BDS2 Lectures

Question 1

How do radiographs work?

Answer 1

X-ray beam is passed through an object before interacting with a receptor.

Beam altered by the materials it passes through.

Creating a pattern of different shades of grey on the final image.

Question 2

Risk of x-rays?

Answer 2

They are forms of ionising radiation so have sufficient energy to remove electrons from atoms to create charged particles (ions).

Leads to tissue damage
- skin burns
- hair loss
- death
- carcinogenesis

Question 3

What are the 2 legislations for radiation use in the UK and who do they protect?

Answer 3

1. Ionising radiation regulations (IRR) 2017 - protects STAFF
2. Ionising radiation medical exposure regulations (IR(ME)R) 2017 - protects PATIENTS

Question 4

Common justifications for radiographs

Answer 4

1. If you can’t exclude dental caries clinically so need for assessing
2. Investigating presence of dental infection around symptomatic teeth
3. Confirming presence of unerupted teeth to aid orthodontic planning

Question 5

Forms of intra-oral radiographs

Answer 5

Bitewings, periapicals (paralleling and bisecting technique) and occlusal

Question 6

Advantages and disadvantages of intra-oral radiographs

Answer 6

Advantages
- high spatial resolution
- minimal superimposition of other anatomy
- fast exposure
- low radiation dose per image

Disadvantages
- limited to imaging of small area
- invasive for patient as equipment is placed in mouth
- difficult technique

Question 7

What are the receptor sizes for the different intra-oral radiographs?

Answer 7

Size 0 - anterior periapicals

Size 2 - bitewings and posterior periapicals

Size 4 - occlusal

Question 8

Ideal vs Reality of Projection Geometry

Answer 8

Ideal
- non-divergent x-ray beam
- tooth immediately next to receptor
- x-ray beam exactly perpendicular to both the tooth and receptor

Reality
- x-ray beam is divergent so teeth appear larger
- tooth is quite close to receptor at best so teeth appear larger
- tooth may not be perpendicular to x-ray beam so appear shorter
- receptor may not be perpendicular to the x-ray beam so teeth appear stretched on final image

Question 9

How to get the best projection geometry?

Answer 9

Maintain sufficient focus to skin distance (FSD) - 200 mm is ideal. Distance maintained using a spacer cone and is measured from x-ray source.

Position receptor as close to tooth as possible
Ensure receptor is stable as possible in mouth
Use image receptor holder with a beam aiming device
Keep patient still

Question 10

What are receptor holders and their benefits?

Answer 10

A device used for intra-oral radiographs which aid positioning and help stabilise the receptors in the mouth.

Benefits
They are reusable
Avoid radiation dose to hands
Reduce chance of receptor shifting in mouth
Less risk of suboptimal images which prevent diagnosis and necessitate repeats.

Question 11

Indications for bitewings

Answer 11

• detecting/monitoring caries
• assessment of restorations
• detecting/monitoring periodontal bone loss

Question 12

Indications for paralleling periapicals

Answer 12

• detection of apical inflammation
• detecting/monitoring periodontal bone loss
• assessment of unerupted teeth
• assessment of root morphology for extraction/peri-radicular surgery
• planning/monitoring dental implants
• evaluation of lesions within alveolar bone

Question 13

Indications for bisecting periapicals

Answer 13

• when unable to position receptor parallel to tooth
• shallow hard palate or lingual surfaces
• young child that can’t tolerate receptor in mouth
• tender tooth so patient can’t bite down on receptor holder
• edentulous patient

Question 14

Benefits and downsides of bisecting periapicals

Answer 14

Benefits
- receptor position more comfortable for patients as it can be flat up against tooth
- positioning is easier and quicker

Downsides
- need to estimate x-ray angulation so varying degrees of distortion
- hard to reproduce
- increased risk of irritating thyroid gland
- altered position of some anatomy
- harder to diagnose occlusal caries as x-ray is coming down on tooth at angle so occlusal surface no longer flat
- higher patient dose than paralleling technique

Question 15

Types of occlusal radiographs (upper and lower)

Answer 15

Upper
- anterior oblique maxillary occlusal (most common)
- lateral oblique maxillary occlusal (right or left)

Lower
- anterior oblique mandibular occlusal
- true mandibular occlusal

Question 16

Indications for occlusal radiographs

Answer 16

• allows for visualisation of the dentition/jaws from a different angle
• for locating unerupted teeth and investigating suspected root/alveolar bone fracture
• provides larger image of the dentition/jaws
• for lesions too big for periapical radiography
• if patient struggling to tolerate periapical holder can be used as alternative for anterior periapicals
• investigating possibility of sialolith in main submandibular ducts
• investigating bucco-lingual expansion of mandible and position of teeth

Question 17

What are thyroid shields and what radiographs would you use them for?

