Orthotic Materials & Fabrication Techniques Flashcards

Which thermoplastic material is most appropriate for fabricating a rigid ankle-foot orthosis (AFO) requiring high durability and resistance to deformation under load?

Answer: Polypropylene

Polypropylene is the standard rigid thermoplastic for AFOs due to its high durability, stiffness, and resistance to deformation under body weight.

When using a heat gun during thermoplastic molding, what is the primary risk if the material is overheated?

Answer: The material may bubble, thin unevenly, or burn

Overheating thermoplastic can cause bubbling, uneven thinning, and burning, compromising structural integrity.

Which type of orthotic padding is best suited for accommodating a bony prominence to relieve focal pressure?

Answer: Closed-cell polyethylene foam

Closed-cell polyethylene foam (e.g., Plastazote) is preferred for accommodating bony prominences because it conforms and does not bottom out as quickly as open-cell foam.

In lamination fabrication, what is the purpose of the PVA (polyvinyl alcohol) bag used during the process?

Answer: To create a vacuum-sealed barrier between resin and stockinette

The PVA bag creates an airtight barrier that prevents resin from contaminating the vacuum pump and ensures even resin distribution.

Which rivet type is most commonly used when permanently joining two rigid thermoplastic components in orthotics?

Answer: Pop (blind) rivet

Pop (blind) rivets are most commonly used in orthotics because they can be installed from one side without access to the back of the joint.

What is the primary advantage of carbon fiber composite over polypropylene for orthotic fabrication?

Answer: Higher strength-to-weight ratio

Carbon fiber composites offer superior strength-to-weight ratio, allowing for lighter, thinner orthoses with equivalent or greater rigidity.

When vacuum-forming a thermoplastic over a positive model, which draping technique helps prevent bridging at concave areas?

Answer: Manually pressing the softened material into concavities before applying vacuum

Manually pressing softened thermoplastic into concave areas before vacuum is applied prevents bridging and ensures intimate contact with the model.