Podcast
Questions and Answers
What is the melting point range of paraffin wax commonly used for histological purposes?
What is the melting point range of paraffin wax commonly used for histological purposes?
How does the viscosity of paraffin wax change with the molecular weight of its components?
How does the viscosity of paraffin wax change with the molecular weight of its components?
What is the traditional advice for the temperature at which paraffin wax should be used for histological purposes?
What is the traditional advice for the temperature at which paraffin wax should be used for histological purposes?
What can happen to tissues that are difficult to infiltrate when using paraffin processing?
What can happen to tissues that are difficult to infiltrate when using paraffin processing?
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Why is paraffin processing not recommended for tissues that are difficult to infiltrate?
Why is paraffin processing not recommended for tissues that are difficult to infiltrate?
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What happens to tissue blocks stored in paraffin for a long time after impregnation?
What happens to tissue blocks stored in paraffin for a long time after impregnation?
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Which wax substitute is more elastic and resilient than paraffin wax?
Which wax substitute is more elastic and resilient than paraffin wax?
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What is the melting point range of Paraplast?
What is the melting point range of Paraplast?
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Which wax substitute permits large dense tissue blocks like bones and brain?
Which wax substitute permits large dense tissue blocks like bones and brain?
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Which wax substitute is harder than paraffin and NOT soluble in water?
Which wax substitute is harder than paraffin and NOT soluble in water?
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Which substitute wax does not require dehydration and clearing if used?
Which substitute wax does not require dehydration and clearing if used?
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Which synthetic wax is recommended for embedding 'eyes' and tissue mats?
Which synthetic wax is recommended for embedding 'eyes' and tissue mats?
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What is the maximum degree of vacuum that the vacuum embedding oven should not exceed?
What is the maximum degree of vacuum that the vacuum embedding oven should not exceed?
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What is the most critical factor that determines the duration and number of changes required for thorough impregnation of tissues?
What is the most critical factor that determines the duration and number of changes required for thorough impregnation of tissues?
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Why do hard tissues require wax with a higher melting point than soft tissues?
Why do hard tissues require wax with a higher melting point than soft tissues?
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How long should tissues be left in the paraffin oven according to practical considerations?
How long should tissues be left in the paraffin oven according to practical considerations?
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What grade of alcohol is used for dehydration in manual tissue processing?
What grade of alcohol is used for dehydration in manual tissue processing?
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What is the purpose of the heavy glass lid covering the vacuum embedding oven chamber?
What is the purpose of the heavy glass lid covering the vacuum embedding oven chamber?
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Why is it necessary to have at least 4 changes of wax during the impregnation process?
Why is it necessary to have at least 4 changes of wax during the impregnation process?
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Why should fresh wax be filtered before use in a wax oven?
Why should fresh wax be filtered before use in a wax oven?
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What happens to tissues as they are heated in the paraffin oven?
What happens to tissues as they are heated in the paraffin oven?
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Which wax melting point range is suitable when the laboratory temperature is between 15 to 18 degrees Celsius?
Which wax melting point range is suitable when the laboratory temperature is between 15 to 18 degrees Celsius?
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What is the purpose of the clearing step in manual tissue processing?
What is the purpose of the clearing step in manual tissue processing?
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What is the function of the stopcock provided in the vacuum embedding setup?
What is the function of the stopcock provided in the vacuum embedding setup?
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What is the main purpose of using DMSO in blends of plastic polymer paraffin waxes?
What is the main purpose of using DMSO in blends of plastic polymer paraffin waxes?
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What type of tissues is celloidin impregnation most suitable for?
What type of tissues is celloidin impregnation most suitable for?
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Why is the wet celloidin method recommended for bones, teeth, large brain sections, and whole organs?
Why is the wet celloidin method recommended for bones, teeth, large brain sections, and whole organs?
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What is true about celloidin solutions for use in impregnation?
What is true about celloidin solutions for use in impregnation?
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What is the main advantage of dry celloidin method over wet celloidin method?
What is the main advantage of dry celloidin method over wet celloidin method?
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How does DMSO affect tissue permeability during processing?
How does DMSO affect tissue permeability during processing?
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Study Notes
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
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Description
Test your knowledge on substitutes for paraffin wax in tissue embedding processes. Learn about synthetic plastic polymers, melting points, and comparison with paraffin wax. Discover substitutes like Paraplast, Embeddol, and Bioloid.
