Dental Materials & Laboratory Techniques Flashcards

Which type of investment material is used for casting high-fusing alloys such as cobalt-chromium?

Answer: Phosphate-bonded investment

Phosphate-bonded investments withstand the high casting temperatures required for cobalt-chromium and other base metal alloys.

What is the primary purpose of using a separating medium on a stone cast before applying wax?

Answer: To prevent wax from bonding to the stone

Separating mediums such as tinfoil substitute create a barrier so wax can be removed cleanly without sticking to the stone model.

The term 'liner' in a porcelain fused-to-metal restoration refers to:

Answer: A thin opaque ceramic layer applied over the metal coping

The opaque liner masks the metal color and establishes the chemical bond between the metal coping and overlying dentin/enamel porcelain.

Which hardener is commonly added to acrylic resin to improve its cross-link density and reduce porosity?

Answer: Ethylene glycol dimethacrylate

Cross-linking agents like ethylene glycol dimethacrylate (EGDMA) form bridges between polymer chains, increasing strength and reducing residual monomer.

When trimming a diagnostic cast, the posterior heel of a maxillary cast should be:

Answer: Parallel to the mid-palatal raphe

Trimming the posterior wall parallel to the mid-palatal raphe ensures symmetrical articulator mounting and accurate representation of midline.

What is the Vickers Hardness Number (VHN) scale primarily used to assess in dental alloys?

Answer: Resistance to surface indentation

The Vickers Hardness test measures a material's resistance to permanent deformation when a diamond indenter is pressed into its surface.

A technician notices small voids (porosity) throughout a cast metal framework after casting. The most likely cause is:

Answer: Insufficient alloy volume in the crucible

Using too little alloy means insufficient metallostatic pressure to fill the mold completely, leading to shrinkage porosity throughout the casting.