The microtome is a mechanical instrument used to cut biological samples into very thin segments for microscopic examination. Biological samples can be embedded and presented in many ways for sectioning. Generally these samples are embedded in blocks of paraffin wax and the most common way to section these samples is achieved by microtome.
Evolution of the microtome
The earliest form of the microtome allowed the manual cutting of fresh or fixed material with a sharp blade. Modern microtomes are designed to cut evenly thin sections of a variety of materials for detailed microscopic examination. A fundamental element for the production of good sections is the microtome knife.
The microtomy virtually begins and ends with a sharp, blemish-free cutting edge. The introduction of disposable blades has made it easier to produce good quality thin sections. However, they are often unsatisfactory for sectioning harder tissues, especially bone. A sharp, blemish-free knife edge is essential to the production of good sections. Since many types of microtomes are commercially available on the market, choosing the correct microtome is essential to producing the best results as needed.
How to make the cut of bones?
The value of histologic examination in the diagnosis and classification of clinical conditions is relied upon by the pathology laboratory’s experience in handling the wide range of specimen types submitted for analysis.
From receipt of the tissue sample to presentation of the slide for microscopic examination, histologists must consider the composition of the specimen. All this in order to determine how it should be managed effectively.
The majority of samples follow a routine cycle of dehydration and wax embedding with paraffin for purposes of sectioning on the microtome. However, due to its high calcium content, bone is a particularly difficult tissue to section and the density of the sample must be taken into consideration. Cutting decalcified sections of bone requires embedding in resin, a specialized microtome, and modified staining techniques.
Therefore, most laboratories decalcify bone samples, allowing them to be embedded in paraffin and processed. Nitric acid and formic acid are used as descaling agents. Formic acid is the most convenient for laboratories that perform molecular analysis, because unlike nitric acid, it does not destroy DNA.
Decalcification varies in time depending on the size and type of bone sample. The quality of a section can also have a major impact on the accuracy and reliability of the diagnosis, and is involved in the selection of the most appropriate microtome.
What is recommended?
Manual sectioning is often recommended for paraffin-embedded specimens due to the need to vary the levels of force used to cut various portions of the specimen.
Tissues common to analysis, on the other hand, sometimes require larger and thicker sections. As a consequence, these samples sometimes require embedding in resin using a fully mechanized microtome that slowly applies force in a constant and controlled manner to generate good quality sections.
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