Bisecting Radiographs Flashcards
What is the geometry for bisecting angle periapical and occlusal radiographs?
- X-ray beam not perpendicular to long axes of tooth or receptor
- Long axes of tooth and receptor not parallel to one another
What is the geometry for bitewings and paralleing periapical radiographs?
- X- ray beam perpendicular to long axes of tooth & receptor
- Long axes of tooth & receptor parallel to one another
What happens if the tooth/receptor are not perpendicular to X-ray beam?
image shortened and stretched
What is the bisecting angle technique?
If the tooth & receptor are tilted at equal but opposite angles
→ the 2 effects counteract one another & image has (adequately) correct dimensions
When is the bisecting angle technique used?
used when unable to position receptor parallel to subject
When is the bisecting angle technique used in periapicals?
Applies to some periapical radiographs
- Shallow hard palate or lingual sulcus
- Young child struggling to tolerate receptor in mouth
- Tender tooth preventing patient biting on receptor holder
- Edentulous patient
When is the bisecting technique used in occlusal radiographs?
Applies to most occlusal radiographs
- Necessary since receptor lies in occlusal plane (therefore not parallel to tee
What are the benefits of holders when using technique for periapicals?
avoid radiation dose to hands
reduces chance of receptor shifting in mouth
some holders will guide positioning of x-ray bean
What are the benefits to bisecting techniques compared to paralleling technique?
Receptor position potentially more comfortable for patients - can be flat up against tooth
Positioning slightly simpler & quicker
What are the downsides to the bisecting techniques compared to the paralleling?
Estimating X ray beam angulation can lead to varying degrees of image distortion
Images hard to reproduce (between appointments & between different operators)
Increased risk of irradiating thyroid gland
Altered positions of some anatomy eg. cemento enamel junction, alveolar bone levels, zygomatic buttress, nose, buccal roots
What anatomy can be altered in bisecting angle technique?
cemento enamel junction, alveolar bone levels, zygomatic buttress, nose and buccal roots
What technique should be used for periapicals usually?
paralleling (better image quality, lower patient dose, better reproducibility)
What is the size of occlusal radiograph receptors usually?
size 4 (larger than intra-oral radiographs)
What does the patient do to the receptor?
bite gently
Occlusal radiographs advantages
- Allow visualisation of the dentition/jaws from a different angle oral radiographs (unerupted teeth & investigating suspected root/alveolar bone fractures)
- Provide a slightly larger image of the dentition/jaws
- Can be used as an alternative to an anterior periapical radiograph if patient struggling to tolerate periapical holder (image typically less diagnostic than a periapical radiograph)
What is the standard maxillary occlusal?
anterior oblique maxillary
How is a anterior oblique maxillary occlusa positioned?
- Align occlusal plane parallel to floor
- Place receptor against upper occlusal plane, centrally within mouth
- Get patient to bite gently
- Position X-ray tubehead
In midline
Aiming downwards through bridge of nose at receptor
Approximate angulation 65
To bisect angle between incisors & receptor
How is a lateral oblique maxillary positioned?
Right or Left
- Align occlusal plane parallel to floor
- Place receptor against upper occlusal plane, towards side of interest (Long axis of receptor aligned antero-posteriorly)
- Get patient to bite gently
- Position x-ray tubehead (over region of interest, aiming downwards through cheek at receptor, approximate angulation 45)
Why is the true mandibular called true?
x-ray beam is perpendicular to receptor
How is a true mandibular positioned?
- Place receptor against lower occlusal plane
- Get patient to bite gently
- Tilt head back as far as comfortably possible
- Keep head supported by headrest
- Position X- ray tubehead (aiming upwards under chin, angled 90, either in midline or aligned with region of interest)
- Note:do not use rectangular collimation
What is a sialoith?
Calcification which forms in a salivary duct, potentially causing blockage
What does an anterior oblique mandibular look like?
large periapical radiograph
How is an anterior oblique mandibular occlusal positioned?
- Align occlusal plane parallel to floor
- Place receptor against lower occlusal plane
- Get patient to bite gently
- Position x-ray tubehead (approximate angulation 45, in midline, aiming upwards through chin point to receptor)
For younger children, what size receptor is used?
size 2
When is a throid shield used?
when thyroid gland is in the primary x-ray bean (maxillary occlusal, bisecting angle periapical)
What is CBCT?
Form of cross-sectional “3D” imaging
Allows structures to be viewed from any angle (without distortion)
Becoming more prevalent in dentistry
When is CBCT used?
Higher radiation dose therefore can only be used if occlusal radiographs unable/failed to answer clinical question
