Oral radiography/radiology

Question 1

6.1 a) What are the advantages and disadvantages of the various radiographic views you could take to assess the periodontal status of a patient?

Answer 1

i) A DPT : shows overall degree of bone loss but the detail of the alveolar margin is lost; it also give a dose of 0.016-0.026 mSv radiation.
ii) Horizontal bitewing radiograph will show bone levels in pts with early to moderate disease, but will only show the posterior teeth.
iii) Vertical bitewings are useful for teeth with large probing depths, but again only for posterior teeth.
iv) A long-cone periapical radiograph gives the best view as there is minimal distortion and this view can be used for all the teeth in the mouth. They are, however, time-consuming to carry out and the give the patient a dose of around 0.014 mSv radiation per set of full mouth periapical films.

Question 2

6.1 b) When writing a radiographic report regarding periodontal bone loss it used to be common practice to express this in millimetres from the cementoenamel junction (CEJ) to the crest of the alveolar bone. Why is this not considered to be accurate?

Answer 2

i) Any direct measurement taken from a RG may be inaccurate as the image it depicts may be distorted by being shortened or lengthened. Also it does not take into account the length of the root of the tooth.

Question 3

6.1 c) What formula is used to represent a more acceptable ay to describe the severity of bone loss nowadays?

Answer 3

i) CEJ to bone crest (in mm)/CEJ to root apex (in mm) x 100.

Question 4

6.1 d) What are the main patterns of bone loss?

Answer 4

i) Horizontal bone loss occurs when the base of the pocket lies coronal to the bony crest, creating a supra-bony pocket.
ii) Vertical bone loss is where more bone loss occurs on one side of the interdental bone crest than the other. This leave the base of the pocket within the bony defect and is an infra-bony pocket.

Question 5

6.1 e) What term would you use to describe the distribution of bone loss?

Answer 5

i) Localised when <30% of sites are affected or generalised when >30% of sites are affected.

Question 6

6.2 a) What do you understand by the term cone-beam computed tomography (CT)/CBCT)?

Answer 6

i) It is a three-dimensional digital radiographic image. A CT image is generated by a CT scanner using X-rays to produce a sectional or slice image of the body. The data are in a numerical (dicon) format and converted into a grey scale representing different tissue densities which generates an image. In conventional of medical CT the x-ray beam is fan-shaped by in CBCT the beam is cone-shaped.

Question 7

6.2 b) What are the main indications of CBCT?

Answer 7

i) It can be used for any condition affecting the maxilla or mandible including:
(1) Cysts
(2) Tumours, both benign and malignant
(3) Antral disease (sinusitis/oro-antral communication/foreign body/trauma/cyst/tumour/bony abnormalities or pathology)
(4) Bony abnormalities and pathology
(5) Implant assessment
(6) Temporomandibular joint imaging
(7) Assessment of unerupted/impacted teeth and odontomes.
(8) Assessment of the relationship of the inferior alveolar/dental nerve to roots of a tooth, usually impacted third molars.
(9) Orthodontic assessment.
(10) Fractures of the facial bones.
(11) Three-dimensional assessment of teeth and periodontal tissues.

Question 8

6.2 c) List two advantages and two disadvantages of CBCT.

Answer 8

(1) Multiplanar imaging and manipulation so the anatomy can be seen in different planes.
(2) Low radiation dose relative to conventional medial CT.
(3) Fast scanning time.
(4) Compatible with implant and cephalometric planning software.
(5) Cheaper and smaller than conventional medical CT.
ii) Disadvantages:
(1) All information/data are obtained in a single scan so patient must remain stationary.
(2) Soft tissue is not imaged in detail.
(3) Artefacts from metal objects, e.g. restorations.
(4) Reconstructed panoramic image is not directly comparable with the conventional dental panoramic radiograph.

Question 9

6.3 a) What is tomography?

Answer 9

i) It is a technique for producing images of a slice or section of an object.

Question 10

6.3 b) How is it achieved? (tomography)

Answer 10

i) The x-ray tube and the film cassette carrier are connected and move synchronously but in opposite directions about a pivoting point. The pivoting point will appear in focus on the radiographs.

Question 11

c) What is a focal trough?

Answer 11

i) Only a slice of the object is in focus on the tomograph and this is called the focal trough.

Question 12

6.3 d) Give 5 indications for dental panoramic tomography?

