Orthodontics · single question
In surgically assisted rapid palatal expansion, the expansion obtained is typically:
Show answer and explanation
Correct answer: B. Greater anteriorly than posteriorly
- A. Expansion is not limited to the posterior segments — the anterior region opens most.
- B. CORRECT. The midpalatal suture opens in a NON-PARALLEL, triangular (wedge-shaped) fashion — wider ANTERIORLY at the incisive region and narrower POSTERIORLY. The posterior resistance comes from the pterygoid plates and the zygomatic buttress. In the frontal plane the split is likewise wider inferiorly (at the alveolar crest) than superiorly. Expect a transient midline diastema anteriorly as the classic clinical sign.
- C. Symmetric parallel expansion is not what happens with a tooth-borne midline expander; it requires bone-borne appliances or additional posterior releases.
- D. The posterior region is the region of GREATEST skeletal resistance (pterygoid plates), so it opens least.
Note: Triangular opening: wide in front, narrow in back (hinge at the pterygoid plates), and wide at the alveolus, narrow superiorly.