Dr. Hessler wrote:
"...what advantages do these have
over traditional steel other than you don't clean them? As steel basically has
an unlimited lifespan, are the disposable molds really cost effective in a
clinical laboratory."
Plastic
molds:
Disadvantages:
Very high cost
(although they can be reused for a while - just don't store in the heated
space of the embedding center or they get warped)
Hard to orient
fragments due to some kind of electrostatic forces that move the pieces
around.
Slow to cool - again
hard to work with small fragments and skin when you want to orient them a
certain way. (though some may see as an
advantage)
Not as flat on the
face as metal, so more trimming - bad for very small
specimens.
Do not hold heat the
way metal does, so cools faster on the sides when time is spent orienting
tissue. I see many more mis-oriented tissues in
plastic molds, and mis-oriented mold/cassette
problems (block face is mis-oriented to the cassette
back, which means the block face is at an angle in the microtome chuck...= more
trimming).
Advantages:
The sides of the mold
are more vertical than the metal mold so a bit easier to cut (smaller face,
sharper edge)
Easy to take off the
block (metal molds are often difficult to remove)
Metal:
Advantages
Very low cost, last
forever
Flat
face
Cool
fast
Disadvantage
Sometimes difficult
to remove - use mold release (but that does take time and requires cleaning
the molds daily in xylene/alcohol - we put them in
the tissue processor and run the clean cycle)
Cracked
blocks? I haven't seen that as a problem. It is mainly in large blocks. You
can put them on a piece of paper over the cooling plate to avoid
that.
It seems
the only real advantage of the plastic is the shorter time spent taking the
mold off the block and avoiding the time it takes to clean the metal ones
(about 15 min/day max)
If I was
paying the bills I wouldn't get the plastic - they are far more expensive and
do not give as good quality face as the metal.
But...I
haven't done a cost analysis of the plastic molds vs
time spent to clean metal molds and then soak in mold release every
day.
-----Original
Message-----
From: Richard
Hessler [mailto:RHESSLER@mail.mcg.edu]
Sent: Tuesday, December 16,
2003 7:56
AM
To:
histonet@lists.utsouthwestern.edu
Subject: [Histonet] Plastic Embedding
Molds
I would like advise about
disposable plastic embedding molds. Was wondering if any clinical labs had
experienced problems with delays and uneven tissue alignment due to static and
slow heat transfer. Also, what advantages do these have over traditional steel
other than you don't clean them? As steel basically has an unlimited lifespan,
are the disposable molds really cost effective in a clinical
laboratory.
Richard B Hessler, MD
Chief,
Section of Anatomic Pathology
Associate Professor of Pathology and
Neurology
The Medical
College of
Georgia