad Roentgen (pronounced rent-
ken), a Bavarian physicist, discovered the x-ray on
November 8, 1895.
 For many years, x-rays were referred to as
roentgen rays, radiology was referred to as
roentgenology, and radiographs were known as
roentgenographs.
 During his lifetime, Roentgen was awarded many
honors and distinctions, including the first Nobel
Prize ever awarded in physics in 1901.

Fig. 38-1 Roentgen, the father of x-rays, discovered the early potential of an
x-ray beam in 1895.
Fig. 38-1

Pioneers in Dental Radiography
 Otto Walkoff made the first dental radiograph.
 Dr. C. Edmund Kells, a New Orleans dentist, is
credited with the first practical use of radiographs
in dentistry in 1896.
 Dental radiography has progressed from these
early discoveries to the science it is today.
 New technology continues to improve our
diagnostic abilities.

Radiation Physics
 All things in this world are composed of energy
and matter.
 Energy is defined as the ability to do work.
 Matter is anything that occupies space and has
form or shape.

Energy
 Although energy can neither be created nor
destroyed, it can change form.
 Atoms contain energy.
 The energy that holds the nucleus together is
called nuclear-binding energy.
 The energy holding electrons, negatively charged
particles, in their shell is known as electron-binding
energy.

Matter
 Matter has many forms, including solids, liquids,
and gases.
 Matter is composed of atoms grouped together in
specific arrangements called molecules.
 A molecule is the smallest particle of substance
that retains the property of the original substance.
 The fundamental unit of matter for discussion in
this chapter is the atom.

Atomic Structure
 The atom consists of two parts:
• a central nucleus
• orbiting electrons
 An atom is identified by the composition of its
nucleus and the arrangement of its orbiting
electrons; at present, 105 different atoms exist.

 The arrangement within the atom is similar to that
of the solar system.
 The atom has a nucleus as its center or sun, and
the electrons revolve (orbit) around it like planets.
 The electrons remain stable in their orbit unless
disturbed or moved. X-rays can disturb the orbiting
electrons.
Atomic Structure- cont’d

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

Nucleus
 The nucleus, or dense core of the atom, is composed of
particles known as protons and neutrons.
 Protons carry positive electrical charges, whereas neutrons
carry no electrical charge.
 Dental x-rays do not affect the tightly bound nucleus of the
atom and are only changed in direction or scattered.
 Dental x-rays cannot make atoms radioactive; thus patients
do not give off x-rays after the x-ray machine stops
producing x-rays.

Electrons
 Electrons are tiny negatively charged particles
that have very little mass.
 Electrons orbit around the nucleus of an atom.
 The orbit path of an electron is called an electron
shell. Each shell can contain only a specific number
of electrons.
 The electrons are maintained in orbit by electron-
binding energy, a force similar to the force of
gravity on earth.

Ionization
 The electrons remain stable in their orbit around
the nucleus until x-ray photons collide with them.
(A photon is a minute bundle of pure energy that
has no weight or mass.)
 X-rays have enough energy to push electrons out
of their orbits and produce ions (an atom that
gains or loses an electron and becomes electrically
unbalanced) in a process called ionization.

Ionization- cont’d
 Ionization is the process by which electrons are
removed from the orbital shells of electrically
stable atoms through collisions with x-ray photons.
 When an electron is removed from the atom, an
ion pair results.
 The harmful ionizing effect of x-rays in humans can
result in a disruption of cellular metabolism and
can cause permanent damage to living cells and
tissues.

Fig. 38-4 A molecule of water (H20) consists of two atoms of hydrogen
connected to one atom of oxygen.
Fig. 38-4

Properties of X-Rays
 The dental assistant must be familiar with the
unique characteristics of x-rays.
 X-rays are a form of energy that can penetrate
matter. Like visible light, radar, radio, and
television waves, they belong to a group called
electromagnetic radiation.
 Electromagnetic radiation is made up of photons
that travel through space at the speed of light in a
straight line with a wavelike motion.

