ORAL DIAGNOSIS Oral Radiology pt 1 Flashcards
(194 cards)
1
Q
generation, emission, and absorption of radiation occur at the ___ level
A
subatomic
2
Q
electrons exist in orbitals around the nucleus and carry an electrical charge of ___
A
negative 1
3
Q
the nucleus contains ___ and ___
A
protons and neutrons
4
Q
protons have a charge of +1 and a mass that is ___x the mass of the electron
A
1836
5
Q
neutrons have no charge and are slightly ___ than protons
A
heavier
6
Q
___ occurs when an electrically neutral atom loses an electron and becomes a positive ion; the free electron is a negative ion
A
ionization
7
Q
electromagnetic radiation is the movement of energy through space as a combination of ___ and ___ fields
A
electrical and magnetic
8
Q
___ theory considers electromagnetic radiation as small bundles of energy called photons that travel at the speed of light and contain a specific amount of energy. electromagnetic radiations comprise a spectrum of radiations with varying energy
A
quantum
9
Q
___ theory considers electromagnetic radiations to be propagated in the form of waves.
A
wave
10
Q
wavelength is inversely proportional to ___
A
- photon energy
- the shorter the wavelength, the higher the energy
11
Q
the spectrum of electromagnetic radiation includes ___. which ones have sufficient energy to ionize biologic molecules, and what are they referred to as?
A
- spectrum includes gamma rays, x-rays, UV rays, visible light, infrared radiation (heat), microwaves, and radio waves, arranged in order of decreasing energies (or increasing wavelength)
- gamma rays, x-rays, and UV radiation have sufficient energy to ionize biologic molecules and are referred to as ionizing radiation
12
Q
describe particular radiation
A
- atomic nuclei or subatomic particles moving at high velocity
- alpha and beta particles and electrons (cathode rays) are examples
13
Q
what are the basic components of x-ray machines?
A
- x-ray tube containing a cathode and an anode
- power supply
14
Q
in the cathode of an x-ray tube, the ___ is the source of electrons within an x-ray tube
A
tungsten filament
15
Q
which part of the cathode electrostatically focuses electrons emitted by the incandescent filament into a narrow beam directed at a small area on the anode (focal spot)?
A
molybdenum focusing cup
16
Q
what are the two components of the anode?
A
tungsten target and copper stem
17
Q
what does the tungsten target of the anode do?
A
converts kinetic energy of electrons generated from the filament into x-ray photons
18
Q
what is the focal spot?
A
- area on the tungsten target (of the anode) onto which the focusing cup directs electrons
- as the size of the focal spot decreases, the sharpness of the radiographic image increases
19
Q
what does the copper stem of the anode do?
A
dissipates heat and reduces risk of target melting
20
Q
what is the purpose of the power supply?
A
- heats the x-ray tube filament
- high-voltage transformer generates high potential differences between the anode and the cathode
- timer that controls time exposure
21
Q
what is the purpose of heating the x-ray tube filament?
A
- provides low-voltage current by use of a step-down transformer that reduces the voltage of the incoming alternating current
- controlled by a milliamperage (mA) switch that regulates the temperature of the filament and the number of electrons emitted
- tube current
22
Q
what is the purpose of the tube current?
A
- flow of electrons through the tube from the filament to the anode and back to the filament
- the quantity of radiation produced by an x-ray tube is directly proportional to the tube current (mA) and the exposure time
- controls the number of photons generated (intensity of the beam) but not the beam energy
23
Q
high voltage transformer:
- the ___ control selects voltage from different levels on the autotransformer and applies it across the primary winding of the high-voltage transformer.
- the high-voltage transformer increases voltage significantly and provides the high voltage required by the x-ray tube to ___ and generate ___.
- ___ refers to the mean energy of an x-ray beam, which increases with increasing ___.
- the number of photons (beam intensity) also increases with increasing ___.
- because the current is alternating (60 cycles/sec), the ___ of the x-ray tube alternates, and the x-ray beam is generated as a series of pulses.
A
- kVp
- accelerate electrons from the cathode to the anode and to generate x-rays
- beam quality
- kVp
- kVp
- polarity
24
Q
what is the purpose of the power supply timer?
