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176 Cards in this Set
- Front
- Back
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what does collimation do
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removes peripheral diverging rays thereby reducing patient dose
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what is the legal requirements of collimation
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60cm from patient
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what is filtration and how is it achieved
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filtering out of low energy x-rays via the use of an aluminium filter over portal
for units < 60kv = 1.5mm units > 70kv = 2.5mm internal filtration is achieved via glass tube housing with metal casing and oil sink |
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what are the inbuilt safety features of the x-ray unit
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1. housing (glass vacuum cylindersurrounded by metal casing)
2. collimator (removes peripheral diverging rays) 3. aluminium filter 4. timer 5. audible warning yellow and red light |
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how does an increase in KV affect the x-rays produced
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1. increase the amount of photons reaching the patient
2. increase the mean energy of the photons produced 3. increase the maximal energy of the photons produced |
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what is the latent image
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exposure to radiation chemically alters photosensitive silver halide crystals in the film to produce the latent image.
xrays interact with bromide ions to produce neutral bromide atoms and free e- which move through the crystal until they reach a sulphur sensitive site where they are trapped. these trapped e- then attract positively charged free interstitial silver ions forming neutral silver which collectively constitutes the latent image |
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what does developer do?
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converts neutral silver in the latent image into solid grains of metalic silver
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what does fixer do
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dissolves remaining unreacted silver bromide crystals leaving only the solid silver which is then the radiographic image
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what are non-stochastic effects
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effects in which degree of severity is proportional to the dose
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what are stochastic effects
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effects in which the probability that something will occur is proportional to the dose
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what factors dictate how sensitive a particular tissue will be to radiation
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1. proportional to cell proliferation rate
2. inversly proprtional to the degree of cell differentiation 3. increases with decreased oxygenation of the tissue blood forming > skin > bone > muscle > nervous |
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what should a PA measure
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entire tooth + 3-4 mm of bone surrounding apical regions
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The ideal BW?
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occlusal plane in the middle
equal amounts of max/man crowns and roots crestal 1/3 of alveolar process ideally no overlap |
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what is cervical burnout
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radiographic artifact that appears as a saucer shaped radiolucency immediately below CEJ and above alveolar crest
more obvious when there is horizontal overlap. Resulting from the differences in densities of adjacent tissues |
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what is the normal difference b/t the crestal bone heigh and the CEJ
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1.5mm
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how should bone loss be described
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local vs generalised
horizontal vs vertical furcation widening of the PDLS |
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what are BW used for
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1. detection of occlusal, interprox, recurrent caries
2. monitoring progression of caries 3. assess existing restorations 4. assess alveolar bone levels 5. dtection of peripheral pathology |
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where should the cone be positioned for a BW
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1. 65 degrees to mid saggital plane
2. radiographic baseline = outer canthus of eye to 1cm above border of mandible 3. place cone at +5-+10 degrees |
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what are PA's used for
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1. detect apical infections
2. crestal bone height and PDLS 3. assess impact of trauma 4. endodontics 5. assess morphology prior to extraction 6. impacted teeth 7. cysts or bone lesions 8. pre and post op assessment 9. evaluation of implants |
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what is the paralleling technique
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film is held parallel to the long axis of the tooth which is only achievable for lower molars unless a positioning device is used
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what are the pros of the paralleling technique
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1. zygomatic butress doesn't get in the way
2. increased accuracy of root apices, cervical line and relationship of alveolar crest to CEJ 3. little length distortion 4. decreased risk of cone cutting |
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what are the cons of paralleling technique
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1. film further away from tooth causing increased penumbra effect
2. can be uncomfortable for patient 3. anatomical restrictions 4. apices may appear close to film edge |
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what is the bisecting angle technique
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beam is positioned perpendicular to the bisecting angle b/t the film and the long axis of the tooth
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what are the pros of bisecting angle
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1. quick
2. comfortable 3. image should be same length as tooth |
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what are the cons of bisecting angle
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1. image distortion (elongation, foreshortening, molar distortion)
2. bone levels are poorly shown 3. crowns are distorted 4. difficult to reproduce |
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what are the factors that control magnification seen on radiographs
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1. object to film distance
2. target/object distance 3. size of the focal spot |
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what is the inverse square law in relation to the radiograph
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as anode/film distance increases, intensity of the beam decreases inversely proportional to the square of the distance I = 1/D squared
therefore at half the distance from the source to the object, the beam is four times more powerful |
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What is SLOB?