Answer 17

Used to minimise radiation exposure to the thyroid gland which is radiosensitive.

Used for
- maxillary occlusal radiographs
- bisecting angle periapicals of maxillary anterior teeth

Question 18

What is CBCT and describe its use

Answer 18

Cone-beam computed tomography. A form of cross sectional 3-D imaging.

Allows structures to be viewed from any angle without distortion.

Can replace occlusal radiographs if they don’t answer clinical question BUT have higher radiation dose.

Good for visualising larger lesions within jaws or investigating suspected alveolar bone fractures.

Question 19

Anterior oblique maxillary occlusal positioning?

Answer 19

• Align occlusal plane parallel to floor
• place receptor against upper occlusal plane central in mouth
• get patient to bite gently
• position X-ray tube head in midline and aim downwards through bridge of nose at receptor
• approx 65 degree angulation to receptor

Question 20

Lateral oblique maxillary occlusal positioning?

Answer 20

• Align occlusal plans to floor
• place receptor up against upper occlusal plane towards side of interest
• get patient to bite gently
• aim downwards through cheek at receptor
• approx 45-55 degree angulation to receptor

Question 21

True mandibular occlusal positioning?

Answer 21

• Place receptor against lower occlusal plane
• get patient to bite gently and tilt head back as far as possible (want occlusal plane vertical)
• position X-ray tube aiming upwards under chin and angled 90 degree to receptor and arch

Question 22

What is a sialolith?

Answer 22

Benign salivary stones - calcified masses that form in salivary duct and potentially cause blockages

Question 23

Anterior oblique mandibular occlusal positioning?

Answer 23

Align occlusal plane to floor

Place receptor against lower occlusal plane

Get patient to bite gently

Position X-ray head in midline and aim upwards through chin to point at receptor

Approx 45 degree angulation

Note; proclined dentition = increased angulation and retroclined = decreased

Question 24

When to use smaller receptors?

Answer 24

For children

Adult unable to tolerate larger receptor

Smaller area of interest

Question 25

What is cervical burnout?

Answer 25

Seen as triangular shaped radiolucency at neck of teeth at mesial/distal aspects right below CEJ Artefactual phenomenon created by the anatomy of the teeth and varied penetration of the X-ray beam as a result of this Often confused as secondary/root caries Beam is LESS ATTENUATED so more of the beam passes through the tooth at the contact areas so appears more radiolucent (darker) in correspondence to other areas.

Question 26

Amalgam restorations on radiographs

Answer 26

Appear radiopaque Consequence of Sn and Zn ions released into underlying demineralised dentine increasing its radiodensity giving a radiopaque zone.

Question 27

Mach band effect

Answer 27

Optical illusion caused by retina Human visual system makes the bright areas look brighter and the dark areas darker Misleading so important to consider the shape of the caries and uniform outlines (caries less defined around the margins)

Question 28

Large radiolucency seen at apices of teeth

Answer 28

Nasal cavities and can see nasal septum dividing these cavities

Question 29

Increased radiolucency between apices of central incisors

Answer 29

Incisive foramen

Question 30

Y of Ennis?

Answer 30

Radio graphic feature which is the superimposition of the nasal cavity floor and the border of the maxillary sinus

Question 31

Radiolucent area above apices of maxillary molars

Answer 31

Maxillary sinus

Question 32

Radiopaque U shaped structure representing when the zygomatic bone attaches to maxilla

Answer 32

Zygomatic process

Question 33

Triangular portion or thumb like radiopacity on posterior maxillary radiographs

Answer 33

Coronoid process

Question 34

Rounded end of the alveolar process of the maxilla and curves upwards at the end of the maxillary alveolar process

Answer 34

Maxillary tuberosity

Question 35

Radiolucent with radiopaque margin at apices of anterior mandibular teeth

Answer 35

Lingual foramen

Question 36

Radiolucent lines going towards apices of the anterior mandibular teeth

Answer 36

Vascular canals

Question 37

Inverted u shaped radiopaque line underneath the anterior mandibular teeth

Answer 37

Thicker bone of the mandibular protuberance

Question 38

Circular radiolucency apical to mandibular premolars

Answer 38

Mandibular foramen

Question 39

Thick radiopaque line below apex of the mandibular molars

Answer 39

Mylohyoid ridge (where it attaches)

Question 40

Depression on lingual aspect of body of mandible

Answer 40

Submandibular fossa ( where submandibular gland sits)

Question 41

Key points to make on pathologies in pathologies

Answer 41

Site and extent of lesion Shape of lesion Margins of lesion (corticated?) Surrounding structures

