Bisecting Radiographs

Question 1

What is the geometry for bisecting angle periapical and occlusal radiographs?

Answer 1

• X-ray beam not perpendicular to long axes of tooth or receptor
• Long axes of tooth and receptor not parallel to one another

Question 2

What is the geometry for bitewings and paralleing periapical radiographs?

Answer 2

• X- ray beam perpendicular to long axes of tooth & receptor
• Long axes of tooth & receptor parallel to one another

Question 3

What happens if the tooth/receptor are not perpendicular to X-ray beam?

Answer 3

image shortened and stretched

Question 4

What is the bisecting angle technique?

Answer 4

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

Question 5

When is the bisecting angle technique used?

Answer 5

used when unable to position receptor parallel to subject

Question 6

When is the bisecting angle technique used in periapicals?

Answer 6

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

Question 7

When is the bisecting technique used in occlusal radiographs?

Answer 7

Applies to most occlusal radiographs
- Necessary since receptor lies in occlusal plane (therefore not parallel to tee

Question 8

What are the benefits of holders when using technique for periapicals?

Answer 8

avoid radiation dose to hands
reduces chance of receptor shifting in mouth
some holders will guide positioning of x-ray bean

Question 9

What are the benefits to bisecting techniques compared to paralleling technique?

Answer 9

Receptor position potentially more comfortable for patients - can be flat up against tooth
Positioning slightly simpler & quicker

Question 10

What are the downsides to the bisecting techniques compared to the paralleling?

Answer 10

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

Question 11

What anatomy can be altered in bisecting angle technique?

Answer 11

cemento enamel junction, alveolar bone levels, zygomatic buttress, nose and buccal roots

Question 12

What technique should be used for periapicals usually?

Answer 12

paralleling (better image quality, lower patient dose, better reproducibility)

Question 13

What is the size of occlusal radiograph receptors usually?

Answer 13

size 4 (larger than intra-oral radiographs)

Question 14

What does the patient do to the receptor?

Answer 14

bite gently

Question 15

Occlusal radiographs advantages

Answer 15

• 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)

Question 16

What is the standard maxillary occlusal?

Answer 16

anterior oblique maxillary

Question 17

How is a anterior oblique maxillary occlusa positioned?

Answer 17

• 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

Question 18

How is a lateral oblique maxillary positioned?

Answer 18

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)

Question 19

Why is the true mandibular called true?

Answer 19

x-ray beam is perpendicular to receptor

Question 20

How is a true mandibular positioned?

Answer 20

• 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

Question 21

What is a sialoith?

Answer 21

Calcification which forms in a salivary duct, potentially causing blockage

Question 22

What does an anterior oblique mandibular look like?

Answer 22

large periapical radiograph

Question 23

How is an anterior oblique mandibular occlusal positioned?

Answer 23

• 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)

Question 24

For younger children, what size receptor is used?

Answer 24

size 2

Question 25

When is a throid shield used?

Answer 25

when thyroid gland is in the primary x-ray bean (maxillary occlusal, bisecting angle periapical)

Question 26

What is CBCT?

Answer 26

Form of cross-sectional “3D” imaging

Allows structures to be viewed from any angle (without distortion)

Becoming more prevalent in dentistry

Question 27

When is CBCT used?

Answer 27

Higher radiation dose therefore can only be used if occlusal radiographs unable/failed to answer clinical question