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Same Lingual Opposite Buccal
If an object is on the buccal side it will move opposite to the way that the tube is moved. If it is on the lingual it will move in the same direction. |
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Constituants of developer? (SHEPS)
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DEVELOPER
Reducing agents that donate electrons to silver ions Elon - Brings out shades of grey quickly. Temp independant Hydroquinone - Gives contrast slowly. Temperature sensitive ACTIVATOR Sodium Carbonate - softens gelatin and maintains alkaline conditions RESTRAINER Potassium Bromide - Delays developer effect, reduces fog PRESERVATIVE Sodium sulphite - Prevents oxidation of Developer Developer must be completely changed every 3-4 weeks |
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What film sizes are used for periapicals?
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Size 0/1 = Vertically placed for anteriors
Size 2 = Horizontally placed for posteriors |
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What film sizes are used for bitewings?
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Size 0 = children
Size 1 = mixed dentition Size 2 = adults |
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Current in the tungsten coil effects what?
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High current give high number of electrons in wire, therefore x-ray number.
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12 Properties of X-rays?
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1. Invisible, longitudinal waves of the EMS that travel as photons
2. Ionising 3. No charge 4. Travel at speed of light 5. Travel in straight lines 6. Damage/kill/mutate cells 7. Effect silver halides 8. Produces photofluorescence in some materials 9. Produced by electrons impacting on matter 10. Shorter wavelength than visible light 11. Emitted at a continuous spectrum - Shortest wavelength determined by tube voltage 12. Differentially absorbed |
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What are the occupational limits on radiation dose?
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20mSv/year over 5 years with no more that 50mSv in any one year
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What interaction produce X-rays?
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Braumstralung: X-rays produced via electron/nucleus interaction
Electron to Electron |
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What are the steps in image processing?
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Developing - Converts exposed silver halide crystals (which contain silver ions) to metallic silver, softens gel emulsion. 4.5 minutes at 20 degrees
Rinsing - 15/20 seconds Fixing - Halt development, remove undeveloped silver halide, harden gel emulsion Washing - remove thiosulphates that would otherwise turn the film brown, 10 minutes Drying |
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Constituants of fixer? (SAPS)
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FIXER
Sodium Thiosulphate - interacts with silver halide making it water soluble and therefore removable ACIDIFIER Acetic Acid - Neutralisers residual alkali therefore stoping development. Provides necessary acidic environmnet for hardener HARDENER Al Potassium Sulphate - hardens gel emulsion PRESERVATIVE Sodium Sulphite - prevents oxidation of residual Developer |
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What is the dental film made of?