Answer 12

i) Assessment of third molars.
ii) Assessment for fracture of the mandible.
iii) To assess bone height in periodontal disease which pockets greater than 5mm in depth.
iv) Orthodontic assessment.
v) To assess bony lesions of the mandible and maxilla.
vi) Implant planning.
vii) To assess bony disorders of the temporomandibular joints.
viii) To assess antral disease.

Question 13

6.3 e) What do you understand by the term ‘ghost shadows’ with respect to dental panoramic tomography?

Answer 13

i) Ghost shadows are shadows cast by anatomical structures such as the cervical vertebrae and the mandible and palate, which are outside of the focal trough on the panoramic radiograph. They appear on the opposite side of the real image counterpart and slightly higher up than the real image.

Question 14

6.3 f) What would an air shadow look like on a dental panoramic tomograph and why do they take on this appearance?

Answer 14

i) Air shadows are radiolucent because there is no photon absorption whereas there is in tissues.

Question 15

6.3 g) What radiation dosage does a patient receive in this procedure?

Answer 15

i) 0.007-0.026 mSv depending on how the radiograph is taken.

Question 16

6.4 a) Name the error that could have occurred to produce the following faults in a panoramic radiograph
(1) The film shows anterior teeth that are out of focus and magnified.
(2) The molars are larger on one side than the other.
(3) There is vertical or horizontal distortion of one part of the image.
(4) The radiograph is too dark.

Answer 16

i) The patient is positioned too far from the film.
ii) The patient has their head to one side or the other so they are asymmetrically positioned in the machine.
iii) The patient has moved while the radiograph was being taken.
iv) Several reasons for RG to dark:
(1) Overexposure – due to increased exposure time either by operator error or faulty equipment.
(2) Overdevelopment – due to excessive time in the developer solution, the solution being too warm or over concentrated.
(3) Fogging – due to poor storage of the film or light leaking onto the film during development.
(4) Patient with very thin tissues.

Question 17

b) What do you understand by the terms development and fixation with regard to radiographs?

Answer 17

i) Development is when the sensitised silver halide crystals in the film emulsion are converted to metallic silver, which is black in colour and produces the black/grey part of the image.
ii) Fixation is when the unsensitised silver halide crystals on the film emulsion are removed. This produces the white/transparent part of the image.

Question 18

6.5 a) How often must a dentist attend a radiation protection update course?

Answer 18

i) 5 hours of radiation protection training every 5 years as part of CPD.

Question 19

6.5 b) List five methods you could use to minimise the radiation dose to a patient having an intraoral radiograph.

Answer 19

i) Justification
ii) High-speed film
iii) Rectangular collimator
iv) Quality control
v) Optimal kV (70 kV)
vi) Digital radiography

Question 20

6.5 c) What do you understand by the term somatic stochastic effects of ionising radiation? What is the safe dose of ionising radiation to prevent these effects?

Answer 20

i) Stochastic means governed by the laws of probability or random. Hence stochastic effects are effects that may develop. There is no safe dose as they might occur after any dose of ionising radiation so every exposure carries the risk of stochastic effects. Obviously the lower the ionising radiation dose the lower the likelihood of damage, although the amount of damage is not related to the size of the inducing dose.

Question 21

6.5 d) How does ionising radiation damage the body?

Answer 21

i) The effects can cause direct or indirect damage.
ii) Direct damage involves ionising biological molecules, e.g. point mutations in DNA.
iii) Indirect damage occurs from ionising water, which leads to the formation of free radicals. These may combine to form highly reactive species which cause damage.

Question 22

6.5 e) What is the estimated risk of developing fatal cancer from dental panoramic radiography?

Answer 22

i) 1:2 000 000

Question 23

6.6 a) From the right column of the table, select the most appropriate image to show the structures and conditions in the left column.

i) A fractured zygomatic arch
ii) Periodontal pocketing around lower incisors
iii) Interproximal caries
iv) Internal derangement of the temporomandibular joint
v) An impacted lower third molar
vi) A fluid level in the maxillary antrum
vii) A blow-out fracture of the orbital floor
viii) A salivary calculus in the submandibular duct
xi) Presence of an impacted permanent upper canine

• Mandibular standard occlusal radiograph
• Bitewing radiographs
  10 *C occipitomental radiograph
• CT scan of the face
• Long cone periapical radiographs
• Bisecting angle periapical radiographs
• MRI scan
• Submentovertex radiograph
• Maxillary standard occlusal radiograph
• Panoramic radiograph
• Reverse Townes radiograph

