Radiology In Orthodontics

Question 1

What two articles legalise ionising radiation?

Answer 1

The Ionising Radiation Regulations (2017) which is concerned for the safety of healthcare workers and the general public
The Ionising Radiation (Medical Exposure) Regulations (2018) which relate to patient protection and safety

Question 2

Why do we take radiographs?

Answer 2

Pre-orthodontic treatment

• assessing the stage of dental development
• presence or absence of permanent teeth
• presence of dental and periodontal pathology
• presence and position of ectopic and supernumerary teeth
• root morphology- crown/root ratio
• assessment of dental/skeletal relationships
• monitoring growth

Question 3

When do we take radiographs?

Answer 3

Deciduous dentition
-following trauma to asses risk to underlying teeth
-determine prognosis of carious teeth
Mixed dentition
-asymmetric eruption of contralateral teeth
-failure of eruption of maxillary incisors
-canines not palpable bucally by 10 years of age
-before carrying out any interceptive treatment
Permanent dentition
-prior to definitive treatment planning
-midway through treatment- assessing treatment effects for further planning, assessing root morphology if suspicious of resorption and root alignment for joint restorative cases, assessing planned tooth movements prior to orthognathic surgery
-following active treatment

Question 4

What radiographs do we take?

Answer 4

Orthopantomogram (OPT)
Occlusal radiographs 
Periapial radiograph 
Bitewing radiographs 
Cephalometric lateral skull radiographs

Question 5

What is the radiation dose of a dental panoramic tomogram?

Answer 5

24 uSV

Question 6

What is the radiation dose of a small field view CBCT?

Answer 6

48-652 uSV

Question 7

What is the radiation dose of a large field of view CBCT?

Answer 7

68-1073 uSV

Question 8

What is the radiation dose of a conventional CT?

Answer 8

534-2100 uSV

Question 9

What information can you get from a cephalogram?

Answer 9

Relationship of maxill and mandible to cranial base
Relationship of the teeth to the jaws
Relationship of the maxillary to the mandibular teeth

Question 10

What is the Eastman analysis?

Answer 10

Relative AP position of the skeletal bases
-SNA 82 degrees +/- 3 degrees- maxillary skeletal base position
-SNB 79 degrees +/- 3 degrees- mandibular skeletal base position
-ANB 3 degrees +/- 2 degrees
Skeletal pattern
-ANB 2-4 class I
-ANB >4 class II
-ANB <2 class III
Inclination of incisors to the skeletal bases
-upper incisor to maxillary plane 109 degrees +/- 5 degrees
-lower incisor to mandibular plane 93 degrees +/- 5 degrees