I have been in histology (clinical and research) for over 20 years and continually see a large air bubble, paraffin cracks, tissue too large for the mold (leaving not enough paraffin around the sample and causing ribbon not to connect or explode as soon as you place the ribbon in the waterbath), good sample but getting too close to the cassette (which causes your blade to hit the chuck holder on your microtome), L-Mold blocks (unless if your lab has the old screw clamp this is typically re-embedded), and other embedding issues.
I have yet to read any book or have any of my friends in the industry tell me any other solution but to re-embed a problem block. Coming from a family of inventors, I was always bothered by these issues, especially when re-embedding takes a long time, the tissue orientation changes and precious parts of the tissue could be lost when you have to re-shave the sample.
I remember a time when my pathologist came up to me complaining that he had a hard time re-orienting himself trying to locate the area of interest on a sample that was re-embedded. Being a supervisor, this troubled me, so I started trying different ways to fix the problem and figuring out what else can be done. I have shown my techniques to different laboratories for which I had worked. When I started working in the field as a vendor, I asked histotechs how they fix such paraffin issues and the answers were always to re-embed the blocks.
Five years ago I decided to share my techniques as a workshop and have since shared these techniques to the California Society for Histotechnology, Arizona Society for Histotechnology, NSH Hawaii Symposium, National Society for Histotechnology, Philippine Association of Medical Technologist and Colorado Society for Histotechnology.
I started using the tissue embedding system as a welder, using the dispensing nozzle, mold and forceps. The trick is to melt the part of the paraffin block that is being fixed with either the dispensing nozzle of the embedding machine or a hot forcep before filling it with more melted paraffin, then trim to square the paraffin block to the desired form. This will ensure proper welding. Adding just hot paraffin on to a room temp block will cause the paraffin filler to pop out easily.
Jesse Del Campo is with Biocare.
The following slideshows illustrate the steps to repair common fixation issues. Click here.