What Is the Nagasaki University Analysis?
The Nagasaki University analysis is a compact cephalometric measurement set that pairs the classic Sella-Nasion skeletal angles with a cranial-base-independent Wits appraisal and a focused look at lower-incisor position. As implemented in BCeph it reports eight measurements spanning the three diagnostic dimensions every work-up needs — sagittal jaw relationship, vertical growth pattern, and incisor position — in a single panel.
What distinguishes the set is its choices at the margins: it carries the Wits appraisal as a built-in sagittal cross-check, and it references the lower incisor to the N–A line (the maxillary reference) rather than the more common N–B. Those two decisions make it a useful second opinion alongside a Steiner-style analysis rather than a duplicate of one.
Shared tracing, identical values. In BCeph the Nagasaki module reuses the same landmark set as Steiner, Tweed, and the Wits appraisal, so its SNA, SNB, ANB, IMPA, Wits, and interincisal values are computed once and are identical across modules. Only the lower-incisor-to-N–A distance is unique to this set. Place your landmarks once and every analysis updates together.
Skeletal Measurements
Four measurements locate the jaws — three sagittal angles on the cranial base and one vertical angle for the growth pattern.
| Measurement | Definition | Norm | Clinical meaning |
|---|---|---|---|
| SNA | Angle at Nasion between lines S–N and N–A | 82° ± 2° | Maxillary position relative to the cranial base. High = maxillary protrusion; low = maxillary retrusion. |
| SNB | Angle at Nasion between lines S–N and N–B | 80° ± 2° | Mandibular position relative to the cranial base. High = mandibular protrusion; low = mandibular retrusion. |
| ANB | Arithmetic difference: SNA − SNB | 2° ± 2° | Sagittal jaw relationship — the primary Class I/II/III skeletal classifier. |
| SN-MP | Angle between the S–N line and the mandibular plane (Go–Me) | 32° ± 5° | Vertical growth pattern. High = hyperdivergent (high-angle); low = hypodivergent (low-angle). |
Reading ANB for skeletal classification
ANB is the headline skeletal value. It expresses the sagittal discrepancy between the apical bases and maps to the skeletal class:
Normal sagittal jaw relationship. Malocclusion, if present, is primarily dental in origin.
Maxilla positioned anteriorly relative to the mandible, or the mandible is retrognathic.
Mandible positioned anteriorly relative to the maxilla, or the maxilla is retrognathic.
Dental Measurements
Three measurements characterise the lower incisor and the overall incisor relationship — with the distinctive Nagasaki choice of referencing the lower incisor to the N–A line.
| Measurement | Definition | Norm | Clinical significance |
|---|---|---|---|
| L1–NA (mm) | Perpendicular distance from the lower incisor tip to line N–A | 4 mm ± 2 mm | Lower-incisor position relative to the maxillary reference line. High = protrusion; low = retrusion. |
| IMPA | Incisor-mandibular plane angle: L1 long axis to Go–Me | 90° ± 3° | Lower-incisor inclination over basal bone. >93° = proclined; <87° = retroclined. |
| Interincisal | Angle between the long axes of U1 and L1 | 131° ± 8° | Overall incisor relationship. Low suggests dual proclination; high suggests dual retroclination. |
Why L1 to N–A rather than L1 to N–B? Referencing the lower incisor to N–B (as Steiner does) describes its position over its own apical base. Referencing it to N–A instead expresses where the lower incisor sits relative to the maxillary apical base — a view that is sensitive to the interjaw relationship, not just the mandible in isolation. Read together with IMPA, it separates "the incisor is tipped" from "the incisor is positioned forward within the face."
The Wits Appraisal: A Built-In Sagittal Cross-Check
The eighth measurement is the one that gives the Nagasaki set its diagnostic robustness.
| Measurement | Definition | Norm | Clinical significance |
|---|---|---|---|
| Wits Appraisal (AO–BO) | Distance between points AO and BO — the projections of A and B onto the functional occlusal plane | 0 mm ± 2 mm | Sagittal jaw discrepancy independent of the cranial base. Positive (AO ahead of BO) = Class II pattern; negative = Class III pattern. |
ANB inherits any peculiarity of the Sella-Nasion line — a steep or flat anterior cranial base shifts SNA and SNB together and distorts their difference. The Wits appraisal sidesteps that by measuring sagittal discrepancy on the occlusal plane instead. When ANB and the Wits agree, the sagittal diagnosis is secure; when they diverge, the disagreement itself is the finding — usually pointing to an atypical cranial base or an occlusal-plane cant that warrants a closer look before treatment mechanics are chosen. Building the Wits into the panel means that cross-check happens automatically. Note that the Wits is a linear measurement and so requires calibration of the cephalogram to report in millimetres.
How the Nagasaki Analysis Guides Treatment Planning
Sagittal diagnosis with redundancy
The set's design philosophy is cross-checked diagnosis. Rather than reporting a single sagittal value and trusting it, it reports ANB and the Wits side by side, so the clinician reads a converged conclusion rather than one number. That redundancy is most valuable exactly when it matters most — in patients whose cranial-base anatomy makes SN-referenced angles unreliable.
Vertical pattern before mechanics
SN-MP fixes the growth pattern early. A hyperdivergent (high-angle) pattern constrains how much the lower incisor can be proclined and shifts anchorage and extraction thinking; a hypodivergent (low-angle) pattern is more forgiving. Reading SN-MP alongside IMPA and L1–NA keeps the vertical constraint in view while the incisor plan is built.
Incisor position within the whole face
By referencing the lower incisor to N–A and reporting the interincisal angle, the set frames incisor position in terms of the interjaw relationship rather than the mandible alone. That is useful in borderline extraction cases, where the question is less "is L1 tipped?" and more "where does L1 sit within the patient's facial pattern, and what will retraction cost the profile?"
Limitations and When to Supplement
The Nagasaki set is a focused panel; round it out where a case needs more:
- Maxillary incisor not isolated. The set reports the interincisal angle but no standalone upper-incisor-to-NA value. For dedicated upper- and lower-incisor positioning to N–A, pair it with the Radney analysis.
- No soft-tissue measurements. There is no lip or profile value in the set. Add the Holdaway analysis or E-line analysis for the soft-tissue picture.
- No facial-height ratio. SN-MP captures the vertical angle but not the posterior-to-anterior face-height proportion; Björk-Jarabak supplies that.
- Norm refinement. Some of the set's norms — notably the L1–NA distance and the wider interincisal range — are applied as practical working values in BCeph and are being validated against the source literature; interpret borderline deviations together with the converging measurements rather than in isolation.
BCeph runs the Nagasaki set alongside Steiner, Tweed, Wits, Radney, the ABO set and nine other modules from a single tracing — so every supplement above is available in the same session.