A
controls the length of the time high voltage is applied to the tube and the time during which the tube current flows and x-rays are produced (time exposure)
25
in the production of x-rays, high-energy electrons produced by the ___ interact with tungsten atoms at the target, resulting in an energy loss, which is converted to ___ and ___
- filament
| - heat and x-ray photons
26
___ is the primary source of x-ray photons from the x-ray tube
bremsstrahlung radiation
27
bremsstrahlung radiation results from ___
- stopping or slowing of high-speed electrons at the target
- an electron is attracted toward positively charged nuclei and loses velocity
- lost kinetic energy is given off in the form of new bremsstrahlung x-ray photons
- bremsstrahlung interactions generate x-ray photons with a continuous spectrum of energy
28
___ results when electrons from the filament collide with and eject an inner orbital electron, which is replaced by an outer orbital electron and release of a photon of specific energy
characteristic radiation
29
what are the factors that control the x-ray beam?
- kilovoltage
- milliamperage and exposure time
- filtration
- collimation
- inverse square law
30
kVp affects both the ___ and the ___ of the x-ray photons
quality and quantity
31
when kVp increases, the total number of photons produced increases, and the mean energy and maximum energy of the x-ray beam ___
increase
32
___ and ___ affect the quantity of the x-ray photons produced
- milliamperage and exposure time
- when mA and exposure time increases, the total number of photons increases, but the mean and maximum energies of the x-ray beam are unchanged
33
filtration is accomplished by placing an ___ in the path of the beam
aluminum filter
34
what does filtration do?
reduces patient dose by preferentially removing lower energy (less-penetrating) photons from the beam
35
after filtration, total number of ___ decreases. what happens to the mean energy of the x-ray beam?
- total number of photons decreases
| - however, because lower energy photons are preferentially removed, the mean energy of the x-ray beam increases
36
governmental regulations require total filtrations to be equal to the equivalent of ___
1.5mm of aluminum for up to 70kVp and 2.5mm of aluminum for higher voltages
37
a ___ is a metallic barrier with an aperture to reduce the size of the x-ray beam and the volume of irradiated patient tissue
collimator
38
dental x-ray beams are usually collimated to a circle of what diameter?
2.75 inches (7cm) in diameter with the collimator typically built into open-ended aiming cylinders
39
how do rectangular collimators reduce further unnecessary patient exposure?
they further limit the size of the beam to just larger than the image receptor
40
what is the inverse square law?
- intensity of the x-ray beam at a given point is inversely proportional to the square of the distance from the source
- changing the distance between the x-ray tube and the patient has a marked effect on beam intensity
- this principle is also applied to operator protection, where the operator stands at a distance of at least 6 feat from the x-ray source to minimize the intensity of the x-ray photons
41
in what ways do x-rays interact with matter?
- coherent scattering
- photoelectric absorption
- compton scattering
42
___ occurs when a low-energy photon passes near an outer electron, the photon ceases to exist, and the excited electron returns to ground state, generating another photon with the same energy as in the incident beam
coherent scattering
43
coherent scattering accounts for approximately ___% of interactions with photons in a dental x-ray beam
8%
44
___ occurs when a photon collides with a bound electron, which is ejected from its orbital, and the incident photon ceases to exist
photoelectric absorption
45
in photoelectric absorption, the frequency of photoelectric interaction is directly proportional to ___
- the third power of the atomic number of the absorber
| - contributes greatly to the differences in radiographic density of enamel, dentin, bone, and soft tissue on radiographs
46
photoelectric absorption accounts for approximately ___% of interactions with photons in a dental x-ray beam
30%
47
___ occurs when a photon interacts with an outer orbital electron, which recoils from the impact, and the incident photon is scattered in a new direction with lower energy
compton scattering
48
compton scattering accounts for approximately ___% of interactions with photons in a dental x-ray beam
62%
49
___ is a measure of radiation quantity; capacity of radiation to ionize air
exposure
50
what is the unit for absorbed dose?
gray (Gy), where 1 Gy equals 1 joule/kg
51
what is effective dose?
