Bisecting Angle Technique & Occlusal Radiography Flashcards
what are the two types of periapical radiographs
- paralleling
- bisecting angle
what are the two types of occlusal radiographs
- maxillary
- mandibular
how do bitewing radiographs and paralleling periapical radiographs follow the ideal projection geometry
- xray beam perpendicular to long axis of tooth and receptor
- long axis of tooth and receptor parallel to to one another
how do bisecting angle periapical radiographs and occlusal radiographs follow the ideal projection geometry
- xray beam not perpendicular to long axis of tooth or receptor
- long axis of tooth and receptor not parallel to to one another
why may an image be shortened
if tooth is not perpendicular to x-ray beam, the image is shortened
why may an image be stretched
if receptor is not perpendicular to x-ray beam, the image is 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
what two types of radiographs do we use the bisecting angle technique
some periapical radiographs and most occlusal radiographs
which 4 cases do we need to use the bisecting angle technique for 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
why should we carry out the bisecting angle technique for occlusal radiographs
Necessary since receptor lies in occlusal plane (therefore not parallel to teeth)
when is the bisecting angle technique used
Used when unable to position receptor parallel to subject (e.g. tooth)
describe the projection geometry for the bisecting angle technique
- Place receptor as close to subject
as possible (without bending) - Estimate the angle between the
long axes of the subject & receptor
* Note proclined/retroclined teeth - Bisect this angle with an imaginary
line - Aim the X-ray beam perpendicular
to this bisecting line
what are the 2 choices for periapical radiography
- bisecting angle (tooth and receptor are not perpendicular to beam)
- paralleling (where they are)
why should you use a holder for periapical radiography
- Avoid radiation dose to hands
- Reduces chance of receptor shifting in mouth
- Some types will guide positioning of X-ray beam
benefits of bisecting angle technique for periapical radiography (vs paralleling technique)
- Receptor position potentially more comfortable for patients
- Can be flat up against tooth
- Positioning slightly simpler & quicker
downsides of the bisecting angle technique
- 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
- e.g. cemento-enamel junction, alveolar bone levels, zygomatic buttress, nose, buccal roots
which technique should be used for periapical radiographs based on official guidelines
paralleling technique as there is improved image quality, better reproducibility and a lower partient dose compared to the bisecting angle technique
types of upper occlusal radiographs
Upper
* Anterior oblique maxillary occlusal
* Lateral oblique maxillary occlusal
* Right or left
types of lower occlusal radipgraphs
Lower
* Anterior oblique mandibular occlusal
* True mandibular occlusal
what is the receptor size for occlusal radiographs
size 4 normally
how to carry out occlusal radiographs
- Positioned in occlusal plane
- Faces up or down depending on which jaw
is being imaged - Orientation dependent on size of mouth &
patient tolerance - Once in position, patient bites together to
hold receptor in place
how to reduce damage on from biting
Can add a protective layer to prevent/reduce
damage from biting
* Cardboard (single use) or plastic (multi-use)
features of occlusal radiographs
Allow visualisation of the dentition/jaws from a different angle
* Particularly useful for localising unerupted teeth & investigating suspected root/alveolar
bone fractures
Provide a slightly larger image of the dentition/jaws
* Particularly useful for lesions too big for periapical radiography
Can be used as an alternative to an anterior periapical radiograph if patient
(esp. young child) struggling to tolerate periapical holder
* But image typically less diagnostic than a periapical radiograph
how to position anterior oblique maxillary occlusal radiographs
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 receptor
* To bisect angle between incisors & receptor
