Cephalometrics and Imaging
Cephalometrics and Imaging tests landmark identification, analysis selection, and interpretation of skeletal and dental relationships. It also tests safe use of CBCT and other imaging.
Core rules
- Common landmarks include sella, nasion, A point, B point, pogonion, menton, gonion, and the incisor tips. Common planes include SN, Frankfort horizontal, palatal plane, and mandibular plane.
- Steiner analysis uses SNA, SNB, ANB, and incisor angles. Approximate adult norms are SNA 82 degrees, SNB 80 degrees, ANB 2 degrees, and interincisal angle 130 degrees. Wits appraisal measures the functional occlusal relationship and is less affected by vertical rotation than ANB.
- Vertical pattern matters: FMA or SN-MP indicates hyperdivergence, and IMPA shows lower incisor compensation. Soft-tissue assessment includes the E-line and lip strain.
- Trace in natural head position, use a calibrated monitor, and repeat doubtful landmarks. CBCT is indicated for impacted teeth, root proximity, airway, and complex skeletal assessment, but apply ALARA.
Worked example
A patient has SNA 84, SNB 78, ANB 6, Wits +7, FMA 31, IMPA 97, and UI-SN 112. Reasoning: this is a skeletal Class II pattern with hyperdivergence and bimaxillary proclination. The high ANB is supported by the Wits value, so it is not just a rotation artifact. Treatment may require extraction or retraction with vertical control, possibly skeletal anchorage; severe cases need orthognathic assessment.
Traps
- Relying on ANB alone when vertical rotation is present.
- Mixing analyses with different norms.
- Accepting a single tracing without checking landmark error.
- Ignoring ethnicity, age, and sex when interpreting norms.