When a Class I ANB Hides a More Complex Skeletal Pattern

One of the most common mistakes in cephalometric interpretation is relying on a single measurement.

This case illustrates why a complete analysis is essential. At first glance, the ANB angle suggests a skeletal Class I relationship. However, a deeper examination reveals a much more complex craniofacial pattern.

Initial Impression: A Skeletal Class I?

The first value many orthodontists examine is the ANB angle.

• ANB: 3.1°

An ANB close to 2° is generally considered normal, and a value of 3.1° would typically be interpreted as a mild skeletal Class I relationship.

If the analysis stopped here, one might conclude that the maxilla and mandible are normally related.

However, cephalometric diagnosis should never be based on ANB alone.

Looking Beyond ANB

The next step is evaluating the individual positions of the maxilla and mandible.

• SNA: 89.52°
• SNB: 86.42°

Both values are significantly above their respective norms.

The maxilla is protrusive relative to the cranial base, and the mandible is also positioned anteriorly.

The relatively normal ANB value is therefore misleading. Rather than indicating normal jaw positions, it reflects the fact that both jaws are protrusive to a similar degree.

This is a classic example of why orthodontists must evaluate skeletal relationships using multiple measurements rather than relying on a single angle.

Wits Appraisal Tells a Different Story

• Wits Appraisal: +5.32 mm

The Wits appraisal indicates a Class II skeletal tendency.

This apparent discrepancy between ANB and Wits is not uncommon.

ANB can be influenced by cranial base morphology and jaw position, whereas Wits evaluates the relationship of points A and B relative to the occlusal plane.

In this case, the Wits value suggests that despite the balanced protrusion of both jaws, a Class II skeletal relationship may still be present.

This highlights the importance of considering multiple sagittal indicators before reaching a diagnostic conclusion.

A Strong Horizontal Growth Pattern

The vertical analysis reveals one of the most striking aspects of this case.

• MMPA: 19.11°
• FMPA: 14.05°
• SN-Mx: 2.02°

All three measurements are significantly below normal values.

These findings indicate a pronounced hypodivergent growth pattern characterized by:

• Reduced lower facial divergence
• Strong horizontal growth tendency
• Increased bite force potential
• Greater skeletal stability

Such patients often present with strong musculature and a relatively low mandibular plane angle.

Facial Height Remains Balanced

• Ar-Go-Me: 128.89°
• %LAFH: 54.62%

Interestingly, despite the marked hypodivergent tendency, overall facial proportions remain balanced.

The lower anterior facial height percentage falls within normal limits, indicating that the patient maintains harmonious vertical facial proportions.

This demonstrates that vertical diagnosis should not be based solely on one measurement.

Dental Compensation and Incisor Position

The dental analysis reveals significant incisor proclination.

• Upper Incisor to Maxillary Plane: 128.52°
• Lower Incisor to Mandibular Plane: 107.65°
• Interincisal Angle: 104.73°

Both upper and lower incisors are markedly proclined.

The reduced interincisal angle confirms this finding.

Such dentoalveolar compensation is frequently observed in patients with protrusive skeletal bases.

The incisors have adapted to maintain acceptable overjet and occlusal relationships despite the underlying skeletal pattern.

A-Pog Analysis

• A-Pog to Lower Incisor: 2.72 mm

Interestingly, the lower incisors remain correctly positioned relative to the A-Pog line.

This suggests that while the incisors are proclined relative to the mandibular plane, they remain reasonably balanced within the overall facial framework.

Soft Tissue Evaluation

• Nasolabial Angle: 105.19°
• Upper Lip to E-Plane: -6.14 mm
• Lower Lip to E-Plane: -5.02 mm

The nasolabial angle is within a harmonious range.

However, both lips are positioned significantly behind the E-plane.

This finding indicates a relatively retrusive soft tissue profile despite the skeletal protrusion observed in the hard tissues.

Such discrepancies between skeletal and soft tissue analyses are common and reinforce the importance of evaluating the patient's facial appearance rather than relying solely on cephalometric norms.

Clinical Summary

This patient presents with:

• Apparent skeletal Class I based on ANB
• Protrusive maxilla and protrusive mandible
• Class II tendency confirmed by Wits appraisal
• Strong hypodivergent growth pattern
• Balanced facial proportions
• Marked upper and lower incisor proclination
• Retrusive soft tissue profile relative to the E-plane

What Can We Learn From This Case?

This case perfectly demonstrates why orthodontic diagnosis cannot be reduced to a single cephalometric value.

An ANB of 3.1° may initially suggest a straightforward Class I skeletal relationship. However, further analysis reveals protrusive jaws, a Class II tendency on Wits appraisal, a strong hypodivergent pattern, and significant dentoalveolar compensation.

The true value of cephalometric analysis lies not in individual numbers, but in understanding how those measurements interact to describe the patient as a whole.

Ultimately, successful diagnosis comes from combining cephalometric findings with clinical examination, facial analysis, and orthodontic experience.