Dental Materials & Laboratory Techniques Flashcards

Which property describes a material's ability to return to its original shape after the deforming stress is removed?

Answer: Elasticity

Elasticity is the property that allows a material to recover its original dimensions once the applied stress is released below the elastic limit.

In lost-wax casting, the spruing technique affects which of the following?

Answer: Metal flow direction and potential porosity sites

Sprue placement determines the path of metal entry, and improper design can cause turbulence, back-pressure porosity, or incomplete fill.

Polyvinyl siloxane (PVS) impression materials set via which reaction?

Answer: Addition polymerization with no by-products

PVS materials cure by addition polymerization between vinyl and hydride groups, producing no volatile by-products and exhibiting excellent dimensional stability.

What is the purpose of degassing a noble metal alloy before casting?

Answer: To remove dissolved gases that cause porosity

Degassing melts the alloy briefly before casting to allow trapped gases to escape, reducing subsurface gas porosity in the final casting.

The Shore A durometer is used to measure hardness of which category of dental materials?

Answer: Flexible silicone and rubber-based materials

The Shore A scale measures the hardness of soft, flexible materials like silicones, rubbers, and soft denture liners.

A feldspathic porcelain crown appears too translucent after firing. The technician should:

Answer: Increase the dentin buildup and re-fire

Excess translucency usually means insufficient dentin mass; adding more dentin porcelain provides greater body opacity before glaze firing.

Which mixing technique is recommended for zinc phosphate cement used as a luting agent to extend working time?

Answer: Slow incremental powder addition on a cool glass slab

A cool (refrigerated) glass slab and slow incremental powder addition dissipate the exothermic heat of reaction, extending working time.