Best film for period disease>
BW, PA (Parallel)
Ideal X-rays uses:
- small or large focal spot?
- long or short target-receptor distance?
- long or short object-receptor distance?
- smallest focal spot (image sharpness)
- longest target-receptor (x-ray source and receptor) PID
- shortest object-receptor (tooth and image receptor)
Which results in more magnification:
- shorter or longer PID?
- shorter or longer object-receptor distance?
- shorter PID (although long PID reduces exposure)
2. longer (although shorter is ideal to prevent distortion)
increase exposure factor causes what to the density?
Increases it (darker it gets)
Higher kVp, mA, time
decreased thickness causes less exposure
number of electrons flowing per second in the x-ray tube
mA (quantity) = TEMPERATURE of the filament = 7-15 mA
- Quality = penetrating power = kVp = speed and energy of electrons = 65 - 100 kVP
Fractionalization
- means total radiation dose is delivered in smaller, but multiple doses
- Increases O2 tension –> Greater tumor destruction
- Has a larger chance for host cellular repair.
Radiation effects to normal marrow
- replaced with fatty marrow and fibrous CT
- By end of Week 2 of therapy, loss o taste buds + mucositis –> pseudomembranes
Osteoradionecrosis risk with ___ Greys of radiation
> 40 Gy
Hypocellular, hypovascular, Hypoxic
Stochastic vs non-stochastic effects
stochastic = direct dose dependent = cancer non-stochastic = have a threshold of radiation = hair loss, infertility
most radiosensitive and radio resistant cells
radiosensitive = small lymphocyte radioresistant = muscle, nerves
X-ray properties
no mass no charge speed of light travels in waves (short waves) straight lines can cause fluorescence (longer waves) cannot be focused to a point
Exposure time of digital vs F-film vs D speed
digital is 50% of F speed (Fast film)
F speed is 60% of D speed
Dental x-rays use 70kV or higher (higher doses lower patients exposure on skin)
Collimation is 2.5 inches max to reduce exposure
most common digital image receptor?
CCD
- contains a silicon chip
- sensitive to light (x-rays)
maximum permissible radiation dose
non-occupation = 0.001 Sv/yr (a pregnant occupation) occupation = 0.05 sv/yr
- stand 6 feet, perpendicular (90 degrees) from source
match high/low contrast with short/long scale contrast with black/grey/white scale with high/low kV
High contrast = black/white = short scale = low kV
Process film by hand: developed –> fixer –> replenisher
- Developer is needed to transform the latent image to a visible one. This removes the halide portion of the silver halide crystals. Silver halide crystals are reacted when touched with x-ray beam –> radiolucency.
- Fixer is ammonium thiosulfate which clears unexposed/under-developed silver halide crystals and hardens it.
Note: the developer chemical is neutralized by an acidifier (acetic/sulfuric acid) that is part of the fixer solution. This is also done in the washing stage before the fixer.
- Replenisher compensates for loss of volume from oxidation and maintains adequate amounts of chemicals for uniform processing
Fixing time (10 minutes) is twice as long as developer (5 minutes)
- There must be __ % of demineralization in teeth to be seen radiographically.
- There must be ___% of bone alteration for PA breakdown to be seen radiographically.
- 30-60%
- 30-50%
PA radiolucency is only seen once cortical plate is perforated
Need only 0.5 - 1.0 mm needed through cortical bone
PA lesions will heal in 6-12 months post successful RCT
SLOB rule angulation
Horizontally 10-15 degrees
What is the most likely cause of a U shaped radiopacity covering the apex of the palatal root of the maxillary 1M?
zygomatic process of the maxilla
Lateral ceph. growth reference point
Anterior cranial base
Lateral ceph magnification: 7-8% acceptable
Hamulus (Hamular process)
- surved, hook shape of the medial pterygoid of the sphenoid bone
- superior attachment for the pterygoidmandibular raphe (a tendon between the buccinator and superior constrictor muscle)
Hamular notch is between the max tuberosity and hamulus
Radiation types
kinetic enegery converts electrons to x-ray photons via:
- General radiation = braking (sudden stop of photons due to Tungsten present = 70% of radiation) or Bremsstrahlung
- Characteristic radiation = electrons dislodge an inner shell electron from tungsten, causing ionization. Other electrons fill it in and produce a photon = small % = occurs only at > 70kVp
Primary radiation = what leaves the tube head
Secondary radiation = formed after the primary beam hits matter.
Scatter radiation = type of secondary radiation where its deflected by matter
Compton scatter = type of scatter where ionization (high E interacts with OUTER ring) takes place (62% of scatter)
Coherent/unmodified scatter = lower E electron causes no interaction
