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Shadow casting rules applied to produce quality: (3 possibilities)
- Target to Image/Duplicate
- Target to Receptor
- Object to Receptor
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___ is cloudiness/unclear x-ray shadow cast….sharper image and slightly less magnification
penumbra
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(shadow casting rule)_____ use smallest possible on the target (radiation source)
focal spot
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function of the receptor?
to recodr the shadow image
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______to reduce the penumbra and magnification (tooth and radiation source)
Far target-object distance
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(shadow casting rule)______— to reduce penumbra and magnification (tooth and Film/PSP/Sensor)
Close object film distance
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(shadow casting rule)Object (tooth) and film/receptor need to be ____ relationship— to prevent distortion of the image
Parallel
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(shadow casting rule)Central ray and the object and film/receptor — ____relationship. to prevent distortion of the image
Perpendicular
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(Sharpness/Definition) Focal spot size
smaller = sharper and vice versa
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(Sharpness/Definition)Target-image receptor distance = PID to film/sensor
Longer the target-image-receptor the more parallel the beam = sharper image
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(Sharpness/Definition)Object-image receptor distance= teeth & receptor. place as close as possible to reduce penumbra. Magnification occurs with increased distance
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(Sharpness/Definition)
Motion =
loss of image detail
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(Sharpness/Definition)
Screen thickness=
intensifying screen lower rad needed but decrease sharpness
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(Sharpness/Definition)Crystal/pixel size of intraoral image receptors=
smaller crystals equal sharper image but needs increased time or rad. Digital depends on pixel sixe and #
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How to acquire a sharp image What is IDEAL?
- small focal spot on the target
- a long target-image receptor distance
- short object-image receptor distance
- Plus;Parallel & Perpendicular
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How image sharpness is lost?
- Large focal spot on the target and
- Long object-film distance results
- Penumbra
- NO Parallel & Perpendicular
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Factors Affecting the Radiographic Image:
Radiographic contrast
- ¤Subject –different absorption
- ¤kVp –high kVp = low contrast
- ¤Scatter radiation- (Compton) reduces integrity
- ¤Film/digital sensor type - manufacturer
- ¤Exposure – over/under = film fogProcessing – temp. time. Manual/digital/PSP
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Factors Affecting the Radiographic Image:
Magnification/Enlargement
- Defined: Increase in the size of the image
- Mostly influenced by the target-object distance
- Object-image receptor distance
- Target-object distance is determined by the length of the PID
- Long PID = more parallel beam = less magnification
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Factors Affecting the Radiographic Image:
Distortion:
- Different parts of the same object are magnified unequally
- Central ray is NOT perpendicular the object and plane of receptor
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Effect of varying exposure factors on image density:
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Exposure Time Variations:
- Defined: x-ray machine is fully activated and x-rays are produced
- If you change exposure time you change DENSITY
- Increase = Darker
- Decrease = Lighter
- This is the easiest to control
- Precalibrated machines (like PCC’s) kVp and mA can NOT be changed – only time can
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Milliamperage (mA) Variations
- Defined = # of x-rays generated/produced in the machine
- Increasing mA = Dark & Dense
- Lower mA = Lighter
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Kilovoltage (kVp) Variations:
- Defined = QUALITY of Wavelength energy produced
- More/Increase =
- Lower/Decrease =
Direct influence on CONTRAST
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Effects of Variations in Distances:
- 1 = x-ray source to skin
- 2 = teeth to receptor
- 3 = source to receptor plane
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Distance:
- Target-surface distance
- Target-object distance
- Object-image receptor distance
- Target-image receptor distanceTarget=PID
- surface=skin surface covering cheek
- object=tooth
- image receptor=sensor
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How does the Density change on the receptor as per the distance?
- Closest (4 feet) = Most Dense
- (8 feet) = Less moderate dense
- (16 feet) = least dense
- ======= distance changes photons
- Need to compensate for distance by increasing / decreasing the photons…>> How is this done?
- Increase the time = allows more e- (photon) production in the tube (power stays the same)
- Will allow the total # of photons to reach receptor
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The Bitewing Examination:
- most frequently performed
- crowns and alveolar bone of both the maxillary and mandibular teeth on a single radiograph
- #1 = incipient caries:
- Hope for remineralization
- Embrasures
- Primarily Molar an PM
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Which is the vertical bwx?
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Which is the horizontal bwx?
