Radiographic Localisation Flashcards
What limitation do 2D radiographs present?
They cannot show the buccal-lingual plane and provide limited spatial positioning.
What are three techniques to overcome 2D radiograph limitations?
Positioning the X-ray beam perpendicular to the desired plane.
Parallax shift technique.
Cross-sectional imaging (e.g., CBCT).
List clinical situations where radiographic localisation is essential.
- Confirming the position of unerupted/impacted teeth.
- Identifying root canals for endodontic treatment.
- Assessing relationships of pathological lesions.
- Visualizing traumatic fractures of teeth/bone.
- Investigating sources of soft tissue pathology.
What critical questions can radiographs help answer about teeth?
“Which way is the tooth facing?”
“Does the tooth have normal roots?”
How can radiographs determine whether a canine is buccal or palatal to the incisors?
By using a second radiograph at a perpendicular angle or employing the parallax technique.
How is the perforated root canal in a multi-rooted tooth localized?
By identifying the canal’s position using radiographic shifts.
What is the simplest method to localize a structure using radiographs and what are the limitations of this method?
Taking a second image perpendicular (90°) to the desired plane.
Anatomical and equipment constraints may prevent achieving a perfect 90° angle.
What is the principle behind the parallax shift technique?
The apparent movement of an object relative to a reference point when viewed from different positions.
What types of shifts can occur in the parallax technique?
Horizontal or vertical shifts.
What are the requirements for successful parallax technique usage?
- At least two radiographs of the object of interest.
- Radiographs taken from sufficiently different angles/positions.
- A shared reference point between radiographs.
- No movement of the object relative to the reference point between exposures.
What radiograph combinations are effective for the parallax technique?
Periapical + periapical from different positions.
Periapical + occlusal.
Panoramic + occlusal.
Occlusal + occlusal from different positions.
Why is the combination of periapical and panoramic radiographs not ideal for parallax?
Because the shift between them is limited and unpredictable.
What mnemonic aids are helpful for applying parallax shifts?
SLOB: Same Lingual, Opposite Buccal.
PAL: “My pal goes with me” (indicating the direction of the object shift).
What can a horizontal parallax shift localize?
Unerupted teeth, e.g., a supplemental premolar lingual to roots.
How is vertical parallax used to localize an unerupted canine?
By taking radiographs at different vertical angles, revealing the canine’s position as buccal or palatal.
