9. Why?
• To prevent the diffusion of water molecule from the dental stone
into the unpolymerized packed dough.
• To prevent the diffusion of monomer from the unpolymerized
packed dough in the mold material.
10. To prevent the diffusion of water molecule from the
dental stone into the unpolymerized packed dough.
But why?
•Affect the polymerization rate as well as the optical and
physical properties of the processed denture.
•The processed denture will craze readily because of the
stresses incorporated by the evaporation of water
during curing.
11. To prevent the diffusion of monomer from the
unpolymerized packed dough in the mold material.
But why?
•If dissolved polymer/monomer is permitted to soak into the
mold surfaces it will be fused to the denture base, it will be
virtually impossible to separate the investing material
from the resin denture base.
• It produces rough surfaces with adherent mold material.
14. More Polymer- Less Monomer
a. Not all the polymer will wet by monomers
and the cured acrylic resin will be granular.
b. Dough will be difficult to manage.
15. Less polymer – more monomer
a.Polymerization shrinkage will be greater than 7%
b. Dough forming time will be prolonged.
c. There will be a tendency for porosity to occur in
the denture.
18. Under packing:
Introduction too little material leads to noticeable denture base porosity.
To reduce the likelihood of over packing
or under packing the mold cavity is packed in
several steps. The powder-liquid mixture should be packed at the dough stage.
Too early packing: If it is packed at the sandy or stringy stage the material will
be of too low viscosity to pack well and will flow out of the flask too easily. It may
also result in porosity in the final denture base.
Delayed packing: If it is packed at the rubbery or stiff stage, the mix will be too
viscous to flow under pressure and metal-to-metal contact of the flask halves will
not be obtained. This may also result in loss of detail in the denture movement
or fracture of the teeth.
19. Curing Cycle
The curing cycle is the technical name for the
heating process employed to control the initial
propagation of polymerization in the denture
mold.
22. Bench Cooling
• The denture flask should be cooled slowly to
room temperature.
• Rapid cooling may result in warpage or distortion of
the denture base because of differences in thermal
contraction of acrylic resin and investing stone.
• 30 min and subsequently immersed in cold water for
10 min
25. Advantages
•
• Elimination of trial closures.
• Reduced risk of monomer vapor inhalation.
• Compensation for curing shrinkage.
• Control of pressure during polymerization,
thus preserving the proper vertical dimension
