processing errors of heat cure acrylic

what are the processing errors of heat cure acrylic resin?

1. porosity

2. movement of teeth

3. denture base and teeth breakage during deflasking

4. fracture or cracked teeth

5. crazing of acrylic resin base or acrylic

6. bleaching of acrylic resin

7. color streaks in the resin material

8. sandy appearance of the resin material

9. stone adheres to the surface of the denture

10. space between the teeth and resin base

what is porosity not ideal in dentures?

• difficult to clean

• not aesthetic

• weak

what causes porosity in denture bases?

1. too rapid rise of temperature in the initial stage of curing

2. thick denture base heated too rapidly

3. lack of dough in the mold at the time of final closure

4. lack of adequate pressure during polymerization

5. packing the resin in the sticky stage rather than the dough stage

how does tooth movement occur?

the teeth change its position during processing

what causes tooth movement during processing?

1. the use of plaster instead of stone in investing the trial denture

2. incomplete closure of the flask

3. excessive and rapid pressure during trial closure

4. overpacking of the mold with the resin material before final closure

what causes denture base and teeth breakage during deflasking?

1. careless flasking (knife blade hits teeth when removing stone cap)

2. hammer used to tap denture out of the flask

what causes the fracture or cracked teeth?

1. improper deflasking, such as using a hammer

2. packing the acrylic dough during the rubber stage, when the material is too stiff, resulting in excessive stress on the teeth

3. excessive and rapid application of pressure during trial packing

4. setting the teeth directly on the cast stone

what does crazing of resin cause?

formation of small cracks which may vary in size from microscopic dimension to visible size. it indicates the beginning of a fracture

what causes crazing of acrylic resin base or acrylic teeth?

1. stresses induced by the contraction of the resin around the tooth by rapid cooling

2. the use of solvents to remove wax from the mold before packing

what causes the bleaching of acrylic resin?

1. contamination of the acrylic resin with acrylic solvents

2. undercured acrylic resin due to incorrect curing time or temperature, resulting in incomplete polymerization

3. incorporation of the tin foil substitute into the acrylic resin during processing

4. incorporation of the jelly-like material from wet cellophane into the resin, causing discoloration or a bleached appearance

what causes color streaks in resin material?

1. improper mixing of the monomer and polymer

2. contamination of the resin mix with dirty hands or instruments

3. adding resin material in layers during trial packing

what causes a sandy appearance of the resin material?

1. excessive delay in curing after packing (more than 30 minutes)

2. evaporation of the monomer liquid leaving insufficient liquid to properly wet the polymer powder

3. insufficient monomer in the mixture (packing a dry mix), resulting in incomplete mixing and a grainy or sandy appearance

what causes stone adherence to the surface of the denture?

1. insufficient separating medium on the mold before packing

2. the application of separating medium contaminated with stone, making it ineffective

3. incomplete removal of wax during boil-out (washing out), which prevents the separating medium from working properly, allowing the acrylic resin to bond to the stone

what causes a space between the teeth and resin base to form?

• delayed curing, leaving the packed flask without curing for a long time, which may allow dimensional changes to occur

• application of separating medium on the teeth, preventing the acrylic resin from bonding properly to the artificial teeth and creating a space between the teeth and the denture base