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Base - hard gelatin, tinted slightly blue
Emulsion - gelatin matrix embedded with silver bromide crystals and some silver iodide crystals and sulphur. |
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whay are x-rays known as ionising radiation
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because they carry sufficient energy to eject e- from the atoms through which they pass
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how is breaking radiation produced
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results from loss of momentum when e- change direction on encounter with a +vely charged nucleus
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how is characteristic radiation produced
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e- from filament displaces e- from tungsten target atom causing ionisation of that atom. An e- from a higher state drops down to fill the valency shell and emits x-ray photons with precise energies
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what are the main components of the x-ray Unit
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1. tube
2. transformer and appropriate circuitry 3.radiation proof housing 4. filtration 5. collimator 6. exposure control timer |
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what are the ways in which the x-rays are focused
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1. cup on cathoder to focus e- stream to ensure that they only strike the target
2. small target area to reduce the penumbra effect |
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what does KV effect
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it controls the speed of the e- stream
- increase energy of e- causes increased penetrating power - max energy (shortest wavelength) photon produced depends on KVpeak - KVp controls contrast |
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what is contrast
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density differences on the radiograph
- range of shades of grey - dental machines have fixed KV of 60-70KV but the exposure time can be altered |
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what does current affect
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The quantity of e- produced at the filament
- indication of intensity - most dental units operate at 7-12mA |
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what are the factors involved in image formation
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1. wavelength (KV)
2. intensity (mA) 3. structure through which the radiation passes 4. thickness of the object 5. Exposure time |
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what are the four factors affecting the radiographic appearance
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1. angulation
2. orientation 3. magnification 4. soft tissues |
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the wavelength of x-rays used in med and dent are approx
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5-11.5 nanometres
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what is the approximate speed of the e- as they hit the target
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1/2 the speed of light
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what does the step down transformer do
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low voltage and high ammperage to heat the filament
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what does the step up transformer do
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high voltage and low amperage across the anode and cathode
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In what ways is collimation provided
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1. set up of transformers and tube housing
2. extension of the tube housing in the form of the tube 3. use of further filtering |
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what are the legal requirements for the exposure timer
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1. visual and audible warning
2. dead man switch |
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what is the alkalinity of the developer
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pH 11
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where should the film be placed if taking a BW of the premolars
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edge of film on midline of lower 3's
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where should the film be placed for molar BW
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ant edge of film should be placed at mesial of 2nd bicuspid
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how do we view BW and PA films
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dots towards us and orientated mesially
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how do we view occlusal films
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dots away for mandibular
dots toward for maxillary |
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what causes elongation
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the beam is at an angle greater than 90 degrees to the bisecting angle line
(too little positive angulation) |
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what causes foreshortening
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the beam is at an angle less than 90 degrees to the bisecting angle line (too much positive angulation)
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what is attenuation
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the process by which the beam of radiation is reduced in energy when passing through matter
attenuation = absorption + scattering |
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What are the BERT values for
- BW / PA - OPG - Chest x-ray - transatlantic flight |
BW/PA
- round collimation = 16hrs - rectangular collimation = 8hrs - using e speed = 8hrs OPG = 28hrs chest xray = 4 days transatlantic flight = 5 days |
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what are the legal requirements for the storage of radiographs
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1. Name of Dr
2. Name of patient 3. Date 4. laminated 5. stored for minimum of 7 years |
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What is the inverse square law?
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relationship between the distance and the intensity of the radiation. The intensity of the radiation varies inversely to the square of the source to film distance. Because photons spread out as they move away from the source it is an important factor for determining the intensity of the beam. The kVp and mA are fixed so the law can be used to determine exposure time
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What is the ALARA principal
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•As Low AS Reasonably Achievable
•Protect Patients and Staff against any possible harmful effects of radiation by : •Maintaining equipment •Good techniques •Extra protective measures |
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Examples of the application of the rules of radiation safety?
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•Use rectangular collimator
•Use high speed films •Lead apron for pregnant women or carers •Staff-stand at least 2m behind tube or behind a barrier •No other staff in room at the time •Never hold a film for a patient |
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Production of X Rays?
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X-rays are produced when high speed electrons are suddenly decelerated when they collide with the target of the x-ray tube
•The speed of the electrons depends on the kV-difference in E potential between Cathode & Anode •When the electrons are suddenly stopped by a heavy metal target made of Tungsten in a solid copper tube (the anode) the kinetic E is converted into heat & x-ray photons of many different wavelengths •This target ( the focal spot) is as small as possible to reduce the PENUMBRA EFFECT and set at an angle to reduce overheating |
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Scattering?
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A change in direction of the photon with or without loss of E (energy)
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Absorption?
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Removal of E from beam
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Attenuation?
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Beam of radiation is reduced in E when passing through matter; Attenuation = Absorption + Scattering
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Ionisation?
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Process of forming an ion pair. Neutral atom loses electron to form +ve ion + -ve electron
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Bremsstrahlung X-ray Production?
