Film faults and SLOB

Question 1

What are film faults?

Answer 1

Appearance or structure that is not usually present on a radiograph and is produced by artificial means

Question 2

What are the three categories of film faults?

Answer 2

Technique errors:

• patient factors
• film placement errors
• film orientation
• projection error

Exposure and processing errors

Film handling errors

Question 3

Describe all four technique errors

Answer 3

Technique errors

1. Patient factors
   • For maxillary radiographs, things like piercings/ glasses and dentures may cast a shadow
   • When patient moves during the procedure, it causes blurring of the image. Needs to be retaken
   • Sometimes the patient opens their mouth and it becomes completely non diagnostic
2. Film placement errors
   • Periapicals: 2-3mm film should be covering apical part of tooth, and 2mm of film above tooth
   • Apex cut off= non diagnostic
   • Sometimes mesio-distal positioning is important; the most distal part of the third molar may not be captured
   • The edge of the film needs to be parallel to the occlusal plane or else roots may cut out
3. Orientating the film
   • For anterior teeth, we need vertical positioning of the film
   • The correct side of the film should be placed. If not, an imprint of the incorrect side will be present in the radiograph
   • The ‘a’ should be positioned towards the incisal/ occlusal edge when taking periapical radiographs
   • The ‘a’ shouldn’t appear as a mirror image of itself as it will confuse the reader in determining which side of the mouth was radiographed
   • Sometimes, a finger artefact may occur if finger is in front of film
   • The film should be parallel with the occlusal plane. If not, the occlusal plane will be sloped
4. Projection error
   • Horizontal angulation incorrect: overlap
   • Cone cutting: tube doesn’t cover entire film
   • Incorrect vertical angulation: foreshortening or elongation
   • Dimensional distortion: the buccal roots of maxillary molars appear shorter because of bisecting angle technique. Overcome with paralleling

Question 4

Describe exposure and processing film errors

Answer 4

• Double errors: the last image on the film wasn’t erased properly by the scanner OR the radiograph was taken and not processed straight away
• Light exposure: sensitive to light. The light will cast a light shadow on the film when a radiograph is taken
• Density: choose the right exposure level and time or else under exposed images will occur (way too light) or over exposed (too dark)
• Contrast: When the contrast is not adjusted as soon as it has been processed through the scanner, the contrast cannot be changed later.
• Noisy images: images need to be scanned at an optimal speed to prevent grainy images
• Non uniform density: when you leave two films on top of each other, it will cast a shadow because of light absorption

Question 5

Describe film handling errors

Answer 5

• Pressure marks: sometimes patients may bite to hard causing cracks to appear
• Damage to receptors: when films bend, the receptors move away from that area. This will appear as a black line and may mimic a fracture
• PSP plates can’t be sterilised so if a spill happens, it may cast a shadow
• Bent film: film bending may happen because of anatomy in maxillae. More common with maxillary radiographs. Picture may appear bent/ elongated and blurry
• CCD sensor dropped: may result in geometric shapes
• Discoloured: only happens to wet films. When chemicals haven’t been washed off it will leave a residue and it will cause a discoloration.

Question 6

What is the SLOB rule?

Answer 6

• Same Lingual Opposite Buccal
• If an object is detected, you move the tube head mesially. If the object in question remains on the same side when the radiograph has been shifted, then it is said to be place lingually
• If the object is question moves to the opposing side when the radiograph has been shifted, then it is said to be placed buccally
• Uses 2 films with different horizontal and vertical angulations