100
4.
EMBEDDING
the specimens in polymerized blocks he should consider the possibility
of water contamination. However, there are certain tissues, particularly
dense connective tissues, which are prone to produce bubbles in spite of
any amount of dehydration. It has been said that these can be reduced
or eliminated by partially degassing the methacrylate monomer before
use. This can be done with an aspirator pump, but, in any case, the
vacuum should not exceed 10 mm Hg, or the methacrylate monomer will
start boiling. Even when large bubbles are present, however, these do
not ordinarily affect the embedded tissue. If the cavities weaken the
support of the block, they can be filled before sectioning by a short
soaking of the trimmed capsule in hot wax.
Moore and Grimley (1957) believe that if dissolved oxygen is replaced
by nitrogen in the monomer, not only will bubbling be reduced, but
the blocks will be more uniform after heat polymerization. They, therefore, advocate storing degassed methacrylate under a dry nitrogen atmosphere. This prepared monomer is then used for the preliminary
soaking of the specimens, and for loading the capsules. Small holes are
punctured in the tops of each capsule, and the capsules are placed upright in small vials in a vacuum desiccator. The capsules then are subjected to a final degassing, after which nitrogen is admitted to the jar
until the capsules are once more at atmospheric pressure. The vials are
then stoppered quickly, leaving the capsules in a nitrogen atmosphere,
after which they are polymerized with heat. This method certainly is
unnecessarily complex for routine use, although it may be of value in
particular situations.
4.8. "Polymerization Damage" and the Use of
"Prepolymerized" Methacrylate
A principal variant method of methacrylate embedding involves
using partially "prepolymerized" methacrylate instead of simple monomers as the initial medium. This technique was developed by Borysko
(1956 and subsequently) in an effort to avoid "polymerization damage"
which may result from conventional procedures.
There since has been much discussion of polymerization damage. It
is thought to result from nonuniform polymerization which disrupts the
fine structure of some tissues under some circumstances. Factors producing it may include shearing effects associated with the volume change
4.
EMBEDDING
the specimens in polymerized blocks he should consider the possibility
of water contamination. However, there are certain tissues, particularly
dense connective tissues, which are prone to produce bubbles in spite of
any amount of dehydration. It has been said that these can be reduced
or eliminated by partially degassing the methacrylate monomer before
use. This can be done with an aspirator pump, but, in any case, the
vacuum should not exceed 10 mm Hg, or the methacrylate monomer will
start boiling. Even when large bubbles are present, however, these do
not ordinarily affect the embedded tissue. If the cavities weaken the
support of the block, they can be filled before sectioning by a short
soaking of the trimmed capsule in hot wax.
Moore and Grimley (1957) believe that if dissolved oxygen is replaced
by nitrogen in the monomer, not only will bubbling be reduced, but
the blocks will be more uniform after heat polymerization. They, therefore, advocate storing degassed methacrylate under a dry nitrogen atmosphere. This prepared monomer is then used for the preliminary
soaking of the specimens, and for loading the capsules. Small holes are
punctured in the tops of each capsule, and the capsules are placed upright in small vials in a vacuum desiccator. The capsules then are subjected to a final degassing, after which nitrogen is admitted to the jar
until the capsules are once more at atmospheric pressure. The vials are
then stoppered quickly, leaving the capsules in a nitrogen atmosphere,
after which they are polymerized with heat. This method certainly is
unnecessarily complex for routine use, although it may be of value in
particular situations.
4.8. "Polymerization Damage" and the Use of
"Prepolymerized" Methacrylate
A principal variant method of methacrylate embedding involves
using partially "prepolymerized" methacrylate instead of simple monomers as the initial medium. This technique was developed by Borysko
(1956 and subsequently) in an effort to avoid "polymerization damage"
which may result from conventional procedures.
There since has been much discussion of polymerization damage. It
is thought to result from nonuniform polymerization which disrupts the
fine structure of some tissues under some circumstances. Factors producing it may include shearing effects associated with the volume change