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The majority of x-rays produced are known as Bremsstrahlung. These x-rays result from the attraction between the high-speed electrons (negative charge) from the filament and the protons (positive charge) in the nuclei of the target atoms. The attraction causes the electron to slow down and change direction, resulting in the release of energy in the form of an x-ray. The closer the electron passes to the nucleus, the greater the energy of the resultant x-ray. If the electron hits the nucleus, a maximum energy x-ray results.
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Density?
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degree of darkening of an exposed and processed film. Created by the amount of developed silver in any area of the radiograph
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Contrast?
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Relative density differences between various image areas on a radiograph.
Increased by:Lowering kVpAn increase in subject contrast |
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Sharpness?
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Measures how well the details (boundaries) of an object are reproduced on a radiograph
Increased by: Source-object distance Object-film distance Film crystal size - motion will decrease sharpness |
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How can magnification be decreased
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Decreased by:
increasing the Source-object and decreasing the distanceObject-film distance |
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how is the penumbra effect reduced
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long cone technique and small focal spot
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What is the max beam size that collimation should allow?
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7 cm in diameter at skin surface.
Switching from 7cm round collimation to rectangular collimation reduces dose by 55%. |
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what are the protection measures for the operator
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Do not hold films for patient
• Utilize barriers if possible, Door with leaded glassWall of room (drywall adequate protection); need mirror mounted opposite doorway so that you can see patient in operatory • Adhere to position-and-distance rule if no barriers available –at least 2m away50 |
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How is film speed computed?
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The raw film Speed (S) is computed as S=0.01/Ks, where Ks is the exposure (Gray) that produces 1 optical density over base plus fog density.
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What is the raw film speed for E and F films
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E = 55
F = 57 |
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Faster film speed in relation to the silver halide crystals?
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Higher Film Speed = Larger size Silver Halide Crystals
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what is the exposure reduction between E and F? D and F?
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E speed to F speed there is an exposure reduction of at least 20%
50-60% when switching from D to F |
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THE ELECTROMAGNETIC SPECTRUM? Wave?
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A wave is defined as:
a variation that transfers Radiant Energy progressively from point to point in a medium Called Electromagnetic Radiation because E that is radiated is accompanied by oscillating electro and magnetic fields |
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Factors affecting the Radiographic image?
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-Angulation
•Magnification •Orientation •Soft tissue shadows |
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Vertical angulation of the tube head for BW's
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The central ray is directed through the centre of the film at + 5 - 10 when thepatient’s occlusal plane is parallel to the floor. The film is usually placed horizontally but may be placed vertically in cases of severe periodontal bone loss
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Writing a report. Order and things covered?
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•Type of film and teeth viewed
•A/D/mixed - age •Film faults •General status of dentition •Perio -bone loss and severity * Other Pathology: Site; Lucency; size; shape; definition; border; affect on other structures * DDx |
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Protocol for mounting films?
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1.Dimple raised towards you
2.Orientate L & R as if the patient is facing you 3.Teeth in the anatomically correct position 4.Correct labelling with the date, patient’s name and registration number 5.Record the operator’s name 6.Laminate films if possible 7.Staples are not to encroach on diagnostic areas of the film. BW’s staple in space at the occlusal surface or any space. Staple periapicals at the occlusal surface |
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Factors affecting appearance of caries?
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X-ray beam angle (horizontal or vertical). This is especially important when trying to identify recurrent caries, since changes in angulation may cause the superimposition of the existing restoration with the carious lesion.
Exposure factors. Caries detection is improved with a lower kVp setting, which provides a higher contrast. If the density of the film is too light or too dark, the diagnostic potential of the film is limited. |
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Caries classification?
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I = insipient (stage 1)
M = moderate (stage 2) A = advanced (stage 3) S = severe (stage 4) |
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Advanced caries?
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1/2 way to the pulp chamber, involves enamel and dentine
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what is meant by film speed?
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the exposure required to produce and optical density of 1.0 above BASE PLUS Fog
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What is meant by grey scale
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Radiographs are greyscale representations of structures. Different shades of grey are produced by the differing densities of the structures
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What are the colour tabs representative of?