- used to estimate risk in humans
| - unit of effective dose is sievert (Sv)
52
___ is the decay rate of radioactive material
radioactivity
53
the radioactivity unit is ___
becquerel (B1), where 1 Bq equals 1 disintegration/sec
54
___ is the study of the effects of ionizing radiation on living systems
radiation biology
55
what are the deterministic effects of radiation biology?
- there is a threshold below which a response is not seen
- severity of response is proportional to dose
- changes resulting from killing of many cells after moderate to high doses of radiation
- example: oral mucositis after radiation therapy
56
what are the stochastic effects of radiation biology?
- there is no minimum threshold dose
- probability of response, rather than severity, is dose-dependent
- changes resulting from damage to DNA of single cells
- examples: radiation-induced cancer and heritable effects
57
what is the direct effect of radiation chemistry?
-direct alteration of biologic molecules (carbohydrates, lipids, proteins, DNA) by ionizing radiation
58
approximately what fraction of biologic effects of x-ray exposure result from direct effects?
1/3
59
what is the indirect effect of radiation chemistry?
- radiation effects mediated through water
- ionizing radiation converts water to hydrogen and hydroxyl free radicals (radiolysis of water), which alter biologic molecules
60
what fraction of radiation-induced biologic damage results from indirect effects?
2/3
61
changes in what biologic molecules is the primary mechanism for radiation-induced cell death, mutation, and carcinogenesis?
nucleic acids (damage to the DNA molecule)
62
describe cellular radiation effects of the nucleus
- nucleus is far more radiosensitive than cytoplasm, especially in dividing cells
- the sensitive site in the nucleus is DNA
- chromosome changes serve as useful markers for radiation injury
63
what are the effects of cellular radiation on cell kinetics?
- mitotic delay
- cell death
- recovery
64
describe mitotic delay as a result of cellular radiation
- mitotic delay occurs after irradiation of dividing cells
| - severity is dose-dependent
65
describe cell death as a result of cellular radiation
- cell death is caused largely by damage to chromosomes, preventing successful mitosis
- radiation also causes cell death by apoptosis
66
describe recover as a result of cellular radiation
- cell recovery involves enzymatic repair of single-strand breaks of DNA
- double-strand breaks (damage to both strands of DNA at the same site) is usually lethal to the cell
67
describe radiosensitivity as it relates to cell type
cells that are mitotically active and undifferentiated and have long mitotic futures (oral mucous membrane basal cells) are more radiosensitive than cells that no longer divide (neurons or striated muscle cells)
68
what are the short term radiation effects at the tissue and organ level?
rapidly proliferating tissues (bone marrow, oral mucous membrane) are lost primarily by mitosis-linked death
69
what are the long term radiation effects at the tissue and organ level?
long-term deterministic effects depend primarily on mitotic activity of the parenchymal cells and the extent of damage to fine vasculature
70
what is the rationale of radiotherapy?
- irradiation often used to treat radiosensitive oral malignant tumors, usually squamous cell carcinomas
- fractionation of total x-ray dose into multiple small doses provides greater tumor destruction than is possible with a large single dose
71
what is the radiation effect on oral mucous membranes?
- near the end of the second week of therapy, as basal epithelial cells die, the mucous membrane begins to show areas of redness and inflammation (mucositis)
- as mucous membrane breaks down, it forms a white-to-yellow pseudomembrane (desquamated epithelial layer)
- at the end of therapy, mucositis is most severe, discomfort is at the maximum, and food intake is difficult
- secondary yeast infection by c. albicans is a common complication and may require treatment
- after radiation therapy is completed, mucosal healing begins and is usually complete by about 2 months
- at later intervals (months to years), the mucous membrane becomes atrophic, thin, and relatively avascular, which complicates denture wearing
72
describe the radiation effect on taste buds
radiation therapy causes extensive degeneration of normal histologic architecture of taste buds and loss of taste acuity during the second or third week
73
describe the radiation effect on salivary glands
- dose-dependent and progressive loss of salivary secretion usually seen in the first few weeks after initiation of radiotherapy
- mouth becomes dry and tender, and swallowing becomes difficult and painful because residual saliva loses normal lubricating properties
- reduced salivary flow that persists beyond 1 year is unlikely to show significant recovery
- salivary changes have a profound influence on oral microflora, often leading to radiation caries
74
what is the radiation effect on teeth?
