Dental radiographs: technique 1

Question 1

What are the three types of intra-oral radiographs?

Answer 1

• peri-apical
• bitewing (horizontal and vertical)
• occlusal (maxillary and mandibular)

(Taken with the receptor inside the mouth)

Question 2

What are the most common extra-oral radiographs

Answer 2

• DPT
• lateral cephalogram
• postero-anterior mandible (PA)
• lateral oblique mandible (facial bones)
• occipito-mental (facial bones)

Question 3

describe the upper maxillary occlusal view, and the lower submandibular occlusal view

Answer 3

• the upper maxillary occlusal shows the anterior part of the maxilla and anterior teeth
• the lower submandibular occlusal shows a plan view of the tooth bearing porion of the mandible and the floor of the mouth

Question 4

describe lateral cephalogram

Answer 4

A lateral cephalogram is a standardized and reproducible form of skull radiography used extensively in orthodontics to assess the relationships of the teeth to the jaws and the mandible to the rest of the facial skeleton. You can also see the soft tissue pattern of the nose and the lips which is useful for surgical planning.

Question 5

Describe postero-anterior mandible view

Answer 5

The PA mandible view is useful for showing a fracture of the mandible. It should be requested in conjunction with a DPT. Two views taken at right angles to one another are always required to show the full extent of a fracture. Due to the shape of the mandible this is quite difficult, but it is quite startling how the appearance of a fracture can change depending on the view selected. Remember it is common for a mandible to fracture in more than one place

Question 6

describe lateral oblique mandible view

Answer 6

Lateral oblique mandible – most commonly done in the dental hospital for children that cannot tolerate a bitewing radiograph, but are also done on adults for mandibular fractures if a DPT is not available

Question 7

describe occipto-mental views of facial bone view

Answer 7

OM views of the face – most commonly done in the first instance when a patient reports to A&E following facial trauma. They will show fractures of the orbits, maxilla and zygomatic arches. Two views are taken, the first with the beam angled at 10 degrees and the second with the beam angled 30 degrees. It is beneficial to take the films erect as this can help demonstrate fluid levels in the antra.

Question 8

what are the main clinical indications for peri-apical radiograhy?

Answer 8

• Detection of apical infection or inflammation
• Detailed evaluation of apical cysts and other lesions within the bone
• Assessment of periodontal status- After trauma to the teeth and associated bone
• Assessment of root morphology before extractions
• Assessment of the presence and position of unerupted teeth
• During endodontics
• Pre-operative assessment and post-operative appraisal of apical surgery
• Evaluation of implants postoperatively

For help in deciding the most appropriate form of imaging you require, you should familiarise yourself with the FGDP Selection Criteria for Dental Radiography.

Question 9

what are the two types of intra-oral radiographic techniques that need to be mastered?

Answer 9

• paralleling technique
• bisected angle technique

Question 10

describe paralleling technique

Answer 10

The paralleling technique is the standard intra-oral technique and on your first practical visit to the x-ray department you will have the opportunity to practice this technique on Dexter the false head.

Question 11

describe bisected angle technique

Answer 11

The bisected angle technique is used when a patient cannot tolerate a holder in their mouth. You can ask the patient to either hold the film in their mouth with their finger, which is not ideal as you are then also irradiating the patient’s finger, or use a holder that looks a bit like a lollipop stick. This technique can also be used during endodontic procedures

Question 12

So what is the difference between the 2 techniques?

Answer 12

Paralleling- Uses a holder to facilitate the positioning- The holder keeps the receptor parallel to the tooth and the x-ray beam- It is an accurate reproducible image Bisected angle- Can be done without a holder, which makes it easier for the patient- Unfortunately it is operator dependent, every time this technique is used it will be done slightly differently which means the image is not reproducible

Question 13

Answer 13

Question 14

What are holders made up of?

Answer 14

• A bite-block - retains the receptor
• an indicator arm/rod - fits into the bite-block
• an aiming ring-slides onto the arm to establish alignment of collimator with receptor

Question 15

Answer 15

Question 16

the x-ray beam should be at right angles to the tooth/receptor, what happens if it isn’t?

Answer 16

• If you have too much angle up you will stretch the teeth making them appear elongated
• And too much angle down will foreshorten the teeth making them appear short and stubby

Question 17

what two things affect image size?

Answer 17

1) the distance of the x-ray source to the receptor
2) and the distance between the object and the receptor

Question 18

In summary, to achieve a useful diagnostic image you need to?

Answer 18

accurately position the receptor in both the horizontal and vertical planes. You want to have your x-ray beam accurately aligned in both the horizontal and vertical planes. And you need a short object to film distance and a long source to object distance.

Question 19

what is the importance of image receptor orientation?

Answer 19

It is also important to pay attention to the image receptor orientation. You want your film to be horizontal (landscape) for posterior teeth, and for anterior teeth in a vertical (portrait)position.

Question 20

describe these bad examples of images taken

Answer 20

Here we have some examples of bad images. In the first image vertical angulation of the beam has foreshortened the teeth and separated the cusps. The second image shows horizontal overlap of the teeth caused by horizontal angulation of either the receptor or the beam, and the third image shows vertical angulation of the beam and also an appearance called cone cutting. This is caused when the corners of the collimator have not been touching the guiding ring and absorbed the radiation preventing the receptor from being exposed and forming the image

Question 21

What are barriers to good positioning?

Answer 21

• Mouth size
• Gag reflex
• Film size
• Digital sensor shape and size

Question 22

Answer 22

Question 23

Answer 23