ABO Orthodontic Biomechanics 3 — Questions and Answers
Question 1: Frontal (direct) bone resorption during tooth movement occurs when applied force is:
- Excessive and crushes the PDL
- Light and preserves PDL vitality (Correct answer)
- Absent
- Only compressive
Correct answer: Light and preserves PDL vitality
Light forces maintain PDL vitality, allowing osteoclasts to resorb bone directly on the pressure side.
Question 2: Undermining (indirect) resorption is associated with:
- Light continuous force
- Hyalinization of the PDL from excessive force (Correct answer)
- Rapid ideal movement
- No cellular activity
Correct answer: Hyalinization of the PDL from excessive force
Excessive force causes PDL hyalinization, and resorption proceeds indirectly from adjacent marrow spaces, delaying movement.
Question 3: During tooth movement, cells responsible for bone formation on the tension side are:
- Osteoclasts
- Osteoblasts (Correct answer)
- Odontoblasts
- Cementoclasts
Correct answer: Osteoblasts
On the tension side, stretched PDL fibers stimulate osteoblasts to deposit new bone.
Question 4: A longer lag phase in the tooth-movement timeline is typically caused by:
- Light optimal forces
- Areas of hyalinization requiring undermining resorption (Correct answer)
- Immediate translation
- Reduced anchorage
Correct answer: Areas of hyalinization requiring undermining resorption
Hyalinized zones must be removed by undermining resorption before movement resumes, creating a lag phase.
Question 5: Which structure primarily transmits orthodontic force signals into cellular bone remodeling?
- Enamel rods
- The periodontal ligament (Correct answer)
- Dental pulp only
- Gingival epithelium
Correct answer: The periodontal ligament
The PDL senses mechanical strain and mediates the biological remodeling of surrounding alveolar bone.
Question 6: Root resorption during orthodontic treatment is most strongly linked to:
- Very light intermittent forces
- Heavy prolonged forces and excessive torque (Correct answer)
- Short treatment duration
- Removable appliances only
Correct answer: Heavy prolonged forces and excessive torque
Heavy, prolonged forces—especially with root torque—increase the risk of orthodontically induced root resorption.
Question 7: The initial displacement of a tooth immediately after force application is due to:
- Bone remodeling
- Compression and viscoelastic response of the PDL (Correct answer)
- Cementum growth
- Enamel deformation
Correct answer: Compression and viscoelastic response of the PDL
The first movement reflects PDL compression and fluid displacement before biologic remodeling begins.
ABO Orthodontic Biomechanics 3
Frontal (direct) bone resorption during tooth movement occurs when applied force is: