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Orthodontics · single question

An open coil spring is used to move a mesially tipped molar distally into an edentulous space. What is the MOST likely unintended effect?

  1. Extrusion of the molar with a decrease in overbite
  2. Root resorption of the adjacent premolar
  3. Intrusion of the molar with an increase in overbite
  4. Bodily distal translation with no vertical change
Show answer and explanation

Correct answer: A. Extrusion of the molar with a decrease in overbite

  • A. Correct. Uprighting a mesially tipped molar rotates the crown distally about the center of resistance, which EXTRUDES the tooth — the cusps drop occlusally. The extruded molar then acts as a posterior fulcrum, propping the bite open and REDUCING the anterior overbite. Anticipate this: plan simultaneous intrusive mechanics or subsequent occlusal reduction.
  • B. Root resorption is a general risk of orthodontic force but is not the characteristic, predictable side effect of molar uprighting.
  • C. Uprighting mechanics extrude rather than intrude, so overbite decreases rather than increases.
  • D. A simple open coil spring delivers a tipping (not bodily) force; true translation requires a couple in addition to the force.

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