Orthodontics · single question
When an anterior palatal expander is placed on a 9-year-old, what type of bone formation occurs at the midpalatal suture?
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Correct answer: B. Intramembranous ossification (direct bone formation without cartilage)
The midpalatal suture is a fibrous (membranous) suture — NOT a cartilaginous growth center. Rapid palatal expansion separates the two palatal halves and new bone fills the gap via INTRAMEMBRANOUS ossification — the same mechanism by which all craniofacial flat bones form (no cartilage intermediate). The clinical term is distraction osteogenesis, but the histological mechanism is intramembranous.
- A. ❌ Endochondral ossification uses a cartilage template — occurs in long bones and at synchondroses, NOT at fibrous sutures.
- B. ✅ Intramembranous ossification — new bone forms directly from fibrous tissue in the suture gap; no cartilage intermediate.
- C. ❌ Appositional growth is general surface bone addition — not specific to the suture gap filling mechanism.
- D. ❌ Distraction osteogenesis is the clinical TECHNIQUE name, but intramembranous ossification is the histological MECHANISM.