Dental Therapy DETH 103 Radiography Theory

Page 2: Intro

• Developed by Saskatchewan Polytechnic

• Textbook: Dental Radiography: Principles and techniques (5th ed.) by Iannucci & Howerton (2017)

• Important info and images protected by Copyright

Page 3: Definitions

• Radiology: The science of radiation

• Radiography: The science of making a radiograph

• Radiograph: The resulting picture (digital or film based)

Page 4: Uses of X-Rays in Dentistry

• Confirm or classify suspected lesions

• Localize lesions or foreign objects

• Provide information during dental procedures (root canals, dental implants, etc.)

• Evaluate growth and development

• Detect diseases and conditions of teeth and surrounding structures that cannot be identified clinically

• Illustrate changes to caries, periodontal disease, and trauma

• Document the condition of a client at a specific point in time

• Aid in the development of a clinical treatment plan

Page 5: Benefits of X-Rays

• Records position of bone and periodontal space

• Assists in clinical diagnosis or evaluation (disease/healing)

• Records bone & periodontal space on all surfaces

• Determines crown/root ratio

• Records dense deposits such as calculus

• Records margins of restorations (overhangs & recurrent decay)

Page 6: Limitations of X-Rays

• Does not show soft tissue (recession or pocketing)

• Difficult to distinguish if treatment was successful

• 2-dimensional images

• Images can distort

• Does not show tooth mobility and difficult to determine fractures

• Bone resorption/disease/calculus must be advanced to show

Page 7: Characteristics of X-Rays

• Invisible and undetectable by the senses

• No mass or weight

• No charge

• Travel at the speed of light

• Travel in short-wavelength, high-frequency waves

• Travel in a straight line and can be deflected or scattered

• Absorbed by matter

• Cause ionization

• Can produce an image on photographic paper

• Cause changes in living cells

Page 8: Discovery of X-Radiation

• Discovered accidentally in 1895 by Wilhelm Roentgen

• Wilhelm Roentgen was studying the movement of electrons through glass vacuum tubes

• X-rays were initially referred to as "unknown"

• Wilhelm Roentgen announced the discovery to the world 40 days later

• Wilhelm Roentgen received the Nobel Prize in 1901

Page 10: Radiation

• Radiation: The emission and propagation of energy through space or a substance in the form of waves or particles

• Electromagnetic Radiation: The propagation of wavelike energy (without mass) through space or matter

• Electromagnetic Radiation includes visible light, radar, radio, and television waves

• Electromagnetic Radiation is arranged in the electromagnetic spectrum according to their energies

Page 11: Electromagnetic Radiation

• All types of electromagnetic radiation have common characteristics

• Electromagnetic radiation can be classified as ionizing or non-ionizing

• Only high-energy radiations are capable of ionization

• The particulate nature of light isn't very well understood

Page 12: Atomic and Molecular Structure

• Matter: Anything that occupies space and has mass

• When matter is altered, energy results

• Atom: The fundamental unit of matter

• All matter is composed of atoms

Page 13: Electrons

• Electrons: Tiny, negatively charged particles

• Electrons have very little mass, approximately 1/1800 as much as a proton or neutron

• Electrons travel around the nucleus in well-defined paths known as orbits or shells

• The shell located closest to the nucleus has the highest energy level

Page 14: Electrons (continued)

• Electrons are maintained in their orbits by electrostatic force between the positive nucleus and negative electrons

• The binding energy of an electron determines its stability in an orbit

• The strongest binding energy is found closest to the nucleus in the K shell

• Electrons in outer shells have weaker binding energy

Page 15: Ionization, Radiation, and Radioactivity

• Ionization: The process of converting an atom into ions

• A neutral atom contains an equal number of protons and electrons

• An atom with an incompletely filled outer shell attempts to capture an electron from an adjacent atom

• An atom that gains or loses an electron and becomes electrically unbalanced is called an ion

Page 17: Parts of a Dental X-Ray Machine and Circuitry

• Control panel

• Extension arm

• Tubehead

Page 19: Control Panel

• Contains an on-off switch, indicator light, exposure buttons, and control devices

• Control devices include time, kilovoltage, and milliamperage

• Plugged into an electrical outlet

Page 21: Extension Arm

• Suspends the x-ray tubehead

• Houses the electrical wires that extend from the control panel to the tubehead

• Allows for movement and positioning of the tubehead

Page 22: Tubehead

• The housing that contains the x-ray tube

• Insulating oils fill the housing and surround the x-ray tube

• The inside is made of glass or lead-lined aluminum

Page 23: Components

• PID (cone): Position Indicating Device - lead tube that directs the primary beam

