Orthodontic Diagnosis and Treatment Planning
Domain 1: Orthodontic Diagnosis and Treatment Planning
The OMSB Orthodontist exam tests whether you can convert records into a prioritized problem list and a plan that fits the patient's growth status, profile, and expectations. Expect questions on record selection, cephalometric and model analysis, indices, anchorage, and treatment sequencing.
Core rules
- Start with the chief complaint and the patient's own goals, then build a problem list in four categories: skeletal, dental, soft tissue, and functional/airway.
- Essential records: panoramic radiograph, lateral cephalogram, intraoral and extraoral photographs, study models or intraoral scans, and a functional examination.
- Cephalometric values are means, not diagnoses. Steiner norms of SNA 82°, SNB 80°, and ANB 2° must be interpreted against facial pattern and ethnicity.
- Space analysis: measure arch length discrepancy in both arches and check Bolton tooth-size discrepancy before extracting or closing spaces. The overall Bolton ratio is about 91.3%, and the anterior ratio about 77.2%.
- Decide timing: growth modification, camouflage, or surgery. A visual treatment objective tests whether the planned tooth movement is mechanically possible.
Worked example
A 13-year-old presents with Class II division 1, overjet 9 mm, overbite 5 mm, mandibular retrognathia, and mild crowding. SNA 81°, SNB 75°, ANB 6°, SN-MP 39°, CVM stage 3. The problem list is skeletal Class II due to mandibular retrusion, increased overjet, deep bite, and crowding. The choice is growth modification versus camouflage. Because the patient is near peak growth, a functional appliance is reasonable, but compliance is uncertain. A sensible plan is Twin Block followed by fixed appliances, accepting that final correction may need extraction or surgery if growth is unfavorable. The VTO shows that 9 mm of overjet cannot be corrected by upper incisor retraction alone without excessive torque loss, so both skeletal and dental changes are needed.
Traps
- Treating ANB in isolation; check Wits, soft tissue, and dental compensation.
- Ignoring a transverse discrepancy; a narrow maxilla can masquerade as Class II.
- Planning space closure without a Bolton check; peg laterals and missing premolars alter ratios.
- Promising a result that depends on growth in a patient who is already post-pubertal.