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grey = D speed single
Green = D speed double Mauve = F speed Single Beige = F speed double |
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what are the components of the film pack?
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a. Sealed plastic waterproof cover with coloured tab to denote film type
b. lead foil sheet reduces film fog produced by backscatter radiation from intraoral structures beyond the film c. black paper card wrapped around the film d. film itself |
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what are Panoramics used for?
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1. establish size and site of path
2. fractures 3. changes in antra 4. condyle head changes 5. 3rd molars prior to surgery 6. general perio appraisment 7. implant and prosthetic cases 8. ortho |
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What is a cephalometric radiograph and what is its purpose?
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lateral projection of the sagittal plane. commonly used in ortho for the assessment of growth and development and assessment of facial and jaw proportions
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The wavelength of x-rays used in med and dent is roughly?
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5.0 to 11.5 nanometers
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what is secondary radiation?
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radiation produced when primary x radiation passes through matter
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ionisation is when?
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An atom loses an electron
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an electron with greatest binding energy would be found in which shell?
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k shell
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Lead aprons should?
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- never be folded
- conform to standard requirements - be regularly inspected |
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what is the vertical angulation of the opg beam?
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-5 to -7 degrees to the horizontal plane so that the beam can pass beneath the occipital portion of the skull
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how are rotational panoramic radiographs taken?
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Rotating a narrow vertical beam of radiation in the
horizontal plane externally around a rotational axispositioned intra orally |
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what equipment is involved in taking an OPG?
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why is it important for the film and the beam to rotate when taking an opg?
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If the film was stationary the magnification in the horizontal plane would be greater than in the vertical plane. By moving the film in the opposite direction to to the horizontal rotation of the beam this discrepancy is eliminated. The vertical and horizontal dimensions match only when the object lies within the central plane. Objects outside this plane may appear distorted and fuzzy.
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How does the position of the object relate to its representation on the film?
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The lateral and more posterior structures are projected
to each side of the panoramic radiograph. |
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Focal Trough / Image layer?
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3D curved zone formed by the continuously changing center of rotation. Structures lying within the focal trough are relatively well defined on the radiograph. Those structures that lie behind the trough will be widened and those infront will be narrow.
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What is the distortional difference between the mand and the max in the OPG?
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Maxillary structures are more spread out than mandibular structures due to the -ve angulation of the beam.
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What are the 7 points to recognise ghost images?
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1. same shape
2. opp side 3. larger vertically 4. higher than real image by approx 7 degrees due to angulation of the beam 5. fuzzy 6. horizontal component will be sharper 7. lies within the hatched area |
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what fault has occured if the image on the left appears wider than that on the right for an OPG?
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The pt has their head turned toward the Left (same side that is mag)
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what fault has occured if the image appears to incline upwards at the sides of an OPG?
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The pt chin is down.
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what fault has occured if the OPG white in the middle?
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Pt is slumped causing a spine-shadow ghost
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what is a ghost image?
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A ghost image is a blurry reverse image of an object
that is imaged superiorly on the contralateral side slightly higher that the height of the actual image |
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wavy distortion of the OPG is due to?
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Pt doing an open/close movement with the jaw
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What fault has occured when downward curvature of the occlusal plane. The rami are
tilted laterally. The palate is superimposed on the apices of the maxillary incisors. |
Patient's head is tilted backwards, that is, the chin
is positioned upwards. |
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What OPG fault has occured when there is horizontal
magnification and unsharpness of anterior teeth. |
Patient's chin is positioned posterior to the focal
trough (zone of sharpness). |
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What OPG fault has occured when there is horizontal
demagnification (narrowing) and unsharpness of anterior teeth. |
Patient's chin is positioned anterior to the focal
trough (zone of sharpness). |
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What OPG fault has occured when One side of the jaws is horizontally demagnified while the other side is magnified.
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Patient's head is positioned towards one side
(laterally) and outside of the focal trough (zone of sharpness), that is, the patient's mid-sagittal plane is not positioned in the middle of the two head positioners. |
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What OPG fault has occured when there is bilateral prominent images of the vertebrae.