Answer 23

i) A fractured zygomatic arch = submentovertex radiograph
ii) Periodontal pocketing around lower incisors = long cone periapical radiographs
iii) Interproximal caries = bitewing radiographs
iv) Internal derangement of the temporomandibular joint = MRI scan
v) An impacted lower third molar = Panoramic radiograph
vi) A fluid level in the maxillary antrum = 10* occipitomental radiograph
vii) A blow-out fracture of the orbital floor = CT scan of the face
viii) A salivary calculus in the submandibular duct = mandibular standard occlusal radiograph
ix) Presence of an impacted permanent upper canine = maxillary standard occlusal radiographs

 Submental vertex radiograph gives the best view of fractured zygomatic arch but is non rarely done, to reduce the radiation dose to patient 2 occipitomental radiographs are usually taken.

Question 24

6.7 a) What do you understand by the ALARP principle?

Answer 24

i) ALARP an acronym that stands for ‘as low as reasonably practicable’ and is meant to minimise exposure to radiation.

Question 25

6.7 b) List seven factors that can help achieve this principle. ALARP

Answer 25

i) Every radiograph should be justified.
ii) All exposures should be kept as low as reasonably practicable – they should be optimised.
iii) There should be limitation of radiation dose.
iv) There should be written guidelines for exposure setting for radiographs.
v) The fastest speed film should be used that will give a good quality image (usually E).
vi) A rectangular collimator should be used.
vii) There should be minimal skin to focus distances (> 60kV = 20cm)
viii) Film holders should be used rather than patients holding the film.
ix) When referring a patient the radiographs should be sent with the patient to avoid further radiation.
x) All radiographs should b evaluated and an entry made in the patient’s notes.
xi) There should be a quality assurance programme in place to optimise results.

Question 26

6.7 c) Should lead aprons be used routinely in dental radiography? Please give a reason for your answer.

Answer 26

i) There is no justification for the routine use of lead aprons in dental radiography as reducing radiation is best achieved by implementing measures such as clinical judgement, equipment optimisation and radiographic technique.

Question 27

6.7 d) What are the annual dose limits of radiation for non-classified workers?

Answer 27

i) 6 mSv

Question 28

6.8 a) What is sialography? Give two indications and contraindications for using it.

Answer 28

i) Sialography involves introduction of a radiopaque medium into the ductal system of a major salivary gland and then taking a radiographic image.

ii) Indications:
(1) Obstructions in the ductal system, e.g. calculi
(2) It is used to assess the structure of the gland and the ductal system and to see if there is any destruction or changes in them.

iii) Contraindications:
(1) Allergy to iodine-containing compounds.
(2) Infection in the gland.
(3) A calculus close to the duct orifice which may be pushed further back by the introduction of contrast medium.

Question 29

6.8 b) Submandibular duct salivary calculi/obstructions can sometimes be seen on routine radiographs. On which radiographic views would you see submandibular duct salivary calculi?

Answer 29

i) Dental panoramic radiograph and lower standard occlusal.

Question 30

6.8 c) Ultrasound can be used for imaging salivary glands. Give four advantages of using ultrasound for this purpose.

Answer 30

i) No ionising radiation used.
ii) Excellent for superficial masses.
iii) Can use it to guide fine needle aspiration.
iv) Can use to differentiate between solid and cystic masses.
v) It can identify radiolucent calculi not seen on radiographs.
vi) It can be used to break up calculi by lithotripsy.
vii) Intraoral masses can be visualised with small probes.

Question 31

6.9 a) Describe what a keratocystic odontogenic tumour (odontogenic keratocyst) may look like on a radiograph.

Answer 31

i) Radiolucent lesion
ii) Well defined
iii) Multilocular although may be unilocular
iv) Rounded margins
v) Adjacent teeth may be displaced
vi) Tooth roots are not usually resorbed

Question 32

6.9 b) Describe what a dentigerous cyst may look like on a radiograph.

Answer 32

i) Radiolucent lesion
ii) Well circumscribed
iii) Usually unilocular but there maybe pseudo-loculation due to bony trabeculae.
iv) Rounded
v) Contains the crown of a tooth or lies adjacent to the crown of a tooth.
vi) Associated tooth is usually displaced.

Question 33

6.9 c) If a patient had a lesion at the angle of their mandible what radiographic views could be taken to demonstrate it and what would each view show?

Answer 33

i) A dental panoramic radiograph, a sectional dental panoramic tomograph or oblique lateral views would show the lesion.
(1) The mesiodistal and superior/inferior dimensions of the lesion would be evident as well as association with any teeth, the inferior dental canal, etc.
(2) A posterior-anterior (PA) view of the mandible will how any buccolingual expansion of the mandible.

