Dental Radiology Final Exam
Types of radiation: scatter, ionizing, background, characteristic, etc. correct answers -
Scattering: COMPTON SCATTER - photon energy is partially absorbed from an outer
shell electron. The electron is ejected from its orbit and the photon is deflected (changes
course). The ejected electron has a negative charge, different course, and a lower
energy. Accounts for 62% of the scattering radiation in diagnostic radiology;
COHERENT SCATTER - when a LOW-energy x-ray photon interacts with an outer-shell
electron. No change in the atom occurs. X-ray photon of scattered radiation is
produced. No loss of energy, no ionization occurs. 8% of the interactions of matter with
the dental x-ray beam.
- Ionizing: FORMS OF PARTICULATE RADIATION - electrons (Beta particles and
Cathode Rays), alpha particles, protons, neutrons; ELECTROMAGNETIC RADIATION -
x-rays, gamma rays, ultra-violet light
- Background: Radiation that is always in the environment. For example, radon in air;
uranium, radium, thorium in earth; cosmic rays; radioactive potassium in food and
water, etc.
- Characteristic: when an incoming electron collides DIRECTLY with an inner shell
electron of a target atom, thus ionizing it; an x-ray photon is released. In order for this to
occur, the incoming electron MUST have kinetic energy AT LEAST equal to or greater
than the electron in the shell it is colliding with - need 70 kVP or higher.
Components/function of film packet. correct answers Film packet: x-ray film: one-film
packet or two-film packet; paper film wrapper: protective sheet that covers the film and
shield the film from light; lead foil sheet: single piece of lead foil to shield the film from
backscattered (secondary) radiation that results in film fog; outer package wrapping:
soft-vinyl or paper wrapper that seals the film packet, protective paper, and lead foil
sheet. It serves to protect the film from exposure to light and oral fluids.
KVP, MA, Exposure Time correct answers - KV: is a measurement of the electrical
force that causes electrons to move from the negative cathode to the positive anode;
when KV INCREASED, the SPEED of the electrons INCREASES, causing them to
stroke the target the GREATER FORCE AND ENERGY, resulting in an x-ray beam with
a SHORTER WAVELENGTH; dental radiography requires the use of 65 to 100 KV
- KVP: is the maximum (or peak) voltage across the x-ray tube; KVP INCREASED =
INCREASED DENSITY (darker); HIGH KVP = more PENETRATING beam and LOW
contrast - many shades of gray; HIGH KVP = INCREASES intensity
- MA: the unit of measure used to describe the number of electrons (or current) flowing
through the cathod filament (conductor); an INCREASE in the NUMBER OF
,ELECTRONS = INCREASED NUMBER OF X-RAYS; dental radiography requires the
use of 7-15; HIGH MA = INCREASES INTENSITY, HIGH DENSITY
- Exposure Time: the interval time during which x-rays are produced; HIGH Exposure
Time = INCREASES INTENSITY, HIGH DENSITY
Functions of items found in the tube head correct answers - Leaded-glass housing:
prevents x-rays from escaping in all directions.
- Cathode: (negative) consists of a tungsten wire filament in a cup-shaped holder;
supplies the electrons necessary to generate x-rays
- Anode: (positive) consists of a wafer-thin tungsten plate embedded in a solid copper
rod; converts electrons into x-ray photons.
*Thermionic Emission: release of electrons due to overheating of tungsten filament,
releasing electrons toward positive anode.
Indirect, direct action theories of radiation correct answers - Indirect: x-ray photons are
absorbed within the cell and cause the formation of toxins, which in turn damage the cell
- Direct: cell damage results when ionizing radiation directly hits critical areas, or targets
within the cell
Types of caries and where located correct answers INTERPROXIMAL
- Incipient Carious Lesion: extends halfway through enamel
- Moderate Carious Lesion: extends more than halfway through enamel; does not
involve the DEJ
- Advanced Carious Lesion: extends through enamel and into dentin; it does not extend
through the dentin more than half the distance toward the pulp
- Severe Interproximal: extends more than halfway to the pulp
OCCLUSAL
ROOT CARIES
Components of the atom correct answers Atom: consists of central nucleus and orbiting
electrons; nucleus - protons and neutrons; electrons
Point of entry for each radiograph projection correct answers - Lateral Jaw, Body
(Mandible): below inferior border of mandible; VA = -15 to -20 degrees; perpendicular to
horizontal plane of receptor
- Lateral Jaw, Ramus (Mandible): posterior to third molar area; VA = -15 to -20 degrees;
perpendicular to horizontal plane of receptor
, - Lateral Cephalometric: centered over receptor and perpendicular to receptor
- Posteroanterior: centered over receptor and perpendicular to receptor
- Waters: centered over receptor and perpendicular to receptor
- Submentovertex: centered over receptor and perpendicular to receptor
- Reverse Towne: centered over receptor and perpendicular to receptor
- Transcranial: 2 inches above and 0.5 inches below, the ear canal opening; VA = +25
degrees; HA = 20 degrees
Radiation injury (types and causes) correct answers *results from ionization or free
radical formation
- Direct: cell damage results when ionizing radiation directly hits critical areas, or targets
within the cell
- Indirect: x-ray photons are absorbed within the cell and cause the formation of toxins,
which in turn damage the cell
External radiographs (names and function) correct answers - Lateral Jaw, Body
(Mandible): to evaluate impacted teeth, fractures, and lesions located in the body of the
mandible
- Lateral Jaw, Ramus (Mandible): to evaluate impacted third molars, large lesions, and
fractures that extend into the ramus of the mandible
- Lateral Cephalometric: to evaluate facial growth and development, trauma, and
disease and developmental abnormalities; shows soft tissue profile
- Posteroanterior: to evaluate facial growth and development, trauma, and disease and
developmental abnormalities; shows sinuses, nasal cavity, and orbits
- Waters: to evaluate the maxillary sinus area; shows sinuses, nasal cavity, and orbits
- Submentovertex: to identify the position of the condyles, demonstrate the base of the
skull, and evaluate fractures of the zygomatic arch
- Reverse Towne: to identify fractures of the condylar neck and ramus
- Temporomandibular Joint (TMJ): to evaluate the TMJ area
Materials used in dentistry to stop x-rays correct answers lead aprons