- irradiation of developing teeth with therapeutic doses severely retards tooth formation
- depending on the severity of the dose, aberrant formation or arrested root development may occur
75
describe radiation caries
carious lesions result from changes in salivary glands and saliva, including reduced flow (resulting in xerostomia), decreased pH, reduced buffering capacity, and increased viscosity
76
how are the best restorative results achieved for restoration of radiation caries?
combination of restorative dental procedures, excellent oral hygiene, and topical applications of sodium fluoride
77
primary radiation damage to mature bone results from ___
radiation-induced damage to the vasculature of the periosteum and cortical bone, which are normally already sparse
78
radiation affect on bone:
- after irradiation, normal bone marrow may be replaced with ___ and ___ that becomes hypovascular, hypoxic, and hypocellular.
- endosteum becomes ___, showing a lack of osteoblastic and osteoclastic activity, and some lacunae of compact bone are empty (indicates ___).
- when these changes are so severe that bone death results, the condition is termed ___ (most serious clinical complication that occurs in bone after irradiation).
- decreased vascularity of the mandible renders it easily infected by ___.
- this infection may cause a nonhealing wound in irradiated bone that is difficult to treat and causes extensive ___.
- fatty marrow and fibrous connective tissue
- atrophic
- necrosis
- osteoradionecrosis
- microorganisms from the oral cavity
- bone loss
79
why is osteoradionecrosis more common in the mandible as opposed to the maxilla?
- the maxilla has a much richer vascular supply
| - mandible is more frequently irradiated
80
when the whole body is exposed to low or moderate doses of radiation, characteristic changes (termed ___) develop, which are quite different from changes seen when a relatively small volume of tissue is exposed
acute radiation syndrome
81
describe radiation effects on embryos and fetuses
- prenatal irradiation may lead to death or specific developmental abnormalities, depending on the stage of development at the time of irradiation
- no effects on embryos or fetuses have been shown from low doses used in dental radiography
82
radiation-induced cancer is a ___ effect
stochastic effect (no threshold below which the effect does not occur)
83
the risk of developing radiation-induced cancer increases with increasing ___
dose
84
are radiation-induced cancers distinguishable from cancers produced by other causes?
no
85
the incidence of leukemia increases soon after radiation exposure of bone marrow and returns nearly to baseline rates within ___ years
40
86
describe radiation-induced solid cancers (what organs, how long after exposure does it appear, and what is the lifetime risk?)
- thyroid, brain, and salivary glands
- generally appears 10+ years after exposure
- elevated risk remains for the patient's lifetime
87
which age population is more at risk for radiation-induced solid tumors and leukemias?
persons younger than 20 years old are more at risk than adults
88
the annual average radiation exposure to individuals living in the US is approximately ___mSv
6.2; this includes exposure from ubiquitous background radiation and man-made radiation sources
89
ubiquitous background radiation contributes to approximately ___mSv, accounting for ___% of radiation exposure of people living in the US
3.1, 50%
90
what is the major contributor to background radiation?
- radon (73%)
| - radon is a gas produced by radioactive decay of uranium in the soil
91
other than radon, what are the other sources of background radiation exposure?
terrestrial, internal radionuclides, and space radiation
92
man-made sources of radiation contribute to approximately ___mSv, accounting for ___% of radiation exposure of people living in the US
3.1, 50%
93
what are the sources of manmade radiation?
- radiation exposure from medical or dental diagnostic and treatment procedures (96%)
- consumer and industrial products and sources (4%)
94
computed tomography (CT) scans are the major contributor to medical radiation exposure, accounting for ___% of man made sources
47%
95
dental x-ray examinations are responsible for ___% of man made radiation exposure
0.26%
96
consumer and industrial produces and sources responsible for radiation exposure include what?
smoking, domestic water supplies, combustible fuels, dental porcelain, television receivers, pocket watches, smoke alarms, nuclear power, and airport inspection systems
97
what is the occupational exposure limit?