Question 34

6.10 a) One technique for taking periapical radiographs is paralleling technique. Name another technique.

Answer 34

i) Positioning of the film packet in any area of the mouth is usually more comfortable for the patient.
ii) It is straightforward and quick.
iii) The length of the crowns and roots should be the same as the teeth being radiographed if the film and tube have been correctly positioned.

Question 35

6.10 c) What are the advantages of using a paralleling technique in periapical radiography?

Answer 35

i) No image distortion
ii) Images are reproducible at different visits and with different operators.
iii) There is no ‘coning off’ of the image.
iv) Rectangular collimation will reduce the radiation dose to patients.
v) Periodontal bone levels and the crowns of teeth are well shown.
vi) No superimposition of the zygomatic buttress on the maxillary molars.

Question 36

6.10 d) Describe how would set up the tube head to take a bitewing radiograph and why?

Answer 36

i) The x-ray beam is angled downwards by 5-8* to account for the curve of Monson on the occlusal plane. It is also aimed through the contact points at right angles to the teeth and the film packet to avoid overlap of the contact areas.

Question 37

6.11 a) When taking a radiograph a certain part of the root is designated as controlled area. What do you understand by this term?

Answer 37

i) The controlled area is within the primary beam until it has gone far enough to be reduced in strength or gone through shielding. It also includes the area around the patient and x-ray tube.

Question 38

6.11 b) How large is this area? Given an example of the radius for a machine taking panoramic dental radiographs and intraoral periapicals.

Answer 38

i) The size of the area depends on the voltage of the equipment. For an intraoral radiograph the radius is 1m and for a panoramic radiograph it is 1.5 (as panoramic machines have a peak operating potential greater than 70 kVp).

Question 39

6.11 c) What measures are advised with regard to the above? Radius for RGs

Answer 39

i) Hazard lights which should be illuminated during the exposure, and signs on the door are needed.

Question 40

6.11 d) Digital radiography is become more popular. What is used instead of a film packet when taking a digital radiograph.

Answer 40

i) A charged couple device (CCD), a complementary metal oxide semiconductor, a photostimulable phosphor imaging plate (PSPP).

Question 41

6.11 e) Give four advantages of digital radiography over conventional radiography.

Answer 41

i) No processing faults
ii) No risk from handling the chemicals involved in processing
iii) Lower radiation dose as the image receptors are more sensitive than conventional film
iv) Ease of storage of images
v) Ease of transfer of images
vi) Electronic enhancement of images

Question 42

6.12 b) Give four indications for taking this view OM30*

Answer 42

i) Suspected fracture of the zygomatic complex
ii) Middle third facial injuries
iii) Le Fort I, II and III fractures.
iv) Nasoethmoidal complex fractures.
v) Orbital fractures (although with the above, except for zygomatic fractures, other imaging such as computed tomography is also often done)
vi) Coronoid process fractures.
vii) Frontal sinus and ethmoid sinus visualisation.

Question 43

6.13 d) A similar image can be used if a patient had a orbital floor fracture. What is often seen in this image?

Answer 43

i) Herniation of orbital contents into the maxillary antrum.

Question 44

6.14 a) Describe what you see on the radiograph shown in the figure.

Answer 44

i) A radiolucent area at the angle and body of the left side of the mandible. It extends from the first premolar to the ascending ramus of the mandible. It is multilocular with distinct septa. The outline is smooth, scalloped and well defined, and there are internal septa. There is bony expansion of the mandible and displacement of inferior dental canal. There is no resorption of tooth roots.

Question 45

6.14 b) What are your differential diagnoses? (multilocular radiolucent area at angle and body of left mandible extending from first premolar and up ascending ramus. multilocular with distinct septa. outline is smooth, scalloped and well defined, and there are internal septa. there is bony expansion of mandible and displacement of ID canal. no resorption of tooth roots.

Answer 45

i) Ameloblastoma
ii) Keratocystic odontogenic tumour (odontogenic keratocyst)
iii) Calcifying epithelial odontogenic tumour (early stage)
iv) Myxoma
v) Ameloblastic fibroma
vi) Haemangioma

Question 46

c) The inferior dental canal is seen clearly on this view. How might the inferior dental canal look on a radiograph if it was associated with an impacted wisdom tooth?

Answer 46

i) Narrowing of the tramlines
ii) Deviation of the tramlines
iii) Loss of the tramlines
iv) Radiolucent banding across the root