RAD02 - Lecture 3 - Bisected angle technique (PA)

Question 1

Define bisected angle periapicals (3)

Answer 1

Its the technique where the X-ray beam is aimed

Perpendicular to the line which bisects (goes through) the angle

Between the long axis of the image receptor and long axis of the tooth

Question 2

What type of technique is used for these images?

Answer 2

Bisected angle

Question 3

When is the bisected angle technique used?

Answer 3

When there is no holder (i.e. uncomfortable, patient gagging) to help guide the tube head into position

Question 4

What type of angulation is circled on this picture?

Answer 4

Vertical angulation

Question 5

What happens if the veritcal angulation is too large?

Answer 5

Image foreshortened

Question 6

What happens if the veritcal angulation is too small?

Answer 6

Image elongated

Question 7

What type of angulation is this image showing?

Answer 7

Horizontal angulation (side to side)

As opposed to vertical angulation (up and down)

Question 8

How can you avoid overlapping? (1)

Answer 8

Central ray should be aimed through the interproximal contact areas in the horizontal plane

Question 9

What 2 things determine the horizontal angulation?

Answer 9

Shape of the arch

Position of teeth

Question 10

Whats the ideal position for the patient-held image receptor and tube head for anterior and posterior teeth - when using the bisected angle technique?

(remember there is no guide for tube head (i.e. aiming ring) because there is no holder)

Answer 10

Anterior = long-axis of image recepor -> vertical

Maxillary inscisors = tube head -> 45^{<strong>o</strong>} (downwards)

Mandibular incisors = tube head -> 25^o (upwards)

Posterior = long axis of image receptor -> horizontal

Maxillary molars = tube head -> 30^o (downward)

Mandibular molars = tube head -> 5^o (upward)

(Use index finger to support the film)

Question 11

What vertical angle should be used for upper anteriors?

Answer 11

45^o

Question 12

What vertical angulation should be used for upper molars?

Answer 12

30^o

Question 13

What vertical angulation should be used for lower incisors?

Answer 13

25^o

Question 14

What vertical angulation should be used for lower molars?

Answer 14

5^o

Question 15

What is the advantages of the bisecting angle technique? (3)

Answer 15

Comfortable

Positioning simple

If all angulations are correct - image should be adequate for diagnostic value

Question 16

What are the disadvantages of the bisecting angle technique? (10)

Answer 16

Many variables -> distort image

Horizontal/vertical angles have to be assessed for each patient

Incorrect vertical angulation -> elongation or foreshortening

Incorrect horizontal angulation -> overlapping (crowns/roots)

Buccal roots of maxillary molars are always foreshortened

Upper roots of maxillary molars are superimposed by shadow of zygomatic buttress

Periodontal bone levels are poorly defined

Crowns often distorted preventing detection of aproximal caries

Coning off is common

Reproducible images are not possible

Question 17

Identify whats wrong with the bisected angle technique compared to the parallel technique

Answer 17

Bone levels obscure

Buccal roots of 6 foreshortened

Zygoma projected over apices

Secondary caries on distal 7 not visible

Question 18

Identify the 3 different image distortions that occured in these images

Answer 18

1 - foreshortening (U1/2)

2 - curving (film bent)

3 - total distortion (film slipped in mouth)

Question 19

Can the bisected angle technique PAs statisfy all the ideal quality criteria for PA radiographs?

Answer 19

No

Question 20

What 4 scenarios would make it hard to use conventional intra-oral radiograph techniques - and often require modifications?

Answer 20

Strong gag reflex

Edentulous alveolar ridges

Unerupted/partially erupted lower 3rd molars

Endodontics - instruments, rubber dam and claps are in the way

Question 21

Give 5 reasons why it is difficult to take a radiograph of a third molar

Answer 21

Impacted

Un- or Partially-erupted

Pericoronitis

Holder cant reach far back in the mouth (paralleling technique)

Entire tooth, surrounding tissue and ID canal have to be recorded in same image

Question 22

What needs to be shown in a radiograph of a lower third molar that requires extraction? (5)

Answer 22

Angulation and relationship to lower second molar

Shape of crown

Shape and number of roots

Relationship of apices -> ID canal

Depth of tooth in the mandible

Question 23

What different types of radiographs can be used for lower 3rd molars?

Answer 23

Periapical

Panoramic

Oblique lateral

Lower occlusal

Question 24

Describe the ideal positioning of an image receptor and x-ray beam for a lower 3rd molar using the paralleling technique (3)

Answer 24

Image receptor needs to be sufficiently posterior (to record apical tissues)

Front edge of image receptor needs to be oppsite the mesial aspect of 1st molar

X-ray beam needs to be aimed between the contact of the molar teeth (at right angles to the image receptor)

Question 25

What landmarks can you use to guide you to the correct position of wisdom teeth? (2)

Answer 25

Lower wisdom teeth -> vertical drop from the outer corner of the eye + 1cm above the lower border of the mandible

Upper wisdom teeth -> notch on the top of the aiming ring

Question 26

How many radiographs need to be taken during RCT?

Answer 26

Pre-op - determine shape and length of crown (for treatment planning)

During - determine working length / confirm position of cones before condensation

Post-op - assess success of obturation and baseline for prognosis of apical disease/healing

After one year - large PA radiolucencies need to be monitored

Question 27

How can you make positioning the image receptor easier for RCT teeth? (3)

Answer 27

Use a special endodontic film or sensor holder

They have a modified bite block -> accomates handles of endodontic files

Whilst maintaing the parallel position of image receptor and tooth

Question 28

How can you ensure you record the separation of root canals in multi-rooted teeth?

Answer 28

Take atleast 2 radiographs of the multi-rooted tooth - at different horizontal angulations of the tube-head