- 50mSv of whole-body radiation exposure in one year
- data from radiation monitoring services show that individuals occupationally exposed in operation of dental x-ray equipment typically receive an annual average of 0.2mSv (0.4% of allowable limit)
98
what is the dose limit for patients exposed to radiation in the course of dental and medical treatment?
no dose limits
99
what is the primary risk from dental radiography? what organs are at risk?
- radiation-induced cancer
- organs at risk include the thyroid gland, red bone marrow, and salivary glands
- although the risk involved with dental radiography is extremely small, no basis exists to assume that it is zero
100
which films should be used for bite-wing exams?
E/F-speed films or digital imaging
101
which films should be used for panoramic and cephalometric radiography?
rare-earth intensifying screens
102
to reduce patient exposure and improve image clarity, an extended (___ inches) source-patient distance (___ distance) should be utilized
16-inch, focal spot-to-film distance
103
rectangular collimation reduces patient exposure by more than ___% compared to round collimation
50%
104
leaded thyroid collars are recommended for individuals younger than ___ years old
- 30
| - leaded lap aprons are required in most states
105
a kilovoltage range of ___kVp is most suitable for dental radiographs
60-80kVp
106
how should exposure time be adjusted to reduce radiation exposure?
- set mA value to highest possible value if variable
- adjust exposure time to achieve optimum radiographic density
- adjust exposure time to account for patient size and anatomic location
107
for operator protection, the operatory should be arranged so that the operator can stand at least ___ feet from the patient and not in the path of the primary x-ray beam during exposure
6
108
how can proper film processing help reduce radiation exposure?
- perform film processing under manufacturer-recommended time and temperature conditions
- use proper safelights
109
x-ray films are composed of an emulsion and a base. what is the emulsion?
- sliver halide grains (primarily silver bromide) are sensitive to x-radiation and visible light; they are flat, tabular crystals in modern emulsions and are attached to base with a collagenous vehicle
- the smaller the crystals, the greater the image resolution
110
x-ray films are composed of an emulsion and a base. what is the base?
a flexible plastic film base that supports the emulsion
111
what is the screen film?
film sensitive to visible light and placed between two intensifying screens when an exposure is made
112
intensifying screens are made of a ___ and a ___
base supporting material and a phosphor layer (usually rare-earth elements lanthanum and gadolinium)
113
phosphors incorporated into intensifying screens fluoresce in proportion to ___
the x-ray energy absorbed
114
use of intensifying screens results in substantial reduction in ___ but decreased ___ because of dispersion of light from the phosphors
- patient dose
| - image resolution
115
___ is the overall degree of darkening of exposed film and is measured as optical density of area of x-ray film
radiographic density
116
in a well-exposed and processed radiograph, the optical density of enamel is about ___, of dentin is about ___, and of soft tissue is about ___
- enamel is 0.4
- dentin is 1.0
- soft tissue is 2.0
117
increasing ___, ___, or ___ increases the number of photons reaching the film and increases the density of the radiograph
mA, kVp, or exposure time
118
reducing ___ increases film density
distance between the focal spot and the film
119
the thicker the subject or the greater its density, the more the beam is ___ and the lighter the resultant image
attenuated
120
___ is the range and number of densities on a radiograph
radiographic contrast
121
___ is the range of characteristics of the subject that influences radiographic contrast
subject contrast
122
___ is the capacity of radiographic films to display differences in subject contrast, that is, variations in intensity of the remnant beam
film contrast
123
___ results from photons that have interacted with the subject by compton or coherent interactions, cause emission of photons that travel in directions other than that of primary beam, and cause an overall darkening of the image that results in loss of radiographic contrast
scattered radiation
124
___ is the amount of radiation required to produce an image of a standard density
radiographic speed
125
the fastest dental film currently available has a speed rating of ___; only films with a ___ or faster speed rating are appropriate for intraoral radiography
- F (preferred speed)
| - D
126
___ is the measure of range of exposures that can be recorded on film
film latitude
127
a film optimized to display a ___ latitude can record a subject with a wide range of subject contrast; a film optimized to display a ___ latitude can distinguish objects with similar subject contrasts
- wide
| - narrow
128
___ is the appearance of uneven density of a uniformly exposed radiographic film
radiographic noise
129
___ is an uneven density resulting from the physical structure of the film or the intensifying screens
radiographic mottle
130
___ are defects caused by errors in film handling (fingerprints or bends in the film), errors in film processing (splashing developer or fixer on a film), or marks or scratches from rough handling
radiographic artifacts
131
___ is the ability of a radiograph to define an edge precisely
sharpness
132
___ is the ability of a radiograph to record separate structures that are close together
resolution (or resolving power)
133
what are 4 causes of increased radiographic blur?
- increased size or decreased number of silver grains in film emulsion
- use of intensifying screens in extraoral radiography
- movement of film, subject, or x-ray source during exposure
- large focal spot or short source-to-subject distance
134
what 3 things improve image sharpness?
- use of as small an effective focal spot as is practical
- increasing the distance between the focal spot and the object by using a long, open-ended cylinder
- minimizing the distance between the object and the receptor
135
what are two ways image size distortion (magnification) can be minimized?
- increasing focal spot to film distance
| - decreasing object to receptor distance
136
what are two ways image shape distortion can be minimized?
- positioning the receptor parallel to the long axis of the object
- orienting the central ray perpendicular to the object and the receptor
137
___ results from excessive vertical angulation when the x-ray beam is perpendicular to the receptor but not the tooth
foreshortening
138
___ results when the x-ray beam is oriented at right angles to the object but not to the receptor
elongation
139
what is the bisecting-angle technique?
the receptor is placed as close to the teeth as possible, and the central ray is directed perpendicular to an imaginary plane that bisects the angle between the teeth and the receptor
140
what is the paralleling technique?
- preferred method for intraoral radiographs
- the receptor is placed parallel with the long axis of the tooth, and the central ray is directed perpendicular to the long axis of the teeth and the receptor
141
describe the SLOB rule
- if the tube is shifted and directed at a reference object (ex. apex of the tooth) from a more mesial angulation and the object in question also moves mesially with respect to the reference object, then the object lies lingual to the reference point
- alternatively, if the tube is shifted mesially and the object in question appears to move distally, it lies buccal to the reference object
142
when a beam of photons exposes an x-ray film, it chemically changes the ___ in the film emulsion (a latent image). exposed areas become ___, and nonexposed areas become ___. the developing process converts a latent image into a ___.
- photosensitive silver halide crystals
- radiolucent
- radiopaque
- visible radiographic image
143
describe the formation of latent images
silver halide crystals contain sensitivity sites that trap electrons generated when the emulsion is irradiated to produce crystals containing neutral silver atoms (latent image)
144
what does the developer solution do?
converts exposed silver halide crystals (with neutral silver atoms at each latent image site) into metallic silver grains that are seen as dark on a radiograph
145
describe the two of developers
- phenidone is the first electron donor that reduces silver ions to metallic silver at the latent image site
- hydroquinone provides an electron to reduce oxidized phenidone back to its original active state so that it can continue to reduce silver halide grains to metallic silver
146
what does rinsing the the film do?
- dilutes the developer, slowing development process
| - removes the alkali activator, preventing neutralization of the acid fixer
147
what does the fixing solution do?
- dissolves and removes undeveloped silver halide crystals (without latent image sites) from the emulsion
- clearing agent (aqueous solution of ammonium thiosulfate (hypo) that dissolves silver halide grains
- hardener (aluminum sulfate complexes with gelatin in the emulsion during fixing and prevents damage to gelatin during the subsequent handling
148
what does final washing of the film do?
ensures removal of all thiosulfate ions and silver thiosulfate complexes that would stain the film if left
149
describe the 7 steps for manual film processing procedures
1. replenish the developer and the fixer and stir the solutions
2. mount films on hangers
3. set timer (typically 5 minutes at 68*F; higher temp correlates with shorter development time)
4. develop films for the indicated time
5. rinse in running water for 30 seconds
6. fix - place hanger and film in fixer solution for 10 minutes
7. wash and dry - after fixation of films is complete, place the hanger in running water for at least 10 minutes to remove residual processing solutions
150
most automatic film processors have an in-line arrangement of rollers. what is their purpose?
to move the film through the developing solutions
151
why are the chemical compositions of the developer and fixer modified in automatic film processing?
modified to operate at higher temperatures than the temperatures used for manual processing and to meet requirements of rapid development, fixing, washing, and drying of automatic processing
152
for both manual and automatic film processing, how many ounces of fresh developer and mixer are added per gallon of solution per day?
