Processing of Acrylic Resin
Denture base material or acrylic polymers are supplied in several form:
-The powder-liquid type
-Either heat or chemically accelerated and gel types
Measure and mix the polymer and monomer according to the manufacturer’s directions
10 cc of monomer and 30 cc of polymer will be enough to back an average sized denture
Pour the monomer into a clean porcelain jar
Add the polymer
Stir with a clean spatula until the monomer and polymer are thoroughly combined
Place the lid on the jar and allow the mixture to stand
Open the jar and test the material with a spatula
Kept the powder and liquid in a sealed jar during the initial stage of reaction to avoid the loss of monomer by evaporation
Incompletely wetted portions can
  -result in a streaked or blanched appearance in the denture because of incomplete polymerization of the plastic during processing and
  -alter the physical properties of the denture base
Care should be taken to avoid air breathing the monomer vapor
The polymer-monomer mixture may be qualitatively described as
sandy
string or sticky
plastic dough or putty like
rubbery or elastic
stiff
When the mixture is doughy but not sticky, the material is ready for packing
Packing
The powder-liquid mixture should be packed into the flask at the dough consistency for several reasons
If it is packed at the sandy or stringy stages, too much monomer will be present between the polymer particles and the material will be of too low a viscosity to pack well and will flow out of the flask too easily
Packing early may also result in porosity in the final denture base
If at the rubber to the stiff stage, the material will be too viscous to flow under the available pressure of the flask press, and metal-to-metal contact of the flask halves will not to be obtained.
Delayed packing will result in loss of detail in the denture, movement or fracture of the teeth and an increase in the contact vertical dimension of the denture
The plastic dough should not be manipulated excessively with bare hands
The monomer is a good solvent for body oils and may pick up dirt from the hands, resulting in a no aesthetic denture.
Monomer may also enter the blood stream through the skin
Pack the material in the upper half of the flask, being sure to press it well to the area around the teeth.
Use the index finger covered with cellophane
To avoid trapping air between the material and the mould pack in one direction , use enough material to insure over packing on the first closure
Place two pieces of wet cellophane between the folds of a towel to remove the excess water
Place the cellophane over the acrylic resin
Put the lower half of the flask in position and press the flask together, using hand pressure
Place the flask in a press and close it very slowly to give the acrylic resin plenty of time to flow.
Finger pressure in adequate until the final closure
Remove the flask from the press, open the flask carefully and trim off the excess acrylic resin with a sharp scalpel
Add a small amount of acrylic resin in three or four places, using new cellophane
Close the press slowly and again remove any excess material as before
Test pack until all excess material has been removed and the metal edges of the parts of the flask are in complete contact
Before final closure, the separating film is removed and discarded
The final closure of the flask, or metal-to-metal contact of the flask halves, is then completed in the press
The flask are placed in a flask press, which maintains the pressure and the denture is processed
Processing = Polymerization of Acrylic Resin
Conversion of the monomer to the polymer when a mixture of the two is subjected to heat
Methods
1- The long polmerization cycle:
 Immerse the flasks in the compress in cold water
Slowly bring the temperature of the water to 160°F constant temperature
Leave them for about 8 hours, after which the water is brought to boiling and the assembly is boiled for 30 minutes.
2- The short polmerization cycle:
 Immerse the flasks in water at 160°F constant temperature for 1,5 hours, then transfer it to boiling water and leave for 30 minutes
The long polymerization cycle is the method of choice if time permits
All polymerization cycles should end with a boiling period to remove the excess monomer
After polymerization, allow the flasks to cool to room temperature before deflasking the dentures
They should cool in the water in which they were polymerized
