Denture Base Materials & Curing Cycles

Denture Base Materials

Curing (Polymerization): After final closure, the flask is kept at room temperature for 30 to 60 minutes (bench curing).

Bench Curing In Dentistry

Purpose of Bench Curing:

• Permits an equalization of pressure throughout the mold.
• It allows time for more uniform dispersion of monomer throughout the mass of dough, since the last material added is usually drier than the fist added to the flask.
• If resin teeth are used, it provides a longer exposure of resins teeth to the monomer in the dough producing a better bond of the teeth with the base material

“Best Ways To Understand Curing Cycles For Denture Bases”

Bench Dental Curing

• After bench curing, the flask is placed in a cold water bath.
• Bench Dental curing is then heated slowly.
• As the temperature of the water bath increases heat starts to conduct inside.
• When the temperature of the acrylic dough reaches about 60°C, benzoyl peroxide (initiator) is decomposed to produce two free radicals.
• Each free radical rapidly reacts with an available monomer molecule to initiate polymerization.
• The polymerization reaction propagates with the liberation of heat (12.9 kcal/mole) because the polymerization reaction is exothermic.
• Since the acrylic resin and stone are poor thermal conductors of heat, the heat of the reaction cannot be dissipated.

“Importance Of Proper Curing Cycles In Denture Fabrication”

• Therefore, the temperature of the resin increases well above the temperatures of surrounding materials and may increase to a value even up to about l20°C–130°C.
• This temperature is greater than the boiling point of a monomer such as 100.8°C.
• So at these temperatures, the residual monomer will boil and the monomer vapor enclosed by hard polymer and a porous structure will be created.
• This type of porosity will not be seen at the surface of the denture base because exothermic heat can be conducted away from the surface of the denture into the investing medium and the temperature in the thin region is not likely to rise above the boiling point of the monomer.
• These do not show gaseous porosity but their heat of reaction is passed onto the interior portions of the dough.
• Bench Dental curing is here the gaseous porosity is seen. In other words, it occurs away from the source of heat, i.e. at the center of a thick portion of the denture when heat cannot be conducted away with sufficient rapidity and the temperature of the resin is likely to cross 100.8°C.

“Risk Factors For Failure In Denture Base Materials”

Dental 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.

For heat-cure acrylic resins, the curing cycle used is of great importance in the quality of the final denture since the polymerization reaction is strongly exothermic.

The following two methods have been suggested to obtain non-porous denture:

1. Slow curing cycle.
2. Fast curing cycle.

Slow curing cycle Dentures 

• Slow Curing Cycle Dentures  involves the processing of denture base resin in a constant temperature water bath at 74°C for 8 hours or longer with no terminal boiling treatment.
• The lower the constant temperature, the longer the time is needed for curing.
• If the bulk of the acrylic is more, better to cure at low temperatures and a longer time is required for curing.
• Slowly raise the temperature of the water bath to about 74°C in about half an hour and maintain the temperature constant for 8 hours or more.

“Early Signs Of Problems With Denture Base Curing Cycles”

Fast Curing Cycle Dentures 

Fast Curing Cycle Dentures involves heating the resin at 74°C for approximately 1½ to 2 hours and then increasing the temperature of the water bath to 100°C and processing for one hour or more.

• Slowly raise the temperature of the water bath to about 74°C in about half an hour and maintain the temperature constant for 1½ hours.
• During this time, more than 95% of monomer is converted to polymer.

“Difference Between Heat-Curing And Cold-Curing Cycles”

• In order to reduce the amount of residual monomer or to ensure complete polymerization, the water in the bath can be boiled for about 1 hour.
• This technique enables a denture to be fabricated in a shorter time.