8oz
153
describe safelighting procedures
- use a kodak GBX-2 safelight filter or equivalent with a 15-watt bulb at least 4 feet from the working surface
- an ML-2 filter should not be used because it fogs the panoramic film
- a "penny test" checks for proper safelighting by determining whether an exposed film, covered with a penny in the dark room, shows an image of the penny after processing. if so, it implies film fogging and light leaks or improper safelighting
154
what is the preferred method for mounting radiographs?
the preferred method of positioning periapical and occlusal films in the film mount is to arrange them with the dot (bump) facing the viewer so that images of teeth are in anatomic position and have the same relationship to the viewer as when the viewer faces the patient, that is, with the right quadrants in the left side of the film mount and the left quadrants in the right side
155
it is estimated that ___% of dental offices uses some form of digital imaging
15-25%
156
what is the difference between analog versus digital imaging?
- analog is a continuous gray scale (conventional film image)
- digital is a gray scaled divided into a discrete number of values (images are composed of many pixels, each having a discrete gray level)
157
digital image gray scales are divided into a discrete number of values, which is a power of ___
2 (typically from 2^8 or 256 gray steps)
| an 8-bit image has 256 gray levels, and a 12-bit image has 2^12 has 4096 gray levels
158
what are the types of digital detectors?
- charge-coupled device (CCD) and complementary metal oxide semiconductors (CMOS)
- photostimulable phosphor plates (PSP)
159
what are charge-coupled devices (CCD) and complementary metal oxide semiconductors (CMOS)?
- silicon sensor captures x-ray energy from exposure as a voltage potential
- silicon chip reads out voltage of each pixel
- usually connected to computer by a wire but may be wireless
- rapid display of image on monitor after exposure
- used for intraoral, panoramic, and cephalometric imaging
160
what are photostimulable phosphor plates (PSP)?
- plates made of barium fluorohalide with traces of europium
- plates capture and store x-ray energy from dental exposure
- after exposure, the plates are placed into the reader where stored energy is released as fluorescence by laser
- reader measure released light from plate and forms image
- time to image display after plate is placed in reader varies from seconds to minutes
161
what are the contrast resolution characteristics of digital detectors?
- ability to distinguish shades of gray
- limited by bit-depth of image capturing receptor
- usually displayed as an 8-12-bit image (256-4096 gray levels)
162
what are the spatial resolution characteristics of digital detectors?
- ability to detect edges or separate two close points
- for intraoral systems, film better than CCD and CMOS, both of which are better than PSP
- for panoramic and cephalometric systems, film, CCD, and PSP are all equivalent
163
what are the detector latitude characteristics of digital detectors?
- range of structures of varying density shown on image
| - PSP better than CCD and CMOS, which are better than film
164
what are the detector sensitivity characteristics of digital detectors?
- dose required to achieve standard gray level
| - doses for CCD and CMOS about half of F-speed film
165
describe brightness and contrast adjustment of digital image display
usually beneficial but may introduce artifacts, particularly in images with narrow latitude
166
describe sharpening and smoothing adjustment of digital image display
- sometimes useful, but sharpening may introduce grainy appearance, and smoothing may give a blurring effect
- excessive image sharpening may also create artifacts at the edges of radiopaque restorations, which may be mistaken for recurrent caries
167
what are occlusal radiographs?
