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Non Metallic Denture Base Materials

Manipulation

Curing

It's heating the packed mould in a water path where both the temperature and time of heating should be controlled to avoid :

Cooling and Deflasking

which results in high residual monomer content

which leads to gaseous porosity

The flask should be cooled slowly because of stresses resulted of the difference in contraction between the flask and the acrylic, slow cooling permits relief of these stresses by plastic deformation.

- Under-curing

Heat techniques

- Evaporation of monomer

- Heat at 72 C for 8 hours or longer ( long cycle )

- Heat at 72 C for 1.5 hours then raise temp. to 100 C for one hour

Deflasking should be done with care to avoid breaking the denture.

Packing

The mixture should be packed in the dough stage for its proper consistency, In packing it's important that the mould is full and there's is sufficient pressure on it.

Proportioning

If packed in the sandy or sticky stage the material will be of too low viscosity to be packed well and will result in porosity in the final denture.

If packed in the stiff stage the material will be too viscous to flow in the flask.

The powder and liquid should be proportioned in the ratio of 3:1 by volume or 2.5:1 by weight.

Finishing and polishing

- Using less liquid leads to a granular acrylic denture base because not all the polymer will be wet by monomer.

- Using too much liquid leads to shrinkage porosity.

...The reaction should be in a sealed jar to avoid loss of monomer by evaporation.

Presented by: Nancy Samir

Stages of mixing polymer and monomer

Wet sand-like mixture

The material becomes tacky

Sandy stage :

Putty-like or dough like material

Sticky stage :

Too rubbery and stiff to be moulded

Dough stage :

Stiff stage :

Different denture base materials are.........

Metallic ,

Non Metallic ( Acrylic Resins )

Advantages & Disadvantages

-Advantages : Esthetically superior to metal bases and easy to repair

-Disadvantages : Lower strength and wear resistance to metals , Porous ,

Dimensional changes during curing

Low thermal conductivity

Thermal expansion : change from room temperature to water temperature.

Contraction : polymerization shrinkage of resin.

Presence of porosities

What is a denture base ?

Thermal contraction : change from temperature of water path to room temperature.

External porosity : shrinkage porosity due to under-curing

Internal porosity : gaseous porosity due to raising the temperature suddenly in the curing stage.

Manipulation defects

Crazing

Cracks on the surface of the resin due to tensile stresses.

A denture base is a material in which the teeth of a denture are set and which rests on the supporting tissues when the denture is in place in the mouth.

Thank you.....

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