Question 42

International Commission for Radiological Protection (ICRP)

Answer 42

Publication 103 recommends a legal framework for radiation safety JUSTIFIED: do more good than harm and has sufficient benefit to patient OPTIMISED: magnitude of radiation exposure and no of people exposed be ALARP LIMITED: system of individual radiation dose limits use so no person recieves unacceptable level of exposure

Question 43

International Atomic Energy Authority (IAEA)

Answer 43

Publish model regulations for use of radiation sources and for management of the associated radioactive waste

Question 44

Ionising radiation regulations (IRR17)

Answer 44

Deals with occupational exposure and exposure to general public Enforced by health and safety executive (HSE) and registration with one is required for use of radiation generator Employer ( NHS or private practice owner ) responsible implementing arrangements for compliance Regulations - 8: radiation risk assessment must be carried out to see level of radiation staff exposed to and safety features which are required - 9: requires exposure to be ALARP - 14: employee must also consult radiation protection advisor (RPA) for regular equipment checks, radiation risk assessment, check if comply with safety features etc

Question 45

Annual radiation dose limits for public and for radiation workers

Answer 45

Radiation worker: 6 mSv/ year Public: 1 mSv/year

Question 46

Ionising radiation (medical exposure) regulations 2017

Answer 46

Deals with medical exposures of patients Enforced by healthcare improvement Scotland and team of inspectors Applies to medical related exposure such as - patients for diagnosis and treatment - health screening - research - asymptomatic individuals - carers - for non medical imaging using medial equipment Employers must set out 14 procedures to be followed - patient identification - entitlement of staff to be practitioner, referrer and operator - ask if pregnant - info given to patient verbally and within leaflet to patient - assessment of patient dose - establish dose constraints - ensure exposure to accidental or unintended exposure to radiation is ALARP

Question 47

IRMER17 sets out roles during medical exposure what are they?

Answer 47

Referrer: must provide sufficient date to practitioner to enable justification for exposure Practitioner: must justify and authorise each exposure and ensure is ALARP and complies with employers procedures Operator: carries out practical aspects affecting patient dose: take. Ray, select equipment, clean film processor Employer: must provide referral criteria and have procedures to ensure clinical evaluation of the outcomes of each medical exposure is recorded

Question 48

Basic framework for carrying out medical exposures

Answer 48

1. Referral for imaging requested by referrer 2. The exam must be justified by a practitioner who can authorise it 3. The exam may be authorised and carried out by an operator 4. Image assessed and reported by operator 5. The image and report are provided to referrer

Question 49

Panoramic radiographs

Answer 49

Extra oral radiograph which provides clear view of entire maxillomandibular region Aka OPT/OPG or DPT Is a form of conventional tomography which was developed to capture a curved slice aligned with shape of the jaw and the slice is displayed as a flat image

Question 50

Problems with panoramic radiographs

Answer 50

Superimposition as many structures will be overlaid on the 2-d image so they obscure each other

Question 51

Tomography

Answer 51

To combat superimposition Allows slices of the subject to be view separately Types - conventional: one slice - computed: multiple slices

Question 52

Misleading shadows on radiographs

Answer 52

Double shadows - crested by structures located near centre of rotation will be captured twice due to central position e.g. hyoid bone, soft palate and cervical spine Ghost shadows - created by structures between X-ray source and centre of rotation. Appear magnified, blurry and higher and appear on opposite side of their true anatomical position

Question 53

Selection criterial for panoramic radiograph

Answer 53

Can be take if: Grossly neglected dentition Part of periodontal bone assessment Bony lesion or unerupted tooth of a size or position that can’t be seen fully on intra oral radiographs Assessment of 3rd molars if planning surgical intervention Part of ortho assessment for knowing state of dentition In GDHS - assessment for fractures of mandible, maxillary sinus pathology, destructive disease of TMJ articular surfaces and pre implant planning

Question 54

Panoramic vs bite wings

Answer 54

See more crown and part of roots Can get panoramic pseudo bite wing image so see cuts of areas we are interested in so less areas receive radiation But not as greatest resolution as bitewings But can see apices

Question 55

Panoramic vs posteroanterior mandible

Answer 55

Show similar areas But it is isn’t a tomograph like panoramic so get more superimposition.

Question 56

Panoramic vs lateral cephalogram

Answer 56

LC is side on view and is used more in ortho and is not a tomograph so get superimposition of left and right

Question 57

Panoramic vs anterior oblique maxillary occlusal

Answer 57

Shows same anatomy just different angle and is only maxillary arch

Question 58

Panoramic vs cone beam CT

Answer 58

CT work out multiple slices so lets us look at different angles unlike panoramic so provides more info. But higher radiation dose and need more expensive equipment for it.