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Pre-BDS3 Radiology > Bisecting Angle Technique & Occlusal Radiography > Flashcards

Bisecting Angle Technique & Occlusal Radiography Flashcards

1
Q

what are the two types of periapical radiographs

A
  • paralleling
  • bisecting angle
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2
Q

what are the two types of occlusal radiographs

A
  • maxillary
  • mandibular
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3
Q

how do bitewing radiographs and paralleling periapical radiographs follow the ideal projection geometry

A
  • xray beam perpendicular to long axis of tooth and receptor
  • long axis of tooth and receptor parallel to to one another
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4
Q

how do bisecting angle periapical radiographs and occlusal radiographs follow the ideal projection geometry

A
  • xray beam not perpendicular to long axis of tooth or receptor
  • long axis of tooth and receptor not parallel to to one another
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5
Q

why may an image be shortened

A

if tooth is not perpendicular to x-ray beam, the image is shortened

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6
Q

why may an image be stretched

A

if receptor is not perpendicular to x-ray beam, the image is stretched

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7
Q

what is the bisecting angle technique

A

If the tooth & receptor are tilted at equal but opposite angles → the 2 effects
counteract one another & image has (adequately) correct dimensions

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8
Q

what two types of radiographs do we use the bisecting angle technique

A

some periapical radiographs and most occlusal radiographs

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9
Q

which 4 cases do we need to use the bisecting angle technique for periapical radiographs

A
  • Shallow hard palate or lingual sulcus
  • Young child struggling to tolerate receptor in mouth
  • Tender tooth preventing patient biting on receptor holder
  • Edentulous patient
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10
Q

why should we carry out the bisecting angle technique for occlusal radiographs

A

Necessary since receptor lies in occlusal plane (therefore not parallel to teeth)

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11
Q

when is the bisecting angle technique used

A

Used when unable to position receptor parallel to subject (e.g. tooth)

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12
Q

describe the projection geometry for the bisecting angle technique

A
  1. Place receptor as close to subject
    as possible (without bending)
  2. Estimate the angle between the
    long axes of the subject & receptor
    * Note proclined/retroclined teeth
  3. Bisect this angle with an imaginary
    line
  4. Aim the X-ray beam perpendicular
    to this bisecting line
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13
Q

what are the 2 choices for periapical radiography

A
  • bisecting angle (tooth and receptor are not perpendicular to beam)
  • paralleling (where they are)
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14
Q

why should you use a holder for periapical radiography

A
  • Avoid radiation dose to hands
  • Reduces chance of receptor shifting in mouth
  • Some types will guide positioning of X-ray beam
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15
Q

benefits of bisecting angle technique for periapical radiography (vs paralleling technique)

A
  • Receptor position potentially more comfortable for patients
  • Can be flat up against tooth
  • Positioning slightly simpler & quicker
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16
Q

downsides of the bisecting angle technique

A
  • 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
17
Q

which technique should be used for periapical radiographs based on official guidelines

A

paralleling technique as there is improved image quality, better reproducibility and a lower partient dose compared to the bisecting angle technique

18
Q

types of upper occlusal radiographs

A

Upper
* Anterior oblique maxillary occlusal
* Lateral oblique maxillary occlusal
* Right or left

19
Q

types of lower occlusal radipgraphs

A

Lower
* Anterior oblique mandibular occlusal
* True mandibular occlusal

20
Q

what is the receptor size for occlusal radiographs

A

size 4 normally

21
Q

how to carry out occlusal radiographs

A
  • 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
22
Q

how to reduce damage on from biting

A

Can add a protective layer to prevent/reduce
damage from biting
* Cardboard (single use) or plastic (multi-use)

23
Q

features of occlusal radiographs

A

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

24
Q

how to position anterior oblique maxillary occlusal radiographs

A

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

25
Q

how to take lateral oblique maxillary occlusal radiographs

A
  • 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
26
Q

why are true mandibular occlusal radiographs true

A

Called “true” because the X-ray beam is
perpendicular to the receptor

27
Q

positioning for true mandibular occlusal radiographs

A

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

28
Q

why are true mandibular occlusal radiographs taken

A

Investigating possibility of sialolith in main submandibular ducts

29
Q

what are sialoliths

A

Calcification which forms in a salivary duct, potentially causing blockage

30
Q

what is the growth pattern for sialolith

A

Concentric growth → may show layering of calcification
* Conform roughly to shape of duct

31
Q

what is cbct

A

Form of cross-sectional “3D” imaging
* Allows structures to be viewed from any angle (without distortion)
* Becoming more prevalent in dentistry

31
Q

posiitoning for anterior oblique mandibular occlusal radiographs

A

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

32
Q

when may you have to use small occlusal radiographs e.g. size 2

A

young child too small for large receptor
adults unable to tolerate large receptor
small area of interest

33
Q

when are thyroid shields used

A

May be necessary whenever the thyroid gland is in theprimary X-ray beam
* Maxillary occlusal radiographs
* Bisecting angle periapical radiographs of maxillary anterior teeth

34
Q

can cbct be used instead of occlusal radiographs

A

Can replace occlusal radiographs in certain cases
* Higher radiation dose therefore can only be used if occlusal radiographs unable/failed to answer clinical question

35
Q

why are cbct good alternatives

A

Good alternative if visualising larger lesions within the jaws or investigating suspected alveolar bone fractures

Pre-BDS3 Radiology (17 decks)

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