radio paper Flashcards
what does a PA capture
shows the indiv teeth and tissue around the pices (at least 3mm)
what do PAs help to assess
- apical status
- severity of careis
- perio status
- presence and posn of unerupted teeth
- posn of 8s
- root morpho
- endo tx
- post op review
2 techniques of taking PAs
bisecting angle technique - beam is angulated at bisecting angle of tooth axis & receptor
parallel technique - place receptor parallel to tooth axis, aim beam parallel to receptor
what does a BW capture
crowns, interprox, ocl surface, EDJ, alveolar crest bone lvl
what are BW used for
detection & monitoring caries
assess resto
assess perio status
what collimator do ocl xrays need
round collimators
what are OPGs used for
overall eval of dentition demonstrate extensive caries / perio eval posn of 8s dvlpt disturbances of mxfacial skeleton trauma intraosseous patho tmj
what to take note for taking OPGs
remove jewellery, hair pins, glasses, RPs no preggo explain procedure to pt put on lead apron correct exposure setting
what is tomography
xray source and receptor rotate simultaneously in opposite direction around a fixed centre of rotation
for OPG, where does xray source come from
comes from the back, angulated slightly upwards by 8deg
OPG magnification is due to…
pt positioning too far back
OPG minification is due to…
pt positioning too far forward
OPG chin tilt too up/down leads to…
v shaped / broad and flat
layers of xray film structure
overcoat (protection)
emulsion (Ag halide crystals)
base (support)
how are latent images formed on xray film
Ag halide suspended in gelatin matrix that contain sensi specks.
Ag halide is ionised, forms Ag+ and e-, diff areas experience diff degree of ionising.
sensi specks traps Ag+ and e- to form latent image.
how are latent image processed?
dvlp soln - reduce Ag+ into black Ag
fixer soln - remove unexposed Ag halide
what do intensifying screens do
active phosphor layer emits light when exposed to xray beam, amplifies incoming xray beam while reducing pt dose. but comes at a cost of lower resolution of film
process of digital imaging
xray photon reach receptor to form latent image
image go through electronic detector to translate qty of xray photons into voltage signal
voltage signal is sampled and quantified
computer display image/shade of grey based on value assigned
how image formed on psp plate
xray cause e- to move from valence band (resting state) to conduction band (excited state)
e- trapped in F centres = latent image
laser in scanners release e-, e- return to valence band and releases light while doing so
light converted into voltage
digitalised & displayed
properties of xray
- electrically neutral
- travels in straight lines
- polyenergetic / heterogenic
- absorbed / scattered by tissues
which component of xray unit produces the xrays
tungsten anode head
ft of xray unit to minimise excessive xray exposure
- tube is made of metal, lined w lead
- plastic port cover for xray to exit from one side only
- appropriate exposure time
- filtration to filter out low energy photons that don’t contribute to image formation
- long collimator used to reduce dose, reduce scatter, restrict width of xray beam until just slightly bigger than film
what are bremsstrahlung radiation
- polyenergetic (forms the curve)
incident e- knock into atomic e-, path of incident e- is deflected bc it loses KE. KE lost = xray
what are characteristic radiation
- heterogenous energy lvl
incident e- knock out k shell e- (inner), outer shell (L/M/N) e- drops to fill the space, excess energy = characteristic xray
describe xray energy curve
y axis - no. of photons (aka mAs) x axis - photon energy (keV) kVp setting = max energy peak = average energy of photon beam spikes = characteristic radiation
effect of increasing exposure time
more time = more photons hit film = increase density of image (image becomes more gao)
effect of increasing filtration
filtration = remove useless low e photons
curve shift down (qty overall decrease)
curve shift right (ave e increase)
hence lower contrast & density
what is attenuation
when xray interacts with matter
what are the 3 ways xray interact w matter
- coherent scattering - photons hit atoms causing atoms to vibrate and emit energy in a different direction. least harmful, least fx on film
- photoelectric absorption - all of incident photon energy absorbed by inner shell e- and is ejected. outer shell e- fills the vacancy and excess energy is emitted as characteristic photon. potential for bio damage bc of ionisation. more likely to occur in matter w high atomic no. (e.g. bones>lungs) hence leading to differential absorption
- compton scattering (MAJORITY) - incident photon knock out e-, excess energy exit atom as a photon. caused by high kVp and results in low contrast. potential for bio damage & scatter radiation that projects onto film as radiation fog
a round collimator PA equivalent to how much bg radiation?
2.5 days of bg radiation in sg.
pano dose = lat ceph dose x3
what is the law of Bergonie & Tribondeau
The radiosensitivity of a tissue is directly proportional to mitotic activity and inversely proportional to degree of differentiation of its cells
–> aka young ppl are more sensitive to radiation risks
stochastic vs deterministic bio fx of radiation?
stochastic: risk is proportional to dose, severity is independent of dose (no threshold). more xrays exposed = higher chance of developing something.
deterministic: severity is proportional to dose. above a certain threshold you will get it.
explain LNT
- x axis = level of radiation dose y axis = addition health risk due to radiation exposure
- black dots represent specific epidemiological data (mostly high radiation doses)
- no data present at low risk, so assume straight line to be extrapolated to 0
- this theory explains higher dose higher risk, no threshold bc risk is present at any exposure level
what efforts done to ensure ALARA
- lead apron, thyroid collar
- filtering, collimator
- high speed film
- long xray tube
- holders for accuracy ( no need retake )
- appropriate exposure time for each xray
what are the 3 principles of radiation protection
- principle of justification (benefit > risk)
- principle of optimisation (alara)
- dose limitation (reach max cap?)
what is pt selection criteria
Selection criteria = a framework used to decide whether xray should be taken. This framework ensures benefit > risk, and is individualized to each person
- Minimize xray exposure
- decrease probability of stochastic fx
- Prevent deterministic fx
layers of carious lesion
DIDSR zone of destruction bacterial invasion zone of demin zone of sclerosis reactionary dentin
classification for interprox caries
r0= no radiolucency r1= outer half of enamel r2= to inner half of enamel, not cross into dentin r3= cross into outer half of dentin r4= into inner half of dentin
3 types of AI and their defining ft
hypoplastic - rough pitted appearance. thinner enamel.
hypomaturation - brown sensi soft teeth. enamel thickness normal. dentin enamel same density
hypocalcified - chalky appearance, enamel thickness normal but softer (bc less mineral content). enamel lower density than dentin
defining ft of DI
gray blue / yellow brown teeth
short worn down crown, low contrast btwn layers
DI 1 - occurs in ppl w OI
DI 2 - no OI. short worn down bulbous crowns
2 types of dentin dysplasia and their defining ft
normal enamel abnormal dentin, abnormal pulp (pulpal obliteration)
extreme tooth mobility
1 - roots dont dvlp properly
2 - hypertrophic dentin (rare)
turners hypoplasia
EH only on 1 tooth, due to trauma on pri tooth
what to consider for pt selection criteria
- Dvlpt of dentition
- Caries risk
- Type of pt (new/recall/other indications upon clinical exam)
- Consider both dental and general health needs
- Must xray be done now?
- What type of xray most beneficial
compare AI
hypoplastic
hypomatured
hypocalcified
hypoplastic - rough pitted appearance
hypomatured - brown
hypocalcified - chalky
attrition
tooth against tooth
abrasion
tooth against non tooth (e.g. toothbrush)
how many PAs required for full mouth?
10
3 biological factors that affect radiosensitivity of cells
- cell metabolic rate
- cell mitotic rate
- cell differentiation/specialisation