Fig. 38-5 Electromagnetic spectrum, showing the various wavelengths of
commonly used radiations.
Fig. 38-5

 The shorter the wavelength, the greater its
energy.
 Because of the high energy of short wavelengths,
they are able to penetrate matter more easily than
are longer wavelengths.
 X-rays have unique properties that make them
especially useful in dentistry.
Properties of X-Rays- cont’d

Fig. 38-6 A, Wavelength is the distance between the crest of one wave and the crest of
the next. B, The shorter the wavelength, the greater the energy and penetration, the
longer the wavelength, the less energy and less penetration.
Fig. 38-6 A & B

Components of the Dental X-Ray
Machine
 Dental x-ray machines may vary slightly in size and
appearance, but all machines will have three
primary components:
• The tubehead
• An extension arm
• The control panel

Fig. 38-7 X-ray machine and arm.
Fig. 38-7

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

Fig. 38-8 Diagram of the dental x-ray tubehead.
Fig. 38-8

Components of the Tubehead
 Metal housing is the metal body of the tubehead
that houses the x-ray tube. It is filled with
insulating oil.
 Insulating oil surrounds the x-ray tube and
prevents overheating by absorbing the heat
created by the production of x-rays.
 Tubehead seal is made of leaded glass or
aluminum, it seals the oil in the tubehead.
 X-ray tube is the heart of the x-ray-generating
unit.

Components of the Tubehead- cont’d
 Transformer alters the voltage of incoming
electric current.
 Aluminum filter is aluminum sheets of 0.5-mm
thickness.
 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.
 Position-indicating device (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.

Fig. 38-10 A, Collimator. B, Filter.
Fig. 38-10 A & B

X-Ray Tube
 This vacuum environment allows the electrons to
flow with minimum resistance between the
electrodes:
• Cathode
• Anode

 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 Cathode

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 the heat away
from the target, thus reducing the 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. 38-12 The production of dental x-rays occurs in the x-ray tube.
Fig. 38-12

Position-Indicating Device
 The open end of the lead-lined position-indicating device
(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 length selected 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.

Extension Arm
 The extension arm encloses the wire between the
tubehead to 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 [kV] selector)
 A single centrally located control panel may be
used to operate several tubeheads located in
separate treatment rooms.

How X-Rays Are Produced
 The x-ray machine is plugged into the wall outlet, and
when the machine is turned on, the electric current
enters the control panel.
 The current travels from the control panel to the
tubehead through electrical wires in the extension arm.
 The current travels through the step-down transformer
to the filament of the cathode.
 The filament circuit uses 3 to 5 volts to heat the
tungsten filament in the cathode portion of the x-ray
tube.
 The heating of the filament results in thermionic
emission.

How X-Rays Are Produced- cont’d
 When the exposure button is pushed, the high-voltage
circuit is activated.
 The electrons in the cloud are accelerated across the x-ray
tube to the anode.
 The molybdenum cup in the cathode directs the electrons
to the tungsten target in the anode.
 The electrons travel from the cathode to the anode.
 When the electrons strike the tungsten target, their energy
of motion (kinetic energy) is converted to x-ray energy and
heat.

How X-Rays Are Produced- cont’d
 Less than 1% of the energy is converted to x-rays; the
remaining 99% are lost as heat.
 The heat is carried away from the copper stem and
absorbed by the insulating oil in the tubehead.
 The x-rays travel through the unleaded glass window,
the tubehead seal, and the aluminum filter.
 The aluminum filter removes the longer-wavelength x-
rays.
 The x-ray beam travels through the collimator.
 The x-ray beam then travels down the lead-lined PID
and exits at the end of the PID.

Types of Radiation
 Primary is the x-rays that come from the target of
the x-ray tube.
 Secondary is x-radiation that is created when the
primary beam interacts with matter.
 Scatter is a form of secondary radiation. It results
when an x-ray beam has been deflected from its
path by the interaction with matter.

Fig. 38-13 Three types of radiation interaction with the patient.
Fig. 38-13

Visual Characteristics
 Contrast
 Density
 Image detail
• These qualities are necessary for a good
radiograph.
 The dental assistant must understand how
variations in the character of the x-ray beam
influence the quality of the resulting radiographs.

Radiolucent and Radiopaque
 Radiolucent structures allow x-rays to pass
through them.
 The image of radiolucent structures appears dark
or black on the radiograph. Air spaces, soft tissues
of the body, and the dental pulp appear as
radiolucent images.
 Radiopaque structures do not allow x-rays to
pass through them.
 The image of radiopaque structures appears white
or light gray on the radiograph. Metal, enamel,
and dense areas of bone appear as radiopaque
images.

Fig. 38-14 Radiolucent and radiopaque objects in a bitewing radiograph.
Fig. 38-14

Contrast
 The ideal contrast of a film clearly shows the
radiopaque white of a metal restoration, the
radiolucent black of air, and the many shades of
gray between.
 Higher kilovoltage produces more penetrating x-
rays and lower radiographic contrast.
 A 90-kVp setting requires less exposure time and
produces a radiograph that has low contrast (more
shades of gray).
 A 70-kVp setting requires a slightly longer
exposure time and produces a radiograph with
high contrast (fewer shades of gray).

Density
 Density is the overall blackness or darkness of a
film.
 A radiograph with the correct density enables the
dentist to view black areas (air spaces), white
areas (enamel, dentin, and bone), and gray areas
(soft tissues).
 The degree of density is controlled by the mAs
(milliampere seconds).

Other Factors Influencing Density
 The distance from the x-ray tube to the patient: If
the operator lengthens the source-film distance
without changing the exposure settings, the
resulting radiographs will be light or less dense.
 The developing time and temperature can affect
the overall density. If the processing time is too
long, the radiograph will appear dark.
 The body size of the patient: A patient who is very
small or thin would require less radiation than a
husky, heavy-boned person.

Geometric Characteristics
 There are three geometric characteristics that
affect the quality of the radiograph. These are:
• Sharpness
• Magnification
• Distortion

Sharpness
 Sharpness refers to how well the radiograph
reproduces the fine details or distinct outlines of an
object.
 Sharpness is sometimes referred to as detail,
resolution, or definition.
 The sharpness of an image is influenced by the
following factors:
• Focal spot size
• Film composition
• Movement

Radiation Safety
 All ionizing radiations are harmful and produce
biologic changes in living tissues.
 The amount of x-radiation used in dental
radiography is small; however, biologic changes do
occur.
 The dental assistant must understand how the
harmful effects of radiation occur and how to
discuss the risks of radiation with patients.

Ionization
 Ionization is the harmful effect of x-rays in humans
that can result in a disruption of cellular
metabolism and cause permanent damage to living
cells and tissues.
 Ionization is the process by which electrons are
removed from electrically stable atoms through
collisions with x-ray photons.
 The atoms that lose electrons become positive
ions; as such, they are unstable structures capable
of interacting with (and damaging) other atoms,
tissues, or chemicals.

Introduction to Physiology
 Functional organization of the human body.
• The cell and its function.
 Genetic control of protein synthesis.

Biologic Effects of Radiation
 Exposure to radiation can bring about changes in
body chemicals, cells, tissues, and organs.
 The effects of the radiation may not become
evident for many years after the time the x-rays
were absorbed.
 This time lag is called the latent period.

Cumulative Effects
 Exposure to radiation has a cumulative effect over
a lifetime.
 When tissues are exposed to x-rays, some damage
occurs.
 Tissues have the capacity to repair some of the
damage; however, the tissues do not return to
their original state.
 The cumulative effect of radiation exposure can be
compared with cumulative effect from repeated
exposure over the years to the rays of the sun.

Acute and Chronic Radiation Exposure
 Acute radiation exposure occurs when a large
dose of radiation is absorbed in a short period of
time, such as in a nuclear accident.
 Chronic radiation exposure occurs when small
amounts of radiation are absorbed repeatedly over
a long period of time. It may be years after the
original exposure that the effects of chronic
radiation exposure are observed.

Genetic and Somatic Effects
 X-rays effect both genetic and somatic cells.
Genetic cells are the reproductive cells (sperm
and ova). Damage to genetic cells is passed on to
succeeding generations. These changes are
referred to as genetic mutations.
 All other cells in the body belong to the group of
somatic tissue. (Somatic means referring to the
body.) X-rays can damage somatic tissue, but the
damage is not passed on to future generations.

Fig. 38-16 Comparison of somatic and genetic effects of radiation.
Fig. 38-16

Critical Organs
 The following organs are considered critical
organs:
• Skin
• Thyroid gland
• Lens of the eye
• Bone marrow

Radiation Measurements
 Radiation can be measured in a manner similar to
time, distance, and weight.
 Two sets of systems are used to define the way in
which radiation is measured.
 The older system is referred to as the traditional
or standard system.
 The newer system is the metric equivalent known
as the Systeme Internationale or SI.

Traditional Units of Radiation
Measurement
 The roentgen (R)
• The radiation absorbed dose (rad)
• The roentgen equivalent [in] man (rem)
 The SI units include:
• Coulombs per kilogram (C/kg)
• The gray (Gy)
• The sievert (Sv)

Maximum Permissible Dose
 The maximum permissible dose (MPD) of
whole body radiation for those who are
occupationally exposed to radiation is 5000 mrem
(5.0 rem) per year, or 100 mrem per week.
 This amount of radiation to the whole body
produces very little chance of injury.
 For nonoccupationally exposed persons, the
current MPD is 500 mrem (5 mSv) per year.
 Dental personnel should strive for an occupational
dose of 0 by adhering to strict radiation protection
practices.

Radiation Risks and Benefits
 Background radiation comes from natural
sources such as radioactive materials in the ground
and cosmic radiation from space.
 Exposure from medical or dental sources is an
additional radiation risk.
 When dental radiographs are prescribed and
exposed, the benefit of disease detection far
outweighs the risk of biologic damage from
receiving small doses of radiation.

Responsibilities of the Dentist
 To prescribe radiographs only for diagnostic purposes.
 To ensure that all radiographic equipment is properly
installed and maintained in a safe working condition.
 To provide appropriate shielding to protect staff and
patients from the effects of radiation.
 To require that anyone exposing radiographs be
properly trained and appropriately supervised while
exposing radiographs.
 To obey all state radiographic licensing requirements,
rules, and regulations.
 To participate in obtaining informed consent.

Equipment for Radiation Protection
 The dental tubehead must be equipped with
appropriate:
• Aluminium filters
• Lead collimators
• Position-indicating devices (PID)
 Equipment should be checked on a regular basis by
state or federal regulating agencies.
 Faulty or malfunctioning equipment should be
repaired immediately.

Aluminum Filter
 The purpose of the aluminum filter is to remove
the low energy, long wavelength, and least
penetrating x-rays from the x-ray beam.
 These x-rays are harmful to the patient and are
not useful in producing a diagnostic-quality
radiograph.
 X-ray machines operating at 70 kVp or above must
have aluminum filtration of 2.5 mm. This is a
federal requirement.

Fig. 38-17 The purpose of placing aluminum disks in the path of the beam is
to filter out the low-energy, long wavelengths that are harmful to the patient.
Fig. 38-17

Collimator
 The collimator is used to restrict the size and
shape of the x-ray beam in order to reduce patient
exposure.
 A collimator may have either a round or
rectangular opening.
 A rectangular collimator restricts the beam to an
area slightly larger than a size 2 intraoral film and
significantly reduces patient exposure.

Fig. 38-18 A, The beam produced by a circular collimator is 2.75 inches in diameter. B,
The beam produced by a rectangular collimator is just slightly larger than a size 2
intraoral film.
Fig. 38-18 A & B

Position Indicating Device
 The position-indicating device (PID) appears as an
extension of the x-ray tubehead.
 It is used to direct the x-ray beam. Round and
rectangular shaped PIDs are available in two
lengths:
• short (8-inch)
• long (16-inch)

Patient Protection
 Lead apron and thyroid collar
• A lead apron and a thyroid collar must be used
on all patients for all exposures.
• This rule applies to all patients regardless of the
patient’s age or sex or the number of films
being exposed.
 The lead apron should cover the patient from the
neck and extend over the lap area to protect the
reproductive and blood-forming tissues from
scatter radiation.
 Many states mandate the use of a lead apron.

Fig. 38-19 The lead apron and thyroid collar must be large enough to cover
the seated patient.
Fig. 38-19

Fast-Speed Film
 The size of the silver bromide crystals is the main
factor in determining the film speed: the larger the
crystals, the faster the film.
 A fast film requires less exposure to produce a
quality radiograph.
 Fast-speed film is the single most effective method
of reducing a patient’s exposure to x-radiation.
 Fast-speed film is available for both intraoral and
extraoral radiography.

Film-Holding Devices
 The use of a film-holding instrument keeps the
patient’s hands and fingers from being exposed to
x-radiation.
 Film holders also hold the film in a stable position
and aid the operator in properly positioning the
film and the PID.

