Occlusal Radiography & Bisecting Angle Technique

Question 1

For occlusal radiography where is the image receptor put

Answer 1

in the occlusal plane

Question 2

What is the size of occlusal radiograph image receptors

Answer 2

7 x 5 cm

Question 3

What are the indications for oblique occlusal

Answer 3

When we want a periapical type assessment but it is not possible to take periapicals
Pathology too large to be seen on a single periapical (would use cone beam ct now)
Trauma and fractures
Localisation using parallax

Question 4

What is the ideal projection geometry

Answer 4

• Image receptor and object in contact and parallel
  
  • Parallel beam of X-rays
  • X-ray beam perpendicular to object plane and image receptor

Question 5

If ideal projection geometry is met what would this mean

Answer 5

image would be identical in size

Question 6

Why can the ideal projection geometry not happen

Answer 6

we cannot have the image receptor and object completely in contact and parallel and there is no parallel beam of x-rays.
The X-ray beam central ray may or may not be perpendicular to the object plane and image receptor

Question 7

Why is there magnification

Answer 7

due to the divergent beam

Question 8

What is bisecting angle technique

Answer 8

done in areas where the paralleling technique is impossible due to poor access making the angle between the tooth and film more than 15 degrees

Question 9

What happens in the bisecting angle technique

Answer 9

• The image receptor and object are partly in contact but not parallel
  
  • The image receptor and object are close together at crowns but apart at apices
    Still use long X-ray focus-skin distance (FSD) as required for machines operating at 60kV and over (@ least 20cm)

Question 10

How is the vertical angle selected

Answer 10

Think of the law of equal triangles, the equal triangle created by the image receptor and the long axis of the tooth, draw a line which bisects that then if you direct the X-ray beam perpendicular to that then apart from the magnification you should get an accurate image

Question 11

What is the x ray beam 90 degrees to in the bisecting angle technique

Answer 11

X-ray beam is at 90 degrees to line bisecting angle formed by long axis of tooth and plane image receptor - correct due to identical triangles

Question 12

If the teeth are proclined how is the vertical angle adjusted

Answer 12

increase vertical angle

Question 13

If the teeth are retroclined how is the vertical angle adjusted

Answer 13

decreased

Question 14

What is the position of the occlusal plane for oblique occlusal

Answer 14

horizontal

Question 15

How is head position measured for maxilla

Answer 15

ala-tragus line (lateral border nose opening - anterior to external auditory meatus is horizontal (parallel to the floor)

Question 16

How is head position measured for the mandible

Answer 16

corner of mouth-tragus line is horizontal (parallel to the floor).

Question 17

How is the head positioned for maxillary occlusal

Answer 17

you want the upper teeth stable and the ala-tragus line horizontal to the ground

Question 18

How is the head positioned for mandibular occlusal

Answer 18

For mandible oblique occlusals the teeth are apart due to image receptors and the mandibular occlusal plane is not the same as the maxillary. The head needs tilted back to get the corner of mouth to the tragus of the ear parallel to the ground

Question 19

What are storage phosphor plates

Answer 19

• Multi use sensors

Question 20

What are phosphor plates protected by

Answer 20

plastic cover

Question 21

How should the phosphor plate be inserted into plastic

Answer 21

so writing can be seen through clear side; seal

Question 22

what side of the storage phosphor plates must face the x ray source

Answer 22

black side

Question 23

Describe how phosphor plates are positioned

Answer 23

• Place inside hinged card protector
  
  • Check dark surface of cover facing up for maxillary teeth and down for mandibular teeth as this it eh active surface
  • Position in mouth, hinged end first and hold it against the teeth you will x-ray
  • Keep the sensor still in the correct position
  • Get the patient to bite gently to hold the protected sensor still
  • Remind them to keep biting gently
  • Watch them to ensure no chewing action
  • Align the tube head and check from 2 directions - the side (measure vertical angulation) and the front

Question 24

What is the horizontal angle

Answer 24

90 degrees to line of arch to avoid overlaps

Question 25

What are the centering points for periapicals

Answer 25

Maxilla - on the ala-tragus line

Mandible - 1cm above lower border

Question 26

What are the centering points for the oblique occlusal

Answer 26

Maxilla - 1cm above ala-tragus line

Mandible: through lower border of mandible

Question 27

what is the guideline vertical angle for upper anterior oblique occlusal

Answer 27

60

Question 28

what is the guideline vertical angle for upper occlusal centre on canine

Answer 28

55

Question 29

what is the guideline vertical angle for upper occlusal centre on premolar

Answer 29

50

Question 30

what is the guideline vertical angle for upper occlusal centre on molar

Answer 30

45

Question 31

what is the guideline vertical angle for lower anterior occlusal

Answer 31

40 to occlusal plane

Question 32

what is the guideline vertical angle for lower occlusal centre laterally

Answer 32

35º to occlusal plane

Question 33

What are the indications for mandibular true occlusal

Answer 33

• Detection of submandibular duct calculi
  
  • Assessment of bucco-lingual position of unerupted teeth - unless advanced imaging indicated
  • Evaluation of pathological bucco-lingual expansion (cysts and benign pathologies)
  • Horizontal displacement of fractures through the dento-alveolar part of the jaw then this can give a good view of the displacement of the bone