CPT Materials, Tools, & Safety in Prosthetics 3 — Questions and Answers
Question 1: Which property of carbon fiber composites makes them preferred over aluminum for high-activity prosthetic feet?
- Lower cost
- Higher energy return and lower weight (Correct answer)
- Greater malleability
- Resistance to UV degradation
Correct answer: Higher energy return and lower weight
Carbon fiber stores and releases mechanical energy during gait while being significantly lighter than aluminum, improving functional outcomes.
Question 2: What does Shore hardness measure in the context of prosthetic materials?
- Tensile strength
- Resistance to permanent indentation (Correct answer)
- Flexural modulus
- Thermal conductivity
Correct answer: Resistance to permanent indentation
Shore hardness quantifies a material's resistance to surface indentation, helping technicians select appropriate liner and padding materials.
Question 3: A technician is mixing two-part urethane foam. Which hazard requires IMMEDIATE attention if the mixture begins to expand faster than expected?
- Inhalation of exothermic vapors (Correct answer)
- Skin contact with uncured resin
- Electrical spark ignition
- UV curing interference
Correct answer: Inhalation of exothermic vapors
Rapid exothermic expansion generates heat and releases isocyanate vapors, which are respiratory sensitizers requiring immediate ventilation and respirator use.
Question 4: When drilling through carbon fiber laminate, which drill bit type is recommended to minimize delamination?
- Standard twist bit
- Brad-point bit
- Diamond-coated bit (Correct answer)
- Spade bit
Correct answer: Diamond-coated bit
Diamond-coated bits cut through carbon fiber cleanly without creating the fraying or delamination that standard metal drill bits cause.
Question 5: Which material property is described as the ratio of stress to strain in the elastic region of a material?
- Ultimate tensile strength
- Yield strength
- Young's modulus (Correct answer)
- Fracture toughness
Correct answer: Young's modulus
Young's modulus (elastic modulus) describes material stiffness—how much a material resists deformation under load before permanent change occurs.
Question 6: What is the correct disposal method for resin-contaminated gloves and mixing cups in a prosthetics lab?
- Standard municipal recycling
- Disposal as hazardous waste per local regulations (Correct answer)
- Incineration in the lab furnace
- Rinsing with water and placing in general trash
Correct answer: Disposal as hazardous waste per local regulations
Uncured resin and resin-contaminated materials are classified as hazardous waste and must be disposed of according to local and federal regulations.
Question 7: Which lamination layup sequence provides the greatest torsional rigidity for a transfemoral socket?
- 0°/0°/0° carbon fiber
- ±45° carbon fiber outer with 90° inner (Correct answer)
- Fiberglass inner with carbon fiber 0° outer
- Random-weave carbon fiber throughout
Correct answer: ±45° carbon fiber outer with 90° inner
Placing carbon fiber layers at ±45° to the principal axis maximizes resistance to twisting forces encountered during ambulation.
CPT Materials, Tools, & Safety in Prosthetics 3
Which property of carbon fiber composites makes them preferred over aluminum for high-activity prosthetic feet?