Fig. 38-20 The patient’s fingers are unnecessarily exposed to radiation when
film holders are not used.
Fig. 38-20

Exposure Factors
 Using the proper exposure factors also limits the
amount of x-radiation exposure to the patient.
 Adjusting the kilovoltage peak, milliamperage, and
time settings controls the exposure factors.
 A setting of 70 to 90 kVp keeps patient exposure
to a minimum.
 On some dental units, the kilovoltage peak and
milliamperage settings are preset by the
manufacturer and cannot be adjusted.

Proper Techniques
 Proper techniques are necessary to ensure the
diagnostic quality of films and reduce the amount
of exposure to a patient.
 Films that are nondiagnostic must be retaken; this
results in additional radiation exposure to the
patient.
 Retakes are a major cause of unnecessary
radiation to patients and must be avoided.

X-Rays During Pregnancy
 The Guidelines for Prescribing Dental
Radiographs issued by the American Dental
Association in conjunction with the Food and Drug
Administration, state that dental radiographic
procedures “do not need to be altered because of
pregnancy.”
 When a lead apron is used during dental
radiographic procedures, the amount of radiation
received in the pelvic region is nearly zero.
 There is no detectable exposure to the embryo or
fetus with the use of a lead apron.

Operator Protection
 A dental assistant who fails to follow the rules of
radiation protection may suffer the results of
chronic radiation exposure.
 By following these rules, dental personnel can keep
their radiation exposure to zero.

Rules for Operator Protection
 Never stand in the direct line of the primary beam.
 Always stand behind a lead barrier if one is
available or a proper thickness of drywall.
 If a lead barrier is not available, stand at right
angles to the beam.
 Never stand closer than 6 feet to the x-ray unit
during an exposure unless you are behind a
barrier.

Personnel Monitoring
 There are 3 types of monitoring devices used to
determine the amount of radiation exposure to
personnel:
• Film badge
• Pocket dosimeter (pen style)
• Thermoluminescent (TLD)

Fig. 38-22 A film badge is used to monitor the amount of radiation that
reaches the dental radiographer.
Fig. 38-22

Equipment Monitoring
 Dental x-ray machines must be monitored for
leakage radiation.
 If a dental x-ray tubehead has a faulty tubehead
seal, leakage radiation results.
 Dental x-ray equipment can be monitored through
the use of a film device that can be obtained from
the manufacturer or from the state health
department.

If the Patient Cannot Cooperate
 If the patient is a child who is unable to cooperate,
the child is seated on the parent’s lap in the dental
chair. Both the parent and child are covered with
the lead apron, and the parent holds the film in
place.

Fig. 38-23 Child sitting on parent’s lap for dental x-ray.
Fig. 38-23

ALARA Concept
 The ALARA concept states that all exposure to
radiation must be kept to a minimum, or “as low
as reasonably achievable.”
 Every possible method of reducing exposure to
radiation should be used to minimize risk.
 The radiation protection measures detailed in this
chapter should be used to minimize patient,
operator, and staff exposure, thus keeping
radiation exposure “as low as reasonably
achievable.”

Patient Questions
 Patients often have questions and concerns about
radiation.
 As a dental assistant you must be prepared to
answer their questions and educate the dental
patient about the importance of radiographs.

Patient Questions- cont’d
 Listed below are some examples of comments you can
make to patients during informal discussions.
• “The doctor orders x-rays based on your individual
needs.”
• “Our office takes every step possible to protect you
from unnecessary radiation.”
• “We use a lead apron and thyroid collar to protect
your body from stray radiation.”
• “We use a high speed film that requires only
minimal amounts of radiation.”
• Do you have any questions before we begin?”

Fig. 38-21 Operator protection guidelines suggests that the dental
radiographer stand at an angle of 90˚ to 135˚ to the primary beam.
Fig. 38-21

Fig. 38-15 A, A film produced with lower kilovoltage exhibits high contrast; many
light and dark areas are seen as demonstrated by the use of a stepwedge.
Fig. 38-15 A

Fig. 38-15 B, A film produced with higher kilovoltage exhibits low contrast;
many shades of gray are seen instead of black and white.
Fig. 38-15 B

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