Orthodontics · patient case question
How is this patient's skeletal and vertical relationship classified?
Patient case: Orthodontic records at seventeen
Patient: Female, 17 years old
Chief Complaint: “My front teeth don't meet and my mouth is always open.”
Background: Healthy. Longstanding tongue thrust and mouth breathing. No previous orthodontic treatment.
Vital Signs: BP 110/68 mmHg · HR 72 bpm
Findings: Convex profile with lip incompetence and a high mandibular plane angle. Cephalometric analysis: SNA 84°, SNB 78°, ANB +6°. Proclined maxillary incisors with no vertical overlap of the incisors in occlusion. The permanent second molars have fully formed roots; the third molars are developing with open apices.
Show answer and explanation
Correct answer: D. Skeletal Class II with an anterior open bite
- A. Skeletal Class III is ANB LESS than 2 degrees, often negative, with a concave profile and a reverse overjet. This patient's SNA exceeds SNB by 6 degrees, which is the opposite relationship.
- B. Skeletal Class I is ANB of roughly 2 to 4 degrees with a straight profile. This patient's ANB is +6. A deep bite is EXCESSIVE vertical overlap of the incisors — the opposite of what is described.
- C. The skeletal classification is right but the vertical description is wrong. There is NO vertical overlap of the incisors, which is an open bite, not a deep bite.
- D. CORRECT. ANB is the angular difference between SNA and SNB and expresses the anteroposterior relationship of maxilla to mandible relative to the cranial base. Normal is roughly 2 to 4 degrees; GREATER than 4 is SKELETAL CLASS II, here from a retrusive mandible (SNB 78) rather than a protrusive maxilla. The absence of vertical incisor overlap in occlusion is an ANTERIOR OPEN BITE, and the combination of Class II with open bite, a high mandibular plane angle, lip incompetence and a tongue thrust is a coherent and common vertical growth pattern.
Note: Keep SKELETAL classification (ANB, from the cephalogram) distinct from ANGLE'S classification (molar relationship, from the teeth). They often agree but need not, because dental compensation can mask a skeletal discrepancy entirely. Other values worth carrying: SNA 82±2°, SNB 80±2°, SN to mandibular plane about 32°, and the Frankfort-mandibular plane angle about 25°.