Revision

Question 1

Describe:

• Density
• Contrast

Answer 1

Density: overall darkness of an image

Contrast: difference between lightness and darkness in an image

Question 2

What are advantages and disadvantages of the bisecting angle technique?

Answer 2

Advantages
• More comfortable for patients
• When experienced, positioning is often quick and simple
• Can produce diagnostic images if angulations are assessed correctly
• Can be used when certain factors prevent paralleling technique from being used

Disadvantages 
• Too many variables
• Technique sensitive
• Zygomatic arch creates a shadow
• Angulations are different between each patient

Question 3

What are advantages and disadvantages of the paralleling technique?

Answer 3

Advantages 
• Geometrically accurate images
• Vertical and horizontal angulations are automatically determined
• Reproducible images
• Good for patients with disabilities

Disadvantages
• Position of film can be uncomfortable (gag)
• Positioning of holder can be difficult for the inexperienced
• Anatomy can make this technique impossible

Question 4

List the radiographic codes for caries

Answer 4

Code 1: Outer 1/2 of enamel
Code 2: Inner half of enamel 
Code 3: Just into dentine
Code 4: Outer 1/3 of dentine
Code 5: Inner 2/3 of dentine

Question 5

List the radiographic codes for periodontal disease

Answer 5

Cervical third

Middle third

Apical third

Question 6

Why do we take PAs?

Answer 6

• Detection of apical changes(infection, inflammation)
• Assessment of periodontal status
• Trauma
• Pre and postop-endodontic treatment
• Pre op assessment in exodontia (tooth extraction)
• Presence and position of unerupted/impacted teeth
• Assessment of periapical/jawpathology
• Assessment for implants

Question 7

Why do we take bitewings?

Answer 7

• Assessment of interproximal caries
• Evaluate periodontal condition
• Assess existing restorations
• Detect secondary caries
• Detect interproximal calculus

Question 8

List the types of film faults

Answer 8

1. Technique errors
• Patient factors
• Film orientation
• Film placement
• Projection

2. Exposure and processing errors
3. Film handling errors

Question 9

What are the limitations of radiographs with detecting periodontal disease?

Answer 9

• Superimposition & 2D image - difficulty determining lingual or buccal bone loss – teeth are superimposed on the bone
• Palatal bone can make detecting furcations challenging- superimposition can hide bone loss in the furcation from view
• External Oblique ridge can mask the apical extent of the bone loss
• Does not provide information on soft tissue components of the periodontium - hard tissue information only
• Significant bone loss required for radiographic detection
• Angulation can alter the appearance of periodontal disease

Question 10

What are the limitations of radiographs with detecting caries?

Answer 10

• Only detectable when a lot of demineralisation has occurred (estimated 50% mineral loss)
• Carious lesions are always larger clinically than they appear radiographically
• Early lesions are not apparent radiographically
• Technique variations can affect the image of the lesion considerably
• Exposure and processing factors affect the overall radiographic contrast

Question 11

What is the focal trough?

Answer 11

The moving source and receptor generate a zone of sharpness, known as the focal trough.
Objects that fall in the centre of the focal trough will be most sharp.
Structures, which fall in front of or behind, the focal trough, can be distorted, magnified or reduced.

Question 12

What are advantages of OPGs?

Answer 12

• Provides a general, broad Image of the maxilla and mandible
• Radiation dose is relatively low
• Quick and relatively convenient
• Great for gaggers/ small mouths
• Easy to demonstrate structures etc. to patients / parents

Question 13

What are disadvantages of OPGs?

Answer 13

• Only structures within the focal trough will be in focus on the final film
• Does not provide the fine anatomical detail of intra - oral films
• Magnification, distortion and overlapping are common

Unsuitable in detecting:

• Small and moderate sized carious lesions
• Early alveolar bone loss

Question 14

What is a real image, and what is a ghost image?

Answer 14

• Real (actual) images of structures in or close to the focal trough
• Ghost or shadows artefact cast by structures on the opposite side or a long way from the focal trough

Question 15

What are examples of ghost shadows?

Answer 15

• Cervical vertebrae
• Body, angle of the ramus of contralateral side of the mandible
• Palate
• Metallic jewelry, dentures and orthodontic appliances cast real shadows and ghost shadows