ABO ABO Orthodontic Appliances and Mechanics 2 — Questions and Answers
Question 1: What material property allows nickel-titanium wires to return to their original shape after deformation?
- Work hardening
- Superelasticity (Correct answer)
- Brittleness
- Ductility
Correct answer: Superelasticity
Nickel-titanium wires exhibit superelasticity (pseudoelasticity), allowing them to undergo large deformations and return to their original form.
Question 2: A Class II elastics configuration runs from the upper canine to the lower first molar. What is the primary skeletal effect?
- Mandibular retrusion
- Maxillary advancement
- Mandibular advancement and/or maxillary retrusion (Correct answer)
- Transverse expansion
Correct answer: Mandibular advancement and/or maxillary retrusion
Class II elastics apply a forward force on the lower arch and a backward force on the upper arch, promoting mandibular advancement and/or maxillary retrusion.
Question 3: Which wire sequence is correct when beginning fixed appliance therapy?
- Stainless steel → NiTi → TMA
- TMA → stainless steel → NiTi
- NiTi → TMA → stainless steel (Correct answer)
- Stainless steel → TMA → NiTi
Correct answer: NiTi → TMA → stainless steel
Treatment typically begins with flexible NiTi for initial leveling, progresses to TMA for detailing, and finishes with stainless steel for torque and finishing.
Question 4: What is the purpose of placing a step bend mesial to an upper molar tube?
- To intrude the molar
- To tip the molar distally
- To prevent the molar from tipping mesially (anti-tip bend) (Correct answer)
- To expand the molar buccally
Correct answer: To prevent the molar from tipping mesially (anti-tip bend)
A step bend mesial to the molar tube creates an anti-tip effect that resists mesial tipping of the molar during space closure.
Question 5: Self-ligating brackets differ from conventional brackets primarily because they:
- Have built-in torque values
- Use a sliding mechanism instead of ligatures to engage the archwire (Correct answer)
- Are made from ceramic material
- Require larger archwires
Correct answer: Use a sliding mechanism instead of ligatures to engage the archwire
Self-ligating brackets use a built-in clip or door to engage the archwire, eliminating the need for elastic or wire ligatures.
Question 6: Which type of force system is produced by a T-loop spring during space closure?
- Pure moment (couple)
- Pure force
- Force and moment system (Correct answer)
- No force or moment
Correct answer: Force and moment system
A T-loop spring produces both a force (to close space) and a moment (to control tipping/torque of teeth) simultaneously.
ABO ABO Orthodontic Appliances and Mechanics 2
What material property allows nickel-titanium wires to return to their original shape after deformation?