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Patient's head and neck are placed excessively forward in the
panoramic machine resulting in bilateral prominent images of the vertebrae. The vertebrae are prominently seen whenever the neck is positioned too forward. The anterior teeth are horizontally demagnified and unsharp. Note if there is upward curvature of the occlusal plane and the medial tilt of the rami then the patient's head is also tilted downwards. |
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What OPG fault has occured if there is horizontal demagnification, giving the
illusion of missing anterior teeth. |
Excessive anterior positioning to the focal trough
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What is the single real image and how is it formed?
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What are double real images and how are they formed?
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What are the double image characteristics?
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What are ghost images and how do they form?
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What are the characteristics of ghost images?
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How is soft tissue seen in the OPG?
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What are the multiple density changes seen in OPG's?
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1. Air obscures hard tissue
2. Soft tissue obscures air 3. Hard tissue obscures soft tissue 4. Ghost images obscure everything |
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Absorbed dose
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The mean energy imparted by ionizing radiation to matter. The unit of absorbed dose
in the joule per kilogram (J/kg). The special name of the unit of absorbed dose is the gray (Gy). |
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Absorption
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Deposition of energy, i.e. removal of energy from the beam
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Ampere (amp):
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is the unit of quantity of electronic current. It equals a flow of 6.25 x 1018 electrons
per second. |
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Anode
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A positive electrode which will attract the negative electrons. It is made of solid copper with a
tungsten target set at an angle. |
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Attenuation
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the process by which a beam of radiation is reduced in energy when passing through
matter. Attenuation= Absorption + Scattering. |
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BERT value
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Background equivalent radiation time- assuming an average background radiation of
3mSv/yr. |
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Cathode
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A negative electrode from which electrons are emitted. Consists of tungsten filament in front
of a molybdenum reflector cup used to focus the electron beam. |
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Contrast
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the differences in density between various image areas on a radiograph.
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Compton effect
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the attenuation process for x-radiation in which an incident photon interacts with an
orbital electron of an atom to produce a recoil electron and a scattered photon of reduced energy. |
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Cumulitve Dose
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the total dose as a result of repeated exposures to radiation of the same region or to other body parts.
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Dead man switch
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a switch used to initiate an x-ray exposure which will automatically terminate the
exposure when released. |
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Density
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the degree of darkening of exposed and processed x-ray film.
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Dose equivalent (H):
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a quantity used to express the risk of deleterious effects of ionizing radiation upon living
organisms, given by the product of D, Q and N at the point of interest in tissue: Where H = DQN Where D = the absorbed dose Q = the quality factor N = the product of any other modifying factors. The unit of dose equivalent is the joule per kilogram (J/kg). The special name of the unit of dose equivalent is the sievert (Sv). |
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Dose rate
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the absorbed dose per unit time.
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Effective dose equivalent
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the quantity used to express the weighted dose equivalent to the whole body when it
is irradiated non-uniformly or partially. |
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Exposure factors
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the X-ray tube potential in kilovolts (peak) (kV peak) and milliamperes (mA) and the
exposure time in seconds (s), or the product of the tube current and exposure time in milliampere seconds (mAs). |
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Fog
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a darkening of the whole or part of a developed radiograph from sources other than the radiation of the
primary beam to which the film is exposed: - Chemical: due to imbalance or deterioration of processing solutions. - Light: unintentional exposure to light before or during processing. - Radiation: from other sources of radiation than the primary beam, e.g. scatter non-protective film storage. |
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Half value layer
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the thickness of a specified material which reduces the kerma rate of a given X-ray beam to
half its original value. |
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ionisation
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Loss of an electron in the outer shell of a neutral atom to become a +ve ion + electron –ve ion.
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Kerma
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the kinetic energy released in material by ionizing radiation. The unit of kerma is the joule per Kilogram (J/kg). The special name of the unit is the gray (Gy).
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kVp
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the potential difference between the anode and cathode of an x-ray tube.
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Latent period
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the time between exposure of tissue to radiation and the manifestation of a response.
