Substitutes for Paraffin Wax Quiz

Fatty Tissue Impregnation

• The duration and number of changes required for thorough impregnation of tissue depend on the size and type of tissue, use of vacuum embedding, and the clearing agent employed.
• Common waxes have melting points of 45°C, 52°C, 56°C, and 58°C, with 56°C normally used for routine work.

Laboratory Temperature and Wax Melting Point

• In a laboratory with a temperature between 20-24°C, paraffin wax with a melting point of 54-58°C can be used.
• If the laboratory temperature is between 15-18°C, paraffin wax with a melting point of 50-54°C is suitable.

Hard and Soft Tissues

• Hard tissues require wax with a higher melting point than soft tissues.

Paraffin Wax Impregnation Methods

• There are three ways of paraffin wax impregnation and embedding of tissues: manual processing, automatic processing, and vacuum embedding.

Manual Processing

• Fixation: 10% buffered formalin for 24 hours
• Dehydration:
  • 70% alcohol for 6 hours
  • 95% alcohol for 12 hours
  • 100% alcohol for 2 hours (three changes)
• Clearing: using xylene or toluene in two changes
• Impregnation: at least four changes of wax are required at 15-minute intervals to ensure complete removal of the clearing agent.

Paraffin Wax Properties

• Paraffin wax is a polycrystalline mixture of solid hydrocarbons produced during the refining of coal and mineral oils.
• It is solid at room temperature but melts at temperatures up to about 65°C or 70°C.
• The most common melting point for histological use is about 56°C to 58°C.

Advantages and Disadvantages of Paraffin Wax

• Advantages:
  • Thin individual serial sections can be cut with ease
  • The process is very rapid
  • Tissue blocks and unstained mounted sections can be stored in paraffin for an indefinite period of time
• Disadvantages:
  • Inadequate impregnation
  • Tissues that are difficult to infiltrate will crumble on sectioning
  • Not recommended for hard tissues

Substitutes for Paraffin Wax

• Paraplast: a mixture of highly purified paraffin and synthetic plastic polymers with a melting point of 56-57°C
• Embeddol: a synthetic wax substitute with a melting point of 56-58°C
• Estewax: a lower-melting-point wax (46-48°C) that is harder than paraffin
• Water-soluble waxes (e.g., Carbowax): plastic polymers with a melting point of 38-42°C or 45-56°C
• Dimethyl sulfoxide (DMSO): added to blends of plastic polymer paraffin waxes to reduce infiltration time and facilitate thin sectioning

Celloidin Impregnation

• Celloidin (Collodion) is a purified form of nitrocellulose suitable for specimens with large hollow cavities.
• It is supplied in thin (2%), medium (4%), and thick (8%) solutions of cellulose dissolved in equal parts of ether and alcohol.

Methods for Celloidin Impregnation

• Wet Celloidin Method: recommended for bones, teeth, large brain sections, and whole organs
• Dry Celloidin Method: preferred for processing whole eye sections

Vacuum Embedding

• Consists of wax baths, fluid trap, and vacuum gauge
• The degree of vacuum should not exceed 500 mmHg

Practical Considerations

• Tissue should not be left in the paraffin oven for more than 4 hours
• Paraffin oven must be maintained at a temperature 2-5°C above the melting point of paraffin to be used for impregnation
• Fresh wax should be filtered before use in a wax oven at a temperature 2°C higher than its melting point