• Central Ray: Imaginary ray traveling in the center of the x-ray beam

Page 24: X-ray Tube

• A glass vacuum tube with all the air removed

• Measures several inches long by 1 inch in diameter

• Includes a leaded-glass housing, negative cathode, and positive anode

Page 25: Anode

• The positive electrode

• Consists of a wafer-thin tungsten plate embedded in a solid copper rod

• Converts electrons into x-ray photons

• The tungsten target serves as a focal spot and converts electrons into photons

• The copper stem (radiator) functions to dissipate heat away from the tungsten target

Page 26: Cathode

• The negative electrode

• Consists of a tungsten wire filament in a focusing cup holder made of molybdenum

• Supplies the electrons necessary to generate x-rays

• The tungsten filament produces electrons when heated

• The molybdenum cup focuses electrons into a narrow beam and directs the beams toward the tungsten target

Page 29: Electricity and Electrical Currents

• Electricity: The energy used to make x-rays

• Electrical current: A flow of electrons through a conductor

Page 30: Electricity and Electrical Currents (continued)

• Milliamperage adjustment: Can increase or decrease the number of electrons passing through the cathode filament

• Kilovoltage peak (kVp) adjustment: Can control the current passing from the cathode to the anode

Physics Note

Transformers (Page 31)

• Transformers are devices used to either increase or decrease the voltage in an electrical circuit.

• They can transform higher voltage to lower voltage or vice versa.

• Three types of transformers are used to adjust electrical circuits: step-down transformer, step-up transformer, and autotransformer.

Step-Down Transformer (Page 32)

• Used to decrease voltage from the incoming 110- or 220-line voltage to the 3 to 5 volts used by the filament circuit.

• Has more wire coils in the primary coil than in the secondary coil.

Step-Up Transformer (Page 33)

• Used to increase incoming voltage to 65,000 to 100,000 volts used by the high-voltage circuit.

• Has more wire coils in the secondary coil than in the primary coil.

Position Indicating Device (PID) (Page 34)

• Components of PID include collimator, aluminum discs or filter, and primary beam.

• Collimator is a metallic barrier used to reduce the size and shape of the X-ray beam.

• Aluminum filters absorb lower energy photons, producing a cleaner image.

• Primary beam is made up of X-rays of different energies and can penetrate the patient's face.

Steps in X-ray Production (Page 35)

• Electricity from the wall outlet supplies power to generate X-rays.

• Step-down transformer decreases the voltage to heat the tungsten filament in the cathode.

• Thermionic emissions create a cloud of electrons.

• Step-up transformer creates high voltage (60-90 kVp) to direct electrons towards the anode at a high speed.

Dental Therapy (Page 36)

• Heat generated during X-ray production is conducted away from the target by copper and absorbed into the insulating oil.

• Less than 1% of the energy creates radiation.

• Copper conducts heat away from the target.

• Tungsten target has a high melting point and acts as the focal spot.

X-ray Production (Page 37)

• X-rays are created when they hit the tungsten target of the anode and escape out of the unleaded glass window of the glass tube.

• Only a small number of X-rays are able to exit the X-ray tube through the unleaded glass window.

• X-rays travel through the unleaded glass window, tube head seal, and aluminum disks.

• The size of the X-ray beam is restricted by the lead collimator.

• The X-ray beam exits the tube head at the opening of the PID.

Definitions of X-Radiation (Page 38)

• Primary radiation is the penetrating X-ray beam produced at the target of the anode.

• Secondary radiation is X-radiation created when the primary beam interacts with matter.

• Scatter radiation is a form of secondary radiation resulting from X-rays being deflected from their path by an interaction with matter.

Interactions of X-Radiation (Page 39)

• X-radiation can have no interaction, be absorbed and cause the photoelectric effect, scatter through Compton scatter, or scatter through coherent scatter.

No Interaction (Page 40)

• X-ray photons pass through the atom unchanged and leave the atom unchanged.

• These photons are responsible for producing densities on film and make dental radiography possible.

Radiation Characteristics (Page 41)

• Radiation characteristics include quality, quantity, and intensity.

Dental Radiography (Page 42)

• Differences between x-ray beam quality and quantity.

• Difference between kilovoltage and milliamperage.

• Inverse square law and its relevance to dental radiography.

Quality (Page 43)

• Quality is determined by voltage and kilovoltage.

• Kilovoltage peak controls the quality, or wavelength and energy, of the X-ray beam.

• Film density, contrast, and exposure time are affected by kilovoltage peak.

X-ray Beam Quality (Page 44)

• Quality refers to the mean energy or penetrating ability of the X-ray beam.

• Wavelength determines the energy and penetrating power of radiation.

• Quality is controlled by kilovoltage.

Voltage and Kilovoltage (Page 45)

• Voltage is the potential difference between two electrical charges.

• Increasing voltage increases the speed and force of electrons striking the target.

Kilovoltage Peak (kVp) (Page 47)

• Kilovoltage peak is the maximum or peak voltage of an alternating current.

• Varying kilovoltages in the tube current produce a polychromatic X-ray beam.

• Kilovoltage peak controls the quality, or wavelength and energy, of the X-ray beam.

Film Density and kVp (Page 48)

• Film density refers to the overall darkness or blackness of a film.

• Increasing kilovoltage makes the film appear darker, while decreasing kilovoltage makes it appear lighter.

Exposure Variables (Page 51)

• Exposure variables include milliamperage (MA), exposure time, and kilovoltage peak (kVp).

• MA controls the quantity of X-rays produced, exposure time controls the amount of time X-rays are produced, and kVp controls the quality of the X-ray beam.

Exposure Time and kVp (Page 52)

• Exposure time is the interval of time during which X-rays are produced.

• An adjustment in exposure time is necessary when kVp is increased.

Quantity (Page 53)

• Quantity refers to the number of X-rays produced in the dental X-ray unit.

• Amperage and milliamperage control the quantity of X-rays produced.

• Exposure time and milliamperage affect film density.

Amperage and Milliamperage (Page 54)

• Amperage determines the amount of electrons passing through the cathode filament.

• Increasing amperage results in an increased number of electrons and X-rays produced.

Milliamperage (Page 55)

• Milliamperage is 1/1000 of an ampere.

• In dental radiography, milliamperage ranges from 7 to 15 mA.

• Higher milliamperage settings increase the temperature of the cathode filament and the number of X-rays emitted.

Milliampere-Seconds (mAs) (Page 57)

• mAs is the product of milliamperes and exposure time.

• When milliamperage is increased, exposure time must be decreased to maintain constant density.

Exposure Time and Milliamperage (Page 59)

• There is an inverse relationship between exposure time and milliamperage.

• When milliamperage is increased, exposure time must be decreased, and vice versa.

X-ray Beam Intensity (Page 60)

• Intensity is the product of the quantity (number of X-ray photons) and quality (energy of each photon) per unit of area per unit of time of exposure.

• Intensity is affected by the number of photons, energy of photons, area, and exposure rate.

Kilovoltage Peak (Page 61)

• Kilovoltage peak regulates the penetrating power of the X-ray beam by controlling the speed of electrons traveling between the cathode and the anode.

• Higher kilovoltage peak settings produce an X-ray beam with more energy and shorter wavelengths, increasing the intensity of the X-ray beam.

Milliamperage (Page 62)

• Milliamperage controls the penetrating power of the X-ray beam by controlling the number of electrons produced and the number of X-rays emitted.

• Higher milliamperage settings increase the intensity of the X-ray beam.

Physics Note

Page 63:

• Exposure Time

  • Affects the number of x-rays produced

  • Longer exposure time produces more x-rays and a more intense x-ray beam

Page 64:

• Distance

  • The distance traveled by the x-ray beam affects the intensity of the beam

  • Target-surface (source to patient's skin)

  • Target-object (source to patient's tooth)

  • Target-film (source to film)

Page 65:

• Distance

  • X-rays travel from their point of origin, they diverge and spread out to cover a larger surface area

  • The intensity of the beam lessens

  • X-ray beam coming from an 8 inch PID is more intense compared to a 16 inch PID

Page 66:

• Inverse Square Law

  • "The intensity of radiation is inversely proportional to the square of the distance from the source of radiation"

  • When the distance is doubled, the beam is one quarter as intense

  • When the distance is halved, the beam is four times more intense

Page 67:

• Dental Therapy Inverse Square Rule

• A B Copyright e 2006 by Saunders, an imprint of Elsevier, Inc. All rights reserved.