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Lead equivalent
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the thickness of lead effecting the same attenuation of a beam of a specified radiation quality
as the material under consideration at a specified Kilovoltage (kV peak). |
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Leakage radiation
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ionizing radiation transmitted through the protective shielding of a radiation source.
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Panoramic radiography
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radiography performed by using an intra-oral X-ray source with extra-oral image
receptors. |
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panoramic tomography
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radiography performed by the controlled rotation of an extra-oral X-ray source and an
extra-oral image receptor around one or more axes in relation to the patient’s head. |
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Scattering
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Change in direction of a photon with or without loss of energy
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Useful beam (from a source of ionizing radiation):
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all ionizing radiation which emerges through the specified
aperture of its protective shielding and its beam collimator. |
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scatter radiation
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ionizing radiation resulting from the interaction of ionizing radiation with matter.
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Sievert (Sv):
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the special name of the unit of dose equivalent equal to 1 joule per kilogram (J/kg).
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Speed or sensitivity of an X-ray film
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the reciprocal of the exposure required to produce an optical density of
1.0 above base + fog for specified exposure and processing conditions. |
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Narrow blurred anterior teeth sometimes
with pseudo-spaces between the teeth. Superimposition of spine on ramus. Bicuspid overlap bilaterally. Useful to see nasal & sinus cavities |
Patient too far forward.
Use incisal bite guide. Line up incisal edge of teeth with notch. Edentulous patients should bite about 5mm behind notch. |
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Wide, blurred anterior teeth, loss of apices.
Ghosting of rami, spread-out turbinates, ears, and nose in image, condyles off lateral edges of film. |
Patient too far back. Use incisal guide.
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Excessive curving of the occlusal plane.
Losses of image of the roots of the lower anterior teeth because real, double & ghost images of palate form a wide opaque line. Mandible widened vertically in anterior region & traversed by double &/or ghost image of the hyoid bone Narrowing of the intercondylar distance and loss of head of the condyles at the top of the film. |
Chin tipped too low. Tip chin down, but ala-tragus line should not
exceed -5o to -7o downward. Use chin rest. |
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Flattening or reverse curvature of occlusal
plane. Loss of image of the roots of the upper anterior teeth. Lengthening of intercondylar distance and loss of head of the condyles at the edges of the film. Hard palate shadow wider and superimposed on the apices of the maxillary teeth. |
Chin raised too high. Tip chin down -5o to -7o.
Use chin rest. |
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Unequal right-left magnification of
posterior teeth & ramus. Inferior turbinate and meati are spread out across the sinus on the magnified side. Opposite sinus may have improved image. Ghost image of ramus more obvious on the narrow side. Severe overlap of contact points and blurring. |
Head twisted. Line up patient’s midline with middle of
incisal bite guide. Close side guide. |
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Mandible appears tilted on film.
Unequal distance between mandible and chin rest at a given point on the right and left sides. One condyle is higher and larger than the other. |
head tilted. Position the chin firmly on both sides of the
chin rest. Close side guide. |
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Ghost image of cervical spine
superimposed on the anterior region. |
Slumped position. Stand-up machines: have the patient step
forward or place feet on markers. All machines: be certain the patient is sitting or standing erect. |
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Sinus not visible on the film.
Top of condyles are cut off. Excessive distance between inferior border of the mandible and lower edge of the film. |
Chin not on the chin rest
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Incisal and occlusal surfaces of the upper
and lower teeth overlapped. |
bite guide not used
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Relative radiolucency obscuring apices of
the maxillary teeth (palato-glossal air space) |
tongue not on palate
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Relative radiolucency on the coronal
portion of the upper and lower anteriors. |
lips open
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Wavy outline of cortex of the interior
border of the mandible. Blurring of the image above wave cortical outline. |
patient moved
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Primary radiation
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radiation frome the tube itself
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secondary radiation
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“scatter radiation” -is produced by primary radiation on
its passage through matter. |
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background radiation
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comes from “normal” objects around us, from food
ingested etc. |
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Bert for Pa and BW's
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16hrs for D speed and half that for e and f.
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