Superimposing Longitudinal Cephalograms on Cranial Structures

Purpose of Superimposition

• To reliably and accurately superimpose cephalograms on cranial and cranial base reference structures.
• Allows orthodontists to assess total changes in teeth, including:
  • Tooth movements within maxilla and mandible
  • Displacements due to jaw growth or treatments.
• Essential for assessing skeletal changes by subtracting tooth movements from total cranial base change.

Importance of Cranial Base Superimpositions

• First step in analyzing skeletal changes with orthodontics.
• Requires stable reference structures that do not change over time.

Structures Not Suitable for Superimposition

• Most cranial base structures grow/remodel over time.
• Posterior cranial base grows during childhood/adolescence.

Suitable Structures for Superimposition

• Anterior and Middle Cranial Base:
  • Minimal growth after age 7-8
  • Structures stable post sphenoethmoidal synchondrosis growth cessation.
  • Anterior Wall of Sella Tercica: Stable after 5-6 years.
  • Cribriform Plate: Stable after 4-5 years.
  • Planum/Jugum Sphenondale: Minimal growth after age 6, possible bony apposition up to 14.
  • Ethmoidal Crests: Minimal growth after 6 years.
  • Cerebral Surfaces of Frontal Bone: Relatively stable after age 7.

Steps to Identify Structures

• Begin with radiopaque surface of anterior wall of sella.
• Locate intersection with anterior clinoid process (Walker point).
• Note the planum sphenoidale and greater wings of the sphenoid.
• Identify the cribriform plate and ethmoidal crests.

Landmarks for Sagittal and Vertical Orientation

• Sagittal Orientation:
  • Contour of anterior wall of sella tercica.
  • Greater wings of the sphenoid.
  • Use average of visible right and left wings.
• Vertical Orientation:
  • Intersection of anterior wall of sella and anterior clinoid processes.
  • Cribriform plate or ethmoidal crest if cribriform plate is not visible.
  • Use planum sphenoidale and cerebral surfaces of frontal bone if needed.
  • Occipit can assist as a rotational reference, though not stable during growth.

Conclusion

• Accurate use of primary and secondary cranial base structures enables reliable representation of changes during treatment or growth.