Extra oral Radiography Including Cephalograms Flashcards
What is extra-oral radiography, and what are its purposes?
Definition: Imaging where both the X-ray source and receptor are located outside the patient’s body, used primarily in dentistry.
Purposes:
- To visualize larger sections of the dentition.
- As an alternative for patients unable to tolerate intra-oral radiography.
- To image non-dentoalveolar regions, including jaws and facial bones.
What are the common types of extra-oral radiographs?
dental specific, skull
Dental-specific:
Panoramic radiographs
Cephalometric radiographs (lateral and postero-anterior)
Skull radiographs:
Occipitomental
Postero-anterior skull/mandible
Reverse Towne’s
True lateral
How is terminology for extra-oral radiographs determined?
Beam direction relative to the head:
- Lateral: Directed at the side of the head.
- Postero-anterior: Starts posteriorly and passes anteriorly.
Beam angulation:
- True: Perpendicular to the head.
- Oblique: Non-perpendicular to the head.
Anatomy transected by the X-ray beam:
Examples include “mandible” or “occipitomental.”
What are the key anatomical reference lines used in extra-oral radiographs?
Mid-sagittal plane: Divides the face symmetrically.
Interpupillary line: Connects the pupils.
Frankfort plane: Connects the infraorbital margin and superior border of the external auditory meatus.
Orbitomeatal line: Connects the outer canthus to the center of the external auditory meatus.
What is cephalometry, and what are its clinical applications?
Definition: The measurement and study of the head using points, angles, and distances on standardised radiographs.
Applications:
Orthodontics and orthognathic surgery.
Monitoring changes over time.
Requires consistent, reproducible radiographs.
What is a lateral cephalogram, and what anatomy does it visualize?
Definition: A standardised, true lateral skull radiograph captured with specialised equipment.
Visualised anatomy:
Teeth, facial bones, soft tissues.
Paranasal sinuses.
Pharyngeal soft tissue and cervical vertebrae.
Sella turcica
Posterior wall of nasopharynx (adenoids)
Hyoid
How are lateral cephalograms used in orthodontics?
what stages
Use cases:
Assessing skeletal discrepancies for functional or fixed appliances.
Locating and assessing unerupted, malformed, or misplaced teeth.
Indicating upper incisor root length.
Stages of use:
Diagnosis, treatment planning, monitoring, and appraisal of results.
What is a cephalostat, and why is it essential?
Definition: A device in cephalogram units ensuring standardised head positioning.
Functions:
Stabilises the head to avoid movement.
Maintains correct distances between the X-ray focal spot, patient, and receptor (typically 1.5–1.8 m).
How can soft tissue profiles be visualised during cephalograms?
Challenges: Soft tissues appear faint when settings are optimised for hard tissues.
Solutions:
Using an aluminium wedge filter to attenuate the X-ray beam.
Software-based post-exposure enhancement.
What are oblique lateral radiographs, and when are they used?
Definition: An extra-oral radiograph showing the posterior jaws without superimposing the contralateral side.
Indications:
Assessing unerupted teeth, jaw lesions, or fractures.
Alternative for patients unable to tolerate intra-oral or panoramic radiographs (e.g., young children, those with involuntary movements).
uncommon now (difficult)
What role does collimation play in extra-oral radiography?
Ensures the field of view is no larger than clinically required to adhere to ALARP principles (As Low As Reasonably Practicable).
Triangular collimation may be used to reduce cranium exposure for non-solid-state units.
How is the patient contact shielded?
what can this cause
Thyroid collar almost always used
- Thyroid gland is relatively radiosensitive
- May obscure hyoid bone & cervical vertebrae
What future potential does CBCT have in replacing cephalograms?
advantages/disadvantages
Advantages:
No anatomical superimposition or magnification.
3D imaging for better pre-operative planning in orthognathic surgery.
Limitations:
Increased radiation dose.
Additional information often not clinically significant for routine cephalometry.