- displays a large segment of a dental arch
| - may include the palate or floor of the mouth and a reasonable extent of contiguous lateral structures
168
concern about radiation protection is most important for children because of their greater sensitivity to ___
irradiation
169
T or F:
| there have been rare occasions of reported incidences of damage to a fetus from dental radiography
false, there have been no reported incidences
170
enamel appears more radiopaque than other tissues because ___
it is the most dense naturally occurring substance in the body
171
arrange the following in order of most radiopaque to most radiolucent: dentin, cementum, enamel, bone, pulp
1. enamel
2. dentin (75% mineralized)
3. bone (comparable to dentin, but less homogenous)
4. cementum (50% mineralized; not usually apparent radiographically)
5. pulp
172
developmentally, the lamina dura is an extension of ___
the lining of the bony crypt that surrounds each tooth during development
173
small variations and disruptions in continuity of the lamina dura may represent ___ and ___
superimpositions of trabecular pattern and small nutrient canals passing from mandibular bone to the PDL
174
the presence of an intact lamina dura around the apex of a tooth strongly suggests ___
a vital pulp
175
the level of the alveolar crest is considered normal when it is not more than ___mm from the CEJ of adjacent teeth
2mm
176
the intermaxillary suture is also called the ___
- median suture
| - appears as a thin radiolucent line in the midline
177
the incisive foramen is also called the ___ or ___
- nasopalatine foramen or anterior palatine foramen
| - it is the oral terminus of the nasopalatine canal
178
the presence of an incisive canal cyst is suspected if the width of the nasopalatine foramen exceeds ___, if enlargement can be ___, or if it appears to have caused ___
- 1cm
- demonstrated on successive radiographs
- divergence of the roots of the central incisors
179
the lateral fossa is also called the ___
incisive fossa
180
how does the lateral fossa (incisive fossa) present radiographically?
- a gentle radiolucent depression in the maxilla near the apex of the lateral incisor
- often misinterpreted as a pathologic condition
181
Review radiographic images for the following anatomic landmarks
enamel, dentin, cementum, pulp, lamina dura, alveolar crest, PDL space, cancellous bone, intermaxillary suture, anterior nasal spine, nasal fossa, incisive foramen, lateral fossa, nose, maxillary sinus, zygomatic process of maxilla, zygoma, pterygoid plates, genial tubercles, mental protuberance, mental fossa, mental foramen, mandibular canal, nutrient canals, mylohyoid ridge, submandibular gland fossa, external oblique ridge, inferior border of the mandible, and coronoid process
182
various dental anomalies such as ___ and ___ can mimic the radiographic appearance of caries
hypoplastic pits and concavities produced by wear
183
approximately ___ of all proximal lesions in enamel cannot be detected by radiography
half
184
carious lesions in children and adolescents most often occur on which surfaces?
occlusal surfaces of posterior teeth
185
a carious lesion developing at the margin of an existing restoration may be termed ___ or ___
secondary or recurrent caries
186
what are local initiating factors detected radiographically that cause or intensity periodontal disease?
calculus and poorly contoured or overextended restorations
187
T or F:
| radiographs can provide information about the depth of soft tissue pockets
false
188
the normal alveolar bone crest lies at a level approximately ___mm below the level of the CEJs of adjacent teeth
0.5-2mm
189
the most common route for furcation involvement of the maxillary permanent first molar is from the ___ side
mesial
190
what is the differential diagnosis for radiographic bone loss around teeth?
- periodontal disease
- squamous cell carcinoma of the alveolar process
- any lesion of bone destruction that has ill-defined borders and a lack of peripheral bone response (sclerosis) should be viewed with suspicion
191
what is the "image layer" of a panoramic image?
- 3-D curved zone or "focal trough" where structures lying within this layer are reasonably well defined on the final panoramic image
- objects outside the image layer are blurred, magnified, or reduced in size and are sometimes distorted
192
when positioning a patient for a panoramic image, the occlusal plane should be aligned so that it is lower anteriorly, angled ___ degrees below horizontal
20-30 degrees
193
___ are routinely used in panoramic radiography because they significantly reduce the amount of radiation required for properly exposing a radiograph
intensifying screens
194
several manufacturers have developed digital acquisiton of panoramic machines. the receptor on such a machine is either an array of ___ or a film-sized ___ rather than film
array of CCDs or a film-sized PSP
