Cracks around tissue in the block are caused by which of the following?

• A. Super cooling of the cold plate
• B. Overheating of the wax
• C. Inadequate dehydration
• D. Air entrapment

Answer: (A)

Thermal stress during cooling leads to cracking. When tissue is embedded in paraffin, the wax surrounds it in a molten state and then solidifies on a cooling surface. If the cooling plate is too cold, the outer layer of the block solidifies and contracts much faster than the interior. This rapid, uneven contraction places tensile stress at the tissue–wax interface, causing cracks to form around the tissue as the block hardens. To prevent this, use a reasonably tempered cooling surface and allow gradual solidification rather than applying a very cold plate. The other factors—overheating the wax, inadequate dehydration, and air entrapment—tend to cause softness, poor infiltration, or voids, rather than the specific cracks around the tissue.