ABO Orthodontic Biomechanics 1 — Questions and Answers
Question 1: What are the three orders of tooth movement in orthodontic wire bending?
- First order (in-out), second order (tip/angulation), and third order (torque/inclination) (Correct answer)
- Fast, medium, and slow movements
- Upper, middle, and lower tooth movements
- Horizontal, vertical, and rotational only
Correct answer: First order (in-out), second order (tip/angulation), and third order (torque/inclination)
First order bends adjust labiolingual (in-out) position, second order bends control mesiodistal tip (crown angulation), and third order bends apply torque to control buccolingual root inclination.
Question 2: What is anchorage in orthodontics?
- Resistance to unwanted tooth movement, using teeth, bone, or devices as a stable base to move other teeth (Correct answer)
- A type of dental cement
- The foundation of a dental office
- How braces are attached to teeth
Correct answer: Resistance to unwanted tooth movement, using teeth, bone, or devices as a stable base to move other teeth
Anchorage refers to the resistance provided against reactive forces during orthodontic tooth movement. Sources include teeth, bone, TADs (temporary anchorage devices), headgear, and functional appliances.
Question 3: What is the difference between NiTi and stainless steel archwires?
- NiTi is superelastic with shape memory for initial alignment; stainless steel is stiffer for precise tooth positioning and finishing (Correct answer)
- They are made of the same material
- NiTi is only used for adults
- Stainless steel is more flexible than NiTi
Correct answer: NiTi is superelastic with shape memory for initial alignment; stainless steel is stiffer for precise tooth positioning and finishing
Nickel-titanium wires are superelastic with shape memory, delivering light continuous forces ideal for initial alignment. Stainless steel wires are stiffer, allowing precise adjustments through bending for detailed finishing.
Question 4: What is a temporary anchorage device (TAD)?
- A small biocompatible screw placed in bone to provide absolute anchorage for orthodontic tooth movement (Correct answer)
- A temporary bracket that falls off easily
- A removable retainer
- A type of headgear
Correct answer: A small biocompatible screw placed in bone to provide absolute anchorage for orthodontic tooth movement
TADs are mini-screws (1.2-2mm diameter) temporarily placed in alveolar or palatal bone under local anesthesia, providing skeletal anchorage that doesn't depend on patient compliance or reciprocal tooth movement.
Question 5: What forces are optimal for orthodontic tooth movement?
- Light, continuous forces (25-75g for tipping, 100-150g for bodily movement) that promote healthy tissue remodeling (Correct answer)
- Maximum force for fastest movement
- Intermittent heavy forces
- No force is needed with modern braces
Correct answer: Light, continuous forces (25-75g for tipping, 100-150g for bodily movement) that promote healthy tissue remodeling
Optimal orthodontic forces are light and continuous, promoting healthy periodontal ligament remodeling and undermining resorption rather than excessive force that causes tissue necrosis, pain, and root resorption.
Question 6: What is the center of resistance of a tooth?
- The point where a single force produces bodily movement without rotation, located approximately at the middle third of the root (Correct answer)
- The center of the tooth crown
- The tip of the root
- The point where the bracket is bonded
Correct answer: The point where a single force produces bodily movement without rotation, located approximately at the middle third of the root
The center of resistance is approximately at the junction of the middle and apical thirds of the root for single-rooted teeth (or between roots for multi-rooted teeth). Force through this point produces pure translation.
ABO Orthodontic Biomechanics 1
What are the three orders of tooth movement in orthodontic wire bending?