importance of paraffin wax quality used in tissues

Type and quality of paraffin wax is important for constructing tissue

Tissue technology allows the representation of hundreds of tissue samples on a standard microscope slide. This is achieved by arraying small cores (0.6 mm in diameter) of paraffin wax embedded tissue samples in a recipient wax block. Sections cut from the array can then be assessed according to standard protocols.

First, it was suggested that when the recipient blocks were made, insufficient wax was poured through the cassette, resulting in weak adhesion between the block and the cassette. However, we ensured that the mold, including the back of the cassette, was filled and that the wax level was not allowed to recede during cooling. Second, rough handling of the arrays could weaken the wax, but we do not believe that this occurred. Third, temperature fluctuations may play a role. Although arrays were constructed and stored at ambient temperature, they were cooled after every 10&15 sections cut, according to standard procedures. We no longer cool arrays during sectioning and quality remains comparable to published studies. Fourth, sections were cut along the length of the array, which may theoretically exert excessive shearing forces on the wax and increase its potential to fracture. Consequently, we now section across the width of the array. Fifth, cores may have been arrayed too deeply into the recipient block, weakening the wax at the cassette surface. Cores are now placed at least 1 mm above the cassette. Sixth, prolonged heating of wax above its melting point may compromise its quality. However, our wax is heated to its melting point of 60°C and kept molten for no longer than one week.

Finally, the quality of wax used to make the recipient block is important. The wax that we had used initially did not contain plastic .

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