Common Casting Defects in Metal Alloys

Porosity in Dental Casting Alloys

• Shrinkage spot porosity is caused by inadequate feeding of the mold with molten alloy during solidification.
• Back pressure porosity is caused by air or gas trapped in the mold during the casting process.

Surface Roughness in Dental Casting Alloys

• Surface roughness is caused by the presence of gas or oxide inclusions in the molten alloy.

Insufficient Feeding of the Mold

• Insufficient feeding of the mold with molten alloy during solidification is caused by premature solidification of the molten metal.

Premature Solidification

• Premature solidification of the molten metal is caused by factors such as inadequate temperature control, incorrect alloy composition, or inadequate sprue design.

Improper Attachment of the Sprue

• Improper attachment of the sprue to the mold can result from incorrect sprue design, inadequate wax pattern, or improper investment of the mold.

Stiffness in Dental Casting Alloys

• High stiffness in a dental casting alloy allows for greater resistance to deformation under masticatory stresses.

Properties Required for Dental Casting Alloys

• Resistance to permanent deformation under masticatory stresses requires a property known as stiffness.
• High ductility is an important factor in the burnishability of dental casting alloys.

Noble Metals in Dental Casting Alloys

• Noble metals in dental casting alloys include gold, platinum, and palladium.
• The primary purpose of using noble metals is to provide corrosion resistance and biocompatibility.

Metal-Porcelain Compatibility

• The compatibility of a metal with porcelain is influenced by the thermal expansion coefficient of the metal.
• The melting temperature of the metal must be higher than the firing temperature of the porcelain to ensure a successful bond.

Ease of Casting

• The primary requirement for ease of casting is low viscosity of the molten alloy.