Deffects In Dental Alloys Cast Single Tooth Restorations

Deffects In Dental Alloys Cast Single Tooth Restorations

Write a short note on localized shrinkage porosity.
Answer:

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Localized shrinkage porosity is also known as shrink spot porosity.

• It is one of the solidification defects.
• These are the irregular voids that are usually found near the sprue casting junction.

It occurs when the cooling sequence is incorrect and the sprue freezes before the rest of the casting. During a correct cooling sequence, the sprue should freeze last.

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Dental Casting Alloy

This allows more molten metal to flow into the mold to compensate for the shrinkage of the casting as it solidifies. If the sprue solidifies before the rest of casting no more molten metal can be supplied from the sprue. The subsequent shrinkage produces voids or pits known as localized shrinkage porosity.

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Shrink-spot porosity is avoided by:

• Using a sprue of the correct thickness.
• Attach the sprue to the thickest portion of the wax pattern.
• Flaring the sprue at the point of attachment or placing a reservoir close to the wax pattern.