COF Materials & Fabrication Basics 2 — Questions and Answers
Question 1: Which thermoplastic material is most commonly used for ankle-foot orthoses (AFOs) due to its balance of rigidity and workability?
- Polyethylene
- Polypropylene (Correct answer)
- Polyurethane
- Acrylic
Correct answer: Polypropylene
Polypropylene is the most widely used thermoplastic for AFOs because it offers good rigidity, fatigue resistance, and is easy to heat-form and trim.
Question 2: At approximately what temperature (°F) does low-temperature thermoplastic become moldable for direct patient fitting?
- 100–120°F
- 140–180°F (Correct answer)
- 220–250°F
- 300–350°F
Correct answer: 140–180°F
Low-temperature thermoplastics soften between 140–180°F, allowing them to be molded directly on or near the patient without risk of burns.
Question 3: What property describes a material's ability to return to its original shape after the deforming force is removed?
- Plasticity
- Elasticity (Correct answer)
- Creep resistance
- Tensile strength
Correct answer: Elasticity
Elasticity is the property that allows a material to recover its original shape after stress is removed, which is important for dynamic orthotic components.
Question 4: Which metal alloy is preferred for orthotic uprights when lightweight construction is a primary concern?
- Stainless steel
- Carbon steel
- Aluminum alloy (Correct answer)
- Copper alloy
Correct answer: Aluminum alloy
Aluminum alloy is preferred when weight reduction is critical because it is significantly lighter than steel while still providing adequate strength for most orthotic applications.
Question 5: What is the primary advantage of closed-cell foam over open-cell foam in orthotic padding?
- Greater softness
- Better moisture resistance (Correct answer)
- Higher heat retention
- Easier trimming
Correct answer: Better moisture resistance
Closed-cell foam resists moisture absorption, making it more hygienic and durable in environments where sweat or water exposure is expected.
Question 6: During vacuum forming of a thermoplastic orthosis, what is the purpose of the vacuum?
- To heat the plastic evenly
- To draw the softened plastic tightly over the model (Correct answer)
- To cool the plastic faster
- To eliminate air bubbles in the material
Correct answer: To draw the softened plastic tightly over the model
The vacuum draws atmospheric pressure against the softened thermoplastic, conforming it precisely to the contours of the plaster model or positive mold.
Question 7: Which characteristic of carbon fiber composite makes it particularly valuable in energy-storing orthotic devices?
- High thermal conductivity
- High stiffness-to-weight ratio with elastic energy storage (Correct answer)
- Ease of field modification
- Radiolucency on X-ray
Correct answer: High stiffness-to-weight ratio with elastic energy storage
Carbon fiber's high stiffness-to-weight ratio allows it to store elastic energy during loading and return that energy during push-off, enhancing gait efficiency.
COF Materials & Fabrication Basics 2
Which thermoplastic material is most commonly used for ankle-foot orthoses (AFOs) due to its balance of rigidity and workability?