Presentation on

Curing of Denture Base ResinsByShafdar Khan Guided by: Dr. Pallavi Madanshetty

Processing the DentureAfter the trial dentures (Acrylic base, wax and teeth) have been waxed, they are prepared for denture processing to substitute the acrylic record base and the wax with a heat cure denture base attached to the teeth.This is done in the following steps:1) Flasking. 2) Wax elimination. 3) Mixing.4) Packing.5) Curing. 6) De-flasking.7) Shaping and Polishing

After wax elimination, packing of denture is done.

The assembled flask is placed

in a bench and pressed slowly. This permits the flow of acrylic resin into minute areas of the mold.

The flask is opened and the flash (excess resins) is removed.

The procedure is repeated until metal to metal contact between the flask rims is achieved.

Bench Curing

After the final closure the flask are kept at room temperature for 30 to 60 mins. This is

known as Bench Curing.

Purpose of Bench Curing:

Permits an equalisation of pressure throughout the mold space.

It allows time for a more uniform dispersion of monomer throughout the mass of dough.

It provides a longer exposure of resin teeth to monomer in the dough producing a better bond of teeth with the base material.

Heat CuringTypes of curing cycles for heat cure acrylic:

1. Long Curing cycle:

Curing is done at a constant water bath at 74 ° C for 8 hours or longer. Longer curing times will not result in degradation properties .

Curing is done at 74 ° C for 1.5 hours and increase the temperature of water bath to boiling for additional 1 hour.

2. Short Curing cycle:

Curing temperature must be maintained at 74 C, because the polymerization reaction is strongly exothermic.

At 70 C decomposition of benzoyl peroxide (initiator in polymer) is rapid enough for polymerization to take place

The heat of reaction is added to the heat used to raise the material to polymerization temperature.

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Points to Remember

As polymerization proceeds, exothermic heat of reaction increases the temperature of polymer to values above the surrounding materials.

This occurs because gypsum and polymer are poor conductors so the heat is dissipated slowly.

In thick sections of denture the temperature rise is greater than in thin sections , so porosity is more likely to occur in thick sections of denture.

Effect of Processing Temperature on Porosity

Temperature

74 ° C 82° C 100° C

Product A No Porosity

Negligible Moderate

Product B No Porosity

Moderate Severe

Other problems associated with rapid heating above 74 ° C are:

production of internal stresses warpage of denture after deflasking crazing around neck of the teeth

Residual monomer

When the denture was packed the monomer content was 26.2%. At 70 ° C, After 1 hour-6.6% 4 hour-4.0%. At 100° C, After 1 hour-0.31% 4 hour-0.29%.It required 168 hours at 70 ° C for the residual monomer to appropriate the value obtained after 1 hour at 100° C.This data supports the use of 1 hour terminal boil for processing dentures.

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