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BWX Principles:
- The receptor is placed in the mouth “parallel to the crowns of both the upper and lower teeth”
- The receptor is stabilized when the patient bites on the bitewing tab or beam alignment device.
- The central ray is directed through the contacts of the teeth, using a +10 degree vertical angulation.
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Bite-Wing Receptors size:
- Size 0
- For posterior teeth of children with primary dentition
- Size 1
- For the posterior teeth of children with mixed dentitions
- Size 2
- For posterior teeth of adults, placed horizontally or vertically
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Correct horizontal angulation BWX?
The central ray is directed perpendicular to the curvature of the arch and through the contact areas of the teeth.
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The positioning of the PID in a vertical or up- and-down plane
- Positive
- The PID is positioned above the occlusal plane and the central ray is directed downward.
- Negative
- The PID is positioned below the occlusal plane and the central ray is directed upward.
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Vertical Angulation for BWX
correct and incorrect?
- Correct vertical angulation: +10-degree
- Incorrect vertical angulation:Results in a distorted image
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Avoid Overlapping on BWX:
- Primary beam is directed toward the mean tangent
- Predetermined area
- Point of entry :Occlusal/incisal plane
- Correct (+10) vertical angle : +5 for children, Error is unequal arches
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Modifications in Bitewing Technique:
Edentulous Spaces
A cotton roll must be placed in the area of the missing tooth to support the bite-wing tab or beam alignment device.
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Modifications in Bitewing Technique:
Bony Growths
The receptor must be placed between the tori and the tongue.
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Most common reason for exposing dental radiographs?
caries detection
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Radiographs in the Detection of Dental Caries
Pathological process:
- Localized destruction of hard dental tissues
- Organic acid from microorganisms
- Process is progressive demineralization
- Deeper/advanced caries = more radiolucency
- May go without clinical detection (proximal)
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Occlusal relationships:
Class I & III
- receptor placement to the mandibular canine and 2nd PM
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Occlusal relationships:
Class II
- receptor placement to the maxillary canine and 2nd PM
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What about the “Tilting/Slanted” image?
Results from a failure to place the image receptor far enough lingually (in toward the tongue) to avoid being pushed down by the palate.
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Vertical Angulation:
- 1) Excessive vertical angulation prevents viewing proximal surface carious lesion
- (2) Proper vertical angulation shows the proximal surface caries
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Horizontal Angulation:
- (1) Incorrect horizontal angle = overlapping between adjacent teeth
- prevents viewing for interproximal caries
- (2) Improved horizontal angulation but caries difficult to view
- (3) Correct horizontal angulation clearly images caries
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Area to examine for interproximal caries?
- Two adjacent teeth contact
- Apical to where the gingival margin is (boxed area)
- Cervical burnout(optical illusion) the region apical to the gingival margin
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4 caries locations:
- Occlusal:
- Chewing/posterior surface
- Break through to DEJ can be imaged
- Seen as a flat radiolucent line
- PFSjQuery11010485798970662775_1506878021409
- Proximal (mesial and distal)
- Impossible clinically to examine
- Demineralized
- Buccal/lingual
- Most easily detected clinically
- Issue: 2D of a 3D (depth?)
- Cemental (root surface)
- Bone loss / recession
- May appear on B,L,M,D
- Ill defined radiolucent
- Below CEJ
- Crescent shape
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Recurrent / Secondary Caries Occurs around:
- restoration margins
- Poor cavity preps
- Defective margins
- Incomplete caries removal
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Rampant Caries Occurs around:
- “growing rapidly”
- Spreading unchecked
- Multiple teeth
- radiolucent
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Arrested Caries Occurs around:
- “stopped or Inactive”
- Cause: shift in oral environment
- Slow down in caries process
- Incipient enamel caries can be remineralized or reversed
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Conditions Resembling Caries
- Nonmetallic restorations
- Mimic decay
- Composite silicate resin
- Key: straight boarders
- Prepared look
- Even radiolucency
- Radiopaque base material
- Mach band effect
- Optical illusion
- Radiolucency caused by overlapping teeth images
- Radiolucent lines
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Conditions Resembling Caries
Cervical burnout
- Presents as a diffuse radiolucent area on the interproximal surfaces of the root apical to the cemento-enamel junction.
- Created by decreased x ray attenuation of the cementum as it is very thin and unable to stop x rays from reaching the image receptor.
- Attenuation is when the quantity of x rays is reduced by either absorption or scatter as it travels through matter
- No visible tooth structure missing in this area.
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