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
how to take lateral oblique maxillary occlusal radiographs
- Right or left
- Positioning
- 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°-55° to receptor
- To bisect angle between teeth & recepto
why are true mandibular occlusal radiographs true
Called “true” because the X-ray beam is
perpendicular to the receptor
positioning for true mandibular occlusal radiographs
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° to receptor & arch
* Either in midline or aligned with region of interest
* Note: do not use rectangular collimation
why are true mandibular occlusal radiographs taken
Investigating possibility of sialolith in main submandibular ducts
what are sialoliths
Calcification which forms in a salivary duct, potentially causing blockage
what is the growth pattern for sialolith
Concentric growth → may show layering of calcification
* Conform roughly to shape of duct
what is cbct
Form of cross-sectional “3D” imaging
* Allows structures to be viewed from any angle (without distortion)
* Becoming more prevalent in dentistry
posiitoning for anterior oblique mandibular occlusal radiographs
Align occlusal plane parallel to floor
* Place receptor against lower occlusal plane
* Get patient to bite gently
* Position X-ray tubehead
* In midline
* Aiming upwards through chin-point at receptor
* Approximate angulation 45° to receptor
when may you have to use small occlusal radiographs e.g. size 2
young child too small for large receptor
adults unable to tolerate large receptor
small area of interest
when are thyroid shields used
May be necessary whenever the thyroid gland is in theprimary X-ray beam
* Maxillary occlusal radiographs
* Bisecting angle periapical radiographs of maxillary anterior teeth
can cbct be used instead of occlusal radiographs
Can replace occlusal radiographs in certain cases
* Higher radiation dose therefore can only be used if occlusal radiographs unable/failed to answer clinical question
why are cbct good alternatives
Good alternative if visualising larger lesions within the jaws or investigating